This whimsical cartoon shows three recently discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth’s orbit (the ecliptic). During the K2 mission, many of the extrasolar planets discovered by the Kepler telescope will have this lucky double cosmic alignment that would allow for mutual discovery—if there is anyone on those planets to discover Earth. The three planets, orbiting a nearby star named EPIC 201367065, are just out of alignment; while they are visible from Earth, our solar system is tilted just out of their view.
The three planets, each just larger than Earth, are 1.5-2 times the size of Earth. The outermost planet orbits on the edge of the so-called “habitable zone,” where the temperature may be just right for liquid water, believed necessary to support life, on the planet’s surface.
“The compositions of these planets are unknown, but, there is a very real possibility the outer planet is rocky like Earth,” said Erik Petigura, a University of California, Berkeley graduate student. “If so, this planet could have the right temperature to support liquid water oceans.”
The planets were confirmed by the NASA Infrared Telescope Facility (IRTF) and the W. M. Keck Observatory in Hawaii as well as telescopes in California and Chile.
The astronomers next hope to determine what elements are in the planets’ atmospheres. If these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, there is not much chance for life.
“A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many extrasolar planets discovered by the Kepler Mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,” said Ian Crossfield, the University of Arizona astronomer who led the study.
The discovery is all the more remarkable because Kepler is now hobbled by the loss of two reaction wheels that kept it pointing at a fixed spot in space. Kepler, launched in 2009, was reborn in 2014 as “K2” with a clever strategy of pointing the telescope in the plane of the Earth’s orbit to stabilize the spacecraft. Kepler is back to mining the cosmos for planets by searching for eclipses, or transits, as planets orbit in front of their host stars and periodically block some of the starlight.
