Seven Earth-Sized Worlds Found

Breakthrough In Search For Life As Seven Earth-Sized Worlds Found Orbiting Nearby Star

Astronomers have made a huge discovery in the search for life beyond our Solar System, describing a whopping seven Earth-sized worlds in orbit around a nearby star. At least three of them may be habitable – and we could find out if they are inhabited within a decade.

The system is around a star called TRAPPIST-1, a small ultra-cool dwarf star 40 light-years away that’s about 8 percent the mass of our Sun and 11 percent its radius, similar in size to Jupiter. Last year, it was revealed that three potentially rocky worlds orbited this star, and now this new study has found four more.

A paper describing the incredible findings, led by Michaël Gillon of the University of Liège in Belgium, was published today in Nature. The discovery was made using NASA’s Spitzer Space Telescope and a variety of ground-based telescopes, including TRAPPIST-South in Chile, to observe the transits of the planets relative to us as they passed across their star.

“The star is so small and cold that the planets are temperate, which means that they could have some liquid water and maybe life by extension on the surface,” Gillon said in a press briefing.


In order of their distance from the star, the planets are called TRAPPIST-1b (the innermost), c, d, e, f, g, and h (the planets d, e, f, and g are newly discovered). The researchers were able to work out the mass, radius, and orbital periods of all seven of the planets, save for the outermost, TRAPPIST-1h, of which only one transit was seen.

TRAPPIST-1b orbits just 0.011 AU from its star (1 AU, or astronomical unit, is the Earth-Sun distance). As such, it completes an orbit in just 1.51 days. The next six planets orbit from 2.42 to about 20 days, and all are similar in size to Earth, ranging from 0.76 times our radius to 1.13.

Being such a cool and dim star, its habitable zone is much closer in than our own Solar System. The planets e, f, and g all orbit in this zone, suggesting they could support liquid water oceans on their surface.

The finding is particularly exciting because, being so close to Earth, we will be able to study the planets of this star in detail. And not just in the future, but right now. Follow-up observations are already underway, and it’s possible we could know if life exists on one or more of these planets very soon by studying the molecular composition of their atmospheres.