First Probe To Orbit Mercury May Help Us Learn How Planets Form

An anonymous reader writes "Next month, the first space probe in nearly 40 years will approach the planet Mercury, with an array of instruments that could help answer fundamental questions about how planets form. The mission is called MESSENGER, for Mercury Surface, Space ENvironment, GEochemistry and Ranging. On March 17 it will pull into orbit around mercury, after more than six years of maneuvering between the Earth, Venus and Mercury itself."

Comments

Badum Kisshhhhh.

[Adambomb]

On the bright side the solar panels don't have to be very large," Blewett said.

I see what you did there.

Re:Badum Kisshhhhh.

[Hognoxious]

Must be awful to be in the dark.

Re:Badum Kisshhhhh.

[Abstrackt]

It's quite brilliant.

Re:Badum Kisshhhhh.

[Anonymous Coward]

I didn't know the Sun had a bright side. What's on the dark side?

Re:Badum Kisshhhhh.

[Anonymous Coward]

A shining example of first class research.

Re:Badum Kisshhhhh.

[Anonymous Coward]

Suffering

Horribly written article

[wvmarle]

That article is far worse than your average /. post: it lacks cohesion, and sounds more like rambling than a serious piece of journalism. I would bet the author hasn't had it proof-read, probably not even by himself. There must be better articles around describing this event.

Re:Horribly written article

[gedankenhoren]

Agreed. "Because Mercury, unlike Earth, is not tilted relative to its orbital plane, there are areas near the poles where the sun would never come up over the horizon. Those areas are a lot colder than the rest of the planet. Most scientists think the mystery material is water. These regions were discovered when ground-based astronomers bounced radio waves off the planet." How is this 'mystery material' that the author is talking about relevant? We can infer, but for a topic that usually sends science reporters into waves of wankery (i.e., **water in space!!!**), I would expect that we wouldn't have to infer at all; or more like, we'd usually have to roll our eyes, not squint.

Re:Horribly written article

[wvmarle]

Oh yes that as well. And he's writing about "this mystery material" without having introduced it beforehand... what mystery material I'd say. Oh and considering the temperature there can be so many other ice-like substances, like methane or carbon dioxide. That there is water in space is no surprise - no water out there would be more of a surprise. I always hear talk about meteors being clumps of rock and ice.

Re:Horribly written article

[Anonymous Coward]

...And he's writing about "this mystery material"...

Personally, I think it's a couple of large lakes of shiny, liquid metal...

Re:Horribly written article

[Anonymous Coward]

It wouldn't have been a mystery material if he'd introduced it, now, would it?

Re:Horribly written article

[Progman3K]

Hmmm... Mercury. Shiny, liquid metal...
I see what you did there

MESSENGER

[Tablizer]

The mission is called MESSENGER, for MErcury Surface, Space ENvironment, GEochemistry and Ranging.

They certainly did a lot of "ranging" coming up with that acronym.

New game-show? "NASA would like to buy a vowel for....ten million dollars!" *clap* *clap*
   

Re:MESSENGER

[Tablizer]

by the way, after budget cuts they shortened it to MESS

Re:MESSENGER

[Anonymous Coward]

I wonder why they don't just say, Messenger for Mercury (who is the messenger of Jupiter in roman mythology) and backronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging.

Re:MESSENGER

[Anonymous Coward]

Hmm. Must be a firefox bug. I see this:

MESSENGER, for Mercury Surface, Space ENvironment, GEochemistry and Ranging.

Isn't that MSSENGER?

Re:MESSENGER

[mangu]

The mission is called MESSENGER, for MErcury Surface, Space ENvironment, GEochemistry and Ranging.

They certainly did a lot of "ranging" coming up with that acronym.

Actually, ranging is an important part of any space mission. What they call "ranging" is measuring the distance from an earth station to the spacecraft and it's what allows then to calculate the orbit the spacecraft is following.

Without accurate ranging the spacecraft would either get lost in space or crash on the planet. With accurate enough ranging one can even find out details about the planer's interior. Thanks to ranging, we know that Mars has a liquid core.

Re:MESSENGER

[maxwell demon]

Also, geochemistry? Shouldn't that be hermechemistry?

Re:MESSENGER

[Anonymous Coward]

No surprise to most /. readers, but engineers love coming up with fun/witty acronyms/initialisms. At a place I co-oped at in college, there was a quick fix that was kind of a hack was named

Base Adhering, Non Distorting, Anti Intrusion Device or BANDAID. It was a band aid solution to the problem and it looked like one too.

Re:MESSENGER

[Waffle Iron]

They certainly did a lot of "ranging" coming up with that acronym.

One of the instruments on the probe is a laser altimeter, which is a kind of LIDAR (which stands for Light Detection and Ranging). So regardless of the stupidity of the overall name, the acronym letter actually fits.

If I were in charge, though, I'd just call it "Messenger" without all-caps. The word itself is fine (and Mercury-related) without trying to cram it into a backronym.

