Martian moons made up of Mars itself

    Examination of Mars’ moons shows Phobos and Deimos are pieces of the planet, according to new study.

    By Katie Willis on October 4, 2018

    The two moons that orbit the planet Mars are likely made up of chunks of Mars itself, a new study suggests. This discovery contradicts a long-standing theory that the moons, Phobos and Deimos, were asteroids captured in Mars’ gravitational pull.

    A fragment of the Tagish Lake meteorite, from the UAlberta Meteorite Collection

    This sample from the University of Alberta’s Meteorite Collection is the largest pristine fragment of the Tagish Lake meteorite, from which the sample used in the study was taken. Image credit: Chris Herd

    The study, co-authored by Professor Chris Herd from the University of Alberta, used reflective spectroscopy to compare a sample of the Tagish Lake meteorite to Phobos and Deimos. The Tagish Lake meteorite is a unique type of dark, carbon-rich meteorite that fell onto the frozen surface of Tagish Lake in northwestern British Columbia in 2000 and was eventually determined to originate from the asteroid belt. The researchers examined the reflection of light from the Tagish Lake sample, comparing this to the reflections of the Martian moons to learn about their composition.

    “The study shows that the Tagish Lake meteorite doesn’t look like the moons of Mars, suggesting that these moons actually originated from Mars itself,” explained Herd, curator of the University of Alberta Meteorite Collection and a professor in the Department of Earth and Atmospheric Sciences. “These bits were blasted off of Mars, rather than stray asteroids.”

    The research was completed using data recorded in 1998, when the Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) passed Phobos during its orbit around Mars.

    “This is similar to what we think happened with Earth’s moon, at a much smaller scale,” said Herd, who supplied the Tagish Lake sample to the research team.

    The paper, “MGS-TES spectra suggest a basaltic component in the regolith of Phobos,” was published in Journal of Geophysical Research: Planets (doi: 10.1029/2018JE005647).


    The Faculty of Science is pleased to participate in World Space Week from October 4 to 10th. Learn more about events planned at UAlberta, including the Space Exploration Symposium, featuring a keynote lecture from planetary scientists Cameron Dickinson and Livio Tornabene.