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Posted by: Rem31 Mar 21 2006, 12:18 AM

How will it be to make a manned landing at Mercury at its closest to the sun (perihelion) on its equator when the sun is in the zenith ,what are the dangers of a landing then? Do we need to be protected against the sunheat and radiation then? How strong is the heat and radiation of the sun then ,and is it dangerous when the solaractivity is high then? What kind of spacesuits do we need then? Better protected suits than we have used on the apollo moonlandings i think. Can you explain how a landing on Mercury will be when it is at perihelion and land on its equator with the sun directly overhead? I hope it will ever happen. Lets start discuss about it.

Posted by: antoniseb Mar 21 2006, 12:25 AM

It sounds like you want the manned spaceflight forum.

Posted by: RNeuhaus Mar 21 2006, 02:25 AM

Up to now, there is no plan to land on Mercury but just to orbit around on the poles by the year 2011 . So the spacecraft must catch up the speed starting from 29.8 km/sec (relative to Sun) when it leaves the Earth and arrives at Mercury at 47.9 km/sec after one Earth Fly-by, 2 Venus Fly-By, and 3 Mercury Fly-By by March 18, 2011. Long trip!

If you want to be closer to Mercury, start visiting at the following URL: http://messenger.jhuapl.edu/the_mission/index.html

Nobody is thinking in exploring on Mercury. It is out of our present paradigma. The next time would be on Moon close to the year 2020 and maybe to Mars close to the year 2030.

Rodolfo

Posted by: Rem31 Mar 21 2006, 03:42 AM

But how will a (hypothetical) manned landing on Mercury be at its perihelion on the equator with the sun in zenith? Can you give an idea of how that looks like ,like i have written in the beginning of this thread? And i really dont understand why we dont put a lander or rovers like on mars on Mercury. We have landed a lander on Venus,Mars,but why not on Mercury? I and a lot of people on earth are waiting for the moment that a lander is on its way to Mercury and that is going to land on this planet to send the first images of the surface of Mercury back to earth ,like the venera,s did on Venus and the vikings and pathfinder did on Mars. The only thing i can say is that we forgot 1 planet ,And that is Mercury. Thanks.

Posted by: BruceMoomaw Mar 21 2006, 04:25 AM

A manned landing on Mercury at perihelion -- or an unmanned one, for that matter -- would be difficult as Hell (which may be appropriate). The problem wouldn't be as severe as that on a Venus lander, but it would be plenty hard -- you would not only need to have an extremely efficient reflecting shield to fend off the heat radiation from the Sun, but also another to deal with that being reflected and emitted from Mercury's surface. (This, in fact, is one reason why the Messenger orbiter will be put into a highly elliptical orbit around Mercury: to give it time to cool off again from each of its low-altitude periapses over Mercury's surface.) As for the design of any EVA walking suit that could cope with that heat: I shudder even to think about the problem. The high-energy particle radiation and X rays from the Sun at that range would also pose a very difficult problem for any manned mission that close to the Sun -- we'll have enough danger from those during long-duration manned trips to Mars and near-Earth asteroids.

However, temperature-wise, there are plenty of other places that either an unmanned or manned lander could touch down on Mercury that would be a cinch. Its near-polar regions are quite tolerably cool -- which is why it has ice as its poles -- and its nightside very quickly cools down after sunset, stays cold, and even stays within modest temperature ranges for a short time after sunrise again.

A polar or nightside landing on Mercury is entirely feasible with the technology we have right now. The trouble, as usual, is simply money. Europe's BepiColombo, which consists of a large and low-altitude European orbiter and a small secondary Japanese one for magnetospheric studies, was originally also supposed to include a very small lander to touch down within about 3 degrees of the pole -- but, since Mercury is an airless world with a gravity field considerably stronger than the Moon's (and therefore requiring a larger mass of braking fuel), in the end the cost and mass of the lander was just too much for ESA's already-strained budget to endure and they cut it out of the mission. At some point it certainly will be done by someone; Mercury's surface almost certainly looks almost indistinguishable from the Moon's, but there are a great many interesting geophysical and compositional instruments they could land there on even a single lander. But that's likely to be a couple of decades off (at least), just for monetary reasons.

Posted by: Richard Trigaux Mar 21 2006, 06:09 AM

If you want to have an idea of what Mercury looks like, lit a good fire into your chimney. Set yourself at the right distance where heat is pleasant. This is like Earth. Now divide the distance by three and look what happens. It is Mercury.

On Mercury at midday, not only the Sum burns like the opening of a furnace, but the ground itself is nearby red hot.
Fortunately the nights are long and they would allow for a lander to work and do interesting job. But it would have no solar energy. From where the projects to land near the poles.

Posted by: edstrick Mar 21 2006, 08:49 AM

Exploring Mercury is difficult. While it's relatively easy to use a single Venus flyby to fly a spacecraft past Mercury, it passes the planet at high speed. Such high speed that it would take an enormous propulsion system to simply get into orbit around the planet. The Mercury Messenger orbiter mission does multiple Mercury flyby's to reduce the spacecraft's aphelion and make it possible to get into orbit with a "reasonable" sized rocket system. And it will take many years to get there.