Re:MESSENGER

[tverbeek]

NASA, if you want to call a probe "Messenger", just call it "Messenger" and explain to the members of the media who slept through middle school that you called it that because Mercury was the Roman messenger of the gods. You don't need to emulate the US Congress and try to justify the names you want to use with backronyms that violate several Geneva Convention prohibitions against torture (e.g. U.S.A. P.A.T.R.I.O.T. Act), and which even Stan Lee would be embarrassed by.

Re:MESSENGER

[camperdave]

No. Although the "geo-" prefix is from the greek word for earth, it is in the sense of "land" or "ground", not in the name of the planet sense.

Re:MESSENGER

[Gilmoure]

So... hermeography? Hermeology?

COOL!

Re:MESSENGER

[Anonymous Coward]

Also, geochemistry? Shouldn't that be hermechemistry?

this.

Re:MESSENGER

[Tablizer]

Yes, but don't almost all non-landing probes do that as part of their standard navigation? It's almost like calling a PC a "compu-fan" because it has a fan(s) inside.

Re:MESSENGER

[Tablizer]

But don't tell the general public that. In the old days they picked a name, such as "Pioneer", and called the probes Pioneer 1, Pioneer 2, Pioneer 3, and so on. Less awkward in my opinion.

shoutout to NASA!

[jrobot]

http://www.nasa.gov/mission_pages/messenger/main/index.html

How is plannet formed?

[Anonymous Coward]

how is plannet formed
how solarsystem get pragnent

Re:How is plannet formed?

[Anonymous Coward]

Good question, babby.

Re:How is plannet formed?

[xmason]

They need to do way instain solarsystem who kill thier plannetss. becuse these plannet cant frigth back? it was on the news this mroing a solarsystem in andrommedah who had kill her three plannets. they are taking the three plannet back to milkyway too solarsysteem to rest my pary are with the staar who lost his plannetts; i am truley sorry for your lots

Video from MESSENGER

[SnoopJeDi]

OT, but one of my favorite spacecraft videos is the departure video from MESSENGER.

Re:Video from MESSENGER

[Anonymous Coward]

it's shit!

Re:Video from MESSENGER

[melikamp]

These videos do not require Flash.

Why six years?

[Anonymous Coward]

Does anyone know what the probe did in those six years between launch and now?

Re:Why six years?

[wisebabo]

A lot of gravity assist maneuvers. It is (energy wise) very difficult to get to put a probe in mercury's orbit, first you have to do a lot of braking to put it into an elliptical orbit to reach mercury's orbit then another lot of braking to make it match mercury's orbit then more braking to put it into (some sort) of elliptical orbit AROUND mercury then (optional) more braking to "circularize" your orbit around mercury!

I think energetically speaking it's about as difficult to send a probe to Mercury as it is to Jupiter even though Jupiter is much farther away. So in order to not have to use a huge (expensive booster), the probe does a bunch of gravity assists by sling-shotting near Venus, Mercury and maybe even the earth. This saves a LOT of fuel but adds a LOT of time (otherwise as you probably guessed it would've gotten there years earlier).

Re:Why six years?

[MichaelSmith]

I think we missed a great opportunity to try a medium sized solar sail. Say a couple of hundred metres in diameter. Inside the orbit of Venus a sail like that would be very efficient.

Re:Why six years?

[m50d]

Apologies if I'm being dumb here, but isn't a solar sail only really useful for moving away from the sun, not towards it?

Re:Why six years?

[MichaelSmith]

An object orbiting the sun could point the sail 45 degrees away from the sun so that sun light is reflected ahead in the orbit. That way pressure from sun light would slow the object down and move it into a lower orbit. Mercury is very difficult to reach because you need to dump a lot of kinetic and potential energy to match orbits with the planet. In other words you have to go a long way down the sun's gravitational well.

Re:Why six years?

[stjobe]

the probe does a bunch of gravity assists by sling-shotting near Venus, Mercury and maybe even the earth.

It sling-shots around Mercury to get to Mercury?

Re:Why six years?

[mister_playboy]

Actually, it's easier to escape the Solar System than go into an orbit around Mercury.

Reaching Mercury from Earth poses significant technical challenges, since the planet orbits so much closer to the Sun than does the Earth. A Mercury-bound spacecraft launched from Earth must travel over 91 million kilometers into the Sun’s gravitational potential well. Mercury has an orbital speed of 48 km/s, while Earth’s orbital speed is 30 km/s. Thus the spacecraft must make a large change in velocity (delta-v) to enter a Hohmann transfer orbit that passes near Mercury, as compared to the delta-v required for other planetary missions.

The potential energy liberated by moving down the Sun’s potential well becomes kinetic energy; requiring another large delta-v change to do anything other than rapidly pass by Mercury. To land safely or enter a stable orbit the spacecraft would rely entirely on rocket motors. Aerobraking is ruled out because the planet has very little atmosphere. A trip to Mercury requires more rocket fuel than that required to escape the Solar System completely. As a result, only two space probes have visited the planet so far. A proposed alternative approach would use a solar sail to attain a Mercury-synchronous orbit around the Sun.

https://secure.wikimedia.org/wikipedia/en/wiki/Mercury_(planet)

Re:Why six years?

