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A Moon of Saturn Has a Sea, Scientists Say

nytimes.com

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Re: A Moon of Saturn Has a Sea, Scientists Say

#31

Post by didgeoridoo »

rkuykendall-com wrote: post #27
maaku wrote: post #4

Earlier quoted context omitted.

> Why bring it back to earth? Wouldn't it be safer & less expensive to return it to ISS instead, (or is that what's implied) ? No, that would involve a very complicated and expensive breaking maneuver to slow down the spacecraft, not to mention getting in exactly the right orbit to rendezvous with the ISS. It's much, much easier to just the payload sturdy enough to survive atmospheric entry and a crash landing.

What about crashing it into the moon? Higher cost, but much less chance of earth contamination. We could then check it out with cheap robots.

An object coming in from a rendezvous with Saturn would be traveling at a ludicrous speed. You would probably vaporize on lunar impact. The Earth's atmosphere can help slow it down to a reasonable velocity--otherwise you have to carry a lot more fuel to burn in a slow-down maneuver.

Re: A Moon of Saturn Has a Sea, Scientists Say

#32

Post by maaku »

mkingston wrote: post #26
maaku wrote: post #4

Earlier quoted context omitted.

> Why bring it back to earth? Wouldn't it be safer & less expensive to return it to ISS instead, (or is that what's implied) ? No, that would involve a very complicated and expensive breaking maneuver to slow down the spacecraft, not to mention getting in exactly the right orbit to rendezvous with the ISS. It's much, much easier to just the payload sturdy enough to survive atmospheric entry and a crash landing.

Expensive breaking is precisely what they're trying to avoid! (Sorry, normally I wouldn't nitpick spelling when the meaning is clear, it was just a funny error!)

Hah! I had to reread twice to spot the mistake. That's too awesome; I'm going to leave it as-is.

Re: A Moon of Saturn Has a Sea, Scientists Say

#34

Post by Crito »

civilian wrote: post #18
TrainedMonkey wrote: post #6

Earlier quoted context omitted.

I doubt in orbit rendezvous with ISS would be safer and cheaper. It might be safer from planetary contamination standpoint, but complexity of such maneuver would handily offset that. On top of that there is a host of other issues due to the cramped space on ISS. For example: not enough space for proper isolation of sample, not enough equipment to properly study sample, and the fact that limited manpower would be avai…

Eh, I've played KSP, an orbital rendezvous in LEO on your return isn't that hard. If you have enough precision and fuel leftover to start a safe decent, you have enough precision and fuel to dock with the ISS. I'm surprised that we aren't equally worried about contaminating Enceladus with terran microbes.

If you are coming in fast from interplanetary space, you'll either need to aerobrake or burn a good deal of fuel to get yourself into LKO. While aerobraking from interplanetary space to put yourself into a nice orbit is easy enough in KSP, in real life things are much more difficult (just for starters, in KSP your station is probably at 0 degrees inclination unless you went out of your way to put it somewhere else...).

Get FAR, RSS, Deadly Rentry, put your space station somewhere around 50 degrees inclination, then try it with suitably small probe. The Stardust spacecraft was 300kg; the sample return capsule was 46kg and reentered at nearly 13km/s.

Just one full small kerbal RCS tank puts you at 250kg, so you'll need to nearly empty that just for starters...

Re: A Moon of Saturn Has a Sea, Scientists Say

#35

Post by danieltillett »

conkrete wrote: post #30
danieltillett wrote: post #25

Earlier quoted context omitted.

Of course it is only a theory, but a very plausible one given the frequency of rock transfer between planets and the toughness of microbes that allow them to survive in space for long time periods (both empirical facts). There is really no way of proving transpermia - even if we to travel to Enceladus and found microbial life there how would we ever prove how it got there.

If we find DNA based microbial life it could certainly be amazing evidence in favor of transpermia. We would at least compare to DNA on earth and analyze similarities. Even plant and animal DNA are very similar (double helix shape)

Actually the easiest way to find life is to just look for DNA (or even better RNA) in the environment of interest. This is basically the way life is found in some of the amazing environments here on earth like the "lost city [0] or far under the earth [1].

Because of the technical simplicity and sensitivity of looking for DNA, any probe sent to any planet or moon would look for DNA first, basically assuming transpermia is true.

[0] http://en.wikipedia.org/wiki/Lost_City_(hydrothermal_field)

[1] http://aem.asm.org/content/74/1/143.full

Re: A Moon of Saturn Has a Sea, Scientists Say

#38

Post by megablast »

hellbanner wrote: post #11

"They found that the moon’s gravity was weaker at the south pole. At first glance, that is not so surprising; there is a depression at the pole, and lower mass means less gravity. But the depression is so large that the gravity should actually have been weaker." They found the gravity was weaker.. but it should actually have been weaker. So is it weaker or stronger?

Weakerer is not yet a word.

Re: A Moon of Saturn Has a Sea, Scientists Say

#39

Post by hrjet »

didgeoridoo wrote: post #31
rkuykendall-com wrote: post #27

Earlier quoted context omitted.

What about crashing it into the moon? Higher cost, but much less chance of earth contamination. We could then check it out with cheap robots.

An object coming in from a rendezvous with Saturn would be traveling at a ludicrous speed. You would probably vaporize on lunar impact. The Earth's atmosphere can help slow it down to a reasonable velocity--otherwise you have to carry a lot more fuel to burn in a slow-down maneuver.

Similar to how a swing-by is used to accelerate a space-vehicle, I wonder if a swing-by could be used to decelerate as well.

Re: A Moon of Saturn Has a Sea, Scientists Say

#40

Post by vilhelm_s »

hrjet wrote: post #39
didgeoridoo wrote: post #31

Earlier quoted context omitted.

An object coming in from a rendezvous with Saturn would be traveling at a ludicrous speed. You would probably vaporize on lunar impact. The Earth's atmosphere can help slow it down to a reasonable velocity--otherwise you have to carry a lot more fuel to burn in a slow-down maneuver.

Similar to how a swing-by is used to accelerate a space-vehicle, I wonder if a swing-by could be used to decelerate as well.

According to Wikipedia, the MESSENGER mission to Mercury used a complicated series of fly-bys of Earth, Venus and Mercury to slow down.
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