Free Astronomy Magazine July-August 2016

et’s disk). If Gillon and colleagues will not reach a conclusion within a short time, a de- finitive answer will in any case arrive in just a few years from the James Webb Space Telescope (6.5 metre diameter), which will be launched in 2018. In the meantime, the number of known planetary systems around ultracool dwarfs is certainly set to increase, given that it is already partially active TRAPPIST’s succes- sor, that is to say, SPECULOOS (from Search for habitable Planets EClipsing ULtra-cOOl Stars), an array of four telescopes, each of 1 metre diameter, that over the next five years will monitor the brightness of about PLANETOLOGY 500 ultracool stars. Big telescopes that will become operational in the next few years will allow researchers to determine also the masses of TRAPPIST-1’s planets, a task to- day impossible even with higher resolution spectrometers (such as HARPS), which do not receive sufficient white light from the star (magnitude 18.8) to be able to analyze it in detail and thus identify the radial ve- locity variations necessary for calculating the masses of disruptive bodies. To do this we will need instruments specifi- cally designed for the infrared radiation, such as SPIRou (from SpectroPolarimètre Infra- Rouge), a high precision spectropolarime- ter/velocimeter that will be installed at the Cassegrain focus of the Canada-France- Hawaii-Telescope (CFHT) dur- ing the next year and that will able of detecting move- ments of the star (or, rather, of characteristic lines of its spectrum) of just 1 metre per second. Alternatively, the masses may be derived from the timing variations of the planets’ transit on the stellar disk; variations caused by the at- tractions between the plan- ets themselves, which in practice lead to early or late transits, whose magnitude is proportional to the mas- ses involved. Making use of this option would however require scheduling an in- tensive photometric moni- toring campaign with the effective involvement of the major telescopes in the world, which would be rather difficult to accom- plish without adequate plan- ning. Regardless of the lines along which the investiga- tion on TRAPPIST-1 system will proceed, there are some chances of finding, right there, the first habitable extrasolar planet. n T he high prop- er motion of TRAPPIST-1 com- pared to some slower stars of the constellation Aquarius: a) 1953, Palomar Observa- tory Sky Survey image; b) 1998, 2MASS image; c) 2015, TRAPPIST telescope image. [M. Gillon et al.] a b c