Put a Ring on it
Dylan Chase-Woods
Sorry Phobos-philes, it looks
like Mars’ largest moon is
headed for an imminent death!
In its place though, we may be
left with an intriguing new
member of Mars’ planetary
system: a ring [1]. While most
moons in our solar system,
including
Earth’s
own,
are
Figure 1: Credit: Image by Tushar Mittal using Celestia 2001-2010,
Celestia Development Team
slowly moving away from their planets,
tides on Earth and the violent volcanic
Phobos is getting closer and closer to Mars
activity of Jupiter’s moon Io [3]. Normally
with each orbit. This means that its
when large objects approach a planet, they
destruction will be inevitable. A new study
are held together by their own internal
by planetary scientists from the University
forces until they impact the surface or burn
of California Berkeley [2], though, shows
up in the atmosphere. But studies of the
evidence that it may come in a different way
geology of Phobos indicate that it is held
than we previously thought. Their results
together very weakly. Phobos is small, only
indicate that instead of crashing to the
about 14 miles across, and has taken a
Martian surface, Phobos may be torn apart
beating from meteors. Its surface is covered
by the gravity of Mars long before that. This
in cracks and craters, including the Stickney
would leave a trail of moon fragments and
crater which is 5.6 miles across (Figure 2).
debris orbiting around mars, forming a
As a result, it is thought that the moon is
stable ring.
composed of highly fractured, incohesive
All objects in orbit are subject to
rock. The new study shows that if the moon
tidal forces, caused by the difference in the
is held together as weakly as it seems, it will
pull of gravity at different parts of the
not be able to hold up to the tidal forces it
satellite. Tidal forces are what cause the
will experience when it gets closer to Mars.
When Phobos reaches this critical point it
As far as stargazers need to be
concerned, not much will change. Unlike
Saturn’s brilliant rings composed largely of
ice, the dust and rock of Mars’s ring will not
reflect much light, so the ring may not even
be visible from earth. From the surface of
Mars, though, it would be quite a sight,
giving future astronomers the promise of
having
something
Figure 2: Phobos with the Stickney Crater. Image
from Viking 1, 1977
forward to. will break apart into rubble and dust that
Sources Cited will continue orbiting, but will spread out to
form a coherent ring.
The
Berkeley
group
studied
meteorites on earth with a similar density to
Phobos, along with examining its craters and
surface geology to determine its structural
strength. The results showed that it would
not be able to withstand the force of Mars’
gravity pulling it apart, and that it could
happen as soon as 20 million years from
now. Further simulations of the resulting
fragments and debris indicate that the
resulting ring could persist for up to 100
million years depending on how far from the
surface it breaks apart.
spectacular
to
look
1. University of California - Berkeley. "Mars
to lose its largest moon, Phobos, but gain a
ring." ScienceDaily, 24 November 2015.
www.sciencedaily.com/releases/2015/11/151
124143506.htm
2. Black, B. A., & Mittal, T. (2015). The
demise of Phobos and development of a
Martian ring system. Nature Geoscience,
8(12), 913–917.
3.
Tidal
Force,
Wikipedia
the
Encyclopedia,
https://en.wikipedia.org/wiki/Tidal_force
Free