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Cassini is going to crash into Saturn later this month to avoid contaminating one of its moons.

Why isn't anyone worried that Cassini will contaminate Saturn itself? Life might exist in Saturn's atmosphere. Different altitudes, pressures & temperatures may have environments where life has evolved. It's closed minded to rule this out.

If we REALLY wanted to not contaminate anything, we should sling it out of the plane of the solar system entirely.

Camille Goudeseune
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user1683285
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    Because it will burn up, thereby destroying anything that could potentially contaminate Saturn. – Polygnome Sep 05 '17 at 11:36
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    The entry of Cassini into the gas giant Saturn will be so hot that any biological contamination with microbes will be destroyed. Cassini has no heat shield. – Uwe Sep 05 '17 at 11:37
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    Its not that easy to "sling" anything outside of the Solar System, specially because they're terminating the mission due to lack of rocket fuel. If the choice is between Saturn and its moons logic dictates that Saturn should be the resting place. Not only the entry into Saturn will cook Cassini but gas planets are not typically seen as suitable to life. – armatita Sep 05 '17 at 11:39
  • @Polgnome The plutonium 238 of the RTGs will not be destroyed by heat. – Uwe Sep 05 '17 at 12:07
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    @Uwe, yes, but responders are reading "contamination" in the question as "biological contamination". A few kg of plutonium introduced to Saturn is not considered to be a problem for future studies of the planet, or to life that might already exist in the atmosphere. – BowlOfRed Sep 06 '17 at 16:46
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    Cassini is going to hit 3x as fast as spacecraft returning from Earth's orbit--energy goes at the square of velocity. Cassini has no heat shield. Any hypothetical inhabitants of Saturn will see some fireworks, that's it. The entry fires will burn it to dust. – Loren Pechtel Sep 07 '17 at 01:18
  • It would take a full-sized booster rocket to eject Cassini from its orbit. The escape velocity from Saturn at Titan's orbit is pretty close to the escape velocity from Earth, so it would take almost as much rocket fuel to get Cassini out of Saturn's orbit as it did to get it out of Earth's gravitational influence. – BillDOe Sep 17 '17 at 19:02
  • only slightly related: When Juno finally de-orbits into Jupiter, will metal sink to the core, or remain in the atmosphere? – uhoh Aug 14 '19 at 16:45

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If we were going to send a probe into Saturn's atmosphere and were concerned about contamination of a potential ecosphere there, we would sterilize the probe first, e.g. with dry heat microbial reduction, to make sure that nothing viable was on the probe.

Cassini has no protection from the entry heat like a probe would, and will be entering at an incredible velocity, so every tiny bit of Cassini will be massively sterilized in the fiery entry, far beyond puny humans ability to do so.

Mark Adler
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  • Human ability to sterilize Cassini was limited, Cassini should not be destroyed or damaged by sterilisation. Much higher temperatures were possible but not allowed. – Uwe Sep 08 '17 at 21:47
  • A solid 20 years in deep space should take care most of what we could have missed as well. – kert Sep 17 '17 at 20:21
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    @kert: don't be so sure. Endospores are exceptionally durable and were found surviving in vacuum of space for a long time. Nothing survives a couple of gigawatts worth of heating though. – SF. Sep 18 '17 at 01:42
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    One point twenty one jigawatts! – Mark Adler Sep 18 '17 at 04:00
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    @SF. and if it does survive, it has earned its right to live – frarugi87 Sep 19 '17 at 13:41
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I was thinking this same thing myself. I did some cursory research and apparantly there is an unidentified strain of a genus of thermally resistant bacteria, Microbispora, that survived the reentry and crash of the Columbia, as well as a strain of thermophilic bacteria, Thermoanaerobacter siderophilus, placed in basalt disks on the exterior of the Russian satellite, Foton-M4, with 1/6 of the cultures surviving.

Granted, Saturn's atmosphere is significantly thicker, but it still seems at least very vaguely plausible that certain extremophiles could survive or be whisked off into the less dense upper atmosphere, kept afloat by the potent winds and storms.

I realize at a certain point it all becomes a matter of "good enough", as there are very few, if any, practical ways to avert any and all risk of contamination, but it still seems like an odd and interesting subject. Love to hear if anybody knows anything more about this! :DDD

Sources:

Microbispora - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144675/

Thermoanaerobacter siderophilus - https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132611

Robert DiRosa
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Cassini encounters Saturn at such high speed that its rapidly surrounded by plasma “hotter than the Sun”. Nothing living aboard Cassini can get through that without being disassociated into plasma. Eventually, all of Cassini will be consumed by that.

Life can be resilient, but it can’t survive being torn apart into bare nuclei and electrons.

From NASA:

The spacecraft rams through Saturn’s atmosphere at four times the speed of a re-entry vehicle entering Earth’s atmosphere, and Cassini has no heat shield. So temperatures around the spacecraft will increase by 30-to-100 times per minute, and every component of the spacecraft will disintegrate over the next couple of minutes…

Temperatures around what remains of the spacecraft eventually exceed those on the surface of the Sun. Heating and expansion of gases inside the propellant tanks may cause them to explode. The tanks make up the spacecraft's central body, so their rupture would blast apart what's left of the spacecraft. The debris is then completely consumed in the planet's atmosphere. Cassini's materials will sink deep into Saturn and mix with the hot, high-pressure atmosphere of the giant planet to be completely diluted.

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Bob Jacobsen
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