Cassini's Grand Finale - Fascinating New Insight

[rootone]

Saturn now has some Plutonium, in it's atmosphere.
That sure will be interesting to alien astronomers.

 

[Stavros Kiri]

Saturn now has some Plutonium, in it's atmosphere.
That sure will be interesting to alien astronomers.

Or to possible future inteligent lifeforms (from the moons). If they solve the mystery they will attribute it to an "ancient alien probe" ...

 

[nikkkom]

Any Pu compounds are not likely to stay in the upper atmosphere for long. They are too heavy.

 

[Stavros Kiri]

Any Pu compounds are not likely to stay in the upper atmosphere for long. They are too heavy.

Good point. Also I was kind of joking in the post above that, but: (Question to everyone)

Is it possible that this whole Cassini business (story) has left some trace in the planet, for its pass, possible to be discovered and "decoded" later by some future civilization?

[Plutonium traces is one case, as it didn't naturaly fit in the planet before - it doesn't match the rest of the expected planet's composition ... . But is that the only trace?]

Another question: why didn't they keep Cassini in natural orbit around Saturn? [Kind of like an allegedly "black knight satelite" ... to be seen or even used in the future ... (even NASA, ESA etc. could perhaps still make some use of it in the future! ...)]

Can it be that the "bacteria contamination (to the moons Titan and Enceladus)" is just an excuse?

 

[fanieh]

Had Cassini exploded on takeoff from the failing rocket engine, wouldn't it have spread the Plutonium to the Earth atmosphere? What is the effect of this? How much radiation can each person receive. Maybe it shouldn't have taken off as it can give precedence for other probes to go up too.

 

[Drakkith]

Had Cassini exploded on takeoff from the failing rocket engine, wouldn't it have spread the Plutonium to the Earth atmosphere?

Possibly, but the RTG's are fairly robust if I remember correctly. They may have had a good chance of surviving relatively intact.

What is the effect of this? How much radiation can each person receive.

The answer is complicated, as it involves many different factors, such as the type of radiation, area the radiation is received at, whether the exposure to the radioactive element is external or internal, and many others. The plutonium in the RTG's is in the form of Plutonium Dioxide, which poses far less danger than many other radioactive isotopes, as it emits alpha particles (which can't even penetrate your skin) and is insoluble in water, being excreted from the body fairly rapidly (minimizing the risk of alpha particle radiation if ingested). Inhalation of particulates is slightly more dangerous I believe.

While I don't know the danger of an explosion on takeoff, NASA did a risk analysis on what would happen if the spacecraft malfunctioned and impacted Earth during its flyby:

The terrestrial flyby was the final instance when the probe posed any conceivable danger to human beings. The maneuver was successful, with Cassini passing by 1,171 km (728 mi) above the Earth on August 18, 1999.[47] Had there been any malfunction causing the probe to collide with the Earth, NASA's complete environmental impact study estimated that, in the worst case (with an acute angle of entry in which Cassini would gradually burn up), a significant fraction of the 33 kg[34] of plutonium-238 inside the RTGs would have been dispersed into the Earth's atmosphere so that up to five billion people (i.e. almost the entire terrestrial population) could have been exposed, causing up to an estimated 5,000 additional cancer deaths over the subsequent decades[48] (0.0005 per cent, i.e. a fraction 0.000005, of a billion cancer deaths expected anyway from other causes; the product is incorrectly calculated elsewhere[49] as 500,000 deaths). However, the chance of this happening were estimated to be less than one in one million.

So we expect there to be about 1 billion cancer deaths from all other causes within the next several decades and the worst case projection is an additional 5,000 deaths spread out over this time period (around an extra 100-250 per year). An explosion on takeoff would almost certainly pose far less risk, as the plutonium cannot spread as far and launches always occur over the ocean, not land, minimizing the risk of direct exposure to the population. That also assumes that the RTG's are completely destroyed in the incident, which may not happen.

Maybe it shouldn't have taken off as it can give precedence for other probes to go up too.

Good. RTG's are excellent power sources for space probes that venture to the outer solar system.

 

[1oldman2]

but the RTG's are fairly robust if I remember correctly. They may have had a good chance of surviving relatively intact.

The folks at NASA/DOE have things worked out pretty well,
https://www.nasa.gov/sites/default/files/files/4_Mars_2020_MMRTG.pdf
https://solarsystem.jpl.nasa.gov/rps/safety.cfm

 

[fanieh]

anyway RIP Cassini!

 

[scottdave]

Here is an article about other manmade probes which have landed (or crash landed) on other planets. I did not realize how many there were. Not all are from the United States. In fact, the first one to touch Mars was from Russia (with Love... Ha!)
http://vis.sciencemag.org/space-graveyard/

 

[fanieh]

My only memory of Cassini was when my friends were signing petition to avoid its launch sometime in 1997. I could recall the fear in everyone. Anyway. I got this video PBS Nova Cassini Death Drive to Saturn https://www.space.com/38150-new-film-nova-death-dive-to-saturn.html It may be a good intro to Cassini for those ignorants like me who didn't know the experiences it underwent the past 20 years... see also http://www.pbs.org/wgbh/nova/?utm_source=promourl&utm_medium=direct&utm_campaign=nova_2017

I'll watch the video after finishing watching some TV series I got... anyway... when will Cassini II (or similar) mission be launched.. would it dig into Europa ocean and catch some whale in action?

 

[Drakkith]

My only memory of Cassini was when my friends were signing petition to avoid its launch sometime in 1997. I could recall the fear in everyone.

Fear of what?

 

[Stavros Kiri]

Fear of what?

I assume he means explosion upon take off (cf. his first post earlier ...)

 

[fanieh]

Fear of what?

fear of Cassini failure in the atmosphere contaminating Earth with all its nuclear payload batteries...

anyway. if an ICBM was hit by an THAAD kinetic missile in the upper atmosphere. what would produce more radiation.. the disintegrating ICBM or the exploding Cassini in the upper atmosphere?

 

[rootone]

fear of Cassini failure in the atmosphere contaminating Earth with all its nuclear payload batteries.

The amount of plutonium is only a kg or so.
Had there been a launch accident it would very likely have come down in one piece.
So not widespread contamination, certainly no nuclear explosion, and I am sure there would have been an emergency fast cleanup plan.

 

[Drakkith]

anyway. if an ICBM was hit by an THAAD kinetic missile in the upper atmosphere. what would produce more radiation.. the disintegrating ICBM or the exploding Cassini in the upper atmosphere?

That's a bit off topic.