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Posted by: gndonald Aug 15 2005, 03:36 PM

While the likelyhood of a Mercury Lander mission is very low, I was wondering if any planning/studies have been done on such a project?

Posted by: Patteroast Aug 15 2005, 04:13 PM

The European 'BepiColumbo' mission planned for the next decade included a lander at once point, but it was cut. I believe this mission also included multiple orbiters and a collaboration with JAXA... but I'm not sure off the top of my head.

I don't see why it would be particularly difficult.. as long as it landed either during the day or the night.. I can't imaging a spacecraft withstanding the temperature difference between them.

Posted by: Bob Shaw Aug 15 2005, 07:05 PM

The problem isn't so much the engineering - a nice vaccuum, and abundant solar power are hardly the worst-case scenarios for a spacecraft - but the Delta-V requirements. Mercury is an expensive place to reach, and is substantially bigger than the Moon, so you have to expend more effort once you get there.

Personally, I'd leave it until some alternative propulsion method was found - solar/ion engine, Prometheus, solar sail, whatever.

Posted by: djellison Aug 15 2005, 07:24 PM

Impactor could work

Doug

Posted by: BruceMoomaw Aug 15 2005, 07:30 PM

ESA studied alternative possible designs for a BepiColombo lander in great detail, until they concluded that they just didn't have the money. Meanwhile, the US has pretty firmly concluded that a Mercury multiple-small-lander mission is the only logical next step after Messenger and BepiColombo, although it's not all that high on NASA's Solar System priority list. (It would likely be a New Frontiers-class mission, costwise.)

Posted by: remcook Aug 16 2005, 08:44 AM

Although the Bepi-Colombo lander is cancelled, ESA has spend some money on studies. So there are people building stuff that won't actually fly...

Posted by: djellison Aug 16 2005, 08:57 AM

Well - studies dont equal flight hardware. Maybe some simulations, maybe some studies, some spreadsheets - but I doubt a single bit of metal was cut.


Doug

Posted by: remcook Aug 16 2005, 03:01 PM

actually, hardware is actually made at this moment. However, they will make it such that it is also possible to use it on Mars, very conveniently

Posted by: JRehling Aug 16 2005, 03:55 PM

Mercury ends up being a fairly challenging target for a lander. Of course, the delta-v needed to get *anything* there is a problem. But even when that hurdle has been cleared, it is the hardest place in the inner solar system to land on. Because it has no atmosphere, all of the braking has to be done with thrust. Unlike the other inner-solar-system world in that category, the Moon, Mercury's got some real gravity -- about same g/escape velocity as Mars. So whereas light thrust will land you on the Moon, you can float down to Venus's surface (which is terrible once you get there), and a combination of thrust, chutes, and maybe bouncing will land you on Mars, Mercury requires a lot of thrust, period. Putting all of that rocket fuel into the payload that has to get to Mercury, the delta-v problem becomes even starker. And then there's the heat. The ESA lander would have landed near the north pole to escape some of the *ground* heat, but the sun is just as bright anywhere it appears in the Mercurian sky (except that seasonally, it is considerably less glaring at aphelion).

Another way to deal with the heat problem would be to land at night and wait for sunrise, dying sometime thereafter. That has the disadvantage of preventing descent imaging. It would be particularly sad to have the thing die when the sun had come up enough to burn the craft but before the landscape had been illuminated!

I don't think anyone would expect the panorama to be anything but a novel notion for wallpaper for your monitor -- there is no reason to suspect the hermean regolith to differ structurally from lunar regolith. We would almost certainly see a landscape like one of the Apollo landscapes, give or take a modest difference in hue. From earth-based remote sensing we already know that Mercury's surface is much lower in Fe than the Moon's; Messenger will tell us more about the raw composition. Overall, I'd say Mercury's surface is more burning with heat than burning with questions that a lander can answer.

