The Discovery and Exploration of the Moons of Mars

Abstract

This chapter describes the discovery of the two moons of Mars, Phobos and Deimos, made in 1877 by Asaph Hall using the giant 26-in. refractor at the U. S. Naval Observatory. Subsequent research over the next century is briefly highlighted, most notably the secular acceleration of Phobos, leading to claims of its artificial nature. A renaissance in moons of Mars studies came with robotic space missions beginning in the 1970s. The description of the discovery of Phobos and Deimos presented here is based on a manuscript discovered by the author in the U. S. Naval Observatory archives, as well as on Hall’s published work. Hall read the manuscript before Washington Philosophical Society on February 16, 1878, 6 months after the discovery of the two moons.