Thursday, February 22, 2007

An ancient apocalypse at Osiris?

NASA and Nature revealed yesterday that the first direct spectroscopic observations of extrasolar planets have been made - of the repeat favorite HD 209458b (unofficially a.k.a. Osiris) and HD 189733Ab (getting reported as HD 189733b).

From today's issue of Nature: "A spectrum of an extrasolar planet"

NASA press release:

The results were totally off the wall. Here's the best part:

"Superposed on this continuum is a broad emission peak centred near 9.65 microm that we attribute to emission by silicate clouds."

Silicate clouds in a gas giant are of course previously unheard of, and I would assume, not yet having read the full Nature article, are dynamically unstable. What would put a silicate dust cloud into the outer atmosphere of a gas giant at 0.045 AU semimajor axis - but a terrestrial planet! One that got too close and plunged headlong into a Jupiter, getting tidally shredded through the Roche limit.

I'm sure it's been depicted in some science fiction novel at some point - but here is evidence of it happening for real. Jeez, can you just imagine? How I would have loved to have sat in a stadium seat with a soda and popcorn to watch that one - from a craft at an appropriate distance.

Also a nice new wet towel to throw at the next person who waxes illogical on the anthropic principle.

I have to wonder if significant amounts of silicate dust in the outer atmosphere is a short-term, dynamic feature, with a characteristic persistence time in only the millions of years after collision of another terrestrial body before the denser rock settles into the inner depths, and we are happening to see Osiris in an era when it relatively recently ate one or more of its rocky brethren. Otherwise, perhaps the rocky material in the HD 209458 system was disrupted from accumulation into planetary-sized bodies from the beginning, a magnification of our own asteroid belt likely due to the constant gravitational pestering of Jupiter in the formation of the solar system; there would have been ample opportunity for either kind of disruption if an almost-Jupiter sized body migrated from the outer solar system to just a few million miles above the star's surface, although Osiris has had plenty of time to settle into its hot-as-hell orbit with eccentricity of about zero.

But, this planet has all kinds of strange new properties; we need to learn more. And each new discovery should be a fresh reminder of the foolish lack of imagination in old models that assumed planets outside our own solar system would be minor variations on the templates of the already familiar planets.

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