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Re: Rocket Lunches

#228
Cassini Loss of Signal moment: https://youtu.be/gM_6lkAZQrs

It's not always asked: why did Cassini have to be vaporized by sending it into Saturn? From Dr. Nathalie Cabrol, of the SETI Institute: it was to prevent microbes from Earth from contaminating the moons of Saturn. I have some problems with this attitude, but it's an explanation worth knowing.

Dr. Cabrol is also an executive producer for an IMAX movie being made from Cassini imagery called In Saturn's Rings. Even the trailer for this thing is stunning....
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Re: Rocket Lunches

#230
Talvieno wrote:
Fri Sep 15, 2017 3:18 pm
Flatfingers wrote:
Fri Sep 15, 2017 3:11 pm
I have some problems with this attitude, but it's an explanation worth knowing.
I'd be interested in hearing you elaborate. :)

Nothing cray-cray; I just don't want physical (especially human) exploration of other worlds discouraged by an unnecessary view of human activity as "contaminating" other places in the Solar System that might -- might -- harbor life.

I'm sympathetic to the pure science argument that if non-terrestrial life exists, it's desirable to study it before risking the introduction of terrestrial life. That's reasonable, up to a point. But I am not sympathetic to any hint of an anti-human-activity argument: "we destroy all we touch" sort of thing.

Basically, I oppose any argument that would hold us back from going out there ourselves to see what's what.

Also, I note that the full mission to Saturn's neighborhood was actually Cassini-Huygens: the ESA dropped the Huygens probe on Titan in 2005, for heaven's sake. I think it's safe to say we've already "contaminated" that corner of our neighborhood.

Let's go find out what happened next.
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Re: Rocket Lunches

#231
Yes, I was thinking that too. Personally I take less issue with contamination policies, though, and I'm much more unhappy about the idea that these expensive things are being destroyed instead of being left in a safe, recoverable orbit so that generations of the future can eventually recover them and put them in museums. Because I would love to be able to visit a museum and see Cassini there.
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Re: Rocket Lunches

#232
My naive understanding is that there's really no such thing as a parking orbit for a small satellite.

Between variable mass concentrations of whatever you're orbiting, and perturbations from other objects, the more time that goes by the more these influences add up. Without external intervention, eventually your orbit decays to impact.

By "external intervention" I mean two things: propellant (and working engines & flight software), and mission operations staff with access to signaling systems. Propellant is finite, and money gets cut off.

I know what you mean, of course. It really would be cool to keep these explorers around. But there are limits to doing so. Better, maybe, to decide for ourselves when the end should come for our robotic minions.
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Re: Rocket Lunches

#233
Flatfingers wrote:
Fri Sep 15, 2017 3:38 pm
Talvieno wrote:
Fri Sep 15, 2017 3:18 pm
Flatfingers wrote:
Fri Sep 15, 2017 3:11 pm
I have some problems with this attitude, but it's an explanation worth knowing.
I'd be interested in hearing you elaborate. :)

Nothing cray-cray; I just don't want physical (especially human) exploration of other worlds discouraged by an unnecessary view of human activity as "contaminating" other places in the Solar System that might -- might -- harbor life.

I'm sympathetic to the pure science argument that if non-terrestrial life exists, it's desirable to study it before risking the introduction of terrestrial life. That's reasonable, up to a point. But I am not sympathetic to any hint of an anti-human-activity argument: "we destroy all we touch" sort of thing.

Basically, I oppose any argument that would hold us back from going out there ourselves to see what's what.

Also, I note that the full mission to Saturn's neighborhood was actually Cassini-Huygens: the ESA dropped the Huygens probe on Titan in 2005, for heaven's sake. I think it's safe to say we've already "contaminated" that corner of our neighborhood.

Let's go find out what happened next.
i dont know about you but i prefer not accidentally damaging something we dont know, cant repair and cant replicate over keeping something that we built in the first place and that has purely sentimental value to us at that point.

We destroyed enough things by carelessness, why not be careful when its easy and convenient?
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Re: Rocket Lunches

#234
Flatfingers wrote:
Fri Sep 15, 2017 3:55 pm
My naive understanding is that there's really no such thing as a parking orbit for a small satellite.
This is not correct in general; e.g. geostationary orbits around Earth are fairly stable; but it is indeed correct for a complex system such as Saturn, especially where Cassini was.
Flatfingers wrote:
Fri Sep 15, 2017 3:38 pm
I'm sympathetic to the pure science argument that if non-terrestrial life exists, it's desirable to study it before risking the introduction of terrestrial life. That's reasonable, up to a point. But I am not sympathetic to any hint of an anti-human-activity argument: "we destroy all we touch" sort of thing.

Also, I note that the full mission to Saturn's neighborhood was actually Cassini-Huygens: the ESA dropped the Huygens probe on Titan in 2005, for heaven's sake. I think it's safe to say we've already "contaminated" that corner of our neighborhood.
Planetary protection is a scientifically valid argument.

Obviously, Huygens probe was sterilised much more thoroughly than the rest of the spacecraft. Nope, silly NASA didn't do that, no additional sterilisation apart from the usual measures, thanks to Cornflakes for pointing me to the relevant page.

However, Titan is ridiculously cold, and I know of no terrestrial bacteria or archaea capable of reproducing at such temperatures as such conditions are not encountered on Earth. Any bacteria/bacterial spores or archaea would be frozen; the only possibility for them to survive and start reproducing would be by submerging them deeper into the Titan's mantle where temperatures would be higher. Considering geological timescales at which that happens, and constant influence of liquid carbohydrates (methane, ethane) that are quite effective at dissolving frozen organic matter, I'd say the chances of that are fairly low to be acceptable.

