Earth-Sized Planets Confirmed, But They're Dead Worlds

NASHVILLE -- There are three planets beyond our solar system about the same size as Earth. Found more than a decade ago, you might not have heard about them as their discovery was clouded in controversy.

But today the dispute is over, the planets are still there, and astronomers have pinned down their sizes with much more precision.

The planets are dead worlds, orbiting a dying star where there is no chance for anything interesting to happen, biologically. Because of this, most planet hunters have shown little interest in them. In fact, it is common for these worlds to be ignored when researchers make lists of known planets. It is seldom mentioned that they were indeed the first-ever extra-solar planets ever discovered.

The roughly Earth-sized planets orbit a neutron star, a dense stellar corpse that's just a hop, skip and a jump from a black hole, density-wise.

Alex Wolszczan of Penn State led a study that found them in 1990.

One of the planets is 4.3 times as massive as Earth and another is three times as heavy, give or take five percent, according to Wolszczan and Caltech postdoctoral researcher Maciej Konacki, who presented their latest results here today at a meeting of the American Astronomical Society. Measurements of the third planet are less firm, but it appears to be about twice as massive as the Moon -- significantly less than Earth.

"They look just like (our) inner solar system," Konacki told SPACE.com.

Except for that lack of biology, that is, and the fact that the outer planet of the threesome goes around the star in just 98 days, far less than the 365 days our Earth needs to make a year.

The researchers pinned down the masses by watching how the planets affect pulses of energy coming from the star. The neutron star spins very rapidly and is called a pulsar, because it unleashes energy in pulses. The pulsar is named PSR 1257+12.

Konacki said they studied advances and delays in the pulses. The work will be detailed in the Astrophysical Journal Letters.

"We know absolutely for sure that these are Earth-sized planets," Konacki said.

All other known planets around other stars are so large -- most dozens of Earth masses -- that they are presumed to be balls of gas, like Jupiter. Several research teams and upcoming space missions aim to find Earth-sized planets around Sun-like stars, which might mean habitability, but nobody can yet say if any exist.

Controversy dogged the finding of the trio because pulsar planets have long existed in the shadows of their larger counterparts, and in part because a separate pulsar planet announced prior to 1990 was retracted. This retraction caused researchers to question whether pulsar planets could be reliably detected or not.

Vanderbilt University's David Weintraub said in an interview that there's no longer any controversy over the pulsar planets' existence, but he added that he and others who are searching for potentially habitable place are not interested in the dead worlds, no matter what their size.

Strange Miniature 'Solar Systems' Revealed

An object smaller than Pluto has been discovered orbiting a dying star in what astronomers said Monday resembles a pint-sized version of our solar system.

In a separate study, a disk of planet-building material was spied circling a dim star-like object just 15 times the mass of Jupiter. The brown dwarf, as it is known, is a cosmically lukewarm ball of gas that straddles the definition between planet and star. The system could evolve into a compact, dim solar system, again with a familiar look.

The two findings suggest tiny, dim solar systems may be common. They also have scientists wondering anew what really constitutes a planet and what sorts of exotic worlds might harbor life.

The results were presented to reporters in a teleconference from an extrasolar planet meeting held at the Aspen Center for Physics in Colorado.

Smaller than Pluto

In one of the discoveries, an object just one-fifth the size of Pluto was called the smallest planet ever found outside our solar system. It could be viewed as a large asteroid, too. It all depends on how one sees the confusing array of orbital relationships that astronomers are uncovering.

The object orbits a burned out, fast-spinning neutron star known as a pulsar. Three other roughly Earth-sized planets were already known to circle the pulsar. Their orbits are similar to those of Mercury, Venus, and Earth.

Though rocky, like Earth, all four objects are considered dead worlds, because the star they circle ended its normal glowing life long ago in a massive explosion. Some astronomers prefer not to even list them in planet catalogues.

The newfound small object orbits the pulsar at a distance equal to that from the Sun to the asteroid belt, which is between the orbits of Mars and Jupiter. Observations suggest it marks the outer fringe of material that went into making the miniature solar system.

"Because our observations practically rule out a possible presence of an even more distant, massive planet or planets around the pulsar, it is quite possible that the tiny fourth planet is the largest member of a cloud of interplanetary debris at the outer edge of the pulsar's planetary system," said Penn State researcher Alex Wolszczan, who since 1990 has led the investigation into the system.

Planet or asteroid?

The pulsar is named PSR B1257+12. It is 1,500 light years away in the constellation Virgo.

"Surprisingly, the planetary system around this pulsar resembles our own solar system more than any extrasolar planetary system discovered around a Sun-like star," said Maciej Konacki of Caltech, who worked on the latest finding.

Most of the more than 130 planets detected around Sun-like stars are large and gaseous, many of them much more massive than Jupiter. The smallest known planet around a Sun-like star is about 14 times the mass of Earth. For the most part, technology has not allowed the discovery of less massive planets, presuming they are out there.

The pulsar planetary system has proved easier to probe, thanks to the central star's rapid spin and clockwork pulsation. Wobbles induced by the gravity of the orbiting objects causes slight perturbations in the pulsations.

Pressed on whether an object so small could really be called a planet, Wolszczan told SPACE.com the term is "just a placeholder." Something that has the mass of one-fifth of Pluto, or twice the mass of asteroid Ceres, could be thought of as a large asteroid, he said.

"I don't think that distinction is really important," Wolszczan said. "What is important that we may have found a large member of the debris orbiting the pulsar at the outer edge of the system."

Whatever it's called, the newfound object and the other three roughly Earth-sized objects all orbit the pulsar in the same plane, just as the planets in our solar system -- with the exception of Pluto -- circle the Sun in much the same plane.

That is "solid evidence," Wolszczan said, that the dead worlds evolved out of a protoplanetary disk, the same type of flat, dusty disk that is thought to have given rise to the comets, asteroids and planets in our solar system.

Another strange system

At the other end of the life cycle for stars and planets, NASA's Spitzer Space Telescope has spotted a disk of potential planet-making material around a young brown dwarf.

Brown dwarfs are not massive enough to jumpstart the thermonuclear fusion that fuels real stars. But they are warm enough to be detected by the infrared telescope.

This one, known as OTS 44, is 500 light-years away. It is among the smallest known brown dwarfs, just 15 times the mass of Jupiter. In terms of heft, it's at the border between stars and planets, insofar as astronomers have figured out where that border is.

The flat batch of orbiting gas and dust looks just like a protoplanetary disk. Apparently no planets have developed yet, but the disk has enough material to create one small gas giant planet and a few Earth-sized, rocky worlds, astronomers said.

"We are seeing the ingredients for planets around a brown dwarf near the dividing line between planets and stars," Giovanni Fazio, an astronomer at the Harvard Smithsonian Center for Astrophysics (CfA). "This raises the tantalizing possibility of planet formation around objects that themselves have planetary masses."

No definition

In fact, astronomers have no formal definition for the term "planet" and in recent years have been arguing what exactly constitutes one at both ends of the spectrum.

Several objects known to be half the size of Pluto or bigger and circling our Sun should be considered planets, some say. Or, others argue, Pluto should not be thought of as a planet. And on the upper end, theorists wonder whether an object must orbit a normal star to be considered a planet, and just how massive a planet can be before it's a dim star.

About the only thing astronomers can say for sure is that almost everything they find in space seems to have the potential for an orbiting companion of some sort. And, it is becoming evident that planet formation as it is thought to have happened in our solar system may occur in a similar manner in significantly different environments.

"There may be a host of miniature solar systems out there, in which planets orbit brown dwarfs," said the CfA's Kevin Luhman.

That speculation is bolstered by the recent announcements of what are likely the first photographs of an extrasolar planet, an object that appears to orbit a brown dwarf. (All other discoveries of planets around other stars involve indirect detection methods.)

For Luhman, "this leads to all sorts of new questions, like, 'Could life exist on such planets?' or 'What do you call a planet circling a planet-sized body? A moon or a planet?'"

Asteroids Likely Found around Sun-like Star

Wherever there might be Earth-like planets, there are likely to be asteroids, too. And now astronomers have found evidence for an asteroid belt around another star similar to our Sun.

Previous studies detected asteroid belts around other stars. But the newfound collection of space rocks -- if that's what it is -- is in a setup that might resemble our solar system, scientists announced Wednesday.