Landing on Mercury is harder. You are orbiting a planet with a deeper gravity well than the moon, and with no atmosphere to reduce speed from orbital velocity. You have to do it ALL with rockets. Bigger rockets than needed to land on the Moon.

When you get there, you will find an impact generated regolith, made of basaltic to anorthositic (we think) rock, very similar -- indeed visually identical -- to lunar highlands plains and cratered terrain sites.

If Mariner 10 had found a truely exotic planet, as un earth-like or un moon-like than Venus or Titan, we'd have a much greater interest in exploring the planet. Certainly, Mercury has been neglected, as has Venus in many ways. But for good reason, I'm afraid.

Posted by: Richard Trigaux Mar 21 2006, 09:08 AM

At least, and orbiter with high resolution mapping and imaging, and IR spectrum analysis, perhaps radar probing, would be fine. We know little about Mercury and we may find unexpected/unexplained things. And the big mystery is why Mercury has no volcanoes. As far as we know. Another thing would be to detect dust storms (from static electricity, as believed on the Moon) or Transcient "Lunar" Events.

After, a lander would have to check isotopes ratios and place a seismometre, so that we have an idea of Mercury inner structure. After?

Posted by: edstrick Mar 21 2006, 10:26 AM

Robert Strom (I think) and subsequent researchers have pretty clearly shown that Mariner 10 images show some volcanic flows and deposits. Their geologic morphology is poorly preserved due to considerable primary and secondary impact cratering, and many of the features were observed at such high sun angle that morphology is poorly if at all visible. What they do see is some crater and inter-crater plains with flow fronts and ponded morphology that is rather unlike basin ejecta deposits that fooled Apollo era geologists into thinking Apollo 16 was going to explore highland volcanism. They also see color boundaries in high sun angle data that look like flows with different color and thus chemistry from adjacent plains and crater deposits.

Everything seems to be pretty seriously old. Relatively young volcanics like on the Moon seem to be absent or very scarce, and "constructional" volcanic features are scarce or absent.

One long recognised factor is that the entire crust has scattered lobate escarpments, apparently compressional thrust faults that indicate the crust has been under compression during most of the visible geologic record. This makes it much harder for magma to find a route to the surface as all the channels and fissures are squeesed tightly shut, as compared with a crust under extension.

Posted by: Richard Trigaux Mar 21 2006, 11:06 AM

hey, that is interesting, and fairly different of the Moon. Maybe Mercury has a completelly different history. Worth sending a visible light mapper and IR spectrometre.

The compression of Mercury crust (and perhaps mantle too) is often explained as the result of the cooling and contraction of its huge iron core. This contraction would have created all the compression faults (perhaps following the Mare Caloris impact). The Mare caloris itself produced considerable destructions, for instance at the antipodes all the mountains were thrown into the air by the shockwave.

Posted by: Richard Trigaux Mar 21 2006, 11:18 AM

An interesting job too for a probe would be sensing Mercury's gravitation field. For this it requires a trajectory coming from afar and going as close as possible from the ground. For this, the probe would perform a very close passage, perhaps some kilometres, which would place it on a very elliptic orbit.

From this orbit, it could make a global map of Mercury.
After, the orbit would be circularized at lowered, so that the probe could make high resolution views.
Ideally, on an airless world, the orbit could be lowered at will, theoretically some kilometres, lower than an airliner. But from a previous discution on a lunar orbiter, it appeared that, due to the presence of mascons on the Moon, such orbit is not stable and it ends up crashing on the ground. A similar problem may exist on Mercury, limiting the lowest altitude.

An interesting prediction, from the crust compression model, is that it could exist many underground tectonic cavities. If there is yet any form of volcanism or outgassing, it would take place here, and the cavities may have a complete atmosphere (with a pressure gradient and all). Eventually this could lead to some outgassing at very low pressure, if there are exit points.

Posted by: ljk4-1 Mar 21 2006, 03:20 PM

Come on, guys - just land at night!

How about landing on the terminator (where the temperature is balanced,
right?) and having the mission follow just ahead of sunrise. The planet takes
59 days to rotate, so it should be slow enough for the explorers.

I saw them do this on the Chronicles of Riddick, so it must be true.

Posted by: JRehling Mar 21 2006, 05:37 PM

To summarize what other posters have written: Mercury is the hardest place in the solar system to land.

It takes more delta-v to get from the Earth to Mercury than to any other planet. Including Pluto. In fact, a minimum-energy voyage to Alpha Centauri would cost less delta-v than a minimum-energy voyage to Mercury! (Of course, the former would take millions of years.)

Among the solid bodies in the solar system, Mercury is unique in terms of having a pretty high escape velocity (roughly a tie with Mars for third-highest, behind Earth and Venus) but NO atmosphere to assist in the deceleration from cruise to landing. So it requires the most hardware to undertake a soft-landing of any solid body in the solar system! That's two categories in which Mercury is THE hardest!

Those two difficulties combine: You have to take all of that soft-landing hardware to Mercury, which means that the launch will involve a very large rocket for a given payload.

The other difficulty, thermal, makes Mercury more difficult than almost anywhere else: Venus is worse in this respect, but only because Mercury has cooler poles and night. Landing on the equator in daytime would make Mercury very hard in that respect too. We don't have any hardware that could survive those surface conditions unless it involved a nuclear-powered refrigerator, and now we've tripled the (not just additive but multiplicative) mass problem.

