First HiRISE Images Coming Soon!, test images to be taken week of March 20 Options

[tedstryk]

What can Mars Express do on Deimos in terms of coverage of the trailing hemisphere? Also, might Rosetta be able to help with this?

[Steve G]

Very nice! But the real 3-D shape would allow a better view than the ellipsoid suggests, as that side appears to be flattened more than this triaxial ellipsoid. And the true shape of the limb at right is unknown. That if nothing else would be a new input to the shape model. This image shows nicely where the cut-off of high resolution imaging falls, not far east of the prime meridian. Then we have a strip about 40 degrees wide of low quality imaging based on just two very early Viking images, and then the outer strip based on only one high phase view. With good lighting we would still learn something new about this region.

By a happy coincidence your simulation date of 15 March is my birthday. I'll take this as a birthday card!

Phil

The only opportunity to image Deimos (or Phobus) would be during the initial orbit phase of the mission. Those long looping orbits, I'm sure, would have presented with a few chances for some good shots. However, it's not a priority, obviously, which is a shame.

What can Mars Express do on Deimos in terms of coverage of the trailing hemisphere? Also, might Rosetta be able to help with this?

Dawn is planning a Mars flyby, isn't it. Oh, that's right, it was cancelled. Apparently Ceres and Vesta, each completely unique in the Solar System, aren't important enough to keep the mission aflaot.

Sorry for the sarcasm, there should have been dedicated asteroid missions decades ago.

[mcaplinger]

By a happy coincidence your simulation date of 15 March is my birthday. I'll take this as a birthday card!

Alas, since a slew is involved it'll take a bit longer to get this planned, but it seems like a worthwhile image, so I'll see if we can get it taken.

[tedstryk]

To "Investigate the global chemical heterogeneity on Phobos and Deimos" is a stated goal of the flyby, and I saw on a sequencing document that coverage on approach should occur, so there may be at least low resolution coverage. However, the documents hadn't been updated for the new trajectory, so exactly how it will play out isn't answered.

[Guest_BruceMoomaw_*]

Bless you, my child. (Has anyone come up with a theoretical explanation for why Deimos and Phobos have such radically different-looking surfaces?)

[Phil Stooke]

Bruce said "Bless you, my child" - is that another birthday greeting?

The best explanation for the difference between P and D would appear to be that of Peter Thomas and colleagues at Cornell: that Deimos is basically completely covered with a thick layer of ejecta from a very large impact. No large crater? Yes, there is. The entire south polar region is saddle-shaped, and is interpreted by Thomas et al. as a crater with a diameter about the same as the diameter of Deimos itself. I happen to agree with this. Phobos lacks anything of this magnitude.

This is a good time to demolish the old idea that such a large impact would destroy the target. Modelling of such impacts does not support this old idea. This also applies to Mimas, where in another thread Bob Shaw mentioned the Voyager-era idea that the Herschel impact 'nearly destroyed' Mimas. It was nowhere near doing that. To destroy a body, the shock front from the point of impact has to completely engulf the target body while still having enough energy to dissipate the fragments. Herschel stopped growing when its shock wave energy/unit area dropped below the point at which it could throw out fragments, obviously long before the wave passed through Mimas entirely. Ditto Stickney on Phobos.

mcaplinger - no, the birthday card was jmknapp's picture! I know the image would take much longer to acquire. Oh, and say Hi to Ken from me!

Ted Stryk asked about Mars Express. I've posted a couple of the SR images elsewhere here. The resolution is probably a bit worse than MOC, but with the proper lighting it could add to the stock of images of that side. So far, though, all MEX images that I've seen show mainly the leading side.

Phil

[David]

This is a good time to demolish the old idea that such a large impact would destroy the target. Modelling of such impacts does not support this old idea. This also applies to Mimas, where in another thread Bob Shaw mentioned the Voyager-era idea that the Herschel impact 'nearly destroyed' Mimas. It was nowhere near doing that. To destroy a body, the shock front from the point of impact has to completely engulf the target body while still having enough energy to dissipate the fragments. Herschel stopped growing when its shock wave energy/unit area dropped below the point at which it could throw out fragments, obviously long before the wave passed through Mimas entirely. Ditto Stickney on Phobos.

It's true that the idea that Herschel Crater was something outlandish now seems slightly quaint. There are relatively bigger impact basins on Iapetus, and megacraters on almost every moon of Saturn, including little Hyperion.

By the way, does anybody know if Herschel Crater is named after William (who discovered Mimas) or John (who named it)?

[SteveM]

To "Investigate the global chemical heterogeneity on Phobos and Deimos" is a stated goal of the flyby, and I saw on a sequencing document that coverage on approach should occur, so there may be at least low resolution coverage. However, the documents hadn't been updated for the new trajectory, so exactly how it will play out isn't answered.