Asteroids in our solar system are said to be the detritus of planet formation. They are the objects that either did not grow large enough to achieve planet status, or they were broken apart by collisions back when the solar system was more chaotic.

Those smash-ups, in fact, are the theoretical key to the new discovery.

Asteroid collisions create lots of dust. NASA's Spitzer Space Telescope was used to spot a thick swarm of dust around a star called HD 69830, 41 light-years away. The scientists believe the dust represents a belt of asteroids in which major collisions occur every 1,000 years or so.

"Because this belt has more asteroids than ours, collisions are larger and more frequent, which is why Spitzer could detect the belt," said George Rieke of the University of Arizona. "Our present-day solar system is a quieter place, with impacts of the scale that killed the dinosaurs occurring only every 100 million years or so."

The results will be detailed in the Astrophysical Journal.

HD 69830 is not exactly a twin to our solar system.

The local asteroid belt sits between Mars and Jupiter. The HD 69830 belt is inside a region equivalent to the orbit of Earth, or perhaps half the diameter of Earth's orbit -- its exact extent is not clear. HD 69830's belt contains about 25 times more material. If there's a planet around the star, its night sky would be graced by a band of light, similar to but 1,000 times brighter than the Zodiacal Light seen from Earth.

"The night sky would be quite spectacular," said lead researcher Charles Beichman of the California Institute of Technology.

There are similarities, too. Here, Jupiter's immense gravity shepherds the outer edge of the asteroid belt. An unseen planet perhaps the size of Saturn or even smaller might play that role around HD 69830, the researchers say.

Present technology is incapable of detecting Earth-sized planets around Sun-like stars, which make this new study compelling to planet hunters.

"Asteroids are the leftover building blocks of rocky planets like Earth," Beichman said. "We can't directly see other terrestrial planets, but now we can study their dusty fossils."

Observations do not reveal whether there are any planets around HD 69830. In a NASA-run teleconference with reporters, researchers said a rocky planet cold be possible. Because the star is only about half as powerful as the Sun, however, its "habitable zone" would be confined to a region closer to the star than Earth is to the Sun.

If the asteroid belt around HD 69830 extends to the equivalent of Earth's orbital diameter, then there would be no room left for a habitable planet, said Jonathan Lunine, a planetary scientist at the University of Arizona. If the asteroid belt is confined to half an Earth-orbit diameter, then a rocky planet could have formed and might be close enough to the star to harbor liquid water, said Lunine, who was not involved in the study.

There is an outside chance the presumed asteroid belt is instead dust boiling off a comet the size of Pluto.

"The 'supercomet' theory is a more of a long shot," Beichman said. More observations by Spitzer and ground-based telescopes are planned. "We'll know soon enough."

Planets Found in Potentially Habitable Setup

Three medium-sized planets of roughly the same mass as Neptune have been discovered around a nearby Sun-like star, scientists announced today.

The planets were discovered around HD 69830, a star slightly less massive than the Sun located 41 light-years away in the constellation Puppis (the Stern), using the ultra-precise HARPS spectrograph on the European Southern Observatory's 3.6-meter La Silla telescope in Chile.

The finding, detailed in the May 18 issue of the journal Nature, marks a first for astronomers because previously discovered multi-planet solar systems besides our own contain at least one giant, Jupiter-sized planet.

"For the first time, we have discovered a planetary system composed of several Neptune-mass planets," said study team member Christophe Lovis of the Geneva Observatory in Switzerland.

The setup is similar to our own solar system in many ways: The outermost planets is located just within the star's habitable zone, where temperatures are moderate enough for liquid water to form, and the system also contains an asteroid belt.

The newly discovered planets have masses of about 10, 12 and 18 times that of Earth and they zip around the star in rapid orbits of about 9, 32 and 197 days, respectively.

Based on their distances from the star, two inner worlds nearest the star are rocky planets similar to Mercury, the scientists suspect. The outermost planet is thought to have a solid core of rock and ice and shrouded by a thick gas envelope.

Recent observations by NASA's Spitzer Space Telescope last year revealed that HD 69830 also hosts an asteroid belt, making it the only other Sun-like star known to have one.

When the asteroid belt was found, it was suspected that there might be an unseen planet that was shepherding the asteroids; it now seems that there is more than one shepherd. The researchers think the asteroid belt could lie between the two outermost planets or beyond the third planet.

The planets have not been photographed. They were found using the Doppler, or "wobble," technique, in which astronomers infer the presence of a planet by measuring the gravitational influence it exerts on its parent star. This technique was used to find most of the more than 180 planets so far discovered.

In the early years of planet hunting, the wobble technique was sensitive enough to spot only large, massive planets because they produce more significant stellar wobbles. However, the technique has since been refined to the point where lower-mass planets can now be detected.

Major Discovery: New Planet Could Harbor Water and Life

An Earth-like planet spotted outside our solar system is the first found that could support liquid water and harbor life, scientists announced today.

Liquid water is a key ingredient for life as we know it. The newfound planet is located at the "Goldilocks" distance-not too close and not too far from its star to keep water on its surface from freezing or vaporizing away.

And while astronomers are not yet able to look for signs of biology on the planet, the discovery is a milestone in planet detection and the search for extraterrestrial life, one with the potential to profoundly change our outlook on the universe.

"The goal is to find life on a planet like the Earth around a star like the Sun. This is a step in that direction," said study leader Stephane Udry of the Geneva Observatory in Switzerland. "Each time you go one step forward you are very happy."

The new planet is about 50 percent bigger than Earth and about five times more massive. The new "super-Earth" is called Gliese 581 C, after its star, Gliese 581, a diminutive red dwarf star located 20.5 light-years away that is about one-third as massive as the Sun.

Smallest to date

Gliese 581 C is the smallest extrasolar planet, or "exoplanet," discovered to date. It is located about 15 times closer to its star than Earth is to the Sun; one year on the planet is equal to 13 Earth days. Because red dwarfs, also known as M dwarfs, are about 50 times dimmer than the Sun and much cooler, their planets can orbit much closer to them while still remaining within their habitable zones, the spherical region around a star within which a planet's temperature can sustain liquid water on its surface.

Because it lies within its star's habitable zone and is relatively close to Earth, Gliese 581 C could be a very important target for future space missions dedicated to the search for extraterrestrial life, said study team member Xavier Delfosse of Grenoble University in France.

"On the treasure map of the universe, one would be tempted to mark this planet with an X," Delfosse said.

Two other planets are known to inhabit the red dwarf system. One is a 15 Earth-mass "hot-Jupiter" gas planet discovered by the same team two years ago, which orbits even closer to its star than does Gliese 581 C. Another is an 8 Earth-mass planet discovered at the same time as Gliese 581 C, but which lies outside its star's habitable zone.

Possible waterworld

Computer models predict Gliese 581 C is either a rocky planet like Earth or a waterworld covered entirely by oceans.

"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius [32 to 104 degrees Fahrenheit], and water would thus be liquid," Udry said.

The scientists discovered the new world using the HARP instrument on the European Southern Observatory 3.6 meter telescope in La Sille, Chile. They employed the so-called radial velocity, or "wobble," technique, in which the size and mass of a planet are determined based on small perturbations it induces in its parent star's orbit via gravity.

Udry said there was a fair amount of time between the calculation of Gliese 581 C's size and the realization it was within its star's habitable zone. "That came at the end," Udry said.

When it did hit him, Udry knew he would be spending time fielding phone calls from the media. "You right away think about the journalists who will like it very much," he told SPACE.com.

More to come

David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA) who was not involved in the study, said the new finding is an "absolutely fantastic discovery."

"It means there probably are many more such planets out there," Charbonneau said in a telephone interview. Whether Gliese 581 C harbors life is still unknown, but "it satisfies for the first time a key requirement."

Charbonneau also praised the team's technical skills. "The wobble induced on the star by each of these planets is really tiny-it's just a few meters a second. That means their measurement precision is exquisite," he said.

David Latham, another astronomer at Harvard-Smithsonian CfA, echoed other scientists' praise of the discovery but said the next step is to find a similar world where the orbit of the habitable planet carries it between Earth and its parent star. This will allow scientists to observe it using the transit technique, whereby the small dimming starlight caused by the planet's passage across the face of its sun can be used to calculate its size.