[BJ_Covert_Action]

You don't use an untested, unvetted technology as your primary and only means of propulsion for a mission whose sole purpose is to study a previously unstudied planet in detail. That would be like betting your life savings on a horse that has never run a horse race before.

Now, that said, if the spacecraft had enough spare capacity (power and mass wise) to pack on a small solar sail for a proof-of-concept demonstration, then, yes, it could have been a great opportunity. But if the technology was not ready, if the risk was too high (controlling a long, deployable, non-rigid moment arm is no trivial task) , or if the budgets for the spacecraft were too tight, then the design team would have vetoed any additional secondary mission (like a tech. demo).

Re:Why six years?

[Patch86]

Yep.

http://en.wikipedia.org/wiki/MESSENGER#Launch_and_trajectory

The "sling shots" are to lose momentum, rather than gain it. As far as I understand it, MESSENGER used a (relatively distant) orbital pass of Mecury to slow down, allowing it to enter it's lower altitude orbit on a later pass.

IANARocketScientist, though.

Re:Why six years?

[Nadaka]

You don't even really need to be able to direct the sail if you can change its surface area. Deploy to maximum at apoapsis and it will slow the craft as it approaches periapsis resulting in a lower periapsis. The hard part (using a solar sail) would be drawing in apoapsis, as you would have to exert thrust towards the sun, you would need use a more conventional thruster and undeploy the solar sail or you will end up increasing the ellipticality.

Re:Why six years?

[ccpoodle]

It takes a lot of delta v to get to Mercury and orbit the planet, so multiple sling shot manuvers were done to keep the cost of the probe from being excessive. Neil

Solar Syatem Simulator

[DanielRavenNest]

This will let you see how things look from any spacecraft: http://space.jpl.nasa.gov/

Movie "Sunshine"

[wisebabo]

Thinking of Mercury also makes me think of the very good horror/sci-fi movie "Sunshine". (Partial SPOILER ALERT).

I really liked it except the intensity of the Sun, even at those distances, was dialed up a bit too high. I mean, when the captain gets "blown" by the very brief exposure to the (dying) sun, it was a little too much considering he was in a very heavily heat shielded suit. And the ship wasn't even yet at Mercury's orbit! I guess just slowly being cooked to death was not dramatic enough for the script writers.

Otherwise, I really liked the movie, the other details were mostly spot on (except there wasn't "zero-G" in a few places in the spacecraft where it should've been) and the fact that they were out of communications with earth even before reaching mercury seemed suspect (I know there could've been crazy radio interference with a wacky sun but a good laser/maser could punch through almost anything). Obviously these were points that the director chose not to deal with because of cost (zero-G) or plot (kept the crew in scary isolation). Anyway, loved some other touches like the room with the fissile material "bomb" which was evidently so dense it had it's own significant and varying gravitational field! And a believable scary "monster!"

Another excellent sun-oriented sic-fi piece is Arthur C. Clarke's story about a trip to the asteroid Icarus (I think it's called "Summertime on Icarus"). I always thought it would be a good way of protecting future long-term travellers to asteroids/comets from solar flares, just temporarily park them in the shadow!

Re:Movie "Sunshine"

[wisebabo]

Oh, and to add to my nit-picking, when the thermally unshielded crew members are exposed to the vacuum of space (now in shadow) they shouldn't instantly freeze solid. They would, of course, eventually do so (if they were kept in shadow) but the thermal conductivity of a vacuum is so low it would take awhile (think Thermos bottles). And evaporative cooling wouldn't be that much faster (even Bedouins in the driest deserts don't get cold from sweating). Still the writer's needed a contrast between fire and ice I guess so whatever.

I think they would however lose consciousness quickly (15 sec.?) though because the dissolved oxygen in their blood would come out of solution (maybe causing the bends) quickly.

Still great movie.

Re:Movie "Sunshine"

[tragedy]

Just a note. Oxygen transport in your body isn't based on the oxygen being dissolved in your blood. It combines chemically with the hemoglobin. So, suddenly exposed to a vacuum, you still might have some gases come out of solution in your body, so maybe the bends, and your body would swell a bit quite possibly accompanied with some discomfort. I'm not sure what would happen with sinuses and eardrums and so forth. Also, if your lungs were full, you probably wouldn't be able to contain the pressure. I'm pretty sure it wouldn't be able to blow out your chest or anything, but there could be internal rupturing, or maybe the air would just force itself out of your mouth and nose. In any case, if you had enough oxygen in your blood to stay conscious for two minutes, then it looks like you'd stay conscious for two minutes regardless of the pressure (as long as you don't pass out from the pain of your ear drums bursting, etc.)

Hmmm. Before posting, something just occurred to me about how good a pressure vessel your lungs might actually be. I looked up the PSI trumpet players manage, because I've heard about how professionals manage to rupture their lungs sometimes and end up with air directly entering their body cavities. I found this which says that student trumpet players were able to manage 35-50 PSI and professionals between 75-95 PSI. The question there is how much of that pressure is actually found in the lungs and how much is produced by clever use of the lungs as a lower pressure air supply, producing the pressure mostly in the mouth and feeding it with careful work? I'm not sure, but it makes it seem that it's quite possible that a healthy adult may very well be able to hold air at around 14.5 PSI without even being forced to breath out. For that matter, if they're in space in the first place, they probably weren't even breathing air at 1 atmosphere to begin with. The US space program uses a mostly oxygen atmosphere at only about 5 PSI.