Takeoff from Mercury would be as difficult as from Mars, and then the cruise back to Earth would be VERY hard: again, the biggest delta-v leap of any planet for a back-to-Earth trajectory.

All told, I'm not sure if anything less than a Saturn V could launch a Mercury equivalent of a MER, assuming that we could build a rover that could survive Mercurian conditions. It's safe to say that the Mercury equivalent of Apollo would involve technology far beyond anything yet developed. Imaginable, perhaps, but not yet developed. And the long cruise to Mercury would mean that a solar storm would have an excellent chance of killing the crew. If you utilize gravity assists from Venus, the cruise gets longer.

It's got sort of a joke-like difficulty to it. I'll predict that by the time we had the rocketry to perform a Mercury human mission, the state of robotics would make any such mission purposeless. But I won't live long enough to collect on that bet.

Posted by: BruceMoomaw Mar 21 2006, 09:42 PM

Even Arthur C. Clarke, the Keeper of the Holy of Holies, said in "Odyssey Three" that, at a time when humans were routinely poking around comets and the like, only two manned landings had ever been made on Mercury -- and neither of them got much attention. The place has certainly got plenty of interest for geologists, but as Ed said it just isn't distinctive enough to have any pizzazz for people not intensely interested in science.

Posted by: JRehling Mar 21 2006, 10:02 PM

A good bang-for-the-buck mission might avoid a high-latitude constraint by making a night landing and carrying a strobe light for imaging the vicinity. Because the surface will not cool immediately after sundown, it would be best not to land in daytime just before sunset. To allow a mission plenty of duration for seismic (or, alternately, lifetime for a rover), it could land about 10-20% of the way into local night, study the vicinity for about 45 days (night on Mercury is 54 Earth days), and then get a sunrise panorama of the background before sunlight cooks the craft.

Another approach would come from the unique fact that the Sun shows retrograde motion on Mercury because the revolution at perihelion overtakes the rate of rotation. A carefully-targeted lander could alight somewhere that was in night, then experienced a very brief "day" of a sunrise-then-sunset. So long as the engineering team could set the lander down precisely, the length of that day could be arbitrarily brief, and a rotatable "parasol" could mean that the craft would take no direct solar heating while the ground would experience only trivial heating in the short run. A lander aimed at just the right longitude could thus experience a short sol (for imaging) and go on to run other studies during a few more Earth days of nighttime before a longer sol cooked the craft.

And of course, there is the polar option. Conceivably, a lander could be sent into an area of eternal night, and never face a thermal constraint at all (except during cruise), but such a landing site would be idosyncratic (and therefore interesting, but differently interesting than just a generic Mercury landing site).

Posted by: ljk4-1 Mar 21 2006, 10:22 PM

Clarke also wrote an SF story in the 1950s about astronauts who
land in the "Twilight Zone" of Mercury - back when its day was still
thought to equal its year of 88 Earth days.

I can recall their encounter with a spindly crab-like creature that
caught prey and defended itself by throwing rocks. It threw a rock
at one of the astronauts, puncturing his spacesuit and causing a
scramble back to the ship.

Posted by: Rem31 Mar 21 2006, 11:42 PM

Are there space artist impressions to find on the web of Mercury,s surface? and other planets? And which are the best and most real and the most beautifull? Can somebody help to find that stuff? Thank you.

Posted by: BruceMoomaw Mar 21 2006, 11:57 PM

I already thought of Idea #1. (Pause for misguided snickers from Alex.) If you want to set up a good multiple-lander seismic network on Mercury -- and a mission with several tiny Mercury landers, which could be very productive scientifically, is on the Decadal Survey's list of longer-range New Frontiers candidates -- then just putting two seismometers at the poles, although they could survive indefinitely there, would be lousy for trying to locate seismic events on the planet. You'd want a third lander (or maybe just a second one) at low latitude, and the only way to get that would be the nighttime lander plan. (Also keep in mind that, given today's instruments, any searchlight that a nighttime lander needed for photos and near-IR maps could be very low-powered -- Huygens' was about as strong as a nightlight. But, to the extent that the payload of a Mercury lander would be seriously limited by mass and data rate, the very first thing I'd throw out would be the camera. It's good for PR, but low-value for science.)

As for the polar landing: except for the possibility that it might be able to study one of the polar ice (or sulfur) deposits, there's nothing particular unusual geologically about Mercury's poles -- which made them the perfect spot for the ESA's planned first-time Mercury lander.




Yeah, that was his Winston kids' SF novel "Islands in the Sky". Poor Arthur -- the Solar System has turned out to be SO much less interesting than he hoped it would be. (Note, though, that the guy whose suit was damaged -- with the result that his legs froze solid and had to be amputated -- then happily made a life for himself on a space station, since legs are actually something of an encumberance in 0-G. That idea has been floating around in the SF world ever since, usually in connection with genetic engineering of humans. As Jack Vance points out, obese people would also be a lot happier living in orbit.)

