Explanation: Ultima Thule is not the object humanity thought that it was last month. When the robotic New Horizons spacecraft zoomed past the distant asteroid Ultima Thule (officially 2014 MU69) in early January, early images showed two circular lobes that when most simply extrapolated to 3D were thought to be, roughly, spheres. However, analyses of newly beamed-back images -- including many taken soon after closest approach -- shows eclipsed stars re-appearing sooner than expected. The only explanation possible is that this 30-km long Kuiper belt object has a different 3D shape than believed only a few weeks ago. Specifically, as shown in the featured illustration, it now appears that the larger lobe -- Ultima -- is more similar to a fluffy pancake than a sphere, while the smaller lobe -- Thule -- resembles a dented walnut. The remaining uncertainty in the outlines are shown by the dashed blue lines. The new shape information indicates that gravity -- which <a href-"https://spaceplace.nasa.gov/planets-round/en/" >contracts more massive bodies into spheres</a> -- played perhaps less of a role in contouring the lobes of Ultima Thule than previously thought. The New Horizons spacecraft continued on to Ultima Thule after passing Pluto in mid-2015. New data and images are still being received.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 6:43 am
by Ann
If they larger lobe of Ultima Thule is so flat, then it can't be very massive, can it? And maybe it is not a lot more massive than the smaller but slightly more "spherical" lobe?
Ann
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 6:52 am
by Nitpicker
I can look skinny in the right lighting, too.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 8:04 am
by distefanom
It's incredible what's out there...
I wonder if in a computer simulation, this result can be obtained in any way...
Talking of things that happen in the universe, have complete different meaning...
At first I thought: the passage of New Horizon was SO IN SINC with Ultimathule so we've seen the faces of the lobes e where not able to see anything of the other side even partially?
It's has been like to flip a coin and have it to land balanced on the side... but also this happens!!!
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 9:51 am
by JohnD
If the spin axis is as shown, could this be not two objects coming together but one that is spinning apart?
John
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 11:37 am
by distefanom
JohnD wrote: ↑Mon Feb 11, 2019 9:51 am
If the spin axis is as shown, could this be not two objects coming together but one that is spinning apart?
John
they should have two objects spinning *already in sinc* in such a way (opposite each other?) that when they did collide (at the almost same rotational speed?), they haven't destroyed each other but only "kissed"... mmmh! very complicated movement!!! isn't it, to happen in the same time, place & soil consistency.... ???
In human timescale it's something almost impossible to happen!!!!
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 12:27 pm
by orin stepanek
They must have connected when the two objects were hot and pliable! How else could hey spin together as one? Shows you really can't judge a book by it's cover!
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 1:47 pm
by ToucanSam
Talk about joined at the hip!
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 2:05 pm
by Odysseus
Why does that seem like the wrong axis for the spin it's describing? Shouldn't the arrow be pointing left (or right) if UT is rolling "towards" us in the image?
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 2:12 pm
by Chris Peterson
Odysseus wrote: ↑Mon Feb 11, 2019 2:05 pm
Why does that seem like the wrong axis for the spin it's describing? Shouldn't the arrow be pointing left (or right) if UT is rolling "towards" us in the image?
What in the image makes you think it's rolling towards us?
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 2:50 pm
by neufer
Ann wrote: ↑Mon Feb 11, 2019 6:43 am
If they larger lobe of Ultima Thule is so flat, then it can't be very massive, can it?
And maybe it is not a lot more massive than the smaller but slightly more "spherical" lobe?
The observed center of the spin axis defines the center of mass of UT
and it clearly lies in Ultima... although not very deeply.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 3:00 pm
by neufer
orin stepanek wrote: ↑Mon Feb 11, 2019 12:27 pm
They must have connected when the two objects were hot and pliable!
How else could they spin together as one? Shows you really can't judge a book by it's cover!
Three or more cold and rigid orbiting objects would have always
been in an unstable n-body orbital system until all but two remained.
Those objects ejected into space would have had maximal angular momentum
leaving the remaining two stable orbital objects with minimal angular momentum.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Odysseus wrote: ↑Mon Feb 11, 2019 2:05 pm
Why does that seem like the wrong axis for the spin it's describing?
Shouldn't the arrow be pointing left (or right) if UT is rolling "towards" us in the image?
What in the image makes you think it's rolling towards us?
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Odysseus wrote: ↑Mon Feb 11, 2019 2:05 pm
Why does that seem like the wrong axis for the spin it's describing?
Shouldn't the arrow be pointing left (or right) if UT is rolling "towards" us in the image?
