There was a convincing sounding conspiracy theory a long time back that the plutonium batteries from another probe (Galileo) being crashed into Jupiter had reached critical mass and caused a nuclear explosion. I seem to recall reading about it and thinking it had some small chance of being true, given the photos of a black spot showing up shortly after the probe dived into the atmosphere.
Just looked it up–it’s Richard C. Hoagland. Given his body of work, I’d say that alone makes it a lot less likely to be true. At best, he’s prone to flights of fancy and wild imagination, and at worst he knowingly stretches the truth so he can sell books.
I understand that we’re getting deep into technicalities here. But that’s overstating the case.
They could have just had Cassini sail by Saturn without it getting close enough to be captured by the gravity well.
I know that would have resulted in less scientific information for the whole mission. I agree with not doing that, and I agree with smashing it into Saturn instead. I’m merely expressing a feeling that it bugs me, due to the (literally) astronomically thin possibility that Saturn had some life Cassini’s explosion could affect. I agree that the gain of scientific knowledge is worth this very minimal risk.
But let’s not overstate the case and say there were no other options. Again, it could have been chosen that Cassini didn’t get that close.
Saturn is huge. Yuuuuuuuge. 70 pounds of plutonium vapor is a drop in a very, very large bucket. Saturn is ~100 times more massive, and ~800 times more voluminous than Earth. Earth is by all accounts, very big compared to a space probe.
I think the scale of Saturn compared to its moons is important to emphasize. Titan is the biggest of Saturn’s moons. It constitutes over 90% of the mass of Saturn’s moons, and it’s still only1600 km across - smaller by far than the continental United States. The rest of the moons are far smaller than that - Titan constitutes over 90% of the mass of Saturn’s collection of moons. Enceladus is smaller than Washington State at 252 km in diameter.
By contrast, Saturn itself is over 36,000 km across. Statistically, hitting something critically important on Saturn is FAR less likely than hitting something on one of its moons.
Cassini has been in Saturn’s gravity well since 2004. That’s what being in orbit means. Escaping Saturn’s gravity well may not be impossible, but it’s really hard, because Saturn has a lot of mass. Even with gravitational slingshots, I very seriously doubt Cassini had enough fuel left on-board to execute such an escape maneuver.
NASA also couldn’t put Cassini in a parking orbit with sufficient confidence that it wouldn’t eventually get nudged into one of Saturn’s moons, because the gravitational interactions of the entire system are extremely complex. The only safe and available option was de-orbiting it.
Was it in Saturn’s gravity well when it was launched? : )
Obviously the plan from the beginning was that it would get captured by Saturn’s gravity well. And again, it’s a plan I agree with because it provided the most information on Saturn.
All I’m saying is, again, it’s overstating the case to say this was the only way it could have happened. It could have been planned another way. That’s what a plan means - choosing to do some things instead of others.
Obviously, we can send probes past planets without them getting captured by their gravity.
And yet bigger than Mercury, which always amazes me, given that the latter is a planet. That’s one of many things that makes Titan so cool. Another: its distance from the Sun.
Yes but you can’t get close enough to a moon like Enceladus for a sufficiently long time to be able to learn anything significant with just a flyby. Cassini changed its mission plan after its early observations demonstrated than an ocean existed. It was able to sample the material being ejected from the moon, to pave the way for later investigation.
Even if Cassini had been flown out of Saturn orbit and then shut down it would have remained a hazard, especially to Saturn and its moons. Its normal to scuttle derelict ships in the ocean. It gets them out of the way in the safest way possible.
Its distance from the sun definitely makes Titan very cool
As planets go I think Ceres is one of the most interesting places. Its easy to land on, relatively easy to fly to, and it may have liquid water under its surface. And like Enceladus its water will be salty, if the salt deposits on the surface are a guide.
You are suffering from a fundamental misunderstanding of how gravity wells work. The last probe to visit Saturn without being caught in its gravity well was Voyager 2. That flyby was measured in weeks, not years.
Cassini has been orbiting Saturn for 13 years, which means it has been in Saturn’s gravity well for 13 years. In order to enter orbit around Saturn in 2004, Cassini had to execute a full-tilt, 96-minute burn of its main engine, expending a huge amount of fuel to go from an interplanetary cruising speed to one which enabled it to spend the last decade+ in orbit. Since then, it has been expending fuel regularly to modify its orbit so that it can closely observe the planet, its rings, and its moons. Now it’s almost out of fuel because of those maneuvers and the constant need to reorient the craft to point instruments in the right direction and then transmit its findings back to Earth. As I’ve said, even with assistance from Saturn’s moons, there would almost certainly not be enough fuel left on-board the spacecraft for it to achieve escape velocity and leave the planet behind entirely. This is why NASA chose to de-orbit it now. The risks to Saturn are less than negligible, and it’s simply far safer to do that than let it stay in orbit until a chance encounter potentially knocks it into a much more scientifically fragile moon.
Sure. But I already agreed with that. As I said, I agree with the purpose of the mission, and that getting close enough to be in the gravity well was worth it to get that information.
I’m just disagreeing with the flat overstatement that there was no other way. This was a way that we chose because we wanted to get that much more information.
Voyager and Pioneer did flybys and we learned something about the Saturn system. Then we had to get closer for a better look so we sent Cassini. The next steps will include a lander on Enceladus and probably a second Titan lander. Both will look more closely for living things and both will have to consider the long term implications of contamination.
In fact now that we know about the Enceladus ocean I question whether it was a good idea for Cassini to drop that lander on Titan. No doubt it was sterilized before flight, but possibly not as well as the next lander will be.
And after that there are going to be subsurface probes. More issues around contamination and the long term disposal of radioactive fuel.
I should also point out that this is not the first probe we’ve crashed into a gas giant, nor will it be the last. Galileo was de-orbited at the end of its mission in the Jovian system in 2003. Juno will be de-orbited at the end of its 37-orbit mission around Jupiter in 2019. The still-in-development Europa Clipper will also be de-orbited into Jupiter (if it ever gets launched) in order to protect the moon it’s being sent to study. It may seem wasteful or reckless, but de-orbiting is absolutely the safest and most economical solution to the question of how to execute long-term detailed scientific exploration of the outer planets. It enables us to get the maximum amount of science out of our investment in these craft, and there is essentially zero risk.
The Planetary Protection Protocol has been around for a long time. We’ve been using it to sterilize probes basically since the beginning of unmanned exploration, and Huygens would have been subject to the same Category IV sterilization standard as any lander we eventually send to Enceladus, Europa, or Titan with the express intent to search for life.
You are suffering from a fundamental misunderstanding of what I’m saying, that can only be due to you not actually reading it.
Please scroll up and read my previous comments, where I acknowledge that it was scientifically worth it to get this close to Saturn.
I understand and have already acknowledged in previous comments that getting the amount of information that we wanted meant Cassini getting close enough to Saturn that the probe was captured by Saturn’s gravity. And I have already said I agree with this decision.
I am simply disagreeing with the overstated case that THE ONLY WAY Cassini could have operated was for it to be sent into Saturn’s gravity well.
Is any part of that unclear? If so, let me know and I will state that part in a way that is clear.
So then, what other way could Cassini been have dealt with to not impact any moon of Saturn AND get us all the data it did without being plunged into the gas giant?