So, it looks like you wouldn't want to just take a stroll out into the hard vacuum of space on a regular basis, but it looks like it's actually pretty survivable in most of our solar system.

Re:Movie "Sunshine"

[anchovy_chekov]

Man.. you just grossed me out.. with science!

Re:Movie "Sunshine"

[MichaelSmith]

Unless the chromosphere of the sun is surrounding you pretty much any mirror will protect you from the sun. And the mirror doesn't have to be heavy. A thin sheet of polished metal will do fine. Good film though. Along with Moon its great to see indie SF films being made.

Re:Movie "Sunshine"

[MichaelSmith]

I think 15 seconds in vacuum is the limit. The lungs will empty immediately. Air is kept there by suction and you lose that in vacuum. Oxygen transport out of the blood and into vacuum means that the blood headed for the brain will have almost no oxygen so once that hits the brain you are gone. Having said that 15 seconds is enough to find the lever and close the door of the emergency airlock then pull the lever to blow the lock though I reckon the pulse of oxygen deprived blood would have knocked Bowman out for a while, giving Hal time to work out a way to finish him off.

Re:Movie "Sunshine"

[bytesex]

You could still be saved by others though, after those fifteen seconds. In space, the question is for how long.

Re:Movie "Sunshine"

[MichaelSmith]

You could still be saved by others though, after those fifteen seconds. In space, the question is for how long.

This guy survived about a minute

Re:Movie "Sunshine"

[Alioth]

You won't stay conscious for more than a few seconds.

The lungs are not a one-way system; effectively, if there is less oxygen in the lungs than there is in the blood, the lungs work in reverse and remove oxygen from the blood. At airline altitudes, the time of "useful consciousness" is something like 30 seconds. At 50,000 feet, time of useful consciousness is between 6 and 9 seconds because the lungs strip the oxygen out of the blood so efficiently. This is why if there is only one crew member in the flight deck, he or she must wear an oxygen mask until the other crew member returns; after all if some hull breach emergency presents itself while he's alone he might be too busy trying to fly the plane to don the oxygen mask.

A rapid decompression can reduce the time of useful consciousness by 50% due to the forced exhalation.

Re:Movie "Sunshine"

[ibsteve2u]

Here's hoping Messenger results aren't being displayed on live TV globally when suddenly the Messenger feeds wink out, and you hear a voice in the background sat "Oh, shit...did you see the size of that flare? I gotta get home to my family".

Re:Movie "Sunshine"

[hazem]

It made me think of Asimov's short story, Runaround, featured in the I-Robot collection (among others, probably). http://en.wikipedia.org/wiki/Runaround

I'm particularly fond of the audiobook version read by Scott Brick.

It features a funny robotics-expert duo, Donnovan and Powell, who are sent to Mercury after a failed mining mission some 20 years earlier. They have robots and plans to bring the station back on line, but of course, there's a problem... involving robots.

Re:Movie "Sunshine"

[Anonymous Coward]

Oxygen transport in your body isn't based on the oxygen being dissolved in your blood. It combines chemically with the hemoglobin. So, suddenly exposed to a vacuum, you still might have some gases come out of solution in your body, so maybe the bends, and your body would swell a bit quite possibly accompanied with some discomfort.

Have you ever watched an open bottle of water exposed to a vacuum? I have. At about 65,000 ft equivalent pressure, the water begins to *violently* splash and pop. It almost knocked the bottle over. And it's not boiling. Water doesn't boil at room temperature until the pressure is much lower. Instead, it's the partial pressure gasses which are escaping from the water.

Exposed to a vacuum, the dissolved oxygen and nitrogen in your blood will come out of solution (i.e. become gaseous) rapidly and violently, once the pressure differential makes it through your skin and outer flesh. Once the process starts, you will begin to experience what are effectively small explosions inside your body, rupturing blood vessels and vital organs. You may think of the bends, but it would be amplified by a factor of 100. You would die a very quick and painful death.

Re:Movie "Sunshine"

[jgtg32a]

I was so pissed off when that movie turned into a damn slasher flick, they were doing everything right up until then.

Re:Movie "Sunshine"

[Anonymous Coward]

This is just wrong

Re:Movie "Sunshine"

[Anonymous Coward]

Accidents with decompression have happened on the ground too, so we actually know what happens.

If you attempt to hold your breath, your lungs will pop. Your best chance of survival is to exhale strongly immediately prior to decompression, but that requires prior knowledge.

Explosive decompression does not kill from asphyxiation (contrary to popular belief). It's actually the bends that gets you first (as wisebabo said). Going from 1 atmosphere to hard vacuum, the boiling point of blood drops and the gasses (mainly nitrogen, this is where wisebabo was wrong) in your blood will start to boil out in approximately 10 seconds. They form bubbles in your blood vessels blocking off blood and such oxygen as the it still contains.

