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Landing on Mercury on equator at perihelion
antoniseb
post Mar 22 2006, 08:45 PM
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QUOTE (ljk4-1 @ Mar 22 2006, 03:09 PM) *
I wonder if Mercury "stopped" its major geology because it did not have
a larger world near it to pull on it and attract more larger planetoids and
comets to hit it?


Another factor may have been that closer to the Sun the velocities of impacting planetoids is so high that a much larger fraction of the debris sprays away from the collision, so it's harder to build up a body down there.
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JRehling
post Mar 22 2006, 09:27 PM
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QUOTE (ljk4-1 @ Mar 22 2006, 12:09 PM) *
My goodness - what if Mercury was "spawned" from Venus just as our
Moon was by a Mars-sized space rock hitting Earth, but this time the
planet was knocked away from Venus into its own solar orbit?


The composition of Mercury makes that very unlikely. The iron making up Mercury would have been in the middle of Venus, so for that origin to work out, there would have had to have been a collision that knocked more middlestuff out than edgestuff. It would be more apt to say that Venus had been knocked off of Mercury. I don't think it happened. wink.gif
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Guest_Richard Trigaux_*
post Mar 22 2006, 09:40 PM
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QUOTE (antoniseb @ Mar 22 2006, 09:45 PM) *
Another factor may have been that closer to the Sun the velocities of impacting planetoids is so high that a much larger fraction of the debris sprays away from the collision, so it's harder to build up a body down there.



At time of formation, this may have been true.

But after, at time of the late meteorite bombing too, explaining why there is so much regolite and so few original features.

The same perhaps goes for Phoebe too, which, with its retrograde orbit, may receive more impacts, and much more violent ones, which largely eroded it.

The more important feature of Mercury is its large iron core. The problem is that, on Earth, such a core is still liquid, and its solidification produces twice more heat that radioactive heating, producing a still intense volcanism four billion years after accretion. On Mercury such a large core, nearby as large as Earth's, should still produce an important volcanism, or at least recently. But mercury's surface is old...

Or maybe not so old, but our usual clock (density of meteorite impacts) would be false, either Mercury gathers more impactors (from its closeness to the Sun) or the impacts are more violent, giving larger craters.

An explanation would be that the accretion of Mercury was slow, and thus cold. But this contradicts what we know of accretion.
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ljk4-1
post Mar 22 2006, 09:41 PM
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QUOTE (JRehling @ Mar 22 2006, 04:27 PM) *
The composition of Mercury makes that very unlikely. The iron making up Mercury would have been in the middle of Venus, so for that origin to work out, there would have had to have been a collision that knocked more middlestuff out than edgestuff. It would be more apt to say that Venus had been knocked off of Mercury. I don't think it happened. wink.gif


Venus being a knock-off of Mercury - that would explain why Mercury has
the big iron core and Venus apparently has little or none, judging by its
lack of a magnetic field and plate tectonics, despite being almost as big
as Earth.

And Venus has no moon.


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and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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edstrick
post Mar 23 2006, 09:33 AM
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Mariner 10 did have a tiny infrared radiometer. It trailed 2 beams across the terminators and nightside, one on final approach and one beam as it was exiting from behind the planet. Interestingly, the nightside of the "departure" hemisphere had more thermal variety than the very bland "approach" hemisphere nightside.
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Rem31
post Apr 28 2006, 09:47 PM
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What kind of experience will it (possibly) be when you land on Mercury ,when it is at perihelion its (closest) distance to the Sun ,and the Sun is overhead in the zenith. How will the heat of the Sun feel then? Does it really feel burning through the glasses of your helmet of your spacesuit? I really love the thought of how it will be to be on Mercury then.
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post Apr 28 2006, 09:53 PM
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All I can say is you like hot weather a lot more than I do, Rem...

I have vague memories of reading, years ago, some document that said that in that particular place at that particular time, Mercury's surface temperature actually does rise to significantly above that of Venus. It's an extremely fuzzy memory, though, and I could be wrong. (I do know that Caloris Basin got its name because its center is pretty close to one of the two points of maximum equatorial surface temperature on Mercury on such occasions -- alternating with another point 180 degrees away, of course.)
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Rem31
post May 10 2006, 12:06 AM
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What are the kind of dangers of a (manned) landing on Mercury at the equator when it is at perihelion (closest to the Sun)? will the astronauts need Sunprotection then?
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post May 10 2006, 08:43 AM
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God, yes. We've mentioned all this before. A manned landing under such conditions presents huge problems even if you don't try to get out of your ship and walk around -- it presents staggering problems for any space suit design. Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).
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Bob Shaw
post May 10 2006, 11:00 AM
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QUOTE (BruceMoomaw @ May 10 2006, 09:43 AM) *
Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).


Bruce:

Or hung in not-quite-orbit under (or better still, behind) a solar sail. A tough environment indeed - and as for the effects of a Solar flare...

