Michael J.S. Belton, the President of Belton Space Exploration Initiatives and an Emeritus Astronomer at the National Optical Astronomy Observatory (NOAO), passed away on Monday, June 4, 2018. He was a member of the Planetary Science Institute (PSI) Board of Trustees. Born in Bognor Regis, England, he received his Bachelor’s degree at the University of St. Andrews in Scotland, and earned his Ph.D. at the University of California, Berkeley. He joined Kitt Peak National Observatory (the precursor to NOAO) in 1964 and carried out research on nearly all objects that fell under planetary science.

Belton was a member of the Mariner 10 team that flew a space probe by Mercury and Venus. As a member of the Mariner Jupiter/Uranus Science Advisory Committee, he helped define what became the Voyager missions to the outer solar system. He was the Leader of the Galileo Mission Imaging Science Team. Galileo studied the Earth’s Moon, made the first close-up observations of an asteroid, Gaspra, and discovered the first moon of an asteroid, Dactyl, as it passed the asteroid Ida on its way to Jupiter. Before arriving, the team observed the impact of the fragments of Comet Shoemaker-Levy 9 into the Jupiter atmosphere and later studied the aftermath in detail. At Jupiter, Belton and his team delved into the nature of the Galilean satellites, the population of small satellites, the jovian ring system, and the planet’s atmosphere.

He was particularly interested in the origin and evolution of planetary systems, the physics of planetary atmospheres, high-resolution groundbased spectroscopy, and had a special affinity for comets. He studied them from ground- and spacebased telescopes and missions. His contributions were focused on understanding the mechanisms of cometary outbursts, determination of rotational states, exploring the interiors of cometary nuclei, how cometary activity can be used to probe the nucleus, and the size distribution of comets. Belton was also a leader of the planetary science community, most notably chairing the first National Research Council Decadal Survey of Solar System Exploration.

For his contributions to the exploration of the solar system, an asteroid was designated 3498 Belton by the International Astronomical Union, and in 1995 the Division for Planetary Sciences of the American Astronomical Society awarded him the Gerard P. Kuiper Prize.

In 2000, he founded Belton Space Exploration Initiatives, LLC.

Among the young astronomers who worked with him on his many projects, Belton was a mentor who unselfishly encouraged their professional growth. He was an engaging, interested, and positive colleague. He was an out-of-the box thinker and visionary in the truest sense.