I think the first mission to Mercury's surface ought to be a combination of Deep Impact and Stardust: a low-flying flyby craft in solar orbit would skim the Mercurian dayside (at 90,0 or 270,0) at aphelion, while an impactor flying just ahead would pound into the surface, blasting some regolith briefly up into a plume, which the flyby craft, trailing behind, would collect, and bring back on its Earth-intersecting orbit. We would obtain shattered fragments of Mercury that would, nonetheless, tell us the isotopic composition of Mercury's crust (which should be sufficiently pulverized already by impacts that smashing a sample once more is no great crime). The great value of THAT observation, aside from telling us about the early solar nebula and Mercury's evolution, is that it might permit the eventual identification of meteorites that originated on Mercury. We probably have, or will have, Mercury meteorites in collections -- identifying them as such would be a huge boost, because actually obtaining a non-fragment Mercury sample return would be a matter of enormous cost.

Posted by: BruceMoomaw Aug 16 2005, 07:53 PM

(1) That Mercury smash-and-grab mission is a real idea -- in fact (although I know virtually nothing about it), there was apprently at one point a Discovery proposal to do just that for one of Mercury's polar regions (to also try and obtain information on the polar deposit composition).

(2) Actually, it is thought likely that Mercury's regolith differs somehat in closeup appearance from the Moon's simply because meteoroids have been smashing into it at much higher speed. At a mnimum, there should be a lot more melted impact glass mixed into it. It's questionable, however, whether any such differences would be interesting enough to be worth a camera. But:

(3) A Mercury lander WOULD have a lot more uses. We very badly need to know more about the planet's strange internal structure -- for which seismometers, magnetometers, and (if possible) heat flow probes would be invaluable. In fact, just plain old measurements of the planet's libration rate by tracking a lander would be very informative about its interior -- Stanton Peale once suggested a Mercury lander that would do nothing else whatsoever!

And while we might be able to get good data on the element makeup of Mercury's crust from a smash-and-grab mission, there are also some important mineralogy measurements (Raman, Mossbauer, X-ray diffractometry) that could probably be done neitehr by such a mission nor by an orbiter. Finally, a surface lander might tell us more about the planet's super-rarified atmosphere than we could discover from an orbiter.

Posted by: DDAVIS Aug 16 2005, 10:30 PM

[quote=BruceMoomaw,Aug 16 2005, 07:53 PM]

(2) Actually, it is thought likely that Mercury's regolith differs somehat in closeup appearance from the Moon's simply because meteoroids have been smashing into it at much higher speed. At a mnimum, there should be a lot more melted impact glass mixed into it. It's questionable, however, whether any such differences would be interesting enough to be worth a camera.

I cannot imagine sending a lander to a planetary body without a camera! It would be interesting to see if the character of the surface varies from the Moon, and if there is a lot more impact glass than the lunar surface one would expect a more pronounced heliogenshein effect than what one sees on the Moon. The higher gravity might cause slightly different crater details on the small scale.

Don Davis

Posted by: djellison Aug 16 2005, 10:46 PM

Well quite - of the planets on which one COULD land - it is only Mercury and Pluto from which we dont have surface imagery

Doug

Posted by: BruceMoomaw Aug 17 2005, 12:57 AM

You're forgetting 2003 UB313, Doug... (Or, alternatively, The Planet That Must Not Be Named. Come to think of it, I hope the Potter craze hasn't gone so far that they end up naming the thing Voldemort.)

Posted by: um3k Aug 17 2005, 01:06 AM

I would much prefer Dumbledore.

Posted by: Richard Trigaux Aug 17 2005, 06:11 AM

JRehling,
your smash and grab idea is interesting. It could be perhaps beterred if the impactor hits the surface with a very low angle, nearby horizontal, so that the plume would be also nearby horizontal. And the main spacecraft would travel right in at low relative velocity, we could perhaps even collect more than dust, little stones.



BruceMoomaw,
just to get the exact movement of Mercury from a lander would require only little electronics for that lander, just retro rocket and guidance devices, and avoiding heat by landing at night. The payload itself would be just a mirror, similar to the ones placed on the Moon, so that it could easily withstand heat and need no electronics, insulators and the like.