At this point, you become incoherent (as in batshit crazy) almost instantly, and lose consciousness a few seconds later. Brain damage begins immediately. (Neurons and muscles can respirate anaerobically, but this does not release sufficient energy to keep the brain alive for long.)

With immediate rescue by a fully equipped medical team, you might be able to survive an exposure of as long as, say, 30 seconds, but after that you'd be a vegetable.

Re:Movie "Sunshine"

[BJ_Covert_Action]

And a believable scary "monster!"

You mean the seemingly psychic space zombie? Sorry, how was that believable again? Or, for that matter, even necessary to the plot?

Re:Movie "Sunshine"

[Anonymous Coward]

If you are lucky enough you may end up in the Heart of Gold

Re:Movie "Sunshine"

[Nadaka]

You are completely ignoring that your skin and muscle is damn strong, and with the exception of your lungs and sinuses, most of your body is going to maintain pressure through physical restraint of your skin and muscle.

Your lungs are good at venting gas and your sinuses are mostly non critical. You are still most likely going to die, but you won't be exploding.

Re:Movie "Sunshine"

[tragedy]

Little late to reply to this, but I'm going to anyway. From what I can find, it looks like you very well may be able to hold the oxygen in your lungs even in a vacuum. Air may be brought into your lungs by suction, which does rely on air pressure, but once it's in there, you hold it in with your trachea mouth, etc. It may or may not be the case that the lungs empty immediately, but what I can find suggests that you can probably manage to hold in the 5+ psi you're likely to have in your lungs. Also, even if your lungs empty, oxygen isn't just going to be pulled out of your blood into space. So, any oxygen already in your blood will stay there. I used to be able to do four underwater laps of our pool when I was a teenager. I experimented a fair amount with holding my breath when I had that pool and I can say with pretty good authority that someone in good health should be able to stay conscious for at least a minute and probably more even after expelling as much air from their lungs as they can and without intentionally hyperventilating first.

Re:Movie "Sunshine"

[Anonymous Coward]

I don't know if you can hold the air in your lungs during slow decompression, I'll take your word for it. But I do know that you won't be able to hold it in during explosive decompression (your lungs might even burst). I definitely wouldn't want to try it. The best survival strategy is to exhale strongly prior to decompression, just in case it is explosive enough to burst your lungs. As I shall explain below, air in your lungs won't help you anyway.

When exposed to a hard vacuum, you will die not from asphyxiation but from the bends. It has absolutely nothing to do with how long you can hold your breath.

In addition to the O2 and CO2 bonded to haemoglobin, your blood contains gases in solution (mainly N2 down here, either N2 or O2 in a typical spacecraft and either N2 or He for divers). When the pressure around your body drops, so does the pressure of the blood and hence its boiling point. This causes the dissolved gases to boil out and form bubbles.

Gas bubbles in your blood will block arteries all over your body, cutting off the oxygen supply to your brain irrespective of how much oxygen you still have in your blood and lungs.

The bubbles will take at least 10 seconds to form after explosive decompression from one atmosphere to hard vacuum, so you have some time to get help. After that, your brain becomes starved of oxygen and you become completely delusional, passing out at 15 seconds or so. You'd be brain dead in well under a minute.

Re:Movie "Sunshine"

[Anonymous Coward]

I didn't say you would explode, I said there would be ruptures in blood vessels all over your body.

Re:Movie "Sunshine"

[petermgreen]

I wonder how much difference the starting atmosphere makes, afaict space suits and some spacecraft use low pressure pure oxygen atmospheres.

Re:Movie "Sunshine"

[tragedy]

I see no reason why your lungs would be weaker in explosive decompression versus slow decompression. Either they can withstand the internal pressure or they can't. Given that you'd probably only need to deal with one third atmosphere, as I go into below, it actually seems pretty likely to me that you'd be able to hold it in your lungs. Whether you did or not would probably depend on how prepared you were when the atmosphere suddenly went away.

I understand about the gas bubbles in your blood. However, I'm considering this in context of an astronaut. My original post on this was a reply to someone's notion that human blood is full of dissolved oxygen and that it would drain out of it if pressure dropped suddenly as a result of being blown out of a spaceship. The thing is, the oxygen in your blood really is mostly contained in hemoglobin. The red blood cells have quite a lot of surface area and the vast majority of oxygen in your blood really does end up chemically bound and therefore resistant to pressure changes. Also, as I pointed out in an earlier post, the US space program doesn't operate at one atmosphere. Instead, they operate at about one third of an atmosphere. The oxygen partial pressure matches that found in Earth's atmosphere. So, there isn't a whole lot of nitrogen or argon in spacecraft air. So, when the pressure drops a third of an atmosphere, an astronaut's blood just isn't going to have that much dissolved gas to bubble out of it and most of what bubbles out wouldn't be biologically inert nitrogen that just sits there, going nowhere, but gases involved in biology like carbon dioxide and oxygen, which would be rapidly chemically re-absorbed. Not to mention the fact that the hypothetical astronaut's internal pressure just isn't going to drop to zero. We're squishy, sure, but we're still pressure vessels, every tissue in our body is going to stretch, but hold at a certain point.

