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Vultur
2008-Oct-09, 10:49 PM
How good is the evidence that the new dwarf planet Haumea is spun into a weird stretched shape? I think it's very interesting and hope it's true (shades of Mesklin!), but it seems there are no pictures of the object...

antoniseb
2008-Oct-10, 11:17 AM
...it seems there are no pictures of the object...

Well, no close ups. You can see it as a dot, or a streak on a field of stars.

grant hutchison
2008-Oct-10, 11:50 AM
The shape is inferred from the light-curve.
Either we have a round object with symmetrically placed dark markings, spinning quickly but nevertheless retaining its round shape; or we have an object that has relaxed hydrostatically into a Jacobi ellipsoid as a result of its fast spin, and which has pretty uniform reflectivity. The second scenario involves fewer assumptions, so is the more favoured.

Grant Hutchison

Vultur
2008-Oct-11, 07:41 AM
OK, thank you.

So the observed light-curve variation is close to how much an icy object at that rotation speed should be deformed?

grant hutchison
2008-Oct-11, 12:58 PM
So the observed light-curve variation is close to how much an icy object at that rotation speed should be deformed?I'd guess that some sort of dialogue with the data has to take place. We know the mass and rotation period. We look to see if we can generate a figure in hydrostatic equilibrium which has plausible underlying assumptions about density and reflectivity. The answer seem to be satisfactory for the people involved in these calculations, since Haumea was recently awarded dwarf planet status: which requires it to be in hydrostatic equilibrium.

Edit: Yeah, here (http://arxiv.org/abs/astro-ph/0509401) is the sort of data exploration that's been going on in the background. It seems that for something the mass of Haumea, hydrostatic equilibrium is the default assumption, and exploration has been aimed at producing the best fit to the light-curve using the most plausible model.

Grant Hutchison

ToSeek
2008-Oct-11, 06:32 PM
Moved from Astronomy to Q&A.