Only then can scientists determine for certain whether the world is rocky or covered by water, Latham said.

Alan Boss, a planetary theorist at the Carnegie Institution of Washington, said the new planet's potential for liquid water made it "fascinating." Gliese 581 C "is the closest planet to another Earth that has been found to date. I hope the SETI folks are listening," Boss said.

Seth Shostak, a senior astronomer at the SETI institute, said the Gliese 581 system has in fact been looked at twice before for signs of intelligent life. The first time was in 1995 using the Parkes Radio Telescope in Australia; the second time occured in 1997 using the 140-foot telescope in Greenbank,West Virgina. Both times revealed nothing.

"It has been looked at twice, but that doesn't mean we shouldn't look at it again," Shostak said. "And indeed we should because this is the best candidate the extrasolar planet guys have come up with yet."

Shostak said he was "jazzed" by the discovery. "This is pointing to something that in the past has only been an assumption, namely that Earth-sized worlds are not rare," he said. "We know of only two [planets in the habitable zone]. We know this one and we know our own. But two is better than one."

Shostak said the Gliese 581 system will likely be looked at again over much wider range of the radio spectrum when the new Allen Telescope Array begins operations this summer.

First planet spotted outside the Milky Way may lie in Andromeda galaxy

London, June 15 (ANI): A team of astronomers has claimed to have seen hints of the first planet to be spotted outside the Milky Way galaxy, in the Andromeda galaxy.

According to a report by BBC News, the team, which has made the finding, is made up of researchers from the National Institute of Nuclear Physics (INFN) in Italy and collaborators in Switzerland, Spain, and Russia.

They exploited a type of gravitational lensing called microlensing to make the discovery.

The effect of large, massive objects between an observer and a distant planet or star can cause distortion or multiple images as the intermediary object's gravity bends the passing light.

Microlensing, by contrast, occurs when a less massive object lies in the middle. The technology is in place to truly see planets of Jupiter's mass and even less in other galaxies

Francesco De Paolis of the INFN and his colleagues developed a computer model to determine the likelihood of detecting an exoplanet via a microlensing event in the Andromeda galaxy.

They modelled the "light curve", the variation in light that a microlensed star would exhibit if it were being orbited by a companion - another star or a planet.

Having determined the clues that a planet in Andromeda would show, they returned to a survey completed in 2004 by the Point-Agape collaboration of astronomers that showed an unusual light curve.

That event, the group says, matches up to its theory and can be attributed to a companion of a mass about six times that of Jupiter.

That suggests either a planet, or a small companion star such as a brown dwarf.

Unfortunately, given that microlensing events from a given pair of objects happens just once, astronomers cannot return to the planet candidate to confirm the idea.

But, Dr De Paolis is encouraged by the possibility of detecting planets at such phenomenal distances.

"The interesting thing is that the technology is in place to truly see planets of Jupiter's mass and even less in other galaxies. It's an exceptional thing," he told BBC News.

Armed with the new theory, the authors of the work are looking to secure time on a larger telescope to continue with their observations in the hope of finding more candidates.

With about 350 extra-solar planets already found in our galactic neighbourhood, Dr De Paolis said, it was likely that such candidates were abundant. (ANI)

Hubble Finds Extrasolar Planets Far Across Galaxy

the planet bonanza was uncovered during a Hubble survey, called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Hubble looked farther than has ever successfully been searched for extrasolar planets. Hubble peered at 180,000 stars in the crowded central bulge of our galaxy 26,000 light-years away. That is one-quarter the diameter of the Milky Way's spiral disk. The results will appear in the Oct. 5 issue of the journal Nature.

This tally is consistent with the number of planets expected to be uncovered from such a distant survey, based on previous exoplanet detections made in our local solar neighborhood. Hubble's narrow view covered a swath of sky no bigger in angular size than two percent the area of the full moon. When extrapolated to the entire galaxy, Hubble's data provides strong evidence for the existence of approximately 6 billion Jupiter-sized planets in the Milky Way.

Five of the newly discovered planets represent a new extreme type of planet not found in any nearby searches. Dubbed Ultra-Short-Period Planets (USPPs), these worlds whirl around their stars in less than one Earth day.

"Discovering the very short-period planets was a big surprise," said team leader Kailash Sahu of the Space Telescope Science Institute, Baltimore. "Our discovery also gives very strong evidence that planets are as abundant in other parts of the galaxy as they are in our solar neighborhood."

Hubble could not view directly the 16 newly found planet candidates. Astronomers used Hubble's Advanced Camera for Surveys to search for planets by measuring the slight dimming of a star due to the passage of a planet in front of it, an event called a transit. The planet would have to be about the size of Jupiter to block enough starlight, about one to 10 percent, to be measurable by Hubble.

The planets are called "candidates" because astronomers could only obtain follow-up mass measurements for two of them due to the distance and faintness of these systems. Following an exhaustive analysis, the team ruled out alternative explanations such as a grazing transit by a stellar companion that could mimic the predicted signature of a true planet. The finding could more than double the number of planets spied with the transit technique to date.

There is a tendency for the planet candidates to revolve around stars more abundant in elements heavier than hydrogen and helium, such as carbon. This supports theories that stars rich in heavy elements have the necessary ingredients to form planets.

The planet candidate with the shortest orbital period, named SWEEPS-10, swings around its star in 10 hours. Located only 740,000 miles from its star, the planet is among the hottest ever detected. It has an estimated temperature of approximately 3,000 degrees Fahrenheit.

"This star-hugging planet must be at least 1.6 times the mass of Jupiter, otherwise the star's gravitational muscle would pull it apart," said SWEEPS team member Mario Livio. "The star's low temperature allows the planet to surrvive so near to the star."

"Ultra-Short-Period Planets seem to occur preferentially around normal red dwarf stars that are smaller and cooler than our sun," Sahu explained. "The apparent absence of USPPs around sun-like stars in our local neighborhood indicates that they might have evaporated away when they migrated too close to a hotter star."

There is an alternative reason why Jupiter-like planets around cooler stars may migrate in closer to the star than such planets around hotter stars. The circumstellar disk of gas and dust out of which they formed extends in closer to a cooler star. Since the discovery of the first "hot Jupiter" around another star in 1995, astronomers have realized this unusual type of massive planet must have spiraled in close to its parent star from a more distant location where it must have formed. The inner edge of a circumstellar disk halts the migration.

Planetary transits occur only when the planet's orbit is viewed nearly edge-on. However, only about 10 percent of hot Jupiters have edge-on orbits that allow the planet to be observed transiting a star. To be successful, transit surveys must view a large number of stars at once. The SWEEPS transit survey covered a rich field of stars in the Sagittarius Window.

The term "window" implies a clear view into the galactic center, but much of the galactic plane is obscured by dust. Hubble monitored 180,000 stars for periodic, brief dimming in a star's brightness. The star field was observed over a continuous seven-day period from Feb. 23-29, 2004. To ensure the dimming was caused by an object orbiting a star, the team used Hubble to detect from two to 15 consecutive transits for each of the 16 planet candidates.

Two stars in the field are bright enough that the SWEEPS team could make an independent confirmation of a planet's presence by spectroscopically measuring a slight wobble in the star's motion due to the gravitational pull of an unseen companion. They used the European Southern Observatory's Very Large Telescope, located on Mount Paranal in Chile, to measure a slight wobble in the star.

One of the planetary candidates has a mass below the detection limit of 3.8 Jupiter masses. The other candidate is 9.7 Jupiter masses, which is below the minimum mass of 13 Jupiter masses for a brown dwarf. A brown dwarf is an object that forms like a star but does not have enough mass to shine by nuclear fusion.

Since the stars are so faint and the field of view is so densely packed with stars, measuring the slight wobble in the star's motion using spectroscopy to confirm most of the planet candidates is not feasible. Future telescopes such as NASA's James Webb Space Telescope will provide the needed sensitivity to confirm most of the planet candidates.

The Hubble SWEEPS program is an important proof-of-concept for NASA's future Kepler Mission, scheduled for launch in 2007. The Kepler observatory will continuously monitor a region of the Milky Way galaxy to detect transiting planets around mostly distant stars. Kepler will be sensitive enough to detect possibly hundreds of Earth-size planet candidates in or near the habitable zone, the distance from a star where liquid water could feasibly exist on a planet's surface.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. The Space Telescope Science Institute conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington.

