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TOPIC: Phobos and Deimos
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Deimos
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Mars Global Surveyor image of Deimos from 10 July 2006

diemosMSG

Credit: NASA/JPL/Malin Space Science Systems


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Blobrana


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Phobos
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Phobos
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Blobrana


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The first and only Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image of Deimos was taken on 10 July 2006, when the Mars Global Surveyor was pointed away from the Martian surface.

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.

deimos.mediumdeimosNAMES
Credit NASA/JPL/Malin Space Science Systems

About a month before the 129th anniversary of its discovery, the Mars Orbiter imaged the smaller of the two Martian moons, when it was about 22,985 kilometres from MGS. This results in an image of approximately 95 meters 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

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Blobrana


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RE: Phobos and Deimos
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This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows the fast-moving shadow of the moon Phobos as it moved across the Martian surface.

The HRSC obtained these unique images during orbit 2345 on 10 November 2005. These observations would not have been possible without the close co-operation between the camera team at the Institute of Planetary Research at DLR and the ESA teams, in particular the mission engineers at ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany.


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Credits: ESA/DLR/FU Berlin (G. Neukum)
Phobos is the larger of the two Martian moons, 27 kilometres by 22 kilometres in size, and travels around Mars in an almost circular orbit at an altitude of about 6000 kilometres. Phobos takes slightly more than 7.5 hours to complete a full revolution around the planet.

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Blobrana


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This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, is one of the highest-resolution pictures so far of the Martian moon Phobos.

The image shows the Mars-facing side of the moon, taken from a distance of less than 200 kilometres with a resolution of about seven metres per pixel during orbit 756, on 22 August 2004.
This colour image was calculated from the three colour channels and the nadir channel on the HRSC. Due to geometric reasons the scale bar is only valid for the centre of the image.


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These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, are Europe’s highest-resolution pictures so far of the Martian moon Phobos.

The image collection shows Phobos in different orientations as seen from orbits 748, 413, 649, 682 and 715 (from clockwise from lower left), while the picture on the lower right is a mosaic made from the Super Resolution Channel on orbit 413.
The images have been derived from the HRSC nadir (vertical view) channel (except the mosaic from the HRSC Super Resolution Channel).


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This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows the Mars-facing side of the moon, taken from a distance of less than 200 kilometres with a resolution of about seven metres per pixel during orbit 756, on 22 August 2004.
This image was calculated from the HRSC nadir (vertical view) channel. Due to geometric reasons the scale bar is only valid for the centre of the image.

Credits: ESA/DLR/FU Berlin (G. Neukum)


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Blobrana


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Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of centre) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977.



This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. North is toward the top with the Sun illuminating the scene from the South (black dots are reference marks).
For scale, Ascraeus Mons is about 200 miles across at its base while asteroid sized Phobos is about 15 miles in diameter. In this spectacular moon-planet image, volcanic calderas (craters) are visible at the summit of Ascraeus Mons -- while impact craters on the sunlit side of Phobos' surface can also be seen!

The Shadow of Phobos

Hurtling through space above the Red Planet, Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - travelling from horizon to horizon in about 5 1/2 hours.


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These three images from the Mars Global Surveyor (MGS) spacecraft record the oval shadow of Phobos racing over western Xanthe Terra on August 26, 1999. The area imaged is about 250 kilometres across and is seen in panels from left to right as red filter, blue filter, and combined colour composite views from the MGS wide-angle camera system.
The three dark spots most easily seen in the red filter image are likely small fields of dark sand dunes on crater floors. Standing in the shadow of Phobos, you would see the Martian version of a solar eclipse!

Credit: Malin Space Science Systems, MGS, JPL, NASA

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In this animation, both martian moons, Deimos on the left and Phobos on the right, travel across the night sky in front of the constellation Sagittarius. Part of Sagittarius resembles an upside-down teapot. Phobos is the brighter object on the right; Deimos is on the left.


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Spirit acquired these enhanced-brightness images with the panoramic camera on the night of sol 585 (Aug. 26, 2005). Scientists will use images of the two moons to better map their orbital positions, learn more about their composition, and monitor the presence of nighttime clouds or haze. Spirit took the six images that make up this animation using the camera's broadband filter, which was designed specifically for acquiring images under low-light conditions.

Larger Animation (580kb)

Two Moons and the Pleiades from Mars


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Image credit: NASA/JPL/Cornell/ Texas A&M

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Spirit has imaged Phobos and Deimos the two Martian moons.
The robot is currently assessing weather features of nighttime Mars.
To do this job, nighttime shots are being taken using the backdrop of stars—as well as Phobos and Deimos—to help pin down atmospheric phenomena.



"We’re looking for any evidence of clouds forming at night, or fog, or haze" - Jim Bell, an Associate Professor in the Cornell University Astronomy Department in Ithaca, New York.

As the two moons pass overhead, Spirit is getting a spectacular view.
While each rover is equipped with a Panoramic Camera—or PanCam—the devices are not telescopes.

"Still, we can do some pretty good astronomy" - Jim Bell.

Spirit has been able to snap shots of both Phobos and Deimos together. “We’re killing two birds with one stone by selecting times when those two moons pass each other in the sky. That does frequently happen…every couple of nights”.


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By taking the nighttime photos, a better understanding of where those two moons are in their respective orbits becomes possible.

"We’re getting some good orbital refinement on the positions of the satellites. They haven’t been monitored by astronomers since the late 1980s" - Jim Bell.

In addition, by using colour filters on Spirit, colours of the two Martian moons can be ascertained.
Deimos looks pretty much like a star, far away. But features on Phobos can be made out.



"You can clearly see that Phobos is an oblong, potato-shaped object in the sky. It’s not as big as the full moon, but it is still pretty decent in size" - Jim Bell.

A soon-to-be-released image will show features on the surface of Phobos, he said, "and this is with not much better than human eye resolution!"
In fact, Phobos is so close and large enough, a person standing on Mars, within a few minutes, would notice the moon moving.

Thanks to the rover’s power levels, a proposal is being made to use Spirit to observe meteor showers this Autumn.

Just like here on Earth, the red planet also sweeps through areas of space laden with comet debris. Scientists want to evaluate the flux of these small particles streaming into the Martian atmosphere.

"There are models that predict certain rates of meteors, and like on Earth, there are shower times" - Jim Bell.

"We’re actually shunting some power during the daytime. So we’d much rather use that power to do some science instead of shunting it out as waste heat" - Jim Bell.

Spirit’s nighttime powers should help record that shower activity.

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