Gravity May Reshape Innermost Martian Moonlet Phobos Into Rocky Ring

Summary: Gravity may reshape innermost Martian moonlet Phobos into a rocky ring after its future breakup, a study published Nov. 23 in Nature Geoscience finds.

artist's impression of ringed Mars resulting from gravitational crushing of Martian moonlet Phobos: Tushar Mittal using Celestia 2001-2010, Celestia Development Team, no usage restrictions, via EurekAlert!

Millions of years in the future, when innermost Martian moonlet Phobos gravitationally breaks up into orbiting debris, Mars may share with the solar system’s gas giants of Jupiter, Neptune, Saturn and Uranus the prominent feature of a ring system.

A study published online Nov. 23, 2015, in Nature Geoscience suggests that the heavily damaged, porous, weak materials composing much of the larger and innermost Martian moonlet, Phobos, will break up in 20 to 40 million years and then orbit as a ring of debris around the Red Planet for 1 million to 100 million years. Analysis by the study’s two authors reveals that not all of the moonlet’s fragments will be captured in an orbiting ring.

Co-authors Benjamin A. Black, a postdoctoral scholar, and Tushar Mittal, a graduate student, both in the Department of Earth and Planetary Science at the University of California, Berkeley, write: “Any large fragment of Phobos that is strong enough to escape tidal breakup will eventually collide with Mars in an oblique, low-velocity impact.”

The gravitational pull, known as tidal force or stress, increasingly exerted by Mars on Phobos is pulling the moonlet ever closer toward its planetary host, at a rate of 6.5 feet (2 meters) each century. The tidal force responsible for the inward migration by Phobos as an intact moonlet eventually will break up the ring, causing the debris to impact the Martian surface at the equatorial region, which lies in the plane of the moonlet’s orbit.

Co-author Tushar Mittal describes the innermost Martian moonlet’s exceptional status: “Phobos is unique in that it is currently one of only a couple of inwardly evolving moons in our solar system that we know about. However, since inwardly evolving moons inadvertently self-destruct, it is possible that more inwardly migrating moons may have existed in the past.”

Earth observers might have difficulty in viewing a Martian ring with an amateur telescope because the darkness of the moonlet’s composite materials does not encourage good light reflection. The shadow cast by the ring onto the Martian surface, however, could be discerned.

Mars is the only one of the four terrestrial, or Earth-like, planets with more than one moon. Its second moon, Deimos, is smaller and slower than Phobos and makes an outer orbit of Mars.

As the only known inwardly migrating moon in the solar system, Phobos offers glimpses of the early solar system through its distinctive satellite profile. The co-authors note: “Our analysis of the evolution of Phobos underscores the potential orbital and topographic consequences of the growth and self-destruction of other inwardly migrating moons, including those that met their demise early in our Solar System’s history.”

Grooves on Phobos, thought to be produced by tidal forces (mutual gravitation pull of Mars and Phobos), could indicate the moon's structural failure leading to possible shaping as orbital debris: NASA/JPL-Caltech/University of Arizona, Public Domain, via NASA

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

artist's impression of ringed Mars resulting from gravitational crushing of Martian moonlet Phobos: Tushar Mittal using Celestia 2001-2010, Celestia Development Team, no usage restrictions, via EurekAlert! @ http://www.eurekalert.org/multimedia/pub/104038.php?from=312689

Grooves on Phobos, thought to be produced by tidal forces (mutual gravitation pull of Mars and Phobos), could indicate the moon's structural failure leading to possible shaping as orbital debris: NASA/JPL-Caltech/University of Arizona, Public Domain, via NASA @ https://www.nasa.gov/feature/goddard/phobos-is-falling-apart

For further information:

Black, Benjamin A.; and Tushar Mittal. "The demise of Phobos and development of a Martian ring system." Nature Geoscience, vol. 8 (2015): 913-917. Published online Nov. 23, 2015. DOI: 10.1038/ngeo2583
Available @ http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2583.html#affil-auth

GeoBeats News. "Scientists Say Mars Could End Up With A Ring." YouTube. Nov. 23, 2015.
Available @ http://www.youtube.com/watch?v=FdYuG7lnLJw

Redd, Nola Taylor. "Mars May Become a Ringed Planet Someday." Space.com > Science & Astronomy. Nov. 23, 2015.
Available @ http://www.space.com/31195-mars-may-get-rings-like-saturn.html
Zubritsky, Elizabeth. "Mars’ Moon Phobos is Slowly Falling Apart." NASA > Mars. Nov. 10, 2015.
Available @ https://www.nasa.gov/feature/goddard/phobos-is-falling-apart