Proxima b: The Detection of the Earth-Type Planet Candidate Orbiting Our Closest Neighbor

Abstract

The detection of Proxima b took 16 years in the making. The planet candidate has a mass similar to our own planet, and it is orbiting Proxima Centauri, a red dwarf in the Alpha Centauri triple system which is also the closest system to the Sun. Proxima b was detected using the radial velocity technique (also known as the Doppler method). Although the technology has been available for almost two decades, improvements in calibration of the instruments and developments of the data-analysis techniques employed were necessary to achieve this goal. In this chapter we first review the basic properties of the star, and we put in context the discovery of the planet in terms of what is known about exoplanet populations around red dwarfs. We also give an overall description of the process and efforts that led to its detection in an historical context. While space-transit photometry has proven to be the most effective method to obtain large statistically significant samples of exoplanets, the requirement of almost perfect alignment of the orbit with the line of sight makes it unlikely that the nearest planets can be detected using this technique. As a result, the radial velocity technique remains the most sensitive one in terms of finding very nearby planets due to its lower sensitivity to the inclination of the orbit. The detection of very nearby planets enables new follow-up opportunities to characterize planetary systems and their environment, ranging from future attempts for direct imaging, characterization of their highenergy radiation environments, and the study of extended structures such as debris disks or asteroid belts. These very nearby planets promise the first chances of characterizing the atmospheres of planets similar to our own and should enable the search for evidence for life beyond the solar system within the next decade. © Springer International Publishing AG, part of Springer Nature 2018.