So, we're talking about a pressure change of less than 1/3rd of an atmosphere with very little nitrogen dissolved in the blood to begin with. 1/3rd of an atmosphere is about 11 feet of water. I'm not a diver, unfortunately, but I still tried to play around with some online dive calculators. As far as I can tell, after diving for a long period of time (none of them seem to allow inputting dive times in the tens of thousands of minutes or more, but, what with diminishing returns, 5 hours out to be pretty close to a saturation point), at 11 feet, you're not at significant danger of the bends, and that's breathing air that's mostly nitrogen, rather than mostly oxygen. There is the risk of a fatal air embolism with a really sudden drop in pressure, but that's once again greatly reduced by the very low concentration of gases in the astronaut's blood.

As for the boiling point, I'm not sure what you're talking about there. The boiling point of water hits human body temperature somewhere around 1 psi. That doesn't mean that your blood actually starts boiling at that point, however. Plenty of extra energy needs to be pumped into water to actually make it boil, even as the boiling point drops. So, even if internal pressure dropped that low, the astronaut's blood would technically be supercritical, but still wouldn't actually boil. As for where you said:

When the pressure around your body drops, so does the pressure of the blood and hence its boiling point. This causes the dissolved gases to boil out and form bubbles.

That's... that's not what's happening there. The dissolved gases are still gases, not liquids. They come out of solution, but no boiling is involved.

Re:Movie "Sunshine"

[Anonymous Coward]

Your observation is correct.

The boiling will still happen in a pure O2 atmosphere, it will only be oxygen bubbles instead of nitrogen. Remember that haemoglobin doesn't prevent oxygen from dissolving in the blood, it merely provides additional, more efficient storage.

Having less gas dissolved in your blood (due to the lower starting pressure) will mean that fewer bubbles form, although I can't give a number. The bubble formation is also dependent on the speed of decompression (which is why I specified that I spoke of explosive decompression).

A slow puncture in a space suit will be a lot more survivable (assuming that the fabric doesn't tear itself open any further), but treating the bends in a spacecraft might be problematic. (If I remember correctly, it's little more than putting the guy in a high pressure atmosphere and hoping that as many bubbles as possible will dissolve before excessive damage occurs.)

Re:Movie "Sunshine"

[Anonymous Coward]

Boiling: When you heat water, gases come out of solution and bubble out. As you continue to heat the water, more and more of the liquid water turns to gas and also forms bubbles. We say that the water is 'boiling' in either case. This is just miscommunication, sorry.

Explosive/slow decompression around the lungs: It's all about the forces involved. Analogy: If you hang a weight by a piece of string and it doesn't break, that doesn't mean that the string won't break when you tie it to the weight and drop the weight. Similarly, when your lungs contain 1/3 atmosphere pressure and a vacuum outside, they will presumably be swollen but not ruptured. But if you have 1/3 atmosphere inside and out, your lungs are not swollen. Sudden removal of outside pressure causes your lungs to swell up rapidly, giving the surface additional kinetic energy which must be overcome when they reach their maximum size.

The bends: I know about haemoglobin. It does not remove oxygen from the blood, it binds to oxygen in addition to that which is always dissolved in the plasma. (Under normal circumstances, about 2% of the oxygen in your blood is in solution.) There will always be gases dissolved in your blood, mainly nitrogen for us. But when you breathe pure O2, more oxygen dissolves in your blood by taking up space otherwise held by nitrogen. This is however decreased by lower pressure in a spacecraft/suit.

The problem is that your diving analogy needs modification (even though I like it):

Consider first the simple (and not exactly correct) case of a bucket of water at 0, 1/3, 1 and 1 1/3 atmosphere. At 1 1/3, the water contains lots of dissolved gas. If you take that bucket to 1, some of the gas will come out. The bucket at 1/3 will lose all of its dissolved gas when taken to 0, since the water will all boil away. As you can see, the amount of gas released is not a function of the difference. (Perhaps the ratio? I should have paid more attention to physics.)

The reason why my above analogy is incorrect is that blood pressure is not the same as outside pressure. For an accurate model of what would happen*, we simply need the function relating pressure to amount of dissolved gas in blood. Then, we must use human blood pressure at 1/3, 1, 1 1/3 and 0** external pressure.

* Ignoring previous data from accidents and assuming that human sacrifices are not proper science.
** Seems we need those human sacrifices after all. ;)

Re:Movie "Sunshine"

[tragedy]

Regarding the piece of string with the weight, that's trying to stretch an analogy just a bit. The analogy you want is a piece of string (let's give it a cross-section of exactly one square inch) with a 5 pound weight hanging from it (from a hook). Hanging there, the string is stretched a bit and has some tension on it, but isn't breaking. The correct comparison is with the same piece of string with no weight on it, then you reach over with the 5 pound weight, supporting it fully, hook it onto the string and let go. The string suddenly stretches and ends up with more tension on it, but the actual amount of force acting on it is never more than 5 pounds rather than your example where the 5 pounds is dropped from a height and, when the string catches, pulls down momentarily with 50 pounds of force. Promoting that situation as a valid example is disingenuous. Yes, it does make a difference how quickly you ramp up the internal pressure, but not a whole lot. And come on, additional kinetic energy? It is true, that there will be some, but trying to pretend it will be anything other than negligible is silly.