While we're on the subject of misguided SF predictions about Mercury, the prize-winner surely has to be Larry Niven's very first SF story, "The Coldest Place", in which the same two astronauts we'd later meet in "Becalmed in Hell" have just landed triumphantly on "the coldest place in the Solar System", and encountered a helium II-based lifeform. The story neatly suckers the reader into assuming that they're on Pluto, until the last sentence reveals it to be the permanent nightside of Mercury instead. Poor Niven got this story published exactly three months before the radar discovery that Mercury's rotation was not synchronous.

Posted by: RNeuhaus Mar 22 2006, 01:35 AM

It is a matter of balance between cost and benefits of solar system exploration according to the present technology. For the case Mercury, the science is not the most interesting of our solar system and it is on the wait list of space exploration of our system solar. As you know from the very good sumarises and reasons from the previous posts, to land on Mercury is one of the most hardest, and very expensive (big rockets to brake and be able to esape from Mercury and Sun gravity pull on its way toward to Earth and also a big rocket to reduce its big Delta-V with 18 km/sec in comparision to the others points of interest in our system solar system such as Icy Jupiter and Saturn Moons for such amount of new knowledgment and discoveries.

In accordance to the above factors, to rover on Mercury is put on wait list for a long time but for orbiters is coming soon by the decade 2010-2020.

Rodolfo

Posted by: RNeuhaus Mar 22 2006, 01:59 AM

The Mercury atmospheric composition:

Extracted from the following URL http://solarviews.com/eng/mercury.htm
In the other words, Mercury has very little atmosphere. Perhaps it has as little as the Mar's ones?

Rodolfo

Posted by: BruceMoomaw Mar 22 2006, 03:40 AM

It has stupendously less than that -- its atmospheric pressure is, I believe, about one-trillionth that of Earth. That is, it is an "atmosphere" only by the strictly scientific sense of the word, like that of Io. Its list of constituents still seems to be growing -- potassium and calcium atoms have now been identified in it, and there may be others. (For instance, there is surely a faint trace of argon-40 in it, decaying naturally out of the potassium-40 in Mercury's rocks.) But it is entirely an "exosphere"; the incredibly faint trace of gas making it up has all been baked out of Mercury's surface crust by meteoroid impacts and/or sputtering of Mercury's surface rocks by high-speed particles of solar radiation.

Posted by: edstrick Mar 22 2006, 07:04 AM

Niven may or may not have been aware of the really weird anomalous data on Mercury that the 3/2 synchronous rotation explained.

Earthbased radio astronomy measurements of the radio (thermal, they presumed, correctly) emission of the disk as a function of phase angle showed that the nightside subsurface was warm, as if the planet wasn't in 1:1 synchronous rotation, instead of at cryogenic temperatures.

D'oh!... turnes out that side faces the sun half the time, too.

Posted by: BruceMoomaw Mar 22 2006, 07:37 AM

He surely wasn't aware of that, or he wouldn't have called it "the coldest place in the Solar System", now would he? Hmmm? (Come to think of it, though, I remember seeing a little reference to it in an issue of Science Digest back in 1964-65 before the radar discovery broke.)

Posted by: edstrick Mar 22 2006, 08:15 AM

I'm assuming he wasn't. It was pretty obscure science at the time. Planetary radio was barely able to measure whole-disk brightness temperatures of planets as a crude function of wavelength and phase angle, and maybe some indication of limb darkening at the shortest wavelengths.

It was a *** THIS IS WEIRD *** type of observation leaving them wondering about calibration and the like.

Posted by: Richard Trigaux Mar 22 2006, 08:37 AM

There was in another thread a discution on the possibility of a http://www.unmannedspaceflight.com/index.php?showtopic=1647&st=30, understand a lander which would be able to withstand the tremendous heat on Venus. On mercury, the conditions are in fact easier, as there is not the tremendously oxydizing Venus atmosphere (but solar radiations instead).

The discutions revolved around things such as using high temperature semicionductors (there are many, even more than at current temperature) or more innovative things such as electrostatic micro-relays, or micro sized vacuum tubes (with performances comparable to transistors). With a few cheap experiments, we could quickly know if really an electronics working at 460°C is feasible. If yes, little development is needed, as most of the technology already exists.

So the idea of a long lived lander on Mercury can be envisioned seriously, not just as a dreamy prospect.

As I explained ealier, an orbiter around Venus with high resolution imaging and IR spectrometre mapping would be the very least to do. To have some small landers with seismometres and an isotopic analysis too. But, as Bruce Moomav explains above, we need several seismometres in the hot zone, not just on the poles.

Posted by: edstrick Mar 22 2006, 11:12 AM

A long lived Mercury lander would have decidedly different objectives from a short-lived one. Also is the landing terrain: normal regolith versus polar ice deposits.

A short life lander could do Surveyor type imaging of the local regolith, but with real UV to mid IR specteral capability. You might have a slow-scan imaging spectrometer that wouild build up a few complete pans at good resoluton over a lander's life. Then you'd have an instrumentation suite that would do Hydrogen to Uranium elemental abundances of samples, isotope measurements, and precision mineralogy.

A long life lander would have to characterize the landing site with imaging and the like, but it's primary goals would be geophysical: Seismic, Magnetic fields, atmosphere, solar-wind interaction.

