Mercury Landers Options

[gndonald]

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?

[edstrick]

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.

[JRehling]

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.

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).

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.

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.