New Horizons' Evocative Farewell Glance at Ultima Thule (phys.org) 37 points by dnetesn 6 days ago | hide | past | web | favorite | 10 comments

 I'm wondering what would be the gravitational force between them. Could you push one from the other with a small bump and set them free?
 Someone over at PhysicsForums[1] estimated the forces on Ultima Thule.While small, the bodies aren't exactly featherweight, they're both on the order of 10^15 kg, so you'd still need quite the push to move them.edit: I see now[2] that the system is much flatter than anticipated, which would affect the mass the calculations in the link I posted. Still, they won't be something you just push around.
 A small explosion might be good enough?
 A rough estimate of the escape velocity for Ultima Thule, assuming it was a sphere of uniform mass (it isn’t) of mostly ice comes out to ~7m/s (https://news.ycombinator.com/item?id=18811511)Even better Jake-Low made a rough estimate of the forces between the two lobes: (https://news.ycombinator.com/item?id=18811366)And just for fun, I also worked out a best guess for the force between the two "lobes": 1.5 x 10^13 N (assuming Ultima Thule is the same density as our Moon)Even ignoring that the two lobes are probably vacuum-welded together, it’s quite a large explosion you’d need to permanently separate the two lobes. Granted combinging two rough estimates to get a sense of the escape velocity of one lobe from the other is super messy, but it’s probably informative as a yardstick.Simply breaking them apart wouldn’t free them, they’d mostly fall back together, you’d need to impart quite a bit of acceleration to one or both lobes to keep them apart. I’m not sure to what extent that would be feasible, but if it was it would take an array of carefully orchestrated nuclear detonations, or huuuuuge rockets along with the nukes.I think.
 Using the assumptions in the post you linked, I got that the gravitational energy bound in that system is on the order of 10^17 Joules. That's about the yield of the Tsar Bomba (so not quite a small explosion, lol), so we could get a thermonuclear device of similar magnitude of those to transfer most its energy into the two, it should separate them.
 Only one way to be sure, you get the spaceship, I’ll get the plutonium pit. Now, people won’t get why were doing this, but we brave and happy few won’t mind.
 > it should separate them.How much damage would that bomb do?(I take it not much otherwise you would have written 'what's left of them' instead of 'them')
 It looks like it would at least make a sizable hole, extrapolating from this document: https://www.osti.gov/servlets/purl/6696719
 Definitely not, they’ve been welded together through collision and vacuum processes. The gravitational attraction has long since been eclipsed by electromagnetic forces.
 It's super fascinating watching this unfold. This object is shaped in a way that really might change the way we understand how solar systems form!

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