On February 22, a group of researchers announced the discovery of a record number of Earth-like planets orbiting a single star 39 light years away: the TRAPPIST-1 system.
Led by an astronomer at the University of Liège in Belgium, the group used transit photometry, one of the most common techniques for identifying exoplanets, to tease out the existence of the seven rocky satellites orbiting the dim star. This method consists of monitoring the light emitted by the star to find out whether it dims periodically – a surefire sign of a planet passing by.
Three of the seven planets around TRAPPIST-1 fall within its habitable zone, a region in which the planets are just at the right distance away from the star for liquid water to exist on their surface. Because TRAPPIST-1 is a dim red dwarf, this distance is much closer than it would be in our Solar System. The furthest planet, TRAPPIST-1h, orbits at less than a tenth of the distance between the Earth and the Sun and has a ‘year’ of only 20 days.
Based on the planets’ densities, it was determined that they are all likely rocky worlds like the Earth, not gas giants like Jupiter or Neptune.
Although the TRAPPIST-1 system has received an outpouring of media attention because of its record number of Earthlike planets, it is still uncertain whether it could support life, and if any life does on those far-away worlds, it would probably be very different from life on Earth.
Scientists think that the planets in the TRAPPIST-1 system are probably tidally locked, meaning that one side of each planet is always facing the star and the other side is always looking away. This may mean that the only regions with liquid water on these planets are the interfaces separating their extremely hot and extremely cold sides.
Another factor to consider is that TRAPPIST-1 is a fairly young star, and may still be releasing large amounts of high-energy radiation that would kill most life found on Earth. Because all the planets are so close to their star, the constant influx of radiation would wear away at their atmospheres, potentially exposing the surface to harmful rays. However, extremophiles, bacteria found on earth living in locations where they are exposed to devastating temperatures and radiation, prove that it is possible for life to thrive even in those conditions.
Current research on these planets focuses on searching for gases associated with life, like water vapor and oxygen. Even if extraterrestrial life isn’t found, studying TRAPPIST-1 will still reveal valuable information on how planet systems form and evolve.
(featured image courtesy of ESO/M. Kornmesser)