Mercury has massive polar ice deposits in permanently shadowed crater bottoms and other locations. Radar data show the deposits are 1) thick, and 2) non-atennuating, with high internal scattering. We see exactly the same type radar return from the exposed permanent martian ice caps (*not* the ice under dirt surrounding the poles), and on Ganymede, Callisto, Europa. Lunar polar ice, which is probably present in small amounts, nowhere has shown the strong depolarized return of these other deposits, and probably consist of some percent of ice mixed with regolity in the cold traps. A Mercury Polar Ice explorer will be of great scientific interest, but it's a very long term priority.

Posted by: JRehling Mar 22 2006, 05:46 PM

I think, when we get ready to shell out the dough to that extent, we'd do just fine having two landers at high northern latitudes and one at the south pole (or reversed POLE-arity on that).

At 75N/S, the solar input to a flat surface is only 26% of that at the equator. The Sun would be 15 degrees above the horizon, and a rotating parasol could block it from directly heating the body of the craft. Then the heat from the ground alone should be tolerable. Two landers at that latitude would differ 180 in longitude, with the third lander near the other pole.

With that geometry, the three stations would not be equally distant, but should be good enough to triangulate seismic events.

Now as for which century this mission concept will fly...

Posted by: Richard Trigaux Mar 22 2006, 07:26 PM

An ion drive would do well on a trajectory to Mercury. Plenty of solar energy.


I cannot calculate if such a trajectory is feasible, but I well see a probe launched at 11km/s from Earth on a sun orbit, spiraling closer an closer from Mercury orbit, until it is caugh in orbit around it. Then it continues braking with its ion drive untill it is on a low orbit. After of course a classical chemical rocket is necessary to land.

Such a mission would need much less fuel than braking all the speed from a direct approach with only a chemical rocket. So it removes part of the cost problem.


I feel that Mercury is not just the grey and boring world we currently imagine. Interesting and unusual geology may exist near the poles if there are sulphur deposits. And where this sulphur would come from? Volcanoes! Oh, better: sulphate rocks from an ancient ocean!!!

I think it is simply incredible that Mercury just stopped any large scale geologic activity sooner than the much smaller Moon. There is a mistery, worth at least an orbiter. With ion drive, it would not be so costy.

Posted by: ljk4-1 Mar 22 2006, 08:09 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?

I also recall a theory in the 1970s that Mercury may have been a moon
of Venus, as it has one of the more eccentric solar orbits of the planets -
plus I am sure bearing some resemblance to our Moon may have been
the "inspiration" for the idea. Any merit to it? Or just not enough evidence?

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? Now we
would have an even greater need to get surface samples back from
both worlds!

Posted by: BruceMoomaw Mar 22 2006, 08:25 PM

Yeah, and at the time the idea that Mercury's rotation was synchronous was Holy Writ -- NOBODY questioned it, so nobody thought of that explanation. (As Clarke says, "In 1965 we learned that the only thing we knew about Mercury was wrong" -- and a hell of a lot of SF stories bit the dust (although those involving the dayside's high temperatures are really as valid as ever).

Incidentally, one instrument on the original strawman list of instruments for Mariner 10 back when they were first planning it (before the actual instrument solicitation) was a copy of the High Resolution IR Radiometer on the Nimbus satellites, which could have imaged the nightside's temperature differences and thus perhaps gotten at least some information on surface features. They also considered a gamma ray spectrometer, but presumably decided that it wouldn't have time to gather good compositional data. Unfortunately, at that time nobody was thinking about near-IR spectrometers as compositional instruments on spacecraft.

Posted by: antoniseb Mar 22 2006, 08:45 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.

Posted by: JRehling Mar 22 2006, 09:27 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.

Posted by: Richard Trigaux Mar 22 2006, 09:40 PM

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.

Posted by: ljk4-1 Mar 22 2006, 09:41 PM

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.

Posted by: edstrick Mar 23 2006, 09:33 AM

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.

Posted by: Rem31 Apr 28 2006, 09:47 PM

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.

Posted by: BruceMoomaw Apr 28 2006, 09:53 PM

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.)

Posted by: Rem31 May 10 2006, 12:06 AM

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?

Posted by: BruceMoomaw May 10 2006, 08:43 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).

Posted by: Bob Shaw May 10 2006, 11:00 AM

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

Posted by: Rem31 May 10 2006, 11:28 AM

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.

Posted by: helvick May 10 2006, 12:19 PM

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.

Posted by: JRehling May 10 2006, 01:35 PM

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.

Posted by: jsheff May 10 2006, 03:52 PM

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

Posted by: JRehling May 10 2006, 05:08 PM

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.

Posted by: Bob Shaw May 10 2006, 05:58 PM

John:

The trouble with Mercury is, that although the environment *could* be coped with at a pinch, the sheer cost in terms of rocketry is worse than enormous. Getting to Mercury at all other than (slowly) by way of multiple Earth-Venus gravity assists is hideously impractical - and landing on it is literally the 'worst-case' scenario in the entire Solar System, what with it's reasonably high gravity and no atmosphere for braking purposes.

To put men there is even more difficult as you'd almost certainly want to do it *quickly* because of Solar flares!

To get to Mercury you really need some major set of breakthroughs in propulsion technology, even above and beyond the few speculative technologies we have some promise of!

Bob Shaw

Posted by: RNeuhaus May 10 2006, 07:06 PM

A comparative view of Sun between Mercury and Earth.

