Free Astronomy Magazine September-October 2021

9 SEPTEMBER-OCTOBER 2021 K elt-25 as seen by Zorro. The Zorro observations show Kelt-25 has no stellar companions, thereby con- firming the na- ture of the transiting giant planet KELT- 25b. [Joey Ro- driguez, Sam Quinn, and Josh Pepper (KELT- TESS); Steve Howell, Nic Scott, and Rachel Matson (NASA Ames)] T he WIYN telescope building against a sun- set sky, with interior light on the telescope. It is owned and operated by the WIYN Consortium and is located at the Kitt Peak National Observatory. [Jean-Baptiste Faure] panion star or does not exist at all. We would need more observations with a different technique to figure that out.” In light of all this, can we perhaps trust in the fact that if there are many more Earth-sized planets than previously believed, the number of potentially habitable planets in- creases proportionally? Apparently yes, but if by “habitable” we mean “something extremely similar to the Earth,” then there is no need to be overly optimistic, especially after the publication at the end of June in the Monthly Notices of the Royal Astronomical Society of a study highlighting the criticalities of de- velopment of biospheres on other planets. The study was conducted by a team of researchers led by Gio- vanni Covone (University of Naples, Italy) and consists of an analysis of the known exoplanets and the con- ditions required so that an oxygen- based photosynthesis could develop on them, one capable of producing a complex Earth-like biosphere. The prerequisites are, of course, that a given planet has a size and mass similar to Earth’s and that it or- bits in the habitable zone of its star, where liquid water can exist on the planetary surface. Only a small mi- nority of planets, among the thou- sands confirmed so far, have these characteristics. Accord- ing to Covone and col- leagues, nowhere among this small minority exist the theoretical conditions to support an Earth-like bios- phere through oxygenic photosynthesis, the process by which plants convert light and carbon dioxide into nu- trients and oxygen. The critical factor in this sce- nario is the stellar radiation necessary to support a large and complex biosphere on a given planet. According to the analysis conducted by the Covone team, only Kepler-442b (a rocky planet 17,000 km in diameter and twice the Earth’s mass) comes close to re-