A still simpler method, although more speculative, would be to send special reflecting glass balls, protected into a kind of low melting point metal or plastic, and shot this on the ground without retrobraking. With a low enough impact velocity, the casings protects the glass balls. (An additionnal idea would be to fly the glass balls just behind a larger impactor, so that the plume would brake them). Once the sun rises, the casings melt, lefting the glass balls naked, so that they could be used for measuring distance with a laser shot. Not all glass balls would work, but if we send many a fair amount could work. This is not worse than landing the MERs into an airbag!




The idea of a lander on Mercury or Venus arises special concerns, due to the extreme heat. Maybe I shall start a thread about the suitable technos for this.

Posted by: JRehling Aug 17 2005, 06:44 AM

[quote=DDAVIS,Aug 16 2005, 03:30 PM]
[quote=BruceMoomaw,Aug 16 2005, 07:53 PM]

(2) Actually, it is thought likely that Mercury's regolith differs somehat in closeup appearance from the Moon's simply because meteoroids have been smashing into it at much higher speed. At a mnimum, there should be a lot more melted impact glass mixed into it. It's questionable, however, whether any such differences would be interesting enough to be worth a camera.

I cannot imagine sending a lander to a planetary body without a camera! It would be interesting to see if the character of the surface varies from the Moon, and if there is a lot more impact glass than the lunar surface one would expect a more pronounced heliogenshein effect than what one sees on the Moon. The higher gravity might cause slightly different crater details on the small scale.

Don Davis

[/quote]

Not to be a party-pooper, but the degree of specularity of Mercury's surface should be something that Messenger can characterize pretty well from orbit (even Earth-based observations have weighed in on this: Moon-Mercury light-curve comparisons are the subject of many papers -- but better resolution will say more). And I'm not sure if different surface g will alter *small* crater shape in unpredictable ways, or any at all -- the speed at which things move away from an explosion should be way, way faster than any planet's gravity would interfere with (very little outbursting material would fall back into a 10 meter crater, no?).

I could imagine there being some very subtle Moon-Mercury differences, but I bet a bit of adjustment (for hue, specularity) to a lunar landscape would be something we (I first wrote "you", but Don might be uniquely able!) couldn't tell from Mercury landscapes in a blind taste test -- of course, we'll have to get loads of Mercury landscapes to know! And there's always the off-chance that something we aren't even dreaming of will make a tangible difference. I don't think we'll see a Mercury lander without a camera anytime soon -- but then, we aren't going to see *any* Mercury lander anytime soon! If the flyby craft on a smash-and-grab mission had a rear-facing camera, however, with the next decades' technology providing quick "shutter speed", we could get something a heck of a lot like a surface panorama -- in fact, a large number of them.

Posted by: edstrick Aug 17 2005, 10:59 AM

JRehling observed " We probably have, or will have, Mercury meteorites in collections "

Maybe but it's doubtful. They'll look, in all probability like lunar highlands breccias, but bulk compsition will be obviously non-lunar... a different pattern of volatile element depletion from what we think really heavily stripped the moon of "volatile" elements, including things like potassium, halogens, lead, zinc... in the mega impact that lead to our double planet.

More distinctive, and telltale, will be oxygen isotope fractionation patterns. The solar system was mixed thoroughally, but not completely, and martian, earth/moon, asteroidal (many different batches) and cometary isotopes are utterly distinctive in an 016/17 vs O16/18 plot.

There is *ONE* oddball meteorite I read about 2 or 3 years ago that resembles lunar meteorites but has an odd oxygen isotope pattern and it was being discussed as a possible mercurian ejecta sample, but I haven't heard a peep in the public reporting since.

Expectations, as I recall, from orbital dynamics stuff is that we should get about 1 merc meteorite for every 100 lunar ones <separate impacts?>.. and we dont' have 100 lunar ones.