I would be most impressed to view the Sun from Mercury at 1/3 closer than Earth.

Rodolfo

Posted by: jsheff May 10 2006, 07:27 PM

I know how horrendous the delta-vee requirements are for landing on Mercury, but they're not, even with present technology, impossibly high. If you remember, the lander portion of Beppi-Columbo was not nixed for technological reasons - it was simply deemed too expensive for the program's budget!

I agree that manned landings, when they happen, will probably not occur within our technological horizon, i.e., this century, and only as a "mopping-up" exercise after the rest of the solar system has been thoroughly explored.

I remember as a kid reading a SF novel by Alan E. Nourse, called, I think, "Brightside Crossing" (You might want to look it up, Rem31, if you can find a copy; it might answer your questions). It may even have been written before Mercury's true rotation period was known. His characters mounted a surface-crawling manned expedition to traverse Mercury's dayside, timed to arrive at the center right when the planet was at perihelion! The expedition was mounted not for the sake of science, but for the glory, as it was "the last great challenge left in the solar system". This was science-fiction, I know, but I wonder ...

Today you have people willing to pay $60,000 and put their lives at great risk to climb Mt. Everest. They do it not for science, nor for the sake of being as high up as they can. (You can, after all, get higher in a aircraft or spacecraft!) They do it for the sheer challenge of it, "because it was there". So the fact that Mercury is, as you say, the most difficult place in the solar system to get to, may not repel people, but may be precisely what makes it an irresistable draw for some. Funny things, these humans...

Posted by: JRehling May 10 2006, 08:27 PM

I've heard the phrase "last great challenge" before referring to various challenges, but never accurately.

Millionaires try to do various things in balloons or on mountains, which is fine, but when they frame some accomplishment in narrow definitions and call it the last great challenge, I laugh. I bid them to accomplish whatever they want, but if they want to have it proven that it wasn't the last great challenge, I'll donate 30 seconds of my time and pitch them one much harder than what they actually accomplished.

Mercury subsolar at perihelion? OK, try going to the center of Mercury. Jupiter. The Sun. Rigel.

Sail around the world in a balloon? OK, try it on an over-the-poles route. Try going around Venus in a balloon. Neptune. The Sun.

Climb Everest without oxygen? OK, try it naked. Try it in 24 hours. Try it walking backwards. Try it on one foot. Try it in January. Olympus Mons. In 24 hours.

Swim the English Channel? OK, swim the Pacific. Swim from Anchorage to Venice. Without coming up for air.

This whole "last challenge" thing is about using a superlative where a comparative would be accurate. Unless by "last" they mean "latest"... but I think they mean "final".

Posted by: Bob Shaw May 10 2006, 08:39 PM

Somehow, I think most of those challenges would be not so much 'final' for the participants as 'terminal'!

Personally, I'll stick to walking backwards for Christmas, across the Irish Sea!

Less chance of ending up deaded, even if you *do* end up fallen in de water!

(exits stage left bearing photograph of 10/- note)

Bob Shaw

Posted by: helvick May 10 2006, 08:50 PM

Absolutely agree with you on this but people are strange as Jsheff pointed out. At some stage some human will just do it so they can say they did it first.

Reinhold Messner has climbed Everest in 4 days, solo and without oxygen in the Monsoon season which isn't quite as extreme as you suggest since he took a bit long and thankfully he wasn't naked as far as we know but it does go to show just how mad people can be.

Posted by: BruceMoomaw May 10 2006, 09:11 PM

Well, all the way back in the 1950s -- when he was still an unabashed hack SF writer rather than a fairly good stylist -- Robert Silverberg wrote a story about an attempt to drive all the way across Mercury's dayside (which ends in failure and the deaths of a couple of the participants). More recently we've had stories about a guy deliberately jumping into that gigantic cleft on Miranda (20 km deep, if I remember correctly), and -- so help me God --another one about the first successful bungee jump from orbit into the atmosphere of Jupiter.

Posted by: ilbasso May 18 2006, 05:47 PM

Bob, you are obviously a member of the East Finchley Wolf Cubs. If you see Blue Bottle, tell him to come home - his mum has found his knees.

Posted by: ljk4-1 May 18 2006, 05:52 PM

And quite recently a double amputee scaled Everest:

http://msnbc.msn.com/id/12811777/

We're hardly done with new goals to achieve.

Posted by: Rem31 Jun 17 2006, 09:00 PM

Do you need also Solarheat and radiation protection when you land on Mercury when it is at (aphelion)? greatest distance from the Sun. I know that you need protection when landing at perihelion ,closest to the Sun. And what will be the best place on Mercury to put a lander down on the Surface?

Posted by: dvandorn Jun 18 2006, 11:52 PM

I don't have detailed numbers for you, but my gut feeling is that the proximity of the Sun is such, aphelion or perihelion, that you'd run into a similar harshness of environment (and need about the same level of protection) either way.

After all, what difference does it make if the heat outside is just about enough to melt lead, or just more than enough to melt lead? Well, except for maybe needing lead-pond floats on your spacecraft... though I will note that there is no evidence of liquid-ponding of *any* materials in the Mariner 10 images.

