NASA Mars Picture of the Day: Deimos!

Mars Global Surveyor Mars Orbiter Camera

MGS MOC Release No. MOC2-1551, 11 August 2006

One might say that today is Deimos’ birthday. To celebrate, we present here the
first and only Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image of this
tiny moon.
Deimos was discovered 129 years ago on 11 August 1877 (U.S. time, it was 12 August UTC),
by U.S. astronomer Asaph Hall. It was the first of two major discoveries that he
made that month; less than a week later, he found the other, inner martian satellite, Phobos.

About a month before the 129th anniversary of its discovery, on 10 July 2006,
Mars Global Surveyor was pointed away from the martian surface, out toward distant Deimos.
Imaging the smaller of the two martian moons
was the result of a combined effort between MGS engineers at Lockheed Martin Astronautics
and MOC operations engineers at Malin Space Science Systems. When the picture was
acquired, Deimos was about 22,985 kilometers (14,285 miles) from MGS. This results
in an image of approximately 95 meters (about 312 feet) per pixel.
Higher resolution images were obtained by the Viking orbiters in the 1970s—some of
those pictures were so good
that boulders could be resolved on the moon’s surface.
While the MOC image is at a lower resolution than the Viking data, acquiring an
image of Deimos helps refine the understanding of the tiny moon’s orbit and geography.
The two craters, Voltaire and Swift, are presently the only craters with names on all
of Deimos. Author Jonathan Swift, in his 1726 Gulliver’s Travels, had
coincidentally surmised that Mars has two moons. Sunlight illuminates the scene
from the upper right.

MGS previously imaged the inner, larger moon, Phobos, on several occasions in 1998 and 2003.
In 1998, MGS was in an elliptical orbit that permitted the spacecraft to actually fly
past the moon; this was not done for Deimos because MGS hasn’t been out past the orbit
of Deimos since it arrived at the red planet in 1997.
To review the MOC images of Phobos, visit:

• Moons of Mars
• 1998 First Phobos Encounter
• 1998 Second Phobos Encounter
• 1998 Third Phobos Encounter, first view
• 1998 Third Phobos Encounter, second view
• 1998 Fourth Phobos Encounter
• 2003 view of Phobos

The MGS MOC team thanks
Philip J. Stooke,
University of Western Ontario (London, Ontario, Canada)
for his input on the geography of Deimos and the locations of Swift and Voltaire.