A new study has confirmed that two Earth-size planets orbiting a nearby star are rocky, thus strengthening the case that these planets may be having conditions suitable for existence of microbial life.
The planets were discovered earlier this year by scientists from MIT, the University of Liège and other schools. They are located 40 lightyears away from Earth and orbit Trappist-1, an extremely cool dwarf star, which appears red as it mostly produces infrared light. The star derives its name from Trappist telescope in Chile which helped researchers discover this planetary system.
According to scientists, two planets of this star system (which actually has 3 planets orbiting the star) are in the so-called Goldilocks Zone, meaning they have 'just right' temperature for liquid water to exist. Moreover, they are "tidally locked" to Trappist-1, meaning their one side would be in eternal daylight, the other in eternal night, much like Earth's moon.
The discovery of these exoplanets was announced in May this year when researchers found that a double transit of the planets is going to occur just after two weeks. A research proposal was written in less than 24 hours, which was reviewed and finally accepted.
"We thought, maybe we could see if people at Hubble would give us time to do this observation, so we wrote the proposal in less than 24 hours, sent it out, and it was reviewed immediately," said Julien de Wit, the first author of the study and a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences.
The team then used Hubble space telescope to watch the rare double transit, with both planets passing nearly in tandem in front of their star. Researchers watched the event closely to observe the dipping and flickering of starlight through the atmosphere of each planet.
"Now for the first time we have spectroscopic observations of a double transit, which allows us to get insight on the atmosphere of both planets at the same time," Dr Wit said.
"We should have been able to see significant variation of the amount of light blocked by the atmosphere, if the atmosphere was large and diffuse, like the ones we have around Jupiter or Neptune."
According to Dr Wit, they didn't see "such large variation, meaning it's most likely a terrestrial planet like Mercury, Venus, Mars and Earth."
The double transit event also helped researchers rule out an atmosphere dominated by hydrogen. Dr Wit says there is also possibility of these planets being "water worlds" - something not present in our solar system or having an atmosphere mainly composed of oxygen.
The scientists now want more telescopes to be established on the ground to probe these planets further.
The detailed findings of the study have been published in Journal Nature.