-the other Doug

Posted by: RNeuhaus Jun 19 2006, 12:46 AM

In spite of the fact Mercury has extermes temperatures between day and night: 427°C and -173 °C and its mean surface temperature of 179 °C, the best place for human supervivence is on the poles. At the poles might have some water ices. But, the problem is that every 44 days (one orbital period is close to 88 days), the North and the South of poles will have alternate soft summer and winter due to its small orbital inclination of 7 degrees.

However, Mercury has own a small magnetic field that is 1% as strong as Earth. This does not help much to protect from solar wind and energetic particles.

Finally, Mercury's Perihelion is 46,001,272 km and Aphelion is 69,817,079 km, difference of 23.8 millions kilometers is much difference than the Earth with its about 3 millions kilometers. That will induce, I seems, a small greater variations of temperatures between the seasons.

All at all, Stephen Hawking recently has told to the press that there is no any an adequate biosphere place for human in our solar system unless we have to travel inter-stars searching for a similar Earth biosphere.

Rodolfo

Posted by: ermar Jun 20 2006, 08:09 PM

Actually, the orbital inclination is irrelevant - what matters is the tilt of the planet's rotation axis with respect to the plane of its orbit. Because Mercury's axial tilt is a miniscule 0.01 degrees, the sun will hardly be seen to move above or below the ecliptic at any point in the year. Any "seasons," then, will be due to the eccentricity of its orbit.

And, interestingly enough, even Mercury's weak magnetic field is enough to deflect the solar wind (at least, most of the time).

Just a few thoughts.

Posted by: RNeuhaus Jun 21 2006, 03:04 AM

Good tought ermar!

I haven't percated that its 7 degree inclination orbital implies a 0.01 degree for sol inclination orbital. Hence, the poles might have some permanent ice since they might be always in the shadow. Not yet sure if there are any volcan or mountain on the poles. Anyway, the climate of Mercury is similar to Moon only for the night side and much harsh for the day side.

Rodolfo

Posted by: Rem31 Jun 22 2006, 09:11 PM

Here is one of the most beautifull photographs of Mercury i can found on the web Taken by the Mariner 10. Mercury was at near (ap)helion ,its greates distance from the Sun. You can see the sharp dark shadows on the picture. One thing is sure ,it will be hot on the dayside areas on the time the pictures were taken. I hope that the link works

Posted by: helvick Jun 22 2006, 11:40 PM

Nope but this should do the trick :
http://photojournal.jpl.nasa.gov/jpegMod/PIA03104_modest.jpg
http://photojournal.jpl.nasa.gov/jpegMod/PIA03104_modest.jpg

Posted by: edstrick Jun 23 2006, 10:50 AM

Note that we *DO* know there's polar volatile <ice, probably> deposits on Mercury. Due to the orbital tilt of the planet, we can look down into the permanently shadowed craters at the poles with earthbased radar and see intense, depolarized radar returns from the shadows that have identical properties to the martian residual polar caps and the surfaces of the icy galilean moons.

Posted by: JRehling Jun 23 2006, 04:10 PM

The old version of that mosaic with visible seams where the brightness changes has had a long lifetime on the web, but the corrections have been made and can be found, with other Mariner 10 imagery, here:

http://cps.earth.northwestern.edu/M10/TXT/encounters.html

Posted by: edstrick Jun 24 2006, 10:24 AM

I note that that page has ONE (the first) of the Mariner 10 WIDE angle camera images of Venus.

Posted by: Rem31 Jun 24 2006, 11:09 PM

Why has the (large) image an brighter and lighter colour than the smaller image of the link i have posted?

Posted by: efron_01 Nov 12 2006, 03:44 PM

about Mercury having been a moon of Venus..
I have seen several articles that asume that Mercury did experience a terror impact itself
early in it's history, blowing a lot of the material of the original planet away.

therefor the iron core is too big for the size of the planet and it would explane it's orbit

Any moons that came from this impact fell down to the planet, or into the sun
It could also explain the sudden rise in impacts on the moon and the earth 4by ago

http://www.space.com/scienceastronomy/060111_hit_and_run.html

http://www.spacedaily.com/reports/Early_Mercury_Impact_Showered_Earth.html

Posted by: nprev Nov 13 2006, 02:11 AM

As I recall, the Arecibo radar images of Mercury's North Pole seem to indicate the same cratered terrain typical of most of the planet. In fact, the ice repositories are thought to primarily reside in some of the deeper craters because they avoid direct exposure to sunlight.

Sure would be a great surface mission...that material has to be virtually primordial...whether it originated via ancient outgassing from Mercury or from cometary impacts is the main question to answer!

Posted by: Alan S Jan 8 2007, 06:21 AM

This might be a topic for a new thread, but since I'm new, I'll just ask my question here.

Apollo Astronaut has advocated an idea of mining Helium-3 from the lunar surface, since we believe that the solar wind impacting the surface of the moon for billions of year should implant this material into the surface matarial. I've done some reading at it appears the certian minerial are more likely to contain the Helium-3 then others (illiment being one that I recall.)

So, here is my question. Assuming engineers can develop a Helium-3 fusion reactor and mining He-3 becomes worthwhile, wouldn't Mercury --being closer to the sun-- contain much more Helium-3 then the moon? I've not seen anything writen about this. Is this a correct idea. Could we mine He-3 from Mercury?