Earth-sized planet discovered in galaxy outside our solar system

EXOPLANET researchers have discovered the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist.
These amazing discoveries are the outcome of more than four years of observations using the most successful low-mass-exoplanet hunter in the world, the HARPS spectrograph attached to the 3.6-metre ESO telescope at La Silla, Chile.
“The exoplanet research is the detection of a rocky, Earth-like planet in the ‘habitable zone’ - a region around the host star with the right conditions for water to be liquid on a planet’s surface,” says Michel Mayor from the Geneva Observatory, who led the European team to this stunning breakthrough.
Planet Gliese 581 e orbits its host star - located only 20.5 light-years away in the constellation Libra (“the Scales”) - in just 3.15 days. “With only 1.9 Earth-masses, it is the least massive exoplanet ever detected and is, very likely, a rocky planet”, says co-author Xavier Bonfils from Grenoble Observatory.
Being so close to its host star, the planet is not in the habitable zone. But another planet in this system appears to be. From previous observations - also obtained with the HARPS spectrograph at ESO’s La Silla Observatory and announced two years ago - this star was known to harbour a system with a Neptune-sized planet and two super-Earths. With the discovery of Gliese 581 e, the planetary system now has four known planets, with masses of about 1.9 (planet e), 16 (planet b), 5 (planet c), and 7 Earth-masses (planet d). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days.
“Gliese 581 d is probably too massive to be made only of rocky material, but we can speculate that it is an icy planet that has migrated closer to the star,” says team member Stephane Udry. The new observations have revealed that this planet is in the habitable zone, where liquid water could exist. “‘d’ could even be covered by a large and deep ocean - it is the first serious ‘water world’ candidate

Lightest' exoplanet discovered

Astronomers have announced the discovery of the "lightest" planet ever detected outside our Solar System.

Situated in the constellation Libra, it is only about twice as massive as the Earth, whereas most other exoplanets identified have been far bigger.

The scientists say the planet's orbit takes it far too close to its star Gliese 581 for life to be possible.

The detection was made by an international team of researchers using a 3.6m telescope at La Silla, Chile.

This is by far the smallest planet that's ever been detected," said group member Michel Mayor, from the Geneva Observatory, Switzerland.

"This is just one more step in the search for the twin of the Earth.

"At the beginning, we discovered Jupiter-like planets several hundred times the mass of the Earth; and now we have the sensitivity with new instruments to detect very small planets very close to that of the Earth," he told BBC News.

The planet joins three others previously detected around its star and takes the designation Gliese 581 e.

As with the previous discoveries, its presence was picked up using the so-called wobble technique. This is an indirect method of detection that infers the existence of orbiting planets from the way their gravity makes a parent star appear to twitch in its motion across the sky.

Astronomy is working right at the limits of the current technology capable of detecting exoplanets and most of those found so far are Jupiter scale and bigger.

To discover one so small is a major coup. The previous record holder was about four times as massive as the Earth.

Because Gliese 581 e takes just 3.15 days to orbit its host star, it lies beyond what scientists call the habitable, or "Goldilocks", zone, where it is neither too hot nor too cold for liquid water to exist.

But one of the other planets in this system does appear to be. Gliese 581 d was first discovered in 2007. The latest research has allowed scientists to refine details of its orbit.

The team now believes planet d (which is about seven Earth-masses in size) circles Gliese 581 in 66.8 days.

"This planet is probably not just rocky; it's very probably an icy planet - but relatively close to the star so at the surface, we should have some big ocean," said Professor Mayor.

"Maybe, it's the first candidate in a new class of planet called an 'ocean planet'."

The exoplanet discovery was announced at the JENAM conference during the European Week of Astronomy & Space Science, which is taking place at the University of Hertfordshire, UK.

A scientific paper detailing the research has been submitted for publication in the journal Astronomy & Astrophysics.

Upcoming challenge

The US space agency (Nasa) recently launched its Kepler telescope dedicated to finding Earth-size planets. It will use a different approach to the HARPS/La Silla set-up.

Kepler will look for the tiny dip in light coming from a star as a planet crosses its face as viewed from Earth.

Michel Mayor commented: "The challenge in coming years will be to find Earth-mass planets in the habitable zones of stars."

He added: "I'm absolutely confident that in one year or two years, we will arrive at [a planet with] the mass of the Earth."

In the future, some of these planets could be imaged in some detail by the next generation of ground telescopes.

One of these projects, the European Extremely Large Telescope (E-ELT) is currently coming to the end of its design process.

"One of the interesting things about today's announcement is that some of the planets in this system would actually be imageable with the next generation of telescopes," said Isobel Hook, from Oxford University and the UK project scientist on the E-ELT.

"The type of technology coming along, such as extreme adaptive optics, will allow you to produce very sharp images. The seven-Earth-mass planet we think could be imaged directly. You would be able to see it go around its star and see what it was made of," she told BBC News.

Tim de Zeeuw, director-general of the European Southern Observatory (Eso) organisation, which will operate the E-ELT, told BBC News: "The E-ELT will make it possible to take images of (Earth-mass planets) and indeed find evidence for many of them.

"This then leads to very interesting questions: do we find many Solar Systems like our own? Or is there only one like us?"

He added: "I don't follow this field daily... (but) the number of cases we have is steadily growing to a size where we can start asking this question and there are some indications that perhaps our Solar System is a little unusual."

The 42m E-ELT comprises five large mirrors. Its adaptive optics system will compensate for the distortions to images of the sky caused by turbulence in the Earth's atmosphere.

Construction of the ground observatory could begin in 2011 if all goes to plan. Eso intends to select a location for the telescope by the end of this year.

Six sites have been shortlisted: three in Chile; one in the Canary Islands, Spain; one in Morocco; and one in Argentina.

Hint of planet outside our galaxy

Astronomers believe they have seen hints of the first planet to be spotted outside of our galaxy.

Situated in the Andromeda galaxy, the planet appears to be about six times the mass of Jupiter.

The method hinges on gravitational lensing, whereby a nearer object can bend the light of a distant star when the two align with an observer.

The results will be published in Monthly Notices of the Royal Astronomical Society (MNRAS).

The team, made up of researchers from the National Institute of Nuclear Physics (INFN) in Italy and collaborators in Switzerland, Spain, and Russia, exploited a type of gravitational lensing called microlensing.

The effect of large, massive objects between an observer and a distant planet or star can cause distortion or multiple images as the intermediary object's gravity bends the passing light. Microlensing, by contrast, occurs when a less massive object lies in the middle.
There is a noticeable increase in the observed intensity of light coming from the aligned pair as the intermediate object focuses the distant one's light.

Because the effect depends on smaller objects that will be moving quickly relative to one another, microlensing events are fleeting, happening over the course of minutes or hours. Moreover, the mutual alignment of two small, far-flung objects with an observer on the Earth is exceptionally rare.

For that reason, dense collections of millions of stars, such as the Andromeda galaxy, are surveyed in order to detect them.

'Exceptional'

Francesco De Paolis of the INFN and his colleagues developed a computer model to determine the likelihood of detecting an exoplanet via a microlensing event in the Andromeda galaxy.

They modelled the "light curve", the variation in light that a microlensed star would exhibit if it were being orbited by a companion - another star or a planet.

Having determined the clues that a planet in Andromeda would show, they returned to a survey completed in 2004 by the Point-Agape collaboration of astronomers that showed an unusual light curve.

That event, the group says, matches up to its theory and can be attributed to a companion of a mass about six times that of Jupiter.

That suggests either a planet, or a small companion star such as a brown dwarf.
Unfortunately, given that microlensing events from a given pair of objects happen just once, astronomers cannot return to the planet candidate to confirm the idea.

But Dr De Paolis is encouraged by the possibility of detecting planets at such phenomenal distances.

"The interesting thing is that the technology is in place to truly see planets of Jupiter's mass and even less in other galaxies," he told BBC News. "It's an exceptional thing."

Armed with the new theory, the authors of the work are looking to secure time on a larger telescope to continue with their observations in the hope of finding more candidates.

With about 350 extra-solar planets already found in our galactic neighbourhood, Dr De Paolis said, it was likely that such candidates were abundant. The difficulty is in catching sight of one through a gravitational lens.

