Thomas Julian Ahrens (April 25, 1936 – November 24, 2010) was an American geophysicist and professor at the Caltech.

His research focused on the study of terrestrial planets and the impact processes on their surfaces.

Ahrens then led the Geophysics Section at the Poulter Laboratory, Stanford Research Institute, from 1962 to 1967.

[3] Ahrens received several honors throughout his career, including the AAAS Newcomb Cleveland Prize in 1984 and election to the National Academy of Sciences in 1992.

The iron-rich endmember of the γ-olivine solid solution series, γ-Fe2SiO4, was named "ahrensite" in his honor in 2013.