Free Astronomy Magazine January-February 2021

47 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING periods of billions of years, obtain- ing planets of different sizes, masses and compositions in different orbits around their central stars. The results of the simulations did not agree with the trends from the observational data, instead predict- ing a reduction in the frequency of cold Jupiter/super-Earth pairs in planetary systems. If the presence of a large planet like Jupiter does improve the chances for life on the inner super-Earths of a solar sys- tem, then this predicted re- duction is not comforting from an astrobiological point of view. Although the re- searchers have taken into consideration super-Earths instead of Earths (only be- cause they are more numer- ous, easier to discover and therefore statistically more relevant), from the point of view of habitability, the dif- ference between the two is not great, making the end result an overall lower pre- dicted number of total solar systems more likely to host a more protected, life-hosting planet. The reasons why observations and simulations do not match may be manifold, ranging from a discrimina- tion attributable, to the current methods of searching for exoplan- ets, to an approximate formulation of the theories concerning the mi- gration of gaseous planets towards the innermost regions of their sys- tems. Leaving out some controversial as- pects of the simulations performed by Schlecker and colleagues, an interesting fact has nevertheless emerged: the planetary systems in which there are a cold Jupiter and at least one super-Earth appear to orig- inate from particularly massive pro- toplanetary disks. In medium-mass discs (and even more so in low-mass ones), there is not enough material in the innermost and temperate re- gions to form super-Earths, nor is there enough material beyond the snow line to form gas giants. Super- Earths with relatively high percent- ages of ice and a thick atmosphere are more likely to form beyond the M artin Schlecker (Max Planck Institute for Astronomy), the lead author of the study discussed in this article [MPIA] snow line and, not being hindered by the presence of a gas giant in an inner orbit, these super-Earths are free to migrate towards more tem- perate regions. It is interesting to note that (virtual) super-Earths and Earths that form in the habitable zone have a percent- age of water/ice and an atmospheric mass significantly lower than those of similar planets that migrated in from outside. It is therefore proba- ble that when the simultaneous presence of a cold Jupiter and a super-Earth (or Earth) is found (in re- ality), the latter is of the “arid” type, therefore similar to our planet and hence potentially more compatible with life as we know it. When instruments such as the James Webb Space Telescope and the Extremely Large Telescope be- come operational in the next few years, it will be possible to more ac- curately assess the role of cold Jupiters in the habitability of plan- etary systems and understand just how much our Jupiter may have protected life on Earth. !