A Star and a Planet; or Two Planets; or a Brown Dwarf and a Planet; or Something Else

"Possible Alien World Around Mini-Star Tests Definition of a Planet"
Space.com (April 8, 2010)

"A planet-like object has been found to be orbiting a cold, miniature star called a brown dwarf, calling into question just what it means to be a planet.

"Brown dwarfs are not quite massive enough to be full-fledged stars; they are not dense or hot enough in their cores to ignite nuclear fusion, the process that powers stars.

" 'Brown dwarfs are nature's "almost stars" - gassy bodies that aren't quite hot enough in their cores to fuse hydrogen,' said researcher Kim McLeod, an astronomer at Wellesley College in Wellesley, Mass.

"And the new discovery of an apparent planet orbiting one of these mini stars seems to blur the line even more between a planet and a brown dwarf.

"In this case, the 'star' weighs about 20 times the mass of Jupiter, but its planet weighs not too much less – about 5 to 10 times Jupiter's mass. ..."

I suppose we could call them platyplanets - since, like the platypus, they don't fit into our existing categories all that well. Somehow, I don't think that name will catch on.

Two - things - pretty close to the same mass (one's only a few times more massive than the other), neither one of which supports nuclear fission, could be called a double planet. But I suppose that's controversial, since there isn't a 'real' star nearby. And planets orbit stars.

The ones we were familiar with, anyway.

Notice: "were familiar with." This is an exciting time to be alive: what was presented as 'well known' in my youth now - isn't. And right now it seems to be the case that, the more we find out about stars and planets, the less we know for sure.

Like this pair. The smaller object apparently formed in less than 1,000,000 years. Which is a crazy-short time on the cosmic scale. Too short. Planets can't form that fast. Or, rather, (most) existing theories had the process requiring a whole lot more time.

I've written about this sort of thing before - it's good news when observed data back up an existing mathematical model. It's better news, I think, when what we observe doesn't. That means we may have a whole new set of possibilities to explore.

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Related posts, at

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"