Where we *should* put a lander down is on the mercury polar ice deposits in permanent shadows in craters. Keeping the lander warm will be the problem, not cool. This stuff is radar-bright and depolarizing.. the radar penetrates many wavelengths into the scattering ice without being absorbed and gets diffusely scattered back out with high reflectance.

Utterly unlike the marginally detected radar signature of lunar polar volatiles, if the detection claims aren't bogus anyway.

Posted by: Richard Trigaux Aug 17 2005, 12:29 PM

What is astonishing with Mercury is that it closely ressembles the Moon, but it does not seems to have volcanic activity, despites the fact that Mercury is much larger than the Moon. The Moon hade huge lava flows about 3-3.2 Gyears ago, forming the "seas". But as fas as I know there are no traces of lava or volcanoes. A popular hypothesis about these lava flow is that they were produced by the cooling and closing of the inner liquid core. But I think the hypothesis of a tidal heating would be interesting too, while explaining why Mercury had not such a volcanic episode.

Another difference (perhaps explaining the lack of volcanoes) is the huge iron core. There is also the network of NE-SW and WN-ES fractures running all around it. A popular hypothesis is that these fractures are due to the shrinking of the iron core when it cooled, perhaps at the occasion of the large impact of Mare Caloris.

Posted by: JRehling Aug 17 2005, 04:02 PM

Studies have differed on how many Mercury ejecta would make it to Earth, with one study going as high as 0.5% of the total (how long a time span one allows for the travel is a factor, since complex orbital dynamics are part of the picture). The percentage of lunar and martian ejecta making it to Earth may be about 40% and 4%, respectively, according to one analysis. We have to assume that the analysis of collections for possible lunar and martian origin has only been done very incompletely, but about 1% of the recent large meteorite finds have been from Mars. We might expect a Mercury meteorite for every 20 or so Martian meteorites (the fact that Mercury has no atmosphere to slow ejecta on the rise is a big help), so with umpteen identified martian meteorites on the record books and others sure to have not yet been detected, I'll stick to my guns and say that it's a definite possibility that we have a Mercury meteorite somewhere, unidentified as such, although I'll grant that the most likely counting numbers for the sum total of them are 0, 1, and 2 -- in no particular order.

Doing my own reasoning here, I'll note that travel times for lunar meteorites is VERY short compared to planetary meteorites, so if an ejecta-launching impact hits any of these worlds every few million years, then we should be getting a steady trickle of impactors from Mercury and Mars, but nothing from the Moon in a typical year, until suddenly a huge number of lunar meteorites are sprung by an impact and they become a common occurrence for several tens of thousands of years. That is to say, the infall of lunar meteorites should be highly stochastic, while the long travel times from Mercury and Mars should put those "streams" into more of a steady state. So a count of lunar meteorites that are atop our current layers of topsoil and polar snows really tells us very little. In fact, lunar meteorite influx in a MEDIAN year may be lower than that from other planets because the sum is so heavily spiked into the times right after an appropriate impact.

NWA 011 was one meteorite that was identified as being possibly Mercurian, although it was high in iron, which goes a long way to nix that (Mercury is crunchy, that is to say iron, on the inside; chewy, that is to say silicate with very low iron, on the outside).



We still aren't sure just what the surface would be for those Mercury polar reflections. It may be dust atop ice, or sulfur, or something else. Of course, a mission would be interesting in any case, if it can poke through a possible dust cover to see what's beneath. It would be disappointing though if the reflective stuff were patchy and our lander missed it by 200 m.

Posted by: centsworth_II Aug 17 2005, 04:44 PM

If getting a refector on Mercury is the objective, how about an impactor filled with thousands of tiny reflective devices -- like confetti -- that are released on impact to cover a large surface area? Or, a giant paint ball that would splat on the surface, coating it with reflective paint?

