James Richard Arnold (May 5, 1923 – January 6, 2012) was the Harold C. Urey Professor of Chemistry (emeritus), and a noted pioneer in the field of planetary and space chemistry at the University of California at San Diego (UCSD), where an endowed lectureship has been established in his name.

It was at Princeton that Masatake (Masa) Honda and Devendra Lal first joined his work, an association amongst them that would last the rest of their lives.

[6] He played a major role in establishing and reforming the Lunar Receiving Laboratory for handling lunar samples returned during the Apollo program,[7][8] including being one of the "Four Horsemen", along with Bob Walker, Paul Werner Gast, and Gerry Wasserburg.

[2] Under the name SHRELLDALFF (from the initials of its members), his team produced important early papers, and he continued long afterwards with lunar studies, including measurements of the bombardment of the lunar surface by cosmic rays, helping to plot the energy output of the Sun over millions of years.

[10] At the request of then-Governor Jerry Brown, he founded the University of California's California Space Institute (CalSpace) in 1979, and was its first director for ten years,[1][11] Asteroid 2143, "Jimarnold", was named for Arnold by its discoverers, E. F. Helin and Gene Shoemaker, in 1980 for his work on computer models of meteorite travel.