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Low temperatures make possible the presence of liquid water on their surface

Scientists have spotted seven Earth-sized planets, with mass similar to Earth, orbiting around a dwarf star the size of Jupiter, just 39 light years from the Sun. The planets’ temperature is low enough to make possible the presence of liquid water on their surface.

In May last year, scientists found three planets passing in front of TRAPPIST-1, the dwarf star. Based on further monitoring of the star from the ground and space, scientists have found four more ‘exo-planets’ orbiting TRAPPIST-1. The results are getting published on Thursday (February 23) in Nature. Michaël Gillon from the Université de Liège, Belgium is the first author of the paper.

Habitable zone of star

“This is the first time we have so many Earth-like planets found around a star. The star is low-mass and small,” Dr. Gillon said during a press briefing. “The seven stars could have some liquid water and maybe life. These planets are found in the habitable zone of the star. This is the first time we have found so many planets in the habitable zone of a star.”

The scientists have been able to make precise mass measurement for six of the seven planets. Though the mass measurements are preliminary, they do indicate that the planets are terrestrial with liquid water. “The seven planets are suitable for detailed atmospheric study,” said Dr. Gillon. “The architecture suggests that the seven planets formed farther from the star and migrated towards the star.”

“We can study the climate and chemical composition of the planets’ atmosphere,” Dr. Amaury H.M.J. Triaud from the Institute of Astronomy, Cambridge, one of the authors of the paper, said during the briefing. “We are first trying to rule out the presence of large hydrogen envelope to make sure that the planets are indeed Earth-like. These will be followed by detailed study of climate and chemical composition to try and find out if there is life on these planets. If there is life on these planets we will know it in a decade.”

Orbital periods

The four newly discovered planets orbit around the star every 4.04 days, 6.06 days, 8.1 days and 12.3 days respectively; the orbital period of two of the three planets discovered last year is 1.51 days and 2.42 days respectively.

 Five planets have sizes similar to that of the Earth, while the remaining two are intermediate in size — between Mars and Earth. Based on the mass estimates, the six inner planets may have a rocky composition. The sixth planet has low density suggesting a volatile rich composition. The volatile content could be either ice layer and/or atmosphere.