What in the image makes you think it's rolling towards us?
That's a great movie scene! The best scene from Indiana Jones and the Raiders of the Lost Ark.
Ann
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
What in the image makes you think it's rolling towards us?
That's a great movie scene! The best scene from Indiana Jones and the Raiders of the Lost Ark.
Ann
Better than when he shoots the guy showing off with the scimitar?
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 6:50 pm
by BDanielMayfield
Gravity "contracts more massive bodies into spheres" only if they have little or no rotation. But if the body has significant rotation gravity will compress the object at the poles and spread it out along its equator. (Centripetal force will effectively counteract gravity at the equator.)
Bruce
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 6:59 pm
by Chris Peterson
BDanielMayfield wrote: ↑Mon Feb 11, 2019 6:50 pm
Gravity "contracts more massive bodies into spheres" unless the body has significant rotation. Then gravity will compress the object at the poles and spread it out along its equator.
Bruce
And for solids, that means a lot of mass. Enough that gravitational attraction overcomes material strength. That weird shaped rock in your yard is going to stay weird shaped until it weathers away. Its self gravity will never turn it into a sphere.
Astronomical bodies smaller than a few hundred kilometers (a bit larger for rock, a bit smaller for ice) won't collapse to spheres. Where we see them as spheres, it's likely they got that way from a more fluid state early in their existence.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
BDanielMayfield wrote: ↑Mon Feb 11, 2019 6:50 pm
Gravity "contracts more massive bodies into spheres" unless the body has significant rotation. Then gravity will compress the object at the poles and spread it out along its equator.
And for solids, that means a lot of mass. Enough that gravitational attraction overcomes material strength. That weird shaped rock in your yard is going to stay weird shaped until it weathers away. Its self gravity will never turn it into a sphere.
Astronomical bodies smaller than a few hundred kilometers (a bit larger for rock, a bit smaller for ice) won't collapse to spheres. Where we see them as spheres, it's likely they got that way from a more fluid state early in their existence.
Victor Weisskopf (MIT) calculated from basic physics that the highest
land mountains on Earth (from their base) must be less than ~4.9 km
http://www.hk-phy.org/articles/mount_hi ... igh_e.html
-----------------------------------------------------------------------------------
For planets smaller than the Earth (with reduced surface gravity ~ g x Rp/Re)
Hp ~ 4.9 km (Re/Rp) or
Rp x Hp ~ 4.9 km x Re [ = 31,200 km2]
Planetary bodies are roundish if : Rp > Hp :
Rp x Rp > 31,200 km2 or
Rp > 175 km.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 8:54 pm
by Boomer12k
Learning all the time....
:---[===] *
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 8:59 pm
by JimM
Interesting that the new spin axis now appears to virtually coincide with the connection between the two lobes. Since that would minimize tension at the connection for a given rate of spin, might we guess that two-component objects Ultima Thule's size suffer enough 'big' collisions to spin them up to a point that they threaten to pull apart, since small collisions would tend to average out?
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 10:03 pm
by alcor
Aah!
At last the Flat Earth has been proven. Perhaps Flat Earth Society should have their next meeting here.
Though I would not recommend it, as the place is both hard to get to and hard to be there.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Thanks for the link. As a visiting speaker at the Univ. of Washington, I witnessed Weisskopf present that derivation while discussing aspects of our macroscopic world and how they're revealed by (almost a unit analysis) fundamental physical constants. To me, his presentation was as basic and elegant as they get.
Re: APOD: New Data: Ultima Thule Surprisingly Flat (2019 Feb 11)
Posted: Mon Feb 11, 2019 10:56 pm
by Ann
neufer wrote: ↑Mon Feb 11, 2019 8:00 pm
Victor Weisskopf (MIT) calculated from basic physics that the highest
land mountains on Earth (from their base) must be less than ~4.9 km
neufer wrote: ↑Mon Feb 11, 2019 8:00 pm
Victor Weisskopf (MIT) calculated from basic physics that the highest
land mountains on Earth (from their base) must be less than ~4.9 km
So according to basic physics, Mount Everest is like a bumblebee that shouldn't be able to fly, but it flies anyway?
Ann
Depending on how you define the base of Mount Everest, it's between 4.2 and 5.2 km from base to top. You get to 8.8 km by building Mount Everest on top of a basement that is well above sea level.
A better example of a mountain that seems to break the above calculation is Mauna Kea, which is about 10 km high. But more than half of that is below the ocean, which might be part of the explanation.
The mountains in the calculation are essentially free standing cones.
New Data: Ultima Thule Surprisingly Flat
