216 Kleopatra -Asteriod has its own moons?!

Originally posted by nataylor
There are 6 known small bodies that have at least 2 moons. It's estimated as many as 2% of all asteroids have moons.

Amazing only 2%. I wonder how they determine that. I just always keep an open mind for things and you never know (way outta box thinking) it could be craft. Just unable to be understood with human eye. But again thats a -way outta box thought...

Thanks

Originally posted by randyvs
Seriously is there a difference between minor planets and asteroids? This seems to widen the scope as far as gravity is concerned. Dosn't appear that mass has much to do with gravity after all.

A minor planet is any natural object in orbit around the sun that is not a planet or a comet. Asteroids are one type of minor planet. Typically, rocky or metallic bodies in orbit around the sun in the inner solar system (inside Jupiter's orbit) are considered asteroids. Those outside the orbit of Neptune are known as trans-Neptunian objects.

And I'm not sure how you determine that this makes it appear mass doesn't have much to do with gravity. Indeed, the opposite is true. It is because of mass, and the gravity generated by it, that these minor planets are able to have moons orbiting them.

reply to post by Ophiuchus 13


Let's do better than just imagine that this is possible...let's do the math.

216 Kleopatra is 217 km long, and its average radius appears to be around 75 km (you can do the measurements and calculations yourself). For a roughly cylindrical object, this gives a volume of:

V = AH = pi*(r^2)*H = pi*(75^2)*217 = 3,834,700 km^3 = 3,834,706,532,788,000 m^3

Assuming an average density of 8000 kg/m^3 (that of an iron asteroid), this gives a mass of 30,677,652,262,304,331,000 = 3.0677652262304331*10^19 kg. As a comparison, this is about 3% the mass of Ceres, the largest object in the asteroid belt.

Judging by the image given of the two moons, they're around 300 km away from Kleopatra. Assuming their mass is negligible compared to Kleo, their orbital period can be calculated from an equation I've been throwing around a lot lately:

T = 2*pi*sqrt(a^3/GM)

where "a" is the semi-major axis, "G" is the gravitational constant, and "M" is the mass of Kleopatra.
Assuming a roughly circular orbit (e = 0), the semi-major axis is 300,000 m.

This gives an orbital period of:

T = 2*pi*sqrt((300000^3)/((6.67428*10^-11)(3.0677652262304331*10^19))) = 22816.5 seconds

This is a period of 6 hours, 20 minutes.

If Kleo were too weak to hold onto a moon, we would expect a much less reasonable (that is, a much larger) value for the orbital period, but for a moon to orbit an object of this size in just 6.34 hours is no surprise. Obviously, 216 Kleopatra has more than enough gravity to attract two moons. Just because it's an asteroid doesn't mean it's a weakling.
And then, of course, there's Pluto...and a whole host of other asteroids/dwarf planets that have moons.

reply to post by CLPrime


WOW! Thank you CLPrime for the data. I like how you laid that out for us and this is why I enjoy the ATS community so much so much data to absorb. So you feel they rotat it and not just trail it as well..

Thanks again

reply to post by CLPrime


Nice math man! Impressive numbers.

To the OP, nice post. S&F!

Maybe one day we will acquire an asteroid as a moon, and if it has moons, that would be quite a site!

reply to post by DrRage


That would be pretty cool indeed. Another moon with little moons. I could imagine the nite sky being brighter from the reflections..
Thanks

reply to post by DrRage


That would be interesting. But here's the thing...to stay in an orbit around Earth, it would have to have a VERY specific velocity to maintain a stable orbit. If it's too fast, it will keep going and won't be caught in Earth's gravity. If it was too slow, it would fall into the Earth.
Now, consider this: if the asteroid did manage to fit itself into a stable orbit around Earth, its moon would orbit outside the safety of that distance and, at its perigee, would be attracted to Earth rather than the asteroid. This would quickly cause the asteroid's moon to fall into the Earth. Either way, the system probably wouldn't be stable...or safe.

Now, if the Moon we already have were to capture a moon, that would be interesting. I'll refrain from doing the math, but I would assume there's a specific, highly eccentric orbit which would be stable in that case, since the moon is relatively massive.
It's also possible that a sort of figure-8 orbit would result, with the secondary moon switching between Earth and the Moon.

Nice

I have to wonder, if Pluto is no longer considered a planet, but a planetoid, and asteroids have different classification, why would an asteroid orbiting another asteroid be classified as a moon. Considering our moon is as large as Mercury, it is a bit demeaning to classify an asteroid orbiting another asteroid, which is considerably smaller than our Moon, as a moon. Maybe they could call it a moonoid.

Wouldn't it be cool if you could set up house on such a system, and have your own little planet. I wonder if it would be like living on a roller coaster with the rate of rotation. Maybe you could stabilize the orbit, burrow underground and create a biosphere. Open up a burger joint, maybe an amusement park to attract tourists.

Originally posted by poet1b
why would an asteroid orbiting another asteroid be classified as a moon. Considering our moon is as large as Mercury,

I see your point exactly. I think a moonoid does fit better with description Or maybe just large or small celestial bodies with orbiting or rotating celestial bodies.
Thanks

reply to post by CLPrime


Nice math skills. Looks like you do this regularly. Where do you get the value for an Iron basis for density?

Do you have any idea what gravity force would exist on the surface of Cleopatra?

I have to speculate, considering the shape of Cleopatra, if we aren't looking at a giant magnate. I wonder if this has been looked into by NASA.

Originally posted by Ophiuchus 13

Originally posted by poet1b
why would an asteroid orbiting another asteroid be classified as a moon. Considering our moon is as large as Mercury,

I see your point exactly. I think a moonoid does fit better with description

Or maybe just large or small celestial bodies with orbiting or rotating celestial bodies.

Thanks

edit on 2/25/11 by Ophiuchus 13 because: (no reason given)

"Moon" is the name given to any natural satellite...any object that orbits another and is not artificial. This is regardless of size. Asteroids have moons just as planets do.

Originally posted by poet1b
reply to post by CLPrime

 

Nice math skills. Looks like you do this regularly. Where do you get the value for an Iron basis for density?

Do you have any idea what gravity force would exist on the surface of Cleopatra?

I have to speculate, considering the shape of Cleopatra, if we aren't looking at a giant magnate. I wonder if this has been looked into by NASA.

I certainly do do this regularly. I love both math and physics, and I am currently taking a bit of a break from a degree with a major in Physics. Granted, my focus is Quantum Mechanics, but the freelance side of me works with QM, Astrophysics, and Cosmology, and I've become well-versed in all three. If I do say so myself

The density of iron is 7874 kg/m^3. This corresponds to the density of an iron-based asteroid.

And there is no gravitational force associated with the surface of Kleo, per se. Gravity is the result of point-mass, which depends only on the centre of mass and not on the shape of an object. Of course, each point within the object exerts a gravitational force, but the net result is a uniform force acting toward the centre.

As for it being magnetic, that's certainly possible. That would also add another force to hold onto those moons, if they're also magnetic (which they should be, if they're just broken-off bits of Kleo, herself).