Launched four year ago, NASA’s Kepler space telescope is narrowing an unprecedented search for alien planets similar to the Earth.
On Thursday, astronomers announced the discovery of three “Super Earths” circling in the habitable zones of two distant stars, one of them quite like the sun.
Than means liquid water, an essential ingredient for life as we know it on planet Earth, could be present. “Super Earth” means larger than the Earth — but not as large as Jupiter or Saturn — and possibly rocky in composition.
“Kepler has brought a resurgence of astronomical discoveries, and we are making excellent progress toward determining if planets like ours are the exception or the rule,” said William Borucki, Kepler science principal investigator at NASA’s Ames Research Center and the lead author of an article describing the findings in the journal Science. A second article on the findings appears in the Astrophysical Journal.
From its vantage point in space, Kepler monitors more than 150,000 stars in the Milky Way galaxy, noting small changes in their brightness that correspond to the passage of a planet, a detection strategy known as the transit method. The observations permit experts to assess the size and orbital period of crossing planets as well as their distance from the host star.
If not too far, or too close from the star, environmental conditions on a planet may be just right for water to flow or pool rather than freeze or boil away. That’s what defines the Kepler mission’s habitable zone.
Kepler’s discovery embraces two planetary systems with a total of three “super Earths” in the habitable regions.
The Kepler 62 system consists of a dwarf star about 20 percent as bright as the sun and about 1,200 light years from the Earth in the constellation Lyra.
Five planets in this system were detected. The habitable zone planets, Kepler 62-e and 62-f, circle the star every 122 days and 267 days respectively.
Kepler 62-f is 40 percent larger than Earth, making it the alien world closest to the size of the Earth known to exist in the habitable zone of another star. Kepler 62-f is likely to have a rocky composition, according to the Kepler team.
Kepler 62-e, orbits on the inner edge, or warmest part of the habitable zone, and is roughly 60 percent larger than Earth.
The two habitable zone worlds orbiting Kepler 62 have three companions in orbits closer to their star, two of them larger than the size of the Earth and one about the size of Mars. The companions are deemed too close to their star for liquid water.
Meanwhile, Kepler 69 is a two planet star system. Kepler 69 is a sun-like star, though a little dimmer, and located about 2,700 light-years from Earth in the constellation Cygnus.
Planet Kepler 69-c is 70 percent larger than the size of Earth. It orbits in Kepler 69’s habitable zone once every 242 days.
“We only know of one star that hosts a planet with life, the sun,” noted Thomas Barclay, a Kepler science team member at the Bay Area Environmental Research Institute, of Sonoma, Calif., who worked on the Kepler 69 discoveries. “Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets.”
A companion to Kepler 69-c, Kepler 69-b, is more than twice the size of Earth and orbits every 13 days, or well inside the habitable zone.
Using the transit method, Kepler has detected 2,740 candidates. Using various analysis techniques, ground telescopes and other space assets, 122 planets have been confirmed.
“The Kepler spacecraft has certainly turned out to be a rock star of science,” John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters inWashington, said in a statement.
“The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity.”