'Lava world' orbits its star in just 8.5 hours
Astronomers have detected a molten world that is 40 times closer to its star than Mercury is to ours.
Astronomers have discovered a scorching-hot "lava world" whose year lasts just 8.5 hours and determined that another planet candidate with an even tighter orbit is likely composed almost entirely of iron.Skip to next paragraph
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The newfound Earth-size exoplanet Kepler-78b is so close to its host star that its surface is likely an enormous ocean of lava, researchers said. Further, the discovery team was able to detect light emitted by the planet — a first for a world so small.
In a separate study, some members of the same research group also calculated that KOI 1843.03 — a potential exoplanet detected last year that zips around its star in just 4.25 hours — must be made primarily of iron to survive the powerful tidal forces so close to its host star. [The Strangest Alien Planets]
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"Just the fact that it's able to survive there implies that it's very dense," Josh Winn of the Massachusetts Institute of Technology, a co-author on both papers, said in a statement. "Whether nature actually makes planets that are dense enough to survive even closer in — that’s an open question, and would be even more amazing."
Both Kepler-78b and KOI 1843.03, which has yet to be confirmed by follow-up observations, were detected by NASA's planet-hunting Kepler space telescope.
Kepler was designed to spot exoplanets by noting the tiny brightness dips caused when they pass in front of, or transit, their host stars from the instrument's perspective. Kepler did this work from shortly after its March 2009 launch until mid-May of this year, when a malfunction robbed the observatory of its precise pointing ability.
NASA is now considering new missions for the prolific spacecraft, which has detected more than 3,500 candidate planets to date, with many more likely waiting to be pulled out of its massive dataset.
While the original $600 million Kepler mission is primarily interested in finding potentially life-supporting, Earth-like alien planets, Winn and his colleagues searched specifically for worlds about the size of our own in extremely tight orbits.
"We've gotten used to planets having orbits of a few days," Winn said. "But we wondered, what about a few hours? Is that even possible? And sure enough, there are some out there."