"It's not easy, obviously," he said. "The problem is that we don't know when a gravitational microlensing event is going to happen.

Introduction of Planets

Do you know what a planet is? If so, you are doing better than professional astronomers! Right now astronomers aren't quite sure how to define a planet.

Maybe you've heard that some astronomers think Pluto is a planet, but others think that it isn't. Pluto is a lot smaller than the other eight planets, even Mercury, which is the second smallest. In recent years, astronomers have discovered a whole bunch of new objects like Pluto. Most of these new worlds are in the Kuiper Belt, a part of our Solar System near Pluto. These Kuiper Belt Objects

(KBOs) are big balls of rock and ice, like Pluto. One of them is probably even larger than Pluto.



Some astronomers think that Pluto and all the KBOs are not planets. Other astronomers think that any KBO at least as big as Pluto should be called a planet. There may be more KBOs bigger than Pluto out there that we haven't found yet. We might have 20 or more planets in our Solar System some day! Some people think that we should still call Pluto a planet, because we've been calling it a planet for many years. Many of those people don't think other KBOs are planets, though.

Astronomers agree about two things. To be a planet, and object must orbit a star. If it orbits something else, like another planet, it is a moon instead. The second point is that the object must be big enough that gravity makes it into a sphere. Many asteroids and comets have odd shapes. They are definitely not planets.

Mars Introduction The Red Planet

Mars is the fourth planet from the Sun and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red color was observed by stargazers throughout history. It was given its name by the Romans in honor of their god of war. Other civilizations have had similar names. The ancient Egyptians named the planet Her Descher meaning the red one.

Before space exploration, Mars was considered the best candidate for harboring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings. In 1938, when Orson Welles broadcasted a radio drama based on the science fiction classic War of the Worlds by H.G. Wells, enough people believed in the tale of invading Martians to cause a near panic.

Another reason for scientists to expect life on Mars had to do with the apparent seasonal color changes on the planet's surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months and cause plant life to become dormant during colder periods.

In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealed was a surface containing many craters and naturally occurring channels but no evidence of artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the landers discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open.

Other instruments found no sign of organic chemistry at either landing site, but they did provide a precise and definitive analysis of the composition of the Martian atmosphere and found previously undetected trace elements.
Atmosphere

The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The six most common components of the atmosphere are:

* Carbon Dioxide (CO2): 95.32%
* Nitrogen (N2): 2.7%
* Argon (Ar): 1.6%
* Oxygen (O2): 0.13%
* Water (H2O): 0.03%
* Neon (Ne): 0.00025 %

Martian air contains only about 1/1,000 as much water as our air, but even this small amount can condense out, forming clouds that ride high in the atmosphere or swirl around the slopes of towering volcanoes. Local patches of early morning fog can form in valleys. At the Viking Lander 2 site, a thin layer of water frost covered the ground each winter.

There is evidence that in the past a denser martian atmosphere may have allowed water to flow on the planet. Physical features closely resembling shorelines, gorges, riverbeds and islands suggest that great rivers once marked the planet.
Temperature and Pressure

The average recorded temperature on Mars is -63° C (-81° F) with a maximum temperature of 20° C (68° F) and a minimum of -140° C (-220° F).

Barometric pressure varies at each landing site on a semiannual basis. Carbon dioxide, the major constituent of the atmosphere, freezes out to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of snow and then evaporates again with the coming of spring in each hemisphere. When the southern cap was largest, the mean daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of the year it was as high as 9.0 millibars. The pressures at the Viking Lander 2 site were 7.3 and 10.8 millibars. In comparison, the average pressure of the Earth is 1000 millibars.

Views of Mars

Views of Mars


Mars with Clouds Mars With Cloud Cover

This image of mars came from a series of pictures taken by the Mars Global Surveyor wide angle cameras. A map was created and then wrapped around a sphere to generate this view of Mars. Here, bluish-white water ice clouds hang above the Tharsis volcanoes. (Copyright 2005 by Calvin J. Hamilton)




Planet Mars Large Mosaic of Mars

This image is a large mosaic of the Valles Marineris [VAL-less mar-uh-NAIR-iss] hemisphere of Mars. It is a view similar to that which one would see from a spacecraft. The lower center of the scene shows the entire Valles Marineris canyon system, more than 3,000 kilometers (1,860 miles) long and up to 8 kilometers (5 miles) deep, extending from Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain and north-central canyons and run north. Many of the channels flowed into a basin called Acidalia Planitia, which is the dark area in the extreme north of this picture. The three Tharsis volcanoes (dark red spots), each about 25 kilometers (16 miles) high, are visible to the west along with Olympus Mons the largest volcano on the planet. Very ancient terrain covered by many impact craters lies to the south of Valles Marineris. The polar cap can be seen to the north. (Copyright Calvin J. Hamilton)

Interior of Mars The Interior of Mars

The current understanding of the interior of Mars suggests that it can be modeled with a thin crust, similar to Earth's, a mantle and a core. Using four parameters, the Martian core size and mass can be determined. However, only three out of the four are known and include the total mass, size of Mars, and the moment of inertia. Mass and size was determined accurately from early missions. The moment of inertia was determined from Viking lander and Pathfinder Doppler data, by measuring the precession rate of Mars. The fourth parameter, needed to complete the interior model, will be obtained from future spacecraft missions. With the three known parameters, the model is significantly constrained. If the Martian core is dense (composed of iron) similar to Earth's or SNC meteorites thought to originate from Mars, then the minimum core radius would be about 1300 kilometers. If the core is made out of less-dense material such as a mixture of sulfur and iron, the maximum radius would probably be less than 2000 kilometers. (Copyright 1998 by Calvin J. Hamilton)

Topography Map of Mars Topography Map of Mars


This image is a newly released topographic map of Mars. The full range of topography on Mars is about 19 miles (30 kilometers), one and a half times the range of elevations found on Earth, The most curious aspect of the map is the striking difference between the planet's low, smooth Northern Hemisphere and the heavily cratered Southern Hemisphere," which sits, on average, about three miles (five kilometers) higher than the north. (Courtesy GSFC/NASA)

Schiaparelli Hemisphere of Mars Schiaparelli Hemisphere

This image is a mosaic of the Schiaparelli hemisphere of Mars. The center of this image is near the impact crater Schiaparelli, 450 kilometers (280 miles) in diameter. The dark streaks with bright margins emanating from craters in the Oxie Palus region, upper left of image, are caused by erosion and/or deposition by the wind. Bright white areas to the south, including the Hellas impact basin at extreme lower right, are covered by carbon dioxide frost. (Courtesy USGS)
Candor Chasm Central Candor Chasm - Oblique View


This image shows part of Candor Chasm in Valles Marineris. It is centered at Latitude -5.0, Longitude 70.0. The view is from the north looking into the chasm. Candor Chasm's geomorphology is complex, shaped by tectonics, mass wasting, wind, and perhaps by water and volcanism. (Courtesy USGS)



Candor Chasm West Candor Chasm (Enhanced Color)


This picture (centered at latitude 4° S, longitude 76° W) shows areas of central Valles Marineris, including Candor Chasm (lower left), Ophir Chasm (lower right), and Hebes Chasm (upper right). Complex layered deposits in the canyons may have been deposited in lakes, and if so, are of great interest for future searches for fossil life on Mars. The pinkish deposits in Candor Chasm may be due to hydrothermal alterations and the production of crystalline ferric oxides. ((Geissler et al., 1993, Icarus 106,380). Viking Orbiter Picture Numbers 279B02 (violet), 279B10 (green), and 279B12 (red) at 240 meters/pixel resolution. Picture width is 231 kilometers. North is 47° clockwise from top.)