What you said about there being more dissolved oxygen because of the missing nitrogen gave me pause for a moment, but on reflection, that just can't be right. It's been a long time since I took any classes in the physical sciences, but I'm pretty certain there's a few things wrong with that. First of all, the amount of a gas that's supposed to end up dissolved in water is supposed to be directly related to the partial pressure of that gas in the atmosphere. So, if the oxygen partial pressure is the same, there should be no additional dissolved oxygen relative to how much there would be on earth. Secondly, hemoglobin is quite reactive, and red blood cells have a lot of surface area and dissolved oxygen isn't immune from chemical reactions, rather it's more susceptible. Put simply, if there were that much extra oxygen dissolved in your blood, it would either be sucked up by hemoglobin.

The figure you give of 2% of the total oxygen in your blood being dissolved and the other 98% being chemically bound sounds about right. Bearing in mind that the 2% figure is going to be an average based on a regular breathing pattern. If you don't breathe in air for a prolonged period of time, that 2% is going to dwindle (in increments of the remaining amount). Hemoglobin does remove dissolved oxygen from the blood, but you keep on infusing the blood with new oxygen by breathing.

Grrr, you're still bothering me with that boiling thing, by the way. You really need to make a distinction between gases dropping out of solution and boiling. When you say: "The bucket at 1/3 will lose all of its dissolved gas when taken to 0, since the water will all boil away" it makes my head hurt. If you drop the pressure to zero, unconstrained water will sublimate away quickly (but maybe not so quickly as you seem to be thinking), but it won't exactly boil, not unless it was already really hot. You need to pump in additional energy to actually induce a phase change even if you've just lowered the boiling point to below the current temperature of the water by lowering the pressure.

Anyway, if you have buckets of water at 0, 1/3, 1, and 1 1/3 atmosphere, and you drop the pressure by 25%, down to 1 atmosphere, you lose 25% of the dissolved gases. If you then drop it by 66.666...% from 1 to 1/3, then you lose 66.666...% of the remaining dissolved gases. If you then drop it 100% from 1/3 to 0 then you lose 100% of the remaining dissolved gases. It looks to me like the amount of gas released is exactly a function of the difference.

Also, as you point out, there will still be internal pressure. Your body will work to a degree as a pressure vessel. Obviously if your body weren't capable of maintaining greater pressure on the inside than exists outside it, it wouldn't function at all, because your blood wouldn't travel around your body.

Re:Movie "Sunshine"

[Anonymous Coward]

Since you take issue with my terminology, I'll return the favour. :) Liquids do not sublimate, they evaporate. Sublimation is a change from solid to gas.

And when you remove the pressure around a liquid, the temperature at which the molecules evaporate is lowered. (Called the boiling point in any part of the world. The boiling point of 100C is specified to be at standard pressure.) This causes the bucket of water to slowly lose mass to evaporation if you reduce the pressure very slowly, boil slowly (yes, I've seen it do this) if you reduce the pressure quickly and boil explosively if you reduce the pressure even faster than that. The exact same effect as heating water.

The above is just an aside, since about the amount of dissolved gas, I did not assume it to be directly proportional to pressure. You are then absolutely correct. A drop from 1/3 atmosphere to 0 sounds very much more survivable than from 1 to 0.

The string with weight analogy is correct, we're just arguing over how long the string must be. If I were you, I wouldn't ignore any variable before I've investigated it, especially in an explosive event. Sounds like we would have to pop some sheep lungs for science?

You are wrong about haemoglobin continuing to suck up any additional oxygen added to the blood, let me explain.

Haemoglobin likes to bind (in order) to CO, O2, CO2 and some other chemicals not relevant to our discussion. The molecule has a maximum number of O2-molecules to which it can bind (for some reason I think 8, but it doesn't matter).

CO reacts very strongly to haemoglobin. It will kick out an O2 molecule and occupy its place permanently (the reason for its toxicity). Haemoglobin likes to bind with more oxygen in a high-oxygen environment, and while CO2 does not technically compete with O2 for position, but dissolved CO2 (carbonic acid) still lowers haemoglobin's love for oxygen. This mechanism is what allows the blood to 'know' when to absorb oxygen and when to release it. In the high O2, low CO2 environment of the lungs, haemoglobin binds to lots of oxygen. In the slightly more acidic and lower O2 (due to cellular respiration) environment of the capillaries, haemoglobin must bind to fewer O2 molecules and hence releases some of those it already has.

When cut off from the oxygen source and CO2 sink of the lungs, and when the oxygen content of the blood has been somewhat reduced by bubble formation, haemoglobin will bind to less oxygen, not more.

I, too, haven't taken physical sciences (or biology) in a long time. This discussion sure has rattled some old brain cells back into position, thanks.

Re:Movie "Sunshine"

[tragedy]

You got me on sublimation. I should have changed that to evaporation. I'd originally started writing a more detailed bit about how an ice layer would form quickly due to evaporative cooling and how it would continue to sublimate but would protect the water trapped inside it, but it was too long winded and depends on conditions that aren't really present in our scenario of an astronaut blown out of a spacecraft anyway. So I erased most of it, but still ended up with sublimation in there instead of evaporation.

