
New Horizons' Evocative Farewell Glance at Ultima Thule - dnetesn
https://phys.org/news/2019-02-horizons-evocative-farewell-glance-ultima.html
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visarga
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?

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magicalhippo
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.

[1]: [https://www.physicsforums.com/threads/net-forces-on-
ultima-t...](https://www.physicsforums.com/threads/net-forces-on-ultima-
thule.963691/) [2]: [http://pluto.jhuapl.edu/News-Center/News-
Article.php?page=20...](http://pluto.jhuapl.edu/News-Center/News-
Article.php?page=20190208)

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saagarjha
A small explosion might be good enough?

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Pharmakon
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](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](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.

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saagarjha
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.

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jacquesm
> 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')

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saagarjha
It looks like it would at least make a sizable hole, extrapolating from this
document:
[https://www.osti.gov/servlets/purl/6696719](https://www.osti.gov/servlets/purl/6696719)

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msarchet
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!