Posted by: edstrick Jan 8 2007, 12:43 PM

The helium 3 is a fraction (in very approximate primordial proportion) of the total helium in the sun and thus the solar wind. (Earth's traces of helium are almost entirely "new" atoms from alpha-particle decay of uranium and thorium and their decay-chains of nucleids. Earth lost most of its helium 3 and only traces show up in certain natural gas wells that contain some primordial gas leaking from inside the Earth)

The solar wind impacts the soil and high velocity nucleii in the wind are "implanted" some micrometers into the impact glass and mineral grains of the regolith. As the regolith gets repeat-pounded by small meteor impacts, it's progressively re-re-re-re shock melted and mixed with regolith glass and mineral fragments. As it gets older, it approaches a steady state where most of the soil is glass and it's just reprocessed in-place, slowly getting thicker from random larger impacts as it gets older.

On mercury, impact gardening may be somewhat faster than on the moon, while solar wind impact will be significantly larger, but the higher surface temps (baking out the soil) at low latitude and the nature of the re-processing of regolith may result in an only modest increase in the helium-3 content per kilo of regolith.

Helium 3 mining is a fantasy for the near and intermediate term future. Fusion power is always 50 years in the future <who said that?>, and deuterium/helium-3 fusion is harder than deuterium/tritium or deuterium/deuterium fusion due to the presence of 2 protons in the He-3 nucleus.

Posted by: ljk4-1 Jan 8 2007, 02:52 PM

Dr. Robert Bussard of the Bussard ramjet interstellar vessel concept fame,
has been promoting a new type of fusion engine called inertial electrostatic
confinement fusion (IEC).

IEC involves "a fusion process that converts hydrogen and boron directly
into electricity producing helium as the only waste product."

See this video of a talk Bussard gave on the IEC for the details:

http://video.google.com/videoplay?docid=1996321846673788606

The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion

By Dr. Robert W. Bussard

57th IAC, Valencia, Spain, October 2-6, 2006

http://www.askmar.com/ConferenceNotes/2006-9%20IAC%20Paper.pdf

So there may be no point in going to Mercury to mine Helium 3. Speaking
of mining Mercury, what minerals might the planet have that would make
going there for that purpose worth it? No doubt mining the planetoids would
be much easier and cheaper. Perhaps Mercury would make a good solar
observation station.

Posted by: JRehling Jan 8 2007, 07:16 PM

I'm not sure if it would be worth going to Mercury for Helium 3 even if that were the only form of fusion and it worked great. In fact, I doubt it. By no means is there anything else on Mercury would going to get and bring back. You'd lose money bringing diamonds back from Mercury even if they were already pre-cut and in fireproof burlap sacks.

This may be hard to believe, but the minimum-energy path to Mercury is greater than that to any other solid object... in the universe. And there's no atmosphere to brake your descent. And the escape velocity is nontrivial for your trip home, with the same delta-v on the way back to Earth. A muscular there-and-back mission could take place FASTER than one to Pluto, but far more expensively.

There would be no reason to send a (visual) solar observatory to Mercury. Why not just orbit the Sun at the same distance -- what use is it to have the ground beneath you, at an alarming increase of delta-v (and spending ~50% of the time unable to see your target) for the privilege?

I'd go back to the start here and opine that it wouldn't be worth going to Mercury for Helium 3 even if the only other form of energy available to the human species was burning wood and scaling back our population to pre-industrial levels. Basically, I don't think it's a break-even no matter what. Mercury is not economically viable.

Posted by: Bob Shaw Jan 8 2007, 10:32 PM

In fact, there's hardly a drop of He to be had on Earth bar from a couple of US sources - and that's not exactly a renewable commodity. Nazi Germany tried to buy helium from the US before WWII for their airship programme, but were refused access as even then it was deemed to be a strategic asset. Thus we got the Hindenberg disaster (actually, barely a hiccup in terms of aeroplane crashes) but equally there were no Nazi nukes. (Yes, I know, it's more complicated than that!)


Bob Shaw

Posted by: nprev Jan 9 2007, 02:25 AM

I think that JR's analysis was right on, if nihilistic (reality can be that way! ) The only use I can think of for Mercury is something like what's happening to the California desert right now. Mercury may be colonized if there's literally no place else left to go in the Solar System in the distant future.

This would of course depend heavily on three rather unlikely background conditions: high-speed economical interplanetary space transportation (propulsion method unknown), one or more extremely prosperous human cultures that have already colonized everywhere else, and truly fearsome population pressure.

EDIT: Heck, let me add one more precondition: Human interstellar travel must be utterly infeasible. If it were, then better real estate would surely be accessible...

Posted by: edstrick Jan 9 2007, 08:39 AM

"...what minerals might the planet have ..."
We dont' really know about low abundance mineralogy, but the bulk of the crust is made from similar rather refractory <high temperature melting and vaporising> minerals as the lunar surface, more specificially the lunar highlands. Calcium feldspar and pyroxenes, and some olivine <maybe> More interesting and unknown in composition are the polar crater volatiles. But they're of science interest, not anything else except very long term value as resources.

Seriously high performance ion drive missions... solar electric will do just fine... can do the hard transport to and form Mercury fairly easily, though not descent/ascent for sample return.