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Diamonds in the Sky

09/06/2021 9:38 PM

Planets form in a spherical shape due to the force of gravity minimizing the potential energy. Rapidly spinning "rubble pile" asteroids such as Bennu and Ryugu form a diamond shape due to a combination of gravity, centrifugal force, and the cohesive forces that form conical piles of accreting material on earth.

Diamond profile asteroids. Near-earth asteroids a Ryugu and b Bennu. Yellow blocks added to panel b suggest accumulated material: note that material nearer the poles feels weaker centrifugal force than material at mid- or low- latitudes. Region in green square is enlarged in Fig. 2a. c Analytic prediction from Eq. 1 using α=0.999,μ=0.4α=0.999,μ=0.4. d Exterior surface defined by discrete element simulation described in text. Image credits Ryugu: JAXA, Bennu: NASA

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Bennu and Ryugu: diamonds in the sky | SpringerLink

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#1

Re: Diamonds in the Sky

09/07/2021 2:41 PM

Looks like some of those constant width shapes that look like they shouldn't roll smoothly.

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#2

Re: Diamonds in the Sky

09/08/2021 12:16 AM

Very interesting. Thanks. I was unable to find a definition for YORP, as used in this article.

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#3
In reply to #2

Re: Diamonds in the Sky

09/08/2021 1:33 AM

Hope these help.
Was curious as well...because in Australian Yorp, or Y'reup means get another round of beers which I guess could explain the wobbly orbits ... but -
"The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect for short, changes the rotation state of a small astronomical body – that is, the body's spin rate and the obliquity of its pole – due to the scattering of solar radiation off its surface and the emission of its own thermal radiation."

https://www.planetary.org/articles/20141211-the-yorp-effect-and-bennu

https://en.wikipedia.org/wiki/Yarkovsky%E2%80%93O%27Keefe%E2%80%93Radzievskii%E2%80%93Paddack_effect

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#6
In reply to #3

Re: Diamonds in the Sky

09/08/2021 2:58 PM

Thanks!

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#4

Re: Diamonds in the Sky

09/08/2021 1:45 AM

. . . with plasticine porters with looking glass ties??

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#5

Re: Diamonds in the Sky

09/08/2021 11:50 AM

On another note, shouldn't a very diffuse gas cloud exist around each of these rubble piles? The gas pressure level would certainly be less than the best vacuum levels found on Earth. But shouldn't the gas pressure level be higher than interplanetary space? I have no idea how one might measure this.

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#7
In reply to #5

Re: Diamonds in the Sky

09/09/2021 7:41 AM

If the gas atoms or molecules at the ambient temperature have a greater velocity than the escape velocity (0.5 - .74 km/hr for Bennu, 30 cm/s for Ryugu) then they wouldn't stick around. The molecular velocity decreases as molecular mass increases as shown below for room temperature.

Molecular Velocities and Kinetic Energy | Gases (nigerianscholars.com)

By the Numbers | 101955 Bennu – NASA Solar System Exploration

Resurfacing processes on asteroid (162173) Ryugu caused by an artificial impact of Hayabusa2's Small Carry-on Impactor - ScienceDirect

There would have to be a source for this gas, or it would disappear in a very short time just as a mud puddle dries up. The very weak gravity would not hold on to it.

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#8
In reply to #7

Re: Diamonds in the Sky

09/09/2021 8:46 AM

I believe the average (ambient) and peak temperatures for both of these rubble piles are considerably less than 25°C. So my supposition of a gas cloud around these objects seems plausible.

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