Planetoid formation, spherical or not.

In summary, the minimum size for a rocky planetoid needed to "crush" it into a spherical shape is 250 km, and the ambient temperature around Earth orbit at that time would be difficult for an object to quickly get rid of heat.
  • #1
anorlunda
Staff Emeritus
Insights Author
11,308
8,731
I am interested in the minimum size of a rocky planetoid needed to "crush" it into spherical shape. I'm also interested in its initial temperature because liquid or plastic masses obviously need much less crushing.

The Wikipedia article "Giant Impact Hypothesis" says,

In 2007, researchers from the California Institute of Technology showed that the likelihood of Theia having an identical isotopic signature as the Earth was very small (less than 1 percent).[19] They proposed that in the aftermath of the giant impact, while the Earth and the proto-lunar disk were molten and vaporized, the two reservoirs were connected by a common silicate vapour atmosphere, and that the Earth–Moon system became homogenized by convective stirring while the system existed in the form of a continuous fluid. Such an "equilibration" between the post-impact Earth and the proto-lunar disk is the only scenario capable of explaining the isotopic similarities of the Apollo rocks with rocks from the Earth's interior. For this scenario to be viable, however, the proto-lunar disk must exist for a time period of about 100 years.

That makes me wonder about the ambient temperature around Earth orbit at that time and the rate of cooling of the initial Lunar ejecta. Ejecta staying molten for 100 years sounds like a long time in cold cold space.

Are there articles for laymen about solid spherical vs non-spherical vs rubble pile planetoid formation?
 
Astronomy news on Phys.org
  • #2
Try looking for keywords 'hydrostatic equilibrium' together with 'dwarf planet'. You should get some good hits.

Here's one good paper by Lineweaver and Norman:
The Potato Radius: a Lower Minimum Size for Dwarf Planets

It's relatively conversational and accessible for laymen.

And for the absolute laziest alternative: the answer is about 250 km give or take maybe a hundred, depending on composition.
 
  • Like
Likes |Glitch| and anorlunda
  • #3
anorlunda said:
That makes me wonder about the ambient temperature around Earth orbit at that time and the rate of cooling of the initial Lunar ejecta. Ejecta staying molten for 100 years sounds like a long time in cold cold space.

In a near-perfect vacuum like space, the only way to get rid of heat is to radiate it away. This process takes MUCH longer than convection and conduction for the same difference in temperature between the hot and cold reservoirs. So while it may be cold in space, it's actually pretty difficult for an object to quickly get rid of heat.

Unfortunately I don't know how long it would take for the ejecta to cool.
 
  • Like
Likes anorlunda
  • #4
Earth is not the ideal oblate spheroid which it *should* be.
It's actually more of a slightly off-center pear shaped thing, (more land above sea level in North hemisphere right now.)
 
  • Like
Likes anorlunda

1. What is a Planetoid?

A planetoid is a celestial object that is smaller than a planet but larger than a comet or asteroid. It is typically made up of rocks, ice, and dust and can range in size from a few kilometers to several hundred kilometers in diameter.

2. How do Planetoids form?

Planetoids are formed through a process called accretion, where smaller objects in space collide and stick together, gradually growing in size. This can happen in a variety of ways, such as collisions between asteroids or the accumulation of debris in the early stages of a solar system's formation.

3. Are all Planetoids spherical in shape?

No, not all planetoids are spherical in shape. The shape of a planetoid depends on its size, composition, and rotation. Smaller planetoids may be irregularly shaped due to their weak gravitational pull, while larger ones tend to be more spherical due to their stronger gravity.

4. Can planetoids become planets?

Yes, it is possible for planetoids to become planets. If a planetoid continues to grow in size through accretion and gains enough mass, it can eventually become a full-fledged planet. This process can take millions or even billions of years.

5. What role do planetoids play in our solar system?

Planetoids play an important role in the formation and evolution of our solar system. They are often considered remnants of the early stages of our solar system's formation and can provide valuable insights into the history and composition of our solar system. They also play a role in the formation of planets and other celestial bodies through their gravitational influence and collisions.

Similar threads

  • Astronomy and Astrophysics
Replies
12
Views
6K
  • Sci-Fi Writing and World Building
Replies
21
Views
853
  • Astronomy and Astrophysics
Replies
2
Views
5K
Replies
17
Views
3K
  • Astronomy and Astrophysics
Replies
2
Views
3K
  • Beyond the Standard Models
Replies
11
Views
2K
  • Astronomy and Astrophysics
Replies
7
Views
8K
  • Earth Sciences
Replies
3
Views
3K
  • Introductory Physics Homework Help
Replies
23
Views
12K
  • MATLAB, Maple, Mathematica, LaTeX
Replies
5
Views
2K
Back
Top