Seeing as the conventional wisdom has it that the dust devil streaks are visible because the DDs sweep loose, bright dust from the ground, darkening it, then yes, it makes sense that the process of "erasing" the tracks is due to re-deposition of dust.

When I used the term "wipe," I was thinking more of how one wipes an Etch-A-Sketch clean, I suppose.

-the other Doug

What strikes me most strongly about this montage is how consistently light and streak-free the surface around the Hills looks at the beginning of last spring/summer's dust devil season.

If we assume that most every dust devil season leaves the area as streaked as the Sol 1207 image appears, then there is obviously a process in place that erases the streaks every winter.

Obviously, the global dust storm of this past summer is one such mechanism -- but there was no global dust storm (or even a localized dust storm) between the prior dust devil season and this last one.

Pretty impressive testament to the power of normal winds to wipe away such streaks every year.

-the other Doug

Doug -- never tell people you've got enough money! Those who are planning to contribute in the near future may decide not to, since you say you don't really *need* any more at present.

To counter that potential sentiment, I'm going on record that, as soon as I can afford it (which ought to be within the next three weeks at most), I'm definitely going to send off whatever the pounds equivalent is of roughly a hundred bucks.

This place is like a second home to me. I spend more time reading and posting here than I spend doing anything else with the exception of my job. I feel it's an *honor* to have the opportunity to help support it.

-the other Doug

I think Vegas ought to have a betting pool on whether one or both MERs will be operating when MSL lands.

-the other Doug

As I've noted, there are thousands and thousands of buried craters evident in the intercrater plains. Looks like a heavily cratered surface, a la the lunar highlands, has been covered over with lava.

-the other Doug

I'd argue that Galileo was Mariner 13 and Cassini is Mariner 14.

And here they thought they'd get around any possible numerological issues by renaming these programs before they got to a Mariner 13...!



-the other Doug

Yes -- I never realized before that one of the Mariner IV images included one of the major outflow channels, but at such a resolution and sun angle as to be unrecognizable for what it was.

-the other Doug

Problem is, the CEV has been redesigned and made smaller once already, based on performance projections for the Stick. We're now at the raw edge of the Stick's current ability to orbit Orion as currently designed. Any reduction in performance will result in a further redesign that will severely limit the CEV's ability to perform its design mission.

I think we may be looking at the potential for changing over to an Atlas V or a Delta IV (in their Heavy configurations) as the first stage for Orion. Any such decision has to be made *very* soon, though.

-the other Doug

Actually, Copernicus-style craters are about as common on Mercury as they are on the Moon. Both are post-LHB. What remains to be seen is how ancient these Hermean inter-crater plains might be -- I've seen some areas on both Mariner 10 images and in these new Messenger images where relatively fresh-looking ray systems disappear in relatively dark and smooth lava flows. That could always be a situation where the ejecta was shadowed, God knows we've seen non-continuous ray systems elsewhere. But a very close look at these places is definitely called for, I think.

As for the preponderance of double-ring craters, every theory I've heard about it tries to lay this observation at the feet of Mercury's gravity field, which is more intense than the Moon's. However, I've never seen a model that successfully predicts the formation of central rings vs. central peaks that doesn't also have to assume a somewhat greater plasticity of the target to achieve those double rings.

-the other Doug

As far as I know, the people designing Bepi-Columbo are not working in concert with the Messenger team in any way. And B-C has a rather checkered history in the first place, it's launch date has been pushed back several times and its mission rescoped even more times.

B-C is one of those projects that I will believe when I see it actually built, launched and working. And not until then. As far as I'm concerned, it makes little sense to worry about whether or not it's a complementary mission to Messenger until the odds of it actually flying improve beyond "maybe someday"... *sigh*...

Besides, unlike the results from Messenger, only three people in the world will ever see more than three or four images from B-C even if it does fly, so I don't know why anyone would be worried about it in the first place.

-the other Doug

You know, Nick, unlike a lot of the people here, you and I can recall when NASA and JPL were pushing hard to get the Grand Tour mission approved. I remember when it was first proposed in the late '60s, I remember when it was canceled, and I remember how elated I felt when its poor second cousin, a simple Jupiter/Saturn flyby, was "tweaked" into something approximating the original GT mission.

Also, IIRC, Voyager 2 could have been targeted for a Pluto flyby, thus completing the original GT mission plan -- but it would have lost its close flyby of Triton. The Pluto option was still possible after the Uranus encounter (though close to the limits of the remaining delta-V in the vehicle), but the craft was deteriorating (scan platform issues, among other things) to the extent that the decision -- and I think the right one -- was made to maximize science during the Neptune encounter.

When it came to deciding between doing as complete a recon of the Neptune system as possible with the healthiest spacecraft you could manage, or giving up Triton on the hope you'd still be operating well (or at all) when you got to Pluto, I think they did make the right decision.

-the other Doug

My most overwhelming impression of the surface, especially on the inbound full-crescent views, is that Mercury's LHB-carved surface has been almost completely covered with lava flows. The population of completely expressed large craters / small basins is relatively small, especially as compared to our Moon. The population of these large craters / small basins which are expressed only as circular deformations of a relatively smooth covering layer is very similar to the population of non-covered craters in the lunar highlands.

