I would like to know if the following properties of this asteroid are realistic without conflicting with each other.

  1. situated in the inner part of the asteroid belt in the Solar System
  2. S-type asteroid: "Relatively bright with an albedo of 0.10-0.22. Composition is metallic iron mixed with iron- and magnesium-silicates. S-type asteroids dominate the inner asteroid belt.". Source
    Geometric albedo: 0.2 approx.
  3. equatorial radius of about 8km. Slightly elongated in shape, similar to 951 Gaspra
  4. gravitational acceleration on the surface along the equator is 0.01 m/s^2. For the story only this acceleration matters.
  5. density lower than 3.0g/cm^3 which is common for known S-type asteroids (could be moderately changed to fit points 2 and 3)
  6. Mining operations are currently (in story) mainly extraction of Magnesium rich enstatite chondrites, Aluminum, Iron.
  7. The asteroid revealed to be rather poor in precious metals and rare elements of which existing surface deposits were quickly exhausted.
  8. The surface contains Olivine and Pyroxene minerals and has a distinctive greenish color
  9. Has a mound on the equator, 30 meters high. It is the highest point along the equator.

Of particular relevance to the story are the radius and gravitational acceleration. If unfeasable radius could be reduced in case of a lower gravity acceleration.
In my research I have found a number of similar asteroids (e.g. 433 Eros) but none with all these properties. Data are often still unknown. But is this asteroid realistic?
I include a drawing that is not in scale but just for clarity.

Edit regarding composition: the asteroid has a Nichel-Iron core as typical with S-Type asteroids. Has Olivine and Pyroxenes on the surface and at mining depth. So Magnesium, Aluminium, Iron are present and mined.

Not in scale drawing

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    $\begingroup$ Please elaborate on point 4. Since the asteroid is clearly not a sphere, methinks the gravitational acceleration on the 'surface' would depend on where the 'surface' was located. $\endgroup$ Jan 10, 2022 at 2:24
  • $\begingroup$ I edited point 4. Actually only the acceleration along the equator matters for the story $\endgroup$ Jan 10, 2022 at 5:05
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    $\begingroup$ Composition is metallic iron mixed with iron- and magnesium-silicates and The asteroid revealed to be rather poor in metals? $\endgroup$
    – L.Dutch
    Jan 10, 2022 at 5:40
  • $\begingroup$ @L.Dutch right, edited point 6 and added 8. The asteroid is lacking precious metals. $\endgroup$ Jan 10, 2022 at 8:51
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    $\begingroup$ Since most of your research and work seems solid and complete I am not sure it will get an answer. A simple "yes" as an answer does not work around here - it fits more as a comment. $\endgroup$ Jan 10, 2022 at 21:26

1 Answer 1


We don't have a great deal of information about the exact composition of asteroids in general, there have been only a handful of physical tests on them, so it would be irresponsible to say, "No, this asteroid can not exist." I will say that “plausible” is an accurate characterization if your rock. But there is a question about your gravity that can't be answered without more information. Calculating the gravitational acceleration at the equator requires knowing the product of the mass of all bodies in the system, not just the asteroid:

$$ \ F=\frac{G\times M _{1} \times M_{2}}{r^{2}}$$

The value of g on earth is typically considered a constant because the objects we let fall are of negligent mass relative to the earth, but objectively, an airplane and a marble have a slightly different value of g. So your g will be very different when calculating for an astronaut, or for another asteroid, or for a starship; and very different depending on how far that other body is from your asteroid. For example, an object of mass 208.6 metric tons would experience an acceleration of 0.1 m/s in relation to the equator of 433 Eros based on the estimated mass of 433 Eros = $\ 7.2 \times 10^{12}$ metric tons, yet a gravitational acceleration is not at all reasonable for a 108 kg astronaut (with equipment) to experience anywhere near 433 Eros; and very likely not possible on your asteroid either.

A 108kg astronaut 8km from 433 Eros have a product of their masses $\ M_t =1.296 \times 10^{18} kg$, experiencing a force of gravity $\ F = 0.810927 N. $ The acceleration of this astronaut toward the asteroid due to gravity will be $\ a=\frac{F}{m} = \frac {0.810927N}{108kg} = 0.00750858\overline {3} ms^{-2}$

Now, I originally drafted this answer responding to a misread of your parameters. You are not expecting a gravitational acceleration of “0.1 $\text{m/s}^2$” but only $ 0.01\text{m/s}^2$. As you can see, the calculation for 108 kg astronaut puts you at 75% of your target. Thus there are several variables your plot may adjust to make these parameters realistic An asteroid of 1.25 times the mass of 433 Eros should land you close enough to your goal; or perhaps give them a heavier EVA suit. You can make the plot line come together with minor adjustments I believe.

But again, depending on what you are having fall to the asteroid and how far away it is this may or may not be reasonable. A small spaceship half the mass of a commercial airliner may feel 0.1 m/s acceleration at the surface of 433 Eros, so without the mass of your asteroid we can't produce a hard science answer. Good thing you weren’t asking for one :)

For the record, even a small rotational spin can negate your gravitational field and make standing on the surface nigh impossible. Consider carefully!

  • $\begingroup$ Very good point. I will clarify in question. The 0.1 g acceleration is relative to an astronaut. So the 108kg mass object. At some point in the story a ship will come near the asteroid. Must determine it's mass and distance. But for the purpose of the story it will stay enough far away from the asteroid and for limited time only. $\endgroup$ Feb 14, 2022 at 11:15

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