A recent study showed that a star system near ours hosted three "potentially habitable planets" but only two of them seem to be more habitable than believed.
Three planets were found to be habitable when discovered in May 2016. They were orbiting the dwarf star, TRAPPIST-1, just 40 light years away from us. All three were the size of the earth and were within the "not-too-hot/not-too-cold habitable zone" in which life forms can survive.
Two of these planets have been found to be like earth, with rocky, not gassy surfaces. "These planets are not mini-gas giants, which is a good thing because they wouldn't be habitable," said lead author Julien de Wit of MIT. "We ruled out that scenario."
Even though the planets are like earth, they are not completely so. "They could be like Earth," said de Wit, "or they could be like Venus, with an atmosphere dominated by carbon dioxide and high-altitude clouds, or maybe like Mars."
Researchers examined the Hubble telescope even as they went by in front of the star they orbit. As the planets were in a double transit across the sun, alterations in the wavelength of the starlight were also measured.
Gas giants such as Jupiter have atmospheres that are lighter and more diffuse and not really conducive to life. But the researchers discovered the opposite in the planets---"the atmospheres were wound fairly tightly around the planets," as expected in rocky planets. More transits of the TRAPPIST-1 planets will now be examined closely in order to see what the atmospheres are like.
Scientists found the TRAPPIST-1 system through a prototype robotic telescope in Chile, but now they are searching to see if comparatively smaller dwarf stars could host such systems. Hence, six more telescopes based on the prototype will soon be erected in Morocco and Chile, which would demonstrate that there are more habitable planetary systems than thought.
"With more observations using Hubble, and further down the road with James Webb, we can know not only what kind of atmosphere planets like TRAPPIST-1 have, but also what is within these atmospheres," de Wit says. "And that's very exciting."
The findings were published in Nature.