Ophir Chasma Ophir Chasma


Ophir Chasma is a large west-northwest-trending trough about 100 km wide. The Chasma is bordered by 4 km high walled cliffs, most likely faults, that show spur-and-gully morphology and smooth sections. The walls have been dissected by landslides forming reentrants; one area (upper left) on the north wall shows a young landslide about 100 km wide. The volume of the landslide debris is more than 1000 times greater than that from the May 18, 1980 debris avalanche from Mount St. Helens. The longitudinal grooves seen in the foreground are thought to be due to differential shear and lateral spreading at high velocities. The landslide passes between mounds of interior layered deposits on the floor of the chasma. (Courtesy USGS)

Landslide in Valles Marineris Landslide in Valles Marineris


Although Valles Marineris originated as a tectonic structure, it has been modified by other processes. This image shows a close-up view of a landslide on the south wall of Valles Marineris. This landslide partially removed the rim of the crater that is on the plateau adjacent to Valles Marineris. Note the texture of the landslide deposit where it flowed across the floor of Valles Marineris. Several distinct layers can be seen in the walls of the trough. These layers may be regions of distinct chemical composition or mechanical properties in the Martian crust. (Copyright Calvin J. Hamilton; Caption: LPI)

Hubble Images of Mars HST 3 Views of Mars at Opposition


These Hubble Space Telescope views provide the most detailed complete global coverage of the Red Planet ever seen from Earth. The pictures were taken on February 25, 1995, when Mars was at a distance of 103 million kilometers (65 million miles). To the surprise of researchers, Mars is cloudier than seen in previous years. This means the planet is cooler and drier, because water vapor in the atmosphere freezes out to form ice-crystal clouds. The three images show the Tharsis, Valles Marineris and Syrtis Major regions. (Credit: Philip James, University of Toledo; Steven Lee, University of Colorado; and NASA)

Channel Ravi Vallis Outflow Source of Channel Ravi Vallis
This image of the head of Ravi Vallis shows a 300-kilometer (186-mile) long portion of a channel. Like many other channels that empty into the northern plains of Mars, Ravi Vallis orginates in a region of collapsed and disrupted ("chaotic") terrain within the planet's older, cratered highlands. Structures in these channels indicate that they were carved by liquid water moving at high flow rates. The abrupt beginning of the channel, with no apparent tributaries, suggests that the water was released under great pressure from beneath a confining layer of frozen ground. As this water was released and flowed away, the overlying surface collapsed, producing the disruption and subsidence shown here. Three such regions of chaotic collapsed material are seen in this image, connected by a channel whose floor was scoured by the flowing water. The flow in this channel was from west to east (left to right). This channel ultimately links up with a system of channels that flowed northward into Chryse Basin. (Copyright Calvin J. Hamilton; Caption: LPI)

Streamlined Islands Streamlined Islands
The water that carved the channels to the north and east of the Valles Marineris canyon system had tremendous erosive power. One consequence of this erosion was the formation of streamlined islands where the water encountered obstacles along its path. This image shows two streamlined islands that formed as the water was diverted by two 8-10 kilometer (5-6 mile) diameter craters lying near the mouth of Ares Vallis in Chryse Planitia. The water flowed from south to north (bottom to top of the image). The height of the scarp surrounding the upper island is about 400 meters (1,300 feet), while the scarp surrounding the southern island is about 600 meters (2,000 feet) high. (Copyright Calvin J. Hamilton; Caption: LPI)

Mars: Valley Network Valley Network
Unlike the features shown in the above two images, many systems on Mars do not show evidence of catastrophic flooding. Instead, they show a resemblance to drainage systems on Earth, where water acts at slow rates over long periods of time. As on Earth, the channels shown here merge together to form larger channels.

However, these valley networks are less developed than typical terrestrial drainage systems, with the Martian examples lacking small-scale streams feeding into the larger valleys. Because of the absence of small-scale streams in the Martian valley networks, it is thought that the valleys were carved primarily by ground water flow rather than by runoff of rain. Although liquid water is currently unstable on the surface of Mars, theoretical studies indicate that flowing groundwater might be able to form valley networks if the water flowed beneath a protective cover of ice. Alternatively, because the valley networks are confined to relatively old regions of Mars, their presence may indicate that Mars once possessed a warmer and wetter climate in its early history. (Copyright Calvin J. Hamilton; Caption: LPI)

Mars South Pole South Polar Cap
This image shows the south polar cap of Mars as it appears near its minimum size of about 400 kilometers (249 miles). It consists mainly of frozen carbon dioxide. This carbon dioxide cap never melts completely. The ice appears reddish due to dust that has been incorporated into the cap. (Courtesy NASA)

Mars North Pole North Polar Cap
This image is an oblique view of the north polar cap of Mars. Unlike the south polar cap, the north polar cap probably consists of water-ice. (Copyright Calvin J. Hamilton)

Mars Laminated Terrain Polar Laminated Terrain
One of the discoveries of the Mariner 9 spacecraft was that the south polar cap of Mars was made of thin layers or laminations of ice and sediment. Four years later, on October 10, 1976, the Viking 2 spacecraft took this picture of the Martian north polar cap. The visible layering occurred as a result of wind born dust settling upon the polar cap. As the caps experience climatic variations, they expand and contract. The layers of dust sediment tend to grow thicker near the poles where ice deposits remain for longer periods of time. The thickness of the deposits indicates they were formed during cyclical climatic variation rather than annual changes. As ice withdraws from a region, wind exposes the layers sculpting valleys and scarps. The formation of layered deposits is an active process today. (Copyright 1998 by Calvin J. Hamilton)

Mars Dunefield Dunefield
This image shows several dune types which are found in the north circumpolar dunefield. This thumnail image shows a section of transverse dunes. The full image has a field of traverse dunes on the left and barchan dunes on the right with a transition zone inbetween. Transverse dunes are oriented perpendicular to the prevailing wind direction. They are long and linear, and frequently join their neighbor in a low-angle "Y" junction. Barchan dunes are crescent-shaped mounds with downwind-pointing horns. These dunes are comparable in size to the largest dunes found on the Earth. (Copyright Calvin J. Hamilton)

Mars Local Dust Storm Local Dust Storm
Local dust storms are relatively common on Mars. They tend to occur in areas of high topographic and/or high thermal gradients (usually near the polar caps), where surface winds would be strongest. This storm is several hundreds of kilometers in extent and is located near the edge of the south polar cap. Some local storms grow larger, others die out. (Copyright Calvin J. Hamilton; caption by LPI)

Mars: White Rock White Rock
This image shows a lesser known, but unusual feature on Mars. It is commonly called "White Rock". The white feature is eroded crater fill, but exactly how it was formed has not been satisfactorily explained. White Rock was not formed by polar processes because it lies near to the equator at latitude -8 degrees and longitude 355 degrees. It has been modified through aeolian erosion showing transverse and longitudinal erosional features. (Copyright 1998 by Calvin J. Hamilton)

Martian Atmosphere Martian Atmosphere
This oblique image taken by the Viking orbiter spacecraft shows a thin band of the Martian atmosphere. This image looks northeast across the Argyre basin. The Argyre basin is about 600 kilometers across with a rugged rim of about 500 kilometers in width. (Copyright 1997 by Calvin J. Hamilton)

Life from Mars: The Discovery

A NASA research team of scientists at the Johnson Space Center and at Stanford University has found evidence that strongly suggests primitive life may have existed on Mars more than 3.6 billion years ago. The NASA-funded team found the first organic molecules thought to be of Martian origin; several mineral features characteristic of biological activity; and possible microscopic fossils of primitive, bacteria-like organisms inside of an ancient Martian rock that fell to Earth as a meteorite. This array of indirect evidence of past life will be reported in the August 16 issue of the journal Science, presenting the investigation to the scientific community at large to reach a future consensus that will either confirm or deny the team's conclusion.

Mars Pathfinder Mission

Panoramic Views of the Landing site from Sagan Memorial Station
Each of these panoramic views is a controlled mosaic of approximately 300 IMP images covering 360 degrees of azimuth and elevations from approximately 4 degrees above the horizon to 45 degrees below it. Simultaneous adjustment of orientations of all images has been performed to minimize discontinuities between images. Mosaics have been highpass-filtered and contrast-enhanced to improve discrimination of details without distorting relative colors overall.

TOP IMAGE: Enhanced true-color image created from the 'Gallary Pan' sequence, acquired on sols 8-10 so that local solar time increases nearly continuously from about 10:00 at the right edge to about 12:00 at the left. Mosaics of images obtained by the right camera through 670 nm, 530 nm, and 440 nm filters were used as red, green and blue channels. Grid ticks indicate azimuth clockwise from north in 30 degree increments and elevation in 15 degree increments.

