Day 1224

Thursday.

Nature
Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
Gillon, et al

One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization.  Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight percent that of the Sun, located 12 parsecs away.  The transiting configuration of these planets, combined with the Jupiter-like size of their host star -- named TRAPPIST-1 -- makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities.  Here, report the results of a photometric monitoring campaign of that star from the ground and space.  The observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1.  The six inner planets form a near-remontant 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. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.


1702.06582
Symmetric Achromatic Variability in active galaxies -- a powerful new gravitational lensing probe?
Vedantham, et al

Report the discovery of a rare new form of long-term radio variability in the light-curves of AG's -- symmetric achromatic variability (SAV) -- a pair of opposed and strongly skewed peaks in the radio flux density observed over a broad frequency range.  Propose that SAV arises through gravitational milli-lensing when relativistically moving features in AG jets move through gravitational lensing caustics created by 1e3-6 Msun subhalo condensates or BH located within intervening galaxies.  The lower end of this mass range has been inaccessible with previous gravitational lensing techniques.  This new interpretation of some AG variability can easily be tested and if it passes these tests, will enable a new and powerful probe of cosmo matter distribution on these intermediate mass scales, as well as provide, for the firs time, micro-arcsecond resolution of the nuclei of AG -- a factor of 30--100 greater resolution than is possible with ground-based millimeter VLBI.