Astrophysics Question?

Question

Someone asked me for help with this question, but is it even possible to answer this question with the information given? If so can someone explain the steps?

Here's the exact phrasing of the question:

An asteroid has an equilibrium temperature measured as 200 Kelvin. What is the object's orbital period around the Sun?

Now below it says to use the information given in the previous question which is:

Assuming the Earth's radius is 637 km, the solar constant is 1370 w/m2, and our planetary albedo is 0.31, then:

(a) Determine total power entering Earth's atmosphere.
(b) The total power that would be asborbed in the absence of an atmosphere.
© Surface temperature assuming it radiated into space all the energy it absorbed.

I don't see how you can possibly tell the orbital velocity from what they give you to solve the problem.

Answer 1

I'm not 100 % certain about this, but here goes.

We have the temperature of the asteroid. This is caused by solar heating, just as global warming on Earh is caused by solar heating. I think we must assume that the asteroid has the same albedo as the Earth. So it absorbs and reflects the same proportion of energy that the earth does.

Find the energy absorbed by the earth per unit area. If the asteroid is at the same radial distance from the sun (same orbital speed) as the Earth, the asteroid will absorb the same energy per unit area, since it has the same albedo.

We're given the equilibrium temperature of the asteroid. the ratio between the surface temperature of Earth and the asteroid shoud be the same as the ratio between their radial distances from the sun.

Once you know the radial distance of the asteroid from the sun, you can easily find the orbital period.

I think.

Anyhow, I hope this at least give you a start. Good luck!

30 NOV 06, 1947 hrs, GMT.

Answer 2

It would be nice if you could solve it with such little information, but I don't see how you would. Not without making a bunch of gargantuan assumptions.

Answer 3

Great explanation at;


http://www.uwmc.uwc.edu/geography/100/rad-temp.htm