BOTTOM IMAGE: Anaglyphic stereoimage created from the 'monster pan' sequence, acquired in four sections between about 8:30 and 15:00 local solar time on sol 3. Mosaics of images obtained through the 670 nm filter (left camera) and 530 and 440 nm filters (right camera) were used where available. At the top and bottom, left- and right-camera 670 nm images were used. Part of the northern horizon was not imaged because of the tilt of the lander. This image may be viewed stereoscopically through glasses with a red filter for the left eye and a cyan filter for the right eye. (Courtesy USGS)

Coordinate Map of Rocks at Pathfinder Landing Site
Mars-local-level (LL frame) coordinate map of rocks counted at the Mars Pathfinder landing site. Positions, apparent diameters (D), and heights (H) were measured to the nearest centimeter in the Marsmap virtual reality environment constructed from the "Monster Pan". (Courtesy USGS)

Many Rovers
Various images of the Sojourner rover shot by the Pathfinder cameras have been composited into the Presidential Panorama. Since the camera's position was consistent, it is thus possible to see these images of the rover in the context of the entire landscape. This provides a visual scale for understanding the sizes and distances of rocks surrounding the lander as well as a record of the travels of the rover. (Courtesy Carol Stoker/NASA AMES)

Sunset over Twin Peaks
This image was taken by the Imager for Mars Pathfinder (IMP) about one minute after sunset on Mars on Sol 21. The prominent hills dubbed "Twin Peaks" form a dark silhouette at the horizon, while the setting sun casts a pink glow over the darkening sky. The image was taken as part of a twilight study which indicates how the brightness of the sky fades with time after sunset. Scientists found that the sky stays bright for up to two hours after sunset, indicating that Martian dust extends very high into the atmosphere. (Courtesy University of Arizona)

Clouds Over the Eastern Martian Horizon
Pink stratus clouds are coming from the northeast at about 15 miles per hour (6.7 meters/second) at an approximate height of ten miles (16 kilometers) above the surface. The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken by the Imager for Mars Pathfinder (IMP) on Sol 16 about forty minutes before sunrise showing areas of the eastern Martian horizon. (Courtesy University of Arizona)

Wind Effects on Martian Soil
This false-color combination image highlights details of wind effects on the Martian soil at the Pathfinder landing site. Red and blue filter images have been combined to enhance brightness contrasts among several soil units. Martian winds have distributed these lighter and darker fine materials in complex patterns around the rocks in the scene (blue). For scale, the rock at right center is 16 centimeters (6.3 inches) long. This scene is one of several that will be monitored weekly for changes caused by wind activity. (Courtesy University of Arizona)

Sojourner at Mermaid Dune
This is an image of the rover Sojourner at the feature called Mermaid Dune at the MPF landing site. Mermaid is thought to be a low, transverse dune ridge, with its long (approximately 2 meter) axis transverse to the wind, which is thought to come from the lower left of the image and blow toward the upper right. The rover is facing to the lower left, the "upwind" direction. The rover's middle wheels are at the crestline of the small dune, and the rear wheels are on the lee side of the feature. A soil mechanics experiment was performed to dig into the dune and examine the sediments exposed. (Courtesy University of Arizona)

Clouds over Mars!
This is the first color image ever taken from the surface of Mars of an overcast sky. Featured are pink stratus clouds coming from the northeast at about 15 miles per hour (6.7 meters/second) at an approximate height of ten miles (16 kilometers) above the surface. The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken about an hour and forty minutes before sunrise by the Imager for Mars Pathfinder (IMP) on Sol 16 at about ten degrees up from the eastern Martian horizon. (Courtesy University of Arizona)

Roadrunner Flats
This enhanced color image of the Pathfinder landing site shows the eastern horizon. The elongated, reddish, low contrast region in the distance is "Roadrunner Flats". This image was taken by the Imager for Mars Pathfinder (IMP). (Courtesy USGS)

Closeup of Mermaid Dune
This pair of images shows a broad view (upper image) and detailed close-up view (lower image) of the disturbed surface near and on Mermaid Dune. Seen slightly right of center in the upper image are two diggings by the rover's wheel. The uppermost rut is in the surface away from Mermaid and is considered to be typical of the surface at the landing site. The closer rut represents the surface at the base of Mermaid on the upwind side. The lower image is an enlargement of the disturbed Mermaid sediments plus those of the underlying substrate; that is, the ground upon which the dune lies. Seen in the close-up are at least two types of sediment, one that seems to be approximately 1.4 cm thick and forms piles with sides sloping at approximately 35 degrees, and another at least 3 cm deep composed of sediment that has a characteristic slope of 41 degrees when piled. It is apparent in the images that there is a size range of sediment present in the rut, sediment that ranges from a few millimeters in size down to below the resolution of the camera. (Courtesy USGS)

Overhead View of Pathfinder Landing Site
Planimetric (overhead view) map of the landing site, to a distance of 20 meters from the spacecraft. North is at the top in this and Plates 3-5. To produce this map, images were geometrically projected onto an assumed mean surface representing the ground. Features above the ground plane (primarily rocks) therefore appear displaced radially outward; the amount of distortion increases systematically with distance. The upper surfaces of the lander and rover also appear enlarged and displaced because of their height. Primary grid (white) is based on the Landing Site Cartographic (LSC) coordinate system, defined with X eastward, Y north, and Z up, and origin located at the mean ground surface immediately beneath the deployed position of the IMP camera gimbal center. Secondary ticks (cyan) are based on the Mars local level (LL) frame, which has X north, Y east, Z down, with origin in the center of the lander baseplate. Rover positions (including APXS measurements) are commonly reported in the LL frame. Yellow grid shows polar coordinates based on the LSC system. Cartographic image processing by U.S. Geological Survey. (Courtesy USGS)

Shark
This false color composite image from the Pathfinder lander shows the rock "Shark" at upper right (Shark is about 0.69 m wide, 0.40 m high, and 6.4 m from the lander). The rock looks like a conglomerate in Sojourner rover images, but only the large elements of its surface textures can be seen here. This demonstrates the usefulness of having a robot rover geologist able to examine rocks up close. (Courtesy USGS)

Rock Garden
This false color composite image of the Rock Garden shows the rocks "Shark" and "Half Dome" at upper left and middle, respectively. Between these two large rocks is a smaller rock (about 0.20 m wide, 0.10m high, and 6.33 m from the Lander) that was observed close- up with the Sojourner rover. (Courtesy USGS)

Cabbage Patch
This Sojourner rover image of the Cabbage Patch shows small rounded objects on the surface that are about 3-4 cm across. Some of these are within excavations, which are about 0.5 cm wide. Several questions arise about the pebbles: Why are they rounded? Where did they come from? What do they mean?

Geologists use MULTIPLE WORKING HYPOTHESES when attempting to explain observations. Some hypotheses that could account for the pebbles are:

1. They were rounded during transport by waters of catastrophic floods and deposited on the Ares Vallis flood plain.
2. They were rounded by wave action on an ancient Martian beach.
3. They were rounded during glacial transport.
4. They are glasses that were produced by melting during impact cratering. The glass was first ejected from the crater, then molded into spherical shapes or drops as it traveled through the atmosphere, and finally was deposited at the sites.
5. They are spatter from lava flows.
6. They are nodules brought up from the deep Martian interior by lava flows or pyroclastic eruptions.
7. They are concretions formed in sedimentary rocks.
8. They came from ancient conglomerate rocks. The pebbles were rounded by water action and subsequently lithified into conglomerate rocks. Later, the waters of catastrophic floods transported the conglomerates and deposited them on the Ares flood plain. The pebbles were then freed from the rocks by weathering.
9. A combination of the above.