Posted by: tty Aug 17 2005, 05:48 PM

Here is a recent study of the probability of finding a mercuriam meteorite:

http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1933.pdf


The conclusion is that probability-wise "we may be getting close..."

tty

Posted by: BruceMoomaw Aug 17 2005, 10:12 PM

We don't want a reflector on Mercury for libration studies -- we need an actual, stationary surface beacon for reeally good measurements. (Remember that this was considered a worthwhile experiment even for the Mars Netlander -- and studies of Mercury's libration are thought to be more important.)

Certainly, when a Merury lander finally occurs, the first one will be in the polar regions (the BepiColombo lander would have landed at about 87 deg latitude). This isn't just because of the polar deposits; it's because that's the one part of Mercury where a lander can have a really long lifetime -- which is crucial for seismic studies.

Posted by: Myran Aug 18 2005, 05:55 AM

Cant but agree with BruceMoomaw, libration studies is one good reason, the other is my own favourite, seismic. All we have about Mercurys interior currently is quesswork, informed guesswork perhaps -but still.
A lander might have to be assisted by a set of impactor probes, at least two.

If such a lander also would get some more toys to maximize the science return like a little shovel, a chemistry set and one Polaroid to imagine the polar-void - all the better.

Posted by: Richard Trigaux Aug 18 2005, 06:40 AM

centsworth_II your idea is interesting, but it would not work as it: glass balls or paint drops arriving on Mercury surface at a cosmic speed would simply explode like meteorites. They need some kind of braking, if not an actual landing. For example they could be dropped on the ground from a low orbit.

But that would not be enough, says BruceMoomaw. So what do you need? an accurate reflector like the ones the astronauts installed on the Moon? I recall that these reflectors were made of an array of diamond-shaped pieces of glass, which has the property of sending back any ray of light right in the direction where it came. This is much more accurate and much more efficient (a much larger part of the light is reflected back to the emitter) than with just randomly scattered glass balls. But an already powerfull laser is required to shot at the Moon reflectors; 12 000 000 000 more power would be required to have Mercury with the same devices. This is perhaps the reason why there was no light reflectors on the top of any of the already numerous Martian landers.

So BruceMoomaw, what do you need? A radio beacon? It would be much more efficient in power, but less accurate. May an orbiter provide enough accuracy? After all, much info on Mars position may be infered from the radio wave emitted by Mars landers and orbiters, much more anyway than with nothing. So I understand that at least an orbiter around Mercury would provide much more data than nothing. And a lander still more.

The ideal would be active laser telemetry (a lander-based laser would reply to an Earth based one) but this would imply to send power lasers in spaceships. Let us have a dream: a powerfull laser geodesic network allowing to know the position of any planet with a micron accuracy...

Posted by: BruceMoomaw Aug 19 2005, 06:40 AM

I honestly don't know why they had it in mind, but Stanton Peale's scheme would definitely have involved an active radio beacon. (This is more easily understandable for the Mars Netlanders, since laser reflectors on Mars would quickly get dust-coated.)

Posted by: JRehling Aug 19 2005, 01:54 PM

Do you mean "why" vs a laser reflector? Mercury is often 1.0 to 1.2 AU from the Earth, and only briefly within 0.7 AU. A laser big enough to be seen after the round-trip (d^4 dispersion of the beam) is either nonexistent or really expensive.

This reminds me of one "mission" plan I had: Send a big sheet of reflective foil to Pluto. It would (if it worked) be its own parachute, as light as it was, even in the thin Pluto atmosphere. No instruments, no power. It could be extremely wide. The idea is that it would settle somewhere on Pluto. Then hope that by the end of the long travel time (or later), lasers big enough to reflect off of it would be developed... or just monitor the dimming of the sheet as frosts accumulate on it.

Posted by: BruceMoomaw Aug 19 2005, 06:23 PM

Well, I know that, John. I presumed that Richard Trigaux (like myself) was thinking about a surface reflector with an orbiter bouncing lidar off it -- just as the libration experiment on the Mars Netlanders would have involved a radio receiver on a Mars orbiter. But I still don't know why such surface laser reflectors (or radar reflectors) couldn't be used in association with an orbiter for Mercury libration measurements.