On to where you said: "the temperature at which the molecules evaporate is lowered. (Called the boiling point in any part of the world. The boiling point of 100C is specified to be at standard pressure.)" No! No! No! Or, rather, yes to the part about evaporation being increased by lower temperature, but a definite no to the temperature at which molecules evaporate being called the the boiling point. Evaporation produces water vapor, hence the name. Water vapor is still technically liquid water (arguably when the individual molecules escape they have enough kinetic energy to be considered steam, but I think it's only really considered a phase change when it happens to a mass of particles rather than just one). Steam is the gaseous phase of water and boiling is when a mass of water converts into steam. The temperature at which water evaporates is well below 100C even at standard air pressure.

On the weight and string analogy. I think my analogy with sudden loading of a string already under light tension from its own weight is much closer to the actual event than dropping a weight. I do agree that there will be some additional kinetic energy which will need to be dealt with faster in a sudden event versus a slower one. However, I also argue that it will only be a small fraction of the overall force from the increase from a relative pressure of 0 PSI to 5 PSI. Sheep lungs for science indeed. I should note as an aside here, that it's not really just the strength of the lungs themselves. The lungs are relatively fragile, being porous and spongy, but since they're porous, the pressure just evens out inside the lungs. The whole chest, including the ribs, diaphragm, other muscles and tissues, etc. must be considered. So when I talk about what the lungs can hold, I'm talking about the whole system.

As for the oxygen being absorbed by hemoglobin, I'm not sure how anything you said about it means that there won't be ongoing absorption of dissolved oxygen in the blood by hemoglobin. It seems to me that the 2% dissolved versus 98% bound figure you gave is probably right, but without an explanation of why it would be otherwise, I have to assume that's an average, probably slightly higher right after you take a breath and slightly lower right before you take the next one. Just a point of diminishing return in absorption of oxygen. However, I have to admit that it certainly seems that the hemoglobin is more likely to be able to absorb dissolved oxygen than the small bubbles when your blood goes fizzy from the pressure drop. Still, it seems like there just isn't that much gas in our scenario and the small bubbles from it aren't going to be much of a problem until they can accumulate into much larger ones and absorption is going to be ongoing to some degree. Also I think we're pretty certain by now that the pressure will drop, but not by that much because the body, and the circulatory system especially, will retain some pressure. Not to mention that the expanding gas, coming out of solution, will itself act as a pressure regulating mechanism to a certain degree. I'm still pretty sure that, since similar pressure drops don't frequently kill divers, the risks for astronauts are about the same.

Overall, I think we just have to figure it out by experimentation. Rather than sheep, I suggest we use humans. Since it would be unconscionable to intentionally do that to humans, I propose we simply properly fund manned space flight. If we do that, and wait a few hundred years, there will probably be enough evidence from accidents to get a good idea of how well astronauts hold up to vacuum.

Dammit NASA!

[adamkennedy]

Messenger is a great name, perfectly respectable with a sort of a cute "ZOMG HI Mercury! LUV Earth!" edge to it.

And then you just had to go and fucking ruin it with a horrendous backronym didn't you.

Re:Dammit NASA!

[LostCluster]

If It goes too fast and on target, would it become an AIM Instant Messenger?

Re:Dammit NASA!

[coofercat]

An opportunity too good to pass up, I suspect. Mercury was also the messenger of the gods: http://en.wikipedia.org/wiki/Mercury_(mythology)

40 years?

[Anonymous Coward]

Have I been dreaming all the other planetary missions?

Re:40 years?

[Anonymous Coward]

Those probes in uranus doesn't count.

Re:40 years?

[Enigma23]

Those probes in uranus doesn't count.

What about the rings around Uranus?

Graph of gravity wells (energy)

[mmogilvi]

http://xkcd.com/681/ has a nice graph of gravitational potential energy differences that need to be overcome when traveling around the solar system (ignoring gravity assists, etc). Mercury is clearly harder to match up with energy-wise than anywhere else besides the sun itself.

Mercury's rotation and orbital period

[williamfrench4]

The article:

Mercury also spins very slowly, and does so in such a way that a single day on Mercury lasts 176 days - two of the planet's years.

Wikipedia:

It completes three rotations about its axis for every two orbits.

Which is correct?

NASA is correct.

[ReedYoung]

http://www.nasa.gov/pdf/168019main_MESSENGER_71504_PressKit.pdf "page 6" (8/33)

Rotates on its axis once every 59 Earth days, but because of its slow rotation and fast speed around the Sun, one solar day (from noon to noon at the same place) lasts 176 Earth days, or two Mercury years

Although I'd say the article is clearer, both the article and Wikipedia are technically correct because Wikipedia talks about three rotations, not days. Calculating the length of a solar day on Mercury requires accounting for the orientation of a point on Mercury to the Sun; as Mercury rotates once, it also travels through 59/88 of an orbit, so one rotation != one solar day on Mercury and the article and Wikipedia are not in contradiction, they just tell different parts of the story. Hope this helps.