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Dwarf star planets may have habitable atmospheres, MIT scientists say

An artist’s rendition of the surface of one of the discovered exoplanets.
An artist’s rendition of the surface of one of the discovered exoplanets.(ESO/M. KORNMESSER)

Scientists believe they’re another step closer to discovering the potential for life beyond earth.

In May, a team including MIT researcher Julien de Wit and scientists from the University of Liege in Belgium detected three planets orbiting a nearby dwarf star, with just the right size and temperature — between - 23 degrees and 106 degrees Celsius — to possibly support life.

In a follow-up study published Wednesday in Nature, de Wit’s team has confirmed that the planets have rocky, rather than gaseous, terrain, and compact, rather than loose, atmospheres — all further indication that they are potentially habitable.

“These are the first potentially habitable, earth-sized planets that...are close enough to allow for atmospheric study,” de Wit said.

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More detailed atmospheric analysis is the next step. After all, many planets, like Venus and Mars, are rocky and have compact atmospheres, but that doesn’t mean they support life. de Wit and the rest of the team need to figure out what elements make up these planets’ atmospheres, a process that could take several years.

“Then we could say, it looks like Mars, or it looks like Earth, or it looks like nothing we’ve ever seen in our solar system,” de Wit said.

The researchers first identified the planets in May. They found three potentially habitable candidates: the two in the new study, and one more, slightly farther from the host star. All were Earth-sized and may have regions with the right temperatures to support liquid water, and even life.

But in order to determine whether they actually were livable, the scientists had to analyze the composition of the planets’ atmospheres. If the exoplanets were primarily gaseous, with puffy atmospheres billowing into space, they would be more like Jupiter than Earth.

Analyzing an exoplanet’s atmosphere is technically challenging. It requires serious technology, like the Hubble Space Telescope — far more high-powered than the compact, 60-centimeter telescope the researchers built to detect the exoplanets.

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By sheer luck, their chance came just two days after the team announced the discovery of the three exoplanets in May. They had realized just weeks before that the two innermost exoplanets were due to double transit soon — a rare phenomenon that occurs when two planets transit, or pass, almost simultaneously in front of their star.

Such an unusual occurrence, they realized, might convince NASA to let them commandeer the Hubble, as it would allow them to study two planets at once, in a two-for-the-price-of-one deal.

They were right.

“This happens every two years, so that definitely would have motivated the Hubble team to accept our proposal,” said study co-author Hannah Wakeford, a researcher at NASA. “To my knowledge, this is the first time it’s ever been done on purpose, and it’s definitely the first time it’s been done with such small planets.”

When planets transit, they block the light the star radiates to earth. Scientists measure how much the starlight dips: if a lot, they conclude the planets are big. If a little, the planets are small. And by analyzing the way the light interacts with the planets’ atmospheres as it passes through, scientists can discern the composition of their atmospheres.

To their excitement, de Wit and his colleagues observed that the transiting planets were indeed not gas giants. The third planet did not transit, so they can’t say anything about its properties yet.

“There’s still so much more about this planetary system that we can look forward to, and we need to study more of, and this is just the beginning,” Wakeford said.

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de Wit didn’t want to say that the findings on the other two confirmed his expectations of the exoplanets as being earthlike.

In fact, he doesn’t even want to speculate on whether these might, somewhere down the line, be the first confirmed homes to extraterrestrial life.

“[Our] solar system is just one example, and it’s quite different from what we’ve been observing outside,” he said. “Because it’s new territory, I would rather keep being surprised and driven by observation.”

Two Earth-sized planets pass in front of their parent star, a red dwarf, about 40 light-years away from Earth in this illustration.
Two Earth-sized planets pass in front of their parent star, a red dwarf, about 40 light-years away from Earth in this illustration. (NASA. G/Bacon (STScI))

Vivian Wang can be reached at vivian.wang@globe.com. Follow her on Twitter @vwang3.