Posted by: JRehling Aug 19 2005, 09:31 PM

I'd take a look at the sensitivity of the approach relative to the magnitude of the phenomenon. Mars gets a yank from Jupiter every 2.5 years or so, rotates every 24.6 hours, and has an axis inclined 23 degrees from its orbit. The last two factors decrease the magnitude of the Mercurian effect by a factor of a few hundred (I don't know about the yanking). The fact that Mercury's radius is smaller makes the problem an additional 30% harder. The approach would have to be *really* sensitive (at least three significant digits) in the martian case to work the same way and tell us about Mercury's libration. I don't have any facts telling me this is *the* answer, but it's gotta be part of the story.

Posted by: Stephen Sep 1 2005, 02:36 AM

If the crater lay in "permanent shadow" wouldn't that cause problems if the lander was solar powered? (I guess you'd need an RTG lander. But that would presumably increase the weight & the expense of the thing. Not to mention political complications here on Earth.

Also how would that affect (direct) communications with Earth? If it shadowed from the Sun wouldn't that increase the risk that Earth would not be visible above the lip of the crater? If it wasnt, you would need some kind of orbital relay, either one already in place (as in the case of the MERs, who had Odyssey already conveniently in orbit around Mars) or one the lander brought along with them (eg Beagle 2 & Mars Express).

It would make for a complex and expensive mission, and so presumably one unlikely to be funded any time soon.

======
Stephen

Posted by: BruceMoomaw Sep 1 2005, 03:01 AM

ESA was thinking about a lander only 3 degrees from the pole, but NOT in shadow. If I remember correctly, they hadn't quite ruled out powering (and heating) it with a small RTG, which of course WOULD make a shadowed-area landing possible. But the purpose of the lander was to get a better geological understanding of Mercury in general -- not of one of the polar deposits in particular.

Posted by: tasp Nov 26 2005, 06:14 PM

Just throwing out some ideas, may be helpful in the long run.

The amazing trajectory Messenger is taking to Mercury would be reversible, wouldn't it? I'm thinking an orbiter/lander could be sent to Mercury (granted this part is going to be heavy) to study the planet, and the lander could collect some surface samples and put them into orbit around Mercury.

A retreiver craft could be sent to collect the samples and then return to earth via a reversed version of the Messenger flight plan.

The key to making this work is that you set it up so that as much of the delta v as possible is provided by gravity assists from Earth, Venus, and Mercury for all the spacecraft involved in the mission.



Also,

To expand on some of the ideas posted in this thread, could a kevlar net orbiting Mercury (tethered to a shielded orbiter) 'snag' debris from a plume generated from an impactor craft?

This might be a 'cheap and dirty' way of retrieving materials from the surface of Mercury as part of mission to return them to earth.

Posted by: Bob Shaw Nov 26 2005, 06:30 PM

The killer with Mercury landings - not counting the interplanetary stuff, where perhaps there might be *reverse* slingshots to be had with some clever planning - is that as it's an airless body you're limited to rocket-based descents. Add the cost of transporting your fuel for ascent and there are some quite rapid diminishing returns! Of course, if there's ice at the poles, in-situ fuel might be an option - otherwise, the 'smash and grab' mission seems about the only game in town!

Bob Shaw

Posted by: BruceMoomaw Nov 26 2005, 09:13 PM

There was, I've heard (though I haven't confirmed it), a smash-and-grab Mercury sampling mission once proposed for Discovery. Meanwhile, the ESA has actually done the preliminary design for a full-fledged Mercury landing and sample return -- although they also did so for Venus, which may give you some idea of how politically realistic the plan is. I'm convinced that, given their cost, it will be a long time before we see a landing and sample-return mission from any large world that doesn't have possible biological evidence -- that is, Mars and (in the longer run, if previous landers turn up something interesting) Europa.

