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.