Bob Shaw


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Rem31
post May 10 2006, 11:28 AM
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And on a manned landing on Mercury at (perihelion) at the equator with the Sun in zenith at Caloris basin ,how hot does the Sun feels then? Will it be a burning Sun or just not. The Sun is even burning hot at (this) moment in my backyard in the Netherlands ,how will that be when compare it with a equatorial Sun on Mercury? What is the kind of protection that the astronauts need against the Sun when they land and walk on Mercury at perihelion at Caloris basin? And my last question ,what kind of cooling will the spacesuits need then? Can you try to answer this questions? Lot of thanks. Rem 31.
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helvick
post May 10 2006, 12:19 PM
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QUOTE (Rem31 @ May 10 2006, 12:28 PM) *
And on a manned landing on Mercury at (perihelion) at the equator with the Sun in zenith at Caloris basin ,how hot does the Sun feels then? Will it be a burning Sun or just not.

Solar insolation will be ~ 4300 watts/sq m and with no atmosphere anything on the surface will have to handle that. By comparison the most extreme solar insolation I've ever dealt with was in the Namib desert in early September - with the Suns Zenith directly overhead. Surface insolation would have been around 1000 watts/sq m and any exposed surface reached 60-70deg C within a matter of a few minutes depending on the material and the wind. On Mercury at perihelion in a place where the sun is directly overhead the surface temperature is driven to ~427deg C.

That is very hot - It's 150-175 degrees C hotter than the maximum temperature used for cooking in a domestic oven.
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JRehling
post May 10 2006, 01:35 PM
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QUOTE (BruceMoomaw @ May 10 2006, 01:43 AM) *
God, yes. We've mentioned all this before. A manned landing under such conditions presents huge problems even if you don't try to get out of your ship and walk around -- it presents staggering problems for any space suit design. Very large-scale daytime surface exploration of Mercury, whenever the human race ever gets around to it, is yet another opportunity to utilize remote-control robots controlled from a nearby, non-landed and Sun-shielded manned ship (which could be hundreds of thousands of km from Mercury, thus avoiding the emitted IR heat from the planet's surface itself).


It could also suffice to put humans on a nighttime location on Mercury (including the permanently-shaded craters near the poles) communicating by satellite with surface robots on the dayside.

These projects should be very competitive proposals a few centuries from now.

Any way you slice it, a landing on Mercury is probably the most resource-intensive of anywhere, even if it's merely a large robotic craft. Any such plan would probably require unforeseeable advances in propulsion (among other things) to ever be funded. And I would seriously expect the state of robotics to move along significantly in such a timeframe, whittling down the utility of human telepresence faster than the means to send people there cheaply increases.

Note that even for humans to fly by Mercury (which would be the least ambitious plan, using their "momentary" telepresence to guide robotic drones below) would either require colossal delta-v on a mission putting them into point-blank range for solar flare radiation for months, or use Venus gravity assists to put them in similar hazard for years with somewhat less delta-v. Requirements for shielding would be ungodly, increasing all of the delta-v requirements. It almost starts to sound like it'd be cheaper to propel Mercury to us, study it at 1AU, and put it back when we're done.
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jsheff
post May 10 2006, 03:52 PM
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As I recall, Mariner 10's discovery of a magnetic field at Mercury was something of a surprise. That, plus the more accurate determination of the planet's density (which turned out to be much higher than all but Earth's) provided by Mariner 10's measurement of the size and mass of the planet, led scientists to posit a large iron core for Mercury. That alone is worthy of study, and while Messenger and BepiColumbo orbiters will constrain the models of the planet's interior, there's nothing like a seismic network of landers to really study the planet's geology. A number of people posting here have suggested that such a network could be emplaced at the poles or at high latitudes, but I see nothing far-fetched about a low-latitude seismic network of landers. All the probes would have to do is land early in the Mercurian night, as others have suggested, and dig into the regolith a few dozen meters! (We are already developing automated drilling technology for Mars exploration.) There is no need for the spacecraft to be "cooked"; a few meters down, there is bound to be a benign temperature regime. Such landers could function for a very long time, whether powered by RTGs or some sort of suitably-hardened solar panels. (And if the latter are developed, SEP would make even the daunting task of reaching and orbiting Mercury not so far beyond present technology, I would think.) But the automated drilling is an enabling technology, no?

- John Sheff
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JRehling
post May 10 2006, 05:08 PM
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QUOTE (JRehling @ May 10 2006, 06:35 AM) *
It could also suffice to put humans on a nighttime location on Mercury (including the permanently-shaded craters near the poles) communicating by satellite with surface robots on the dayside.


It occurred to me that humans on Earth have, at times, a speed-of-light-time to Mercury of about 5 minutes. There are various wrinkles to that, with solar conjunction interfering with communication and it being the nightside that would face us, but those have workarounds. All told, I think a scheme that makes do with 10-minute roundtrip time and slow teleoperation would beat the almost insane challenges of sending people near Mercury. Never say never, but it makes me wonder if in a hypothetical prosperous and space-faring future, Saganite paradise and all, we still might nonetheless never send people to Mercury. It would seemingly have to be done just for the point of doing it. Odd that it would be true for a place that comes within 0.8 AU of us more often than anyplace but Venus and the Moon, but then the Sun is the only place besides the Moon that is always within 1.1 AU of us, and we're not sending people there, either.
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