Neat Space Science Thing of the Day · 3:36am Sep 25th, 2024
Apparently Earth once had rings like Saturn.
And they caused a major extinction event, but you can't have everything be good...
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Apparently Earth once had rings like Saturn.
And they caused a major extinction event, but you can't have everything be good...
Interesting. I'd not read about a theory for them that late, only Hadean eon. Impressive they could survive for long post-Moon, given its sheer mass. I suppose they must have been outside Lunar orbit, or somehow threaded the gravitational needle?
theres also a report about how Mars might not be as dead as we once thought...Olympus Mons is still growing and it might erupt again, that means that the mantel of Mars is still very much active...
I suppose there could have been 2 events where the Earth had orbital rings. The creation of the moon itself, and when the asteroid that wiped out the dinosaurs hit the Earth.
5806378 Nope. Way, WAY inside Lunar orbit. You only get rings if something passes inside the Roche limit of a planet. The Roche limit depends on the size of the object being torn apart, but a decent rule of thumb is "within five radii of the parent body". For Earth that'd be roughly the same level as geosynchronous orbit, or a little lower. But you're right that the Moon's gravitational influence would make the rings very short-lived indeed- on the order of a few decades at most.
5806382 The (sadly limited) returns from seismometers on Mars suggests that not only is its mantle still fluid, but its core itself is still fluid- that is, it has no solid metallic core. (The most recent theory I read about that has it that the nickel and iron in the core is mixed with sulfur and other contaminants that both keep it liquid at lower temperatures and render it non-magnetic. But that just leads to the question: how did Mars have a magnetic field in the past, if the sulfur's been there all that time? And we know it DID have a magnetic field at one point...)
5806416 The dinosaur-killer's ejecta wouldn't have formed rings. First, it would have sprayed out in all directions rather than in a single plane. Second, its trajectories would have been wrong- anything that didn't get thrown out at escape velocity would inevitably have come back down on a ballistic trajectory, without orbiting. It wouldn't have had sufficient lateral momentum.
My first thought was the 'string of pearls' impact on Jupiter. Remember, our moon is WIERD. It's far closer and larger than ordinary planetary moons, making us more of a two-planet orbital. Any random chunk of rock wandering into the vicinity has a fair chance of either gravity-braking or gravity-acceleration as the swinging moon picks it up and either adds or subtracts velocity. The moon does a fairly good job of keeping the above-geosync free of competitors, and practically nothing actually orbits it because the concept of a stable orbit around the moon involves a lot of calculations and billions of dollars to Boeing (and even then, their plan for a lunar station is one step short of insanity. A short step.)
5806426
Ah fair enough. My mental image was clearly too packed in. I wonder how it caused an impact period of forty million years then as the article suggests, if the ring was so short lived? Debris escaping to solar orbit and replenishing the supply when alignments occur? Or is it just the margin of error of the dating at work?
Regarding Mars' core, that's really interesting!
5806435 As I understand it, the "lunar" station is actually an Aldrin cycler, which ultimately orbits Earth and just does Moon fly-bys about once a month. It's quite stable. A base directly orbiting the moon would indeed be more problematic, but it could probably be kept in orbit for a 25-year service life with not much more resources (aside from getting things there) than ISS.
5806442 The 40 million years is the entire range of the geological period in question, and right now it's as close as we can measure the timing of those impacts. They were almost certainly a lot closer together.
5806458
Makes sense. I'd be surprised if the error bars were smaller than that, so long ago, but suspecting and knowing are different things as you proved above with my orbital mechanics bungle.
I really should dig out my GCSE astronomy & astrophysics textbook and brush up at some point.
That's very neat, especially with that "temporary mini-moon" in the news.
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