Posted by: tty Nov 27 2005, 04:42 PM

The best and fastest way to acquire Mercury samples is almost certainly to search for meteorites here on Earth.
I'm reminded of an old saying in paleontological circles: "The best place to find unknown fossil species is in museum drawers".

tty

Posted by: edstrick Nov 27 2005, 08:43 PM

Two or three years ago, there was some reporting on an odd meteorite that had distinctive isotope patterns and chemistry. There was some speculation it was Mercury ejecta, but that interpretation didn't seem strongly favored. I don't recall it's name/designation. I've heard no further discussion of it, and have wondered what the status on it is. Meteoritical Society meeting abstracts may have contained something but I haven't broused them extensively.

Posted by: DEChengst Nov 27 2005, 09:20 PM

But that wouldn't be as interesting. The great thing about a sample return mission is that you can select the rocks that you'll be researching. There are a lot of Martian meteorites, but we would learn at lot more if we could get our hands on some Meridiani Planum sedimentary rocks.

Posted by: JRehling Nov 28 2005, 01:55 AM

I can't find the reference to the Mercury smash-and-grab sample return either, although I had found it on the web a couple of years ago. It was a real "outsider" proposal, conceived from someone not really working in space exploration, IIRC, and I don't know if it was an official Discovery proposal or not -- yet it is a solid idea. Certainly this kind of sample return is not as useful scientifically as having a rover move around and delicately select a geologist's wishlist, but what this kind of mission lacks in benefit, it makes up for in cost savings.

NWA 011 is the name of the meteorite that was speculated upon as being mercurean in origin. Here are some discussions of the item's origin, however, that don't even mention the word "Mercury", FWIW:

http://web.utk.edu/~lataylor/pub-list/Floss-1153.pdf
http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1094.pdf
http://aaa.wustl.edu/Work/pub_files/northwestafrica011.html

There can only be so many rocky parent bodies in our solar system's past/present that were large enough to exhibit major radiogenic heating, and Mercury is one of them. Perhaps we'll end up with an exhaustive list one day and identify the Mercury meteorites by elimination. But we're not close to that day...

A smash-and-grab sample return would not only have its own value, but would also possibly clinch the identification of Mercury meteorites in our possession. In terms of delta-v, we more or less need a solar orbit that has aphelion at 1 AU and perihelion at 0.48 AU -- that is more delta-v than a Venus/Mars lander, but then the craft would essentially be an Earth lander without instruments. It would be highly desirable to perform remote sensing of the impact site, a la Deep Impact -- the instruments should perhaps be mainly contained on the impactor, since instruments on the return craft wouldn't have any use after the impact while flying back to Earth.

Posted by: BruceMoomaw Nov 28 2005, 02:11 AM

Keep in mind that this thing will fly past Mercury at damn high speed, and thus its sample grains may be largely melted. However, since a comparably high-speed flyby of Europa is considered scientifically worthwhile, I presume one of Mercury is too.

Posted by: ljk4-1 May 30 2006, 06:15 PM

In this 1971 book, Beyond the Moon: Future Explorations in Interplanetary Space
by C. B. Colby, there is a chart of then future planetary missions:

http://sun3.lib.uci.edu/~jsisson/beyond.htm

For Mercury, they indicate an orbiter for 1982. Was there ever an actual plan
to orbit Mercury in the early 1980s?

Of course the chart also declares a manned lunar base in 1978 and manned
expeditions to Venus and Mars in 1982 and 1981, respectively.

Posted by: BruceMoomaw May 31 2006, 05:45 AM

NASA never -- and I mean never -- put any Mercury orbiter anywhere in even the also-ran listings of its desired future planetary missions, until Chen-Wan Yen, in the late 1980s, came up with the complex but workable kind of multiple gravity-assist flyby setup that Messenger is now using. Until then it was thought to be far too expensive and complex for what (to quote Ken Croswell in 1991) "isn't a sexy planet." Indeed, I didn't hear a peep about Mercury as a possible high-priority target until the Discovery Program AOs started.