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Emily LakdawallaJuly 23, 2008

More information on the Mars Express Phobos flyby today (no pictures yet)

I've communicated further with Agustin Chicarro about the Mars Express flyby of Phobos today. It seems Mars Express does not communicate with Earth again until Friday, meaning that the images likely will not be released until at least Monday.

Also, I just received the following message from Tom Duxbury containing lots more details on today's flyby.

"The Mars Express spacecraft, about 1 hour and 12 minutes after its closest flyby (pericentre passage) of Mars on orbit #5851 at 04:46:23 Jul 2008 GMT, flew within 90 kilometersof the surface of Phobos. This distance was matched by the US Viking Oribiter 1 in 1977 and the Soviet Phobos 88 orbiter in 1989. However, the Mars Express Orbiter will return images with 5 times the spatial resolution of Viking while the Phobos 88 orbiter was lost during its descent to the surface of Phobos and its images taken at this distance were never recovered.

Moving around Phobos

ESA / DLR / FU Berlin (G. Neukum) / animation by Emily Lakdawalla

Moving around Phobos
This animation contains 10 views of Phobos captured by Mars Express on different orbits. It begins with a nearly north polar view on the anti-Mars hemisphere, and moves southward a bit before rotating into the leading hemisphere.
"The Mars Express orbiter approached Phobos just north of the largest crater Stickney on the leading side of Phobos and passed over the northern hemisphere at more than 2 kilometers per second. The approach was just to the illuminated side of the terminator while the closest encounter and departure occurred on the dark side of the terminator. Special pointing of the cameras was planned to view the surface illuminated by sunight. Closest approach occurred about 52 degrees north latitude, and the departure exited Phobos below the equator and east of the anti-Mars point.

"The high resolution, color, and stereo images will have a spatial resolution as good as 5 meters per pixel while the super-resolution channel will have a spatial resolution as good as 1 meter / pixel." In practice, the super-resolution channel has a serious blur, so although its resolution is somewhat better than the high-resolution camera, it's not 5 times better. "The close flybys are expected to yield a mass and density of Phobos accurate to 1%, and the radar sounding may shed light on the origin of Phobos by possibly determining if Phobos is a loose accretion of Mars material or a solid chunk of an asteroid. The surface will also be observed in multispectral visual and infrared wavelengths to determine the uppermost surface composition. The dust and plasma environment will be sampled."

Thanks, Tom, for that information!

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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