In our solar system, only one planet
is blessed with an ocean: Earth. Our home world is a rare, blue jewel
compared with the deserts of Mercury, Venus, and Mars. But what if our
sun had not one but two habitable ocean worlds?
Astronomers have found such a planetary system orbiting the star
Kepler-62. This five-planet system has two worlds in the habitable zone —
the distance from their star at which they receive enough light and
warmth that liquid water could theoretically exist on their surfaces.
Modeling by researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) suggests that both planets are water worlds, their surfaces completely covered by a global ocean with no land in sight.
“These planets are unlike anything in our solar system. They have endless oceans,” said lead author Lisa Kaltenegger
of the Max Planck Institute for Astronomy and the CfA. “There may be
life there, but could it be technology-based like ours? Life on these
worlds would be under water with no easy access to metals, to
electricity, or fire for metallurgy.
Nonetheless, these worlds will still be beautiful, blue planets
circling an orange star — and maybe life’s inventiveness to get to a
technology stage will surprise us.”
Kepler-62 is a type K star slightly smaller and cooler than our sun.
The two water worlds, designated Kepler-62e and -62f, orbit the star
every 122 and 267 days, respectively.
They were found by NASA’s Kepler spacecraft, which detects planets
that transit, or cross the face of, their host star. Measuring a transit
tells astronomers the size of the planet relative to its star.
Kepler-62e is 60 percent larger than Earth, while Kepler-62f is about
40 percent larger, making both of them “super-Earths.” They are too
small for their masses to be measured, but astronomers expect them to be
composed of rock and water, without a significant gaseous envelope.
As the warmer of the two worlds, Kepler-62e would have a bit more
clouds than Earth, according to computer models. More distant Kepler-62f
would need the greenhouse effect from plenty of carbon dioxide to warm
it enough to host an ocean. Otherwise, it might become an ice-covered
snowball.
“Kepler-62e probably has a very cloudy sky and is warm and humid all
the way to the polar regions. Kepler-62f would be cooler, but still
potentially life-friendly,” said Harvard astronomer and co-author Dimitar Sasselov.
“The good news is — the two would exhibit distinctly different colors
and make our search for signatures of life easier on such planets in
the near future,” he added.
The discovery raises the intriguing possibility that some star in our
galaxy might be circled by two Earth-like worlds — planets with oceans
and continents, where technologically advanced life could develop.
“Imagine looking through a telescope to see another world with life
just a few million miles from your own. Or, having the capability to
travel between them on a regular basis. I can’t think of a more powerful
motivation to become a space-faring society,” said Sasselov.
Kaltenegger and Sasselov’s research has been accepted for publication in The Astrophysical Journal.
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