There are, however, other moons in Saturn system with conditions much more similar to our own planet - namely, Enceladus, which is the first moon for which we got a direct confirmation of the existence of a water ocean beneath the crust. And Cassini's orbit lies dangerously close to it - in fact, it's because we changed it to allow closer passes on Enceladus to sample water that geysers spew out :ghost:

So, we have a place where a water ocean is directly confirmed, and a probe that might contaminate it, staying in unstable orbit that passes close to it. Looks like a valid concern to me :ghost:
Survivor of the Josh Parnell Blackout of 2015.
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Re: Rocket Lunches

#236
outlander wrote:
Sat Sep 16, 2017 6:09 am
Flatfingers wrote:
Fri Sep 15, 2017 3:55 pm
My naive understanding is that there's really no such thing as a parking orbit for a small satellite.
This is not correct in general; e.g. geostationary orbits around Earth are fairly stable; but it is indeed correct for a complex system such as Saturn, especially where Cassini was.

I notice you use the qualifier word "fairly." ;)

outlander wrote:
Sat Sep 16, 2017 6:09 am
Planetary protection is a scientifically valid argument.

Please feel free to make this argument in greater detail.

Note that I'm not preemptively disagreeing. I'm just curious how you support your statement beyond the phrase "planetary protection."

outlander wrote:
Sat Sep 16, 2017 6:09 am
There are, however, other moons in Saturn system with conditions much more similar to our own planet - namely, Enceladus, which is the first moon for which we got a direct confirmation of the existence of a water ocean beneath the crust. And Cassini's orbit lies dangerously close to it - in fact, it's because we changed it to allow closer passes on Enceladus to sample water that geysers spew out :ghost:

Image

??? You're claiming that the proximity of an infinitesimally tiny spacecraft (Cassini) to Enceladus caused the jets of water vapor that were imaged as Cassini approached this moon of Saturn?

Please tell me this was a joke.
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Re: Rocket Lunches

#238
Flatfingers wrote:
Sat Sep 16, 2017 11:38 am
??? You're claiming that the proximity of an infinitesimally tiny spacecraft (Cassini) to Enceladus caused the jets of water vapor that were imaged as Cassini approached this moon of Saturn?

Please tell me this was a joke.
It wasnt a joke.
He also isnt claiming that :ghost:

Hes claiming that the geyser discovery caused us to put cassini so dangerously close to enceladus in the first place.
Which put it into a position where a tiny orbital perturbation could it bring down on enceladus to contaminate the eventual local ecology
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Re: Rocket Lunches

#239
Hey, I'm a believer in the Principle of Charity: interpreting what other people say in the most friendly and reasonable way.

But I look at this sentence:

"it's because we changed [Cassini's orbit] to allow closer passes on Enceladus to sample water that geysers spew out"

and it's hard not to see a perfectly plausible reading of that as "Cassini provoked the water jets."

Obviously I'd rather not think that was the intended meaning! So I asked outlander to clarify.
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Re: Rocket Lunches

#240
Yeah, Cornflakes clarified it for you well enough :)

Basically, geysers were found when Cassini passed by Enceladus for the first time in what would have been otherwise a totally routine and boring approach; the whole program was changed to accommodate closer passes over Enceladus' South Pole to take samples of the water that geysers were spitting out. It was a tremendous success for science.

As for planetary protection, it's both easy and complicated...but it boils down to two separate problems - detection and contamination.

Detection is about getting positive results from experiments designed to find life. We can't cram a full microbiology lab into a small spacecraft, so experiments we design won't be able to tell us whether the life is indigenous to the place we are studying or was brought there from Earth by some previous mission. It'd be just 'life is detected because such and such reactions are taking place'. It'd require a sample return mission to tell with any degree of certainty, and that's in another league entirely when it comes to cost, and has its own set of problems (bringing potentially harmful biological stuff to Earth). So it's better to prevent such a situation from happening.

Contamination is not a well-studied problem because all examples of that are from Earth. Basically, when you introduce new species into a previously-isolated ecosystem, it's guaranteed to upset the ecological balance there, all the way down to full extinction of local species. If you need examples, check out the rat problem on South Georgia, or dingo problem in Australia, or phylloxera plague that once all but killed European wine industry... there are literally hundreds of such local ecological disasters! And that's on the same planet. While our pathogenic bacteria and viruses probably won't affect whatever lives on another planet, totally harmless non-pathogenic bacteria found in the soil or rock or water would compete for exactly the same resources as the local life, and would upset the balance of the local eco-system in ways we can't even predict.

My personal view on that matter is that since we don't see any obvious sign of biological activity on other planetary bodies, if there is life, then it exists in a precarious state of equilibrium with its harsh environment, and probably isn't very advanced. Life on Earth had many billions of years of brutal fight for survival in ever-changing climatic and atmospheric conditions, resulting in organisms that are very capable yet very efficiently built. Their effect on the extraterrestrial environment might be absolutely disastrous.

Just once example from the Earth's history - a great part of oxygen we breathe is produced by the small organisms called diatomes. They weren't the first organisms to utilise silica to build their shells, sure, but they managed to tap the reservoir of silica in the ocean waters that was mostly untouched previously. They spread like a plague and colonised pretty much the entire planet, resulting in massive carbon dioxide uptake and oxygen production, leading to a significant reduction of the greenhouse effect and the resulting global freeze known as Snowball Earth.

Something similar could happen to extraterrestrial biosphere, and the resulting mass extinction would be our fault.

As for 'fairly stable' orbits, I used this word because satellites in geostationary orbit would wobble around due to precession and whatnot. But they won't fall to Earth on their own, and unless some other passing body (say, an asteroid) perturbs their orbit they'd stay there indefinitely. Low Earth Orbit is different - there's still some air there, so anything you put there gets slowed down by friction.
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