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NH Ultima Thule Encounter Observations & Results, post-flyby discussion as the data arrives
Marcin600
post Jan 16 2019, 08:38 AM
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QUOTE (Ian R @ Jan 16 2019, 09:19 AM) *
My speculation is that the two lobes were never individual objects in the first place, and that the original fast rotation of MU69 -- back when it was newly formed and more prone to deformation -- caused a 'blob' to begin to separate from the main body due to centripetal forces, which in the end weren't enough for the two components to part completely.

Just a stab in the dark from a layperson!



I think that this is one of many possibilities. In any case, things seem to be more complicated than they originally seemed
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Marcin600
post Jan 16 2019, 09:03 AM
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For example, two bodies could be originally separate and flattened independently as a result of rotation. More data from New Horizons is needed.
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stevesliva
post Jan 16 2019, 03:40 PM
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QUOTE (Marcin600 @ Jan 16 2019, 04:03 AM) *
For example, two bodies could be originally separate and flattened independently as a result of rotation.


Or accretion.

This is definitely real? If I focus on just the neck/isthmus then it does appear real, but I worry it's just an artifact.
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pdalek
post Yesterday, 05:33 AM
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Ultima Thule looks like a snowman. A big snowman is a good way to think about formation and properties.

Comets have density about that of handmade snowballs. U-T is probably similar.
Calculating gravitation and centrifugal acceleration will show it is gravitationally bound over the entire surface and so was not formed by stretching a sphere.

The escape velocity is about that of a human thrown snowball. Fall velocities would be similar. At such velocity, a small snowball acreating under gravity will splat. For a large falling snowball, self gravitation will keep the ball in shape. Higher impact velocity would change things, but without large nearby planets to shift orbits, this is unlikely.

The compressive strength ordinary packed snow is sufficient to prevent a 19km and a 14km balls from merging to a much more compact space. It is easy to estimate the contact area.

Modelling the gravitational field shows local down is up to about 30 degrees from surface normal near the neck. This is about the angle of repose of lightly packed snow.
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Marcin600
post Yesterday, 08:15 AM
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As Stevesilva supposes, the slightly flattened shape of Ultima (and Thule?) - if it is not a low resolution artifact - may be the result of the specificity of the accretion process itself - in one plane, a bit like an accretion disc (?)

I think the wonderful New Horizons team is already working on the interpretations.
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john_s
post Yesterday, 12:00 PM
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QUOTE (Ian R @ Jan 16 2019, 12:19 AM) *
I took one of the GIF animations and made an aligned and 'bouncy' version:

Looks as if the lobes are less spherical than they are hamburger shape!


Hi Ian-

Thanks for that very revealing "de-rotated" animation. We on the science team had been planning to do the same thing, but you beat us to it. When I sent the team a link to your animation, it sparked quite an e-mail storm. UT continues to surprise!

Thanks again,
John
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Explorer1
post Today, 05:13 AM
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New post from Alan: http://pluto.jhuapl.edu/News-Center/PI-Per...tive_01_17_2019

In addition to data downlink from MU69, some distant observations of the unchosen flyby target in March, and some extra fuel for post 2020 maneuver to a more distant object.
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