Conclusion? Mercury was resurfaced (if imperfectly) *after* the LHB, and now only exhibits "uncovered" craters from the three and a half billion years since its end.

-the other Doug

I still have this image in my head of an antenna farm consisting of 10,000 old DirecTV and/or Dish Network 50cm dishes, all attached to altazimuth drives and being pointed by a central computer complex. Just lay the thing out on any convenient piece of desert or tundra, and run the multitude of signals received through rectifiers to pull out the weak signals coming from far away.

I'm sure there are good reasons why this would never work, but it seems like a good, cheap way to quickly put together a temporary addition to the DSN.

-the other Doug

Tasp raises a good point, though, Nick. Mercury's orbit sees more objects cross its path than any other planetary orbit in the system. First, it's the smallest piece of real estate in the system occupied by a planetary orbit, and second, ever since we've seen several comets *per year* glide directly into the Sun, we know that there are a lot of bodies infalling through its orbit.

A lot of those bodies will be the result of fragmentation of larger comets, so a lot of the Hermean impactors would expected to be relatively small (less than a km in widest dimension, most fist-sized or smaller) and travelling at very high speeds relative to Mercury.

From that, I would expect the impact flux to be higher (at this point in time) on Mercury than on any other Solar System body.

I'd also point out, to those who were contemplating the possibility of cometary or asteroidal debris finding its way into a Mercury orbit, that with the largest flux of potential impactors, Mercury would also see the largest flux of near-misses. And that while it can be difficult for a fly-by object to achieve an orbit if you consider it as a two-body problem, the proximity of the Sun makes any such trajectory a three-body problem, which opens up all sorts of otherwise unlikely-sounding possibilities for orbital insertions.

-the other Doug

Thanks, guys!

Now, where did that swear jar go...?

WOW!

Yep, that's Mercury, all right. The fold-over ridges and the central rings in the larger craters give it away. Kewl -- first close-ups of Mercury in 30 years!!!

-the other Doug

Broken link:

FATAL ERROR: cannot connect to mySQL server
host: sd-mysql:3307
user: regieal1

-the other Doug

OK -- 30 kilobits per second, I can see. At 30 kilobytes per hour, you would be getting about 210 kilobytes over seven hours, and even the jpeg'ed images we've already seen are larger than that. Each.

Unless there is some kind of uber-compression going on here of which I'm not aware, I would think it would be hard to fit 1,200 images into a file only 210 KB large.

-the other Doug

Umm... 25 to 30 kilobits per hour? At that rate, wouldn't it take about 40 hours to receive a kilobyte?

Just how compressed is this data?

-the other Doug

Hmm... isn't this right about the time that the Sun is supposed to shift the polarity of its magnetic field?

We've had fields-and-particles spacecraft out taking measurements over the last few solar magnetic field cycles. Does anything happen at such times that would impact (either figuratively or literally) three different deep-space probes, all at once?

Just wondering...

-the other Doug

Interesting.

I wonder if this was inspired by the only real-life story I can recall of an insectoid hitchhiker on a manned spaceflight? During the ASTP mission, the Apollo crew discovered a Florida mosquito flying around inside the Docking Module when they opened it up to check it out.

-the other Doug

Good discussion, wherever it eventually ends up "belonging"...

Yeah, I know there's no proof that we've actually seen a piece of suevite yet. I do sincerely believe that there must be a fair amount of impact melt on Mars, if only because, as HDP has pointed out, impact processes have likely predominated surface change on Mars for a long, long time. And Mars has been very dry (over much of the globe), to a pretty decent depth, for a long time, too. You'd expect to see less and less hydrous effects on the impact melts as Mars has become drier and drier, would you not?

Then again, no one really knows how much water is locked up in rocks and ices beneath Mars' surface. I guess it's possible that Mars retains enough subsurface volatiles to continue to preferentially degrade impact melts over other impact products, leaving much of the planet covered with ejected chunks of rock (some of it not even very shocked), and very little melt.

I don't suppose it's possible for Oppy to go visit this little chunk of what could possibly be suevite and take a real long sniff...?

-the other Doug

Ummm... if CA was appreciably different from planned, doesn't that have a fairly significant effect on the trajectory?

-the other Doug

Yes, and the solution to the ECO sensor problem? Solder the pin connectors! This is apparently a fix that people came up with for a very similar problem in Centaur upper stages nearly 40 years ago. It took this amount of time and effort for someone to check another program's Lessons Learned Book... *sigh*...

-the other Doug

Reminds me of the only morbid chuckle I came across on February 1, 2003. In CNN's coverage of the Columbia disaster, at one point, the titles that run under the talking heads read "Columbia broke up while traveling at 15 times the speed of light." I looked at the person I was watching the TV with and said "Well, that was the problem, right there!"

-the other Doug

Impact melt can also form a lining within the crater. In smaller craters, a glassy lining is made up of impact melt. (Since we have never landed in or taken samples of the floor of a large lunar impact crater, we have almost no data on how abundant impact melts might be in the floor units of large impact craters.)

If this *is* local, I would imagine that the suevite was emplaced in the ejecta and has since eroded out of one of the prominent capes. Being harder than the surrounding rock, it would simply fall out of the cape structure and tumble down the inner slope of the crater.

-the other Doug