Free Astronomy Magazine March-April 2022

24 MARCH-APRIL 2022 ASTRO PUBLISHING T his video takes the viewer on a journey at 20% the speed of light to the nearest star, Proxima Centauri. The planet Proxima b is visible, orbiting its star every 11.2 days. This planet is located within the star’s habitable zone, which means that liquid water may exist on its surface. [PHL @ UPR Arecibo, ESO. Music by Lyford Rome] R endering of Proxima b orbiting the red dwarf Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears between the planet and Proxima Centauri. Proxima b is somewhat more massive than Earth and orbits in the habitable zone of Proxima Centauri, where the tem- perature is suitable for the exis- tence of liquid water on its surface. [ESO/M. Kornmesser] brightness of the star both known). In the case of Proxima b, as well as for all other known exoplanets, the first way is not feasible due to the impossibility, with current instru- ments, of obtaining planetary im- ages larger than a pixel. Furthermore, many of those planets are very close to their stars (espe- cially true for red dwarfs) and it is impossible to “extract” them from the dazzling starlight. Almost al- ways practicable is, however, the second way, that of transits on stel- lar disks, which, even so, are geo- metrically rare. At this point, the question we must ask ourselves is the following: for at least a short stretch of its orbit, does Proxima b pass in front of the Prox- ima Centauri disk as observed from Earth? Astronomers have been ask- ing this question from the very first day of the planet’s discovery. If Prox- ima b were observed in transit, we would immediately have confirma- tion that its mass coincides with the minimum estimated one, and we could easily deduce the diameter, identifying the planetary type with sufficient precision. Spectroscopic observations could also tell us if the planet has an atmosphere and which gases it is mainly composed of; to accomplish this, it is sufficient (but not simple) to subtract from the stellar spectrum acquired during a transit the one acquired out of transit: the difference is indicative of the gases that make up the plan- etary atmosphere (if one exists). Unfortunately, as previously men- tioned, Proxima Centauri is very noisy