Free Astronomy Magazine January-February 2021

46 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING the temperate orbital region. The opposite is less frequent, in the sense that it is somewhat common to find super-Earths (and to a lesser extent also Earths) in systems where a relatively cold gas giant is missing or has not yet been discovered. Schlecker’s team tried to add in- sights into this rough picture by sim- ulating the evolution of 1000 plane- tary systems around solar-like stars. Starting from different initial condi- tions of gas and dust masses, disk sizes, and the positions of planetary embryos, the researchers traced the development of those systems over I n this hypothetical protoplanetary disk, the so-called “snow line” is highlighted, the distance from the star beyond which water freezes, determining the outer limit of the habitable zone. [A. Angelich (NRAO/ AUI/NSF)/ALMA (ESO/NAOJ/NRAO)]