Am I right that you're referring to the planned Rosetta flyby? Google turned up that phrase on an ESA page describing the OSIRIS instrument flying on Rosetta. Orbiter Instruments: OSIRIS: Optical, Spectroscopic, and Infrared Remote Imaging System.

-- Easily Confused

[mcaplinger]

What can Mars Express do on Deimos in terms of coverage of the trailing hemisphere? Also, might Rosetta be able to help with this?

Rosetta, though the Mars flyby is a lot closer than I would have guessed, doesn't get all that close to Deimos, nor does the geometry look very favorable. See http://www.space.irfu.se/rosetta/sci/mars/
MEx would be able to do better on the occasion of a close flyby -- you'd think there would be some. (Edit: oops, no, the MEx orbit only goes a bit outside that of Phobos.)

[jmknapp]

Alas, since a slew is involved it'll take a bit longer to get this planned, but it seems like a worthwhile image, so I'll see if we can get it taken.

Also consider what Phil said about different sun angles. Looks like the subpoint of MGS on Deimos ranges +/- 5 degrees in latitude and longitude from 0,0. Also over the ~30 hour period there's an opportunity to get just about any phase angle. Here's an animation of one 30-hour period in May:

MGS Deimos animation, May 26-27, 2006 (7.5MB MPG)

The jumps occur when MGS goes behind Mars and no view of Deimos is available.

[Jyril]

By the way, does anybody know if Herschel Crater is named after William (who discovered Mimas) or John (who named it)?

William, of course. I don't think naming moons is more important than discovering them.

[ljk4-1]

The only opportunity to image Deimos (or Phobus) would be during the initial orbit phase of the mission. Those long looping orbits, I'm sure, would have presented with a few chances for some good shots. However, it's not a priority, obviously, which is a shame.
Dawn is planning a Mars flyby, isn't it. Oh, that's right, it was cancelled. Apparently Ceres and Vesta, each completely unique in the Solar System, aren't important enough to keep the mission aflaot.

Sorry for the sarcasm, there should have been dedicated asteroid missions decades ago.

This must be a tradition with JPL - they had no formal plans with Mariner 9 to
image Phobos and Deimos until the global dust storm of 1971 essentially forced
them to show the public something other than a bland ball.



MRO took a distant image of Deimos:

http://photojournal.jpl.nasa.gov/catalog/PIA02699

Original Caption Released with Image:

This image showing the position of the Martian moon Deimos against a background of stars is part of a successful technology demonstration completed by NASA's Mars Reconnaissance Orbiter before arrival at Mars.

The spacecraft's Optical Navigation Camera was used in February and March 2006 to demonstrate the use of pictures from a small camera for calculating precise location of a Mars-bound spacecraft by comparing the observed positions of Mars' two moons to their predicted positions relative to background stars. While this technique was not necessary for the Mars Reconnaissance Orbiter's own navigation, the demonstration prepares the way for relying on it for navigating precise arrivals for future missions that land on Mars.

This example image from the Optical Navigation Camera was taken on March 6, 2006, at a distance of 1.08 million kilometers (671,000 miles) from Deimos. That moon, the smaller of Mars' two, has a diameter of 15 kilometers (9 miles), and orbits 23,459 kilometers (14,577 miles) above the planet's surface.

[mcaplinger]

Also over the ~30 hour period there's an opportunity to get just about any phase angle.

There are a few operational constraints; we're not allowed to point within 30 degrees of the Sun. I've been assuming that the half-phase, trailing-illuminated case is of most interest. Phil, does that sound right? I don't think I can sell a survey of phase angles, at least initially.

Thanks for the animation; very useful.

[Guest_AlexBlackwell_*]

Rosetta, though the Mars flyby is a lot closer than I would have guessed, doesn't get all that close to Deimos, nor does the geometry look very favorable. See http://www.space.irfu.se/rosetta/sci/mars/
MEx would be able to do better on the occasion of a close flyby -- you'd think there would be some. (Edit: oops, no, the MEx orbit only goes a bit outside that of Phobos.)

If memory serves me, the original Deep Space 1 (DS1) mission profile, which involved a Mars flyby, would have also allowed an extremely close flyby of either Phobos and/or Deimos. I remember discussing this specifically with one of the mission designers at the 1997 International Astronautical Congress in Torino, Italy. Of course, with the launch delay DS1 lost the Mars flyby opportunity.

[Phil Stooke]

"I've been assuming that the half-phase, trailing-illuminated case is of most interest. Phil, does that sound right?"

Yes, perfect!

Basically, as I've said, anything which adds to our coverage in this area is great. Peter Thomas will have an extra bit of input for his shape model. If in the future an additional image or two should be possible, anything which gave different phases would help too. Sub-solar longitudes on Deimos of about 225 and 315 would help reveal topography in this area.

Phil