Scientists find three Earth-like planets in habitable zone of ultracool brown dwarf star

Scientists have announced the discovery of three Earth-like planets orbiting a nearby star that could host life, according to a new report in the journal Nature.

Just 40 light years away, the planets were the first to ever be found orbiting an ultracool dwarf star. Because they are orbiting so close, the dim light thrown out by the star could be enough to sustain life, the study team said.

“The kind of planets we’ve found are very exciting from the perspective of searching for life in the universe beyond Earth,” study author Adam Burgasser, a professor of physics at the University of California San Diego, said in a news release.

How did scientists discover the planets?

Watching the distant star over a 62-day period, the study team saw three intermittent dips in brightness that signaled the presence of three planets, regularly casting their shadows back to Earth. Follow-up studies revealed these planets are probably close to the same size as Earth. Two of the planets orbit the star at periods of 1.5 days and 2.4 days. The study team said the third planet take between 4.5 and 73 days to orbit its sun.

“With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun,” said co-author Michaël Gillon of the University of Liège in Belgium. “The structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”

The team established the three planets are about Earth-sized and may be rocky. Moreover, the inner two planets two to four times the quantity of solar energy that the Earth does, since their star is much fainter than the Sun.

This means these two planets are inside the habitable zone for this system, an orbital ring of distances where liquid water can exist and temperatures can support life.

The study ream said it is still likely that they have habitable regions on their exterior, although details such as their clouds, and atmospheres-if they have atmospheres-make it hard to calculate if exterior conditions are really well suited for life. The third, outer, planet’s orbit is not yet well known, but it surely gets less solar energy than the Earth does, but maybe still enough to lie inside the habitable zone.

The astronomers said the two planets nearest to the star could possibly be tidally locked, with one face perpetually facing the star and the other constantly dark. That could restrict circulation of water and atmosphere, which might become captured on the cold, dark side, even though the astronomers speculate that life could exist in the continuous dawn at the day side’s western edge. Alternatively, tidal forces could keep the planets’ exterior cozy even on the dark side, but it could also cause brisk geothermal activity that makes the surfaces unstable.

“Fortunately, we may be able to answer these questions in the near future, as the geometry of the system makes it likely that we will be able to detect the atmospheric gases of these planets in the next decade with the launch of the James Webb Space Telescope,” Burgasser said. “This facility will allow us to search for biogenic gases–oxygen or methane for example–that would firmly indicate the presence of life, or search for other gas species that would tell us about the planets’ compositions, geothermal activity and evolutionary history.”

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Image credit: UC San Diego

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