Seven Earth-sized planets have been discovered orbiting a single ultra-cool dwarf star 40 light years away. Depending on atmospheric conditions, all seven could potentially be habitable, making the system a prime target for scientists hunting for another Earth. The planets were discovered in the TRAPPIST-1 system by a team led by Michaël Gillon, of the University of Liège in Belgium. TRAPPIST-1 is named for the TRAnsiting Planets and PlanetesImals Small Telescope, which is actually two 0.6-metre telescopes located in Chile and Morocco that together monitor 60 ultracool dwarf stars and brown dwarfs, looking for evidence of exoplanets. Three of TRAPPIST-1’s planets – b, c and d – were discovered using the TRAPPIST-South telescope in Chile by Gillon and his team last year. The additional four new planets make the TRAPPIST-1 system the first planetary system known to host so many Earth-sized worlds, not to mention potentially habitable worlds. All seven planets transit their star; that is, they cross in front of the star’s disc, blocking some of the starlight. The amount of light each planet blocks tells us their diameters, and how regularly they transit tells us their orbital period, from which we can calculate their distance from the star.
The long-awaited fly-by of Pluto by the New Horizons spacecraft, on 14 July 2015, was an event 85 years in the making, following Pluto’s discovery by Clyde Tombaugh in 1930. Since then, Pluto has gone from planet to dwarf planet, but despite protestations from the New Horizons team, its reclassification never really changed the mission or the importance of what it would find at Pluto.