Kepler Finds First Earth-Sized Planets

Just a couple of weeks after announcing the discovery of a planet within a distant solar system that is orbiting in what astronomers called the habitable zone for life, another exciting announcement adds two more confirmed planets to the list.

Since its launch in 2009, the Kepler Space Telescope has been scanning hundreds of thousands of distant stars, looking for the slightest wobble, which would indicate the gravitational pull of planets as they orbit their sun. The Kepler team has been studying and investigating dozens of Earth-like candidates, including two around Kepler 20 in the constellation Lyra.

The star Kepler 20 houses two planets nearby that are Earth-like in size. One is just three percent larger in diameter than Earth and the other is nine-tenths the size of Earth. But unlike the previous discovery of Kepler 22b — a watery world with a temperature of about 72 degrees — these are rocky planets with scorching temperatures too hot for any life we can imagine.

They are situated in a tightly packed planet pile with three other known planets, all very near the host star. Kepler-20e has an orbit of six days, while Kepler-20f has an orbit of 19.6 days.

Kepler 20e and Kepler 20f are the closest sized planets to Earth discovered to date. The confirmation of these two planets is significant because planets the size of Earth are just hard to find and this shows that Kepler is up to the task. This gives scientists hope that they will find life outside of our solar system.

Kepler 20e and Kepler 20f Compared to Earth and Venus

It may be a bacteria, mold or single-celled life form but astrobiologists are encouraged by this news.

Linda Elkins-Tanton, who studies planetary formation at the Carnegie Institution for Science in Washington says the larger of the two planets, Kepler-20f, is especially intriguing. She says, “If it was formed with water, which I think is possible, it could have been habitable in the past.”

Alan Boss, also an astronomer at the Carnegie Institution says science would be remiss not to look for life-inhabiting planets outside of our solar system. He says, “That does not mean that we necessarily think that only exact Earth twins could be inhabited, just that we at least had better be able to find Earth twins, and then along the way we will be certain to uncover all sorts of other types of exoplanets that should be habitable, and perhaps even inhabited.”

Francois Fressin is the lead author of the paper announcing the discovery which appears in the journal Nature. He says though the planets are about the right size they are definitely not right for life. Kepler 20e is about 1,400 degrees F while Kepler 20f is 800 degrees.

In his paper, he writes, “Theoretical considerations imply that these planets are rocky, with a composition of iron and silicate.” And he notes, “The outer planet could have developed a thick water vapour atmosphere.”

Boss puts this discovery and the Kepler 22b discovery a couple of weeks ago in perspective as he tells ABC News, “In less than 20 years, we have gone from not knowing if any other planets exist in the universe, to being able to look out at the night sky and realize that essentially any star we can see has at least one planet, and a good number of those are likely to be habitable.”

He adds, “That is a revelation that has not yet dawned on the general public, and even astronomers are having their minds blown when they think about it.”

Just ten years ago University of Washington astronomers Peter Ward and Donald Brownlee created the Rare Earth hypothesis, which suggested that the conditions for life are so particular that for us to find any sign of life elsewhere would be nearly impossible. In that time, astronomy as a whole has revised that theory.

But Ward and Brownlee’s also posited the idea of a habitable Goldilocks zone around a star which is neither too hot nor too cold and where the conditions for life are just right. That planet must orbit its star at a distance similar to that of Earth or Kepler 22b.

So far Kepler has found 54 planets that lie in the habitable zone around distant stars. But the team is backlogged with another 2,000 probable planets that await further study.