(Courtesy USGS)

Pebbles and Cobbles at Mars Pathfinder Site
Pebbles are seen in lander images, along with cobbles. For example, in this picture, we see the same pebbles that were visible in the Sojourner rover image of the "Cabbage Patch". In addition, a cobble within the rock "Lamb" (upper left) is apparent. This indicates that Lamb may be a conglomerate (Lamb is 0.32 m x 0.15 m). (Courtesy USGS)

Pebbles, Cobbles, and Sockets
This Rover image of "Shark" (upper left center), "Half Dome" (upper right), and a small rock (right foreground) reveal textures and structures not visible in lander camera images. These rocks are interpreted as conglomerates because their surfaces have rounded protrusions up to several centimeters in size. It is suggested that the protrusions are pebbles and granules. (Courtesy USGS)

Sockets and Pebbles
This close-up Sojourner rover image of a small rock shows that weathering has etched-out pebbles to produce sockets. In the image, sunlight is coming from the upper left. Sockets (with shadows on top) are visible at the lower left and pebbles (with bright tops and shadowed bases) are seen at the lower center and lower right. Two pebbles (about 0.5 cm across) are visible at the lower center. (Courtesy USGS)

Topographic Map of Pathfinder Landing Site
Topographic map of the landing site, to a distance of 60 meters from the lander in the LSC coordinate system. The lander is shown schematically in the center; 2.5 meter radius circle (black) centered on the camera was not mapped. Gentle relief [root mean square (rms) elevation variation 0.5 m; rms adirectional slope 4O] and organization of topography into northwest and northeast-trending ridges about 20 meters apart are apparent. Roughly 30% of the illustrated area is hidden from the camera behind these ridges. Contours (0.2m interval) and color coding of elevations were generated from a digital terrain model, which was interpolated by kriging from approximately 700 measured points. Angular and parallax point coordinates were measured manually on a large (5m length) anaglyphic uncontrolled mosaic and used to calculate Cartesian (LSC) coordinates. Errors in azimuth on the order of 1O are therefore likely; elevation errors were minimized by referencing elevations to the local horizon. The uncertainty in range measurements increases quadratically with range. Given a measurement error of 1/2 pixel, the expected precision in range is ~ 0.3 meter at 10 meter range, and ~ 10 meters at 60 meter range. Repeated measurements were made, compared, and edited for consistency to improve the range precision. Systematic errors undoubtedly remain and will be corrected in future maps compiled digitally from geometrically controlled images. Cartographic processing by U.S. Geological Survey. (Courtesy USGS)

Mars Exploration Rovers Mission

NASA's twin robot geologists, the Mars Exploration Rovers, Spirit and Opportunity, were launched toward Mars on June 10 and July 7, 2003, in search of answers about the history of water on Mars. Spirit successfully landed on January 3, 2004 at 8:35 p.m. Pacific Standard time. Opportunity sucessfully landed on January 24, 2004 at 9:05 p.m. PST, Saturday.



Primary among the mission's scientific goals is to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The spacecraft are targeted to sites on

opposite sides of Mars that appear to have been affected by liquid water in the past. The landing sites are at Gusev Crater, a possible former lake in a giant impact crater, and Meridiani Planum, where mineral deposits (hematite) suggest Mars had a wet past.

After the airbag-protected landing craft settle onto the surface and open, the rovers roll out to take panoramic images. These will give scientists the information they need to select promising geological targets that will tell part of the story of water in Mars' past. Then, the rovers will drive to those locations to perform on-site scientific investigations over the course of their 90-day mission.

The Rationale for Exploring Mars

Mars Exploration

The human exploration of Mars will be an enterprise that confirms the potential for humans to leave their home planet and make their way outward into the cosmos. Though just a small step on a cosmic scale, it will be a significant one for humans, because it will require going away from Earth with very limited capability to return. Once committed to a journey to Mars, astronauts will not be able to return until the alignment of the planets allows their return. This is the most radical difference between this exploration and all previous explorations. There is a very narrow window within which return is possible, and the commitment to launch is a commitment to three years in space.

Mars is an intriguing and exciting planet, and there are many adventures and findings that await explorers. We must prepare for these before we go, providing the tools that the explorers will use, anticipating as much as possible the situations they will encounter and preparing them for the unexpected. For the first time in a space exploration mission, it will be up to the crew to solve their own emergency problems. At the distance of Mars from the Earth, it can be as much as 40 minutes from the time a message goes out from Earth to the time an answer is received back on Earth. The crews and their systems must be able to accomplish their objectives in a highly autonomous manner.

Exploration Program Objectives

1. Science

Mars is an intriguing planet, for what it can tell us about the origin and history of planets and of life. Visible to the ancients, and distinctly reddish in the night sky, the next planet has always been an attractive subject for imaginative science fiction. As the capability for space exploration grew in the 1960's, it became clear that Mars is not, like Earth, a planet teeming with life, and is now a hostile environment for humans. The images of Mariner 4 showed a Moon-like terrain, dominated by large impact craters. This terrain now is believed to an represent ancient crust, similar to the Moon's, formed in an initial period of planetary differentiation. Mariner 9 showed for the first time that Mars was not totally Moon-like, but exhibits later volcanic and tectonic features. Large volcanos of relatively recent activity and large crustal rifts due to tensional forces demonstrate the working of internal forces. The absolute time scale is not accurately calibrated, however, by analogy with the Moon, the initial crustal formation may have occurred between 4 billion and 4.5 billion years ago, and the apparent freshness of the large martian volcanos suggests their formation within the last billion years.

Mars' atmosphere consists largely of carbon dioxide, with a typical surface pressure of about .01 Earth atmospheres, and surface temperatures that may reach 25 C on the equator in mid-summer, but are generally much colder. At these pressures and temperatures, water can not exist in liquid form on the surface. However, Mariner 9 and the subsequent Viking missions observed features which indicate that liquid water has been present on Mars' surface in past epochs. Evidence of both running water and standing water has been noted. The interpretation is that the atmosphere of Mars was thicker and warmer in former times, and perhaps much like the Earth's early atmosphere before the appearance of oxygen. Three questions arise: (a) What was the reason for the change of atmospheric conditions on Mars? (b) What are the implications of such changes for environmental changes on Earth?; and (c) Is it possible that life arose in the early Earth-like history of Mars (and, if it arose, can it still be found somewhere on Mars)?

These three scientific questions are at the core of the Mars scientific exploration defined by the Reference Mission. They can all be addressed principally by understanding the geological characteristics of the planet - the types of rocks present, their absolute and relative ages, the distribution of subsurface water, the history of volcanic activity, the distribution of life-forming elements and compounds, and others. These attributes all have to be understood in the context of what we know about the Earth, Moon and other bodies of our solar system.

2. Human Expansion

The dream of human exploration of Mars is intimately tied to the belief that new lands create new opportunities. In human history, migrations of people have been stimulated by overcrowding, exhaustion of resources, the search for religious or economic freedom, competitive advantage, and other human concerns. Rarely have humans entered new territory, then completely abandoned it. In the past, there have always been a few people who were adventurous enough to adopt a newly-found territory as their home. Most of these settlements have eventually become economically self-sufficient, and have enlarged the genetic and economic diversity of humanity. The technological revolution of the 20th Century, with high speed communication and transportation and integrated economic activity, has reversed the trend toward human diversity; however, settlement of the planets can once again enlarge the sphere of human action and life.

The settlement of Mars presents new problems and challenges. Principal among these is the absence of a livable natural environment. That, and the current high cost of transportation are the main barriers to human expansion there. The fact that humans, once on Mars, can not easily return to the Earth, and then only at specified times approximately 26 months apart, makes it necessary to develop systems with high reliability and robustness. The creation of a livable, artificial environment, is technically feasible. The high cost of transportation will ultimately be reduced. The Reference Mission is not a program to settle Mars; however, the objectives of the Reference Mission are to establish the feasibility of and the technological basis for human settlement of the planet.

3. International Cooperation

The space age gained its start in a period of intense technical and social competition between east and west, represented by the Soviet Union and the United States. Competition during the International Geophysical Year resulted in the Soviet Union being the first to launch a satellite into Earth orbit, and served as a challenge and reminder to the United States that technological supremecy was not solely the province of the United States. The start of the Apollo program was a political decision based more on the perception of the political and technological rewards to be gained by attacking a truly difficult objective in a constrained time period. The space race began, the United States won it, and a few years later, the Soviet Union had collapsed.

Fortunately, the Russians did not view the Apollo success as a reason to terminate their program, and they continued to develop capabilities that are fully on a par with United States capabilities in many areas. Also, during the post-Apollo time frame, space capability grew in Europe, with the formation of the European Space Agency, in Japan, China and other countries.

The basis has been laid for a truly international approach to Mars exploration. The exploration of Mars should be an international enterprise.

It would exhibit a great vanity for any country to undertake human exploration of Mars alone, particularly when others, who may not now have the required magnitude of capability or financial resources, do have the underlying technological knowhow. Mars should be an objective in which all humanity can share. An underlying requirement for the Reference Mission is that it be implemented by a multinational group of nations and explorers.