Most stars in our Milky Way Galaxy are much smaller and dimmer than the Sun. Low-mass stars that are about 80 times the mass of Jupiter have core temperatures that are just high enough to convert hydrogen into helium. The brightness of these stars is less than one-thousandth that of the Sun. An example [see attached] of such a star is TRAPPIST-1 –– which is located only 12 parsecs (39 light years) away. Last year, there was a report that three Earth-sized planets circling TRAPPIST-1 were detected.
Now, it has been reported that the star has, in fact, seven planets –– all of comparable mass and size to that of Earth. The transiting configuration of these planets, combined with the Jupiter-like size of their host star, TRAPPIST-1, now makes possible in-depth studies of their atmospheric properties. Authors report herein the results of photometric monitoring of that star from ground and space observatories.
The six inner planets form a near-resonant chain –– such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers; this architecture suggests that the planets formed farther from the star and migrated inwards. Furthermore, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces. These findings are consisten with the known universe comprising hundreds of millions of Earth-sized planets located in temperate zones compatible with Life as we know it.
Nature 23 Feb 2o17; 542: 456–460 [article] & 421–423 [News’n’Views]