Phobos, the larger of Mars' two tiny satellites, pictured near the limb of Mars by the robot spacecraft Mars Express in 2010. Image: G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA; Acknowledgement: Peter Masek
New study explains how the Martian moon Phobos was formed - space science news

By comparing mid-infrared spectra from Phobos (that had been collected already in 1998 by the Mars Global Surveyor) with those of an asteroid found near Tagish Lake in British Columbia, scientists believe that Phobos is not an asteroid captured by the gravity of Mars, as had been argued before, but has formed after a huge impact during early Martian history. The spectra have no similarity with the asteroid, and revealed that Phobos is made of basalt. Basalt is volcanic rock, and one of the major components of the surface of Mars. Thus, scientists have found evidence for the origin of Phobos that might be further confirmed once the Martian Moon eXploration spacecraft and the OSIRIS-Rex and Hayabusa2 asteroid explorers complete their missions to collect samples and return them to Earth for analysis.

Read the full story: AGU 100
Scientific publication: Journal of Geophysical Research – Planets