News: August 2006 Archives

Looks like there is now some hard evidence for dark matter. More commentary and explanation here. (Apparently it doesn't rule out MOND, but it does confirm that dark matter exists, which has been one of the most embarrassing questions in physics for a couple of decades now — given that visible matter accounts for only about 4% of the energy density of the universe, where is the rest hiding?

The two big question marks in our knowledge of what the universe is made of are dark matter (which doesn't interact with the type of matter we're familiar with, but which clumps gravitationally) and dark energy, which I can't get my head around (how the hell does something have negative pressure?). Dark matter appears to account for 22% of the universe, with dark energy making up the other 70-something percent (darn it, why is the universe seven-tenths made up of something I don't understand even the layman's definition of?). And today it looks like we're down one question mark.

Last week, the International Astronomical Union began work on a rather important counting-angels-on-the-head-of-a-pin exercise: defining precisely which bodies orbiting our sun qualify for the appellation of "planet". Naturally, this has provoked considerable controversy, and I've been watching the ongoing arguments with amusement (especially the debate between SF writers John Scalzi and Scott Westerfield, who are both jolly excellent chaps, if a trifle over-excited right now — I blame the brain-eater).

One of the causes of controversy is the dubious status of Pluto. Pluto is way smaller than Mercury — indeed, it's smaller than Luna — and orbits the sun in a rather eccentric catch-me-if-you-can way. Back in 1930 a case was made for it being a planet before its size was established, but these days it's clearly just one of the easiest to see among a whole pack of also-rans, including Ceres (in the asteroid belt, over there), Charon (which it co-orbits with), Xena, Quaoar, and a bunch of other large Kuiper belt bodies. Rather than demote Pluto to the status of a mere chunk of rock like any other KBO, the IAU has compromised by defining a new class of planet, called a "Plutonoid".

This is bullshit. We all know that the only real planets — the big ones that accreted from the solar disk right at the beginning — are Jupiter, Saturn, Nepture and Uranus. They're self-accreting bodies that aren't massive enough to undergo fusion and that formed in orbit around a star. OK? That's a planet.

Naturally you're biased: you live on Earth after all. But I have to tell you, these days we have this theory called the heliocentric model that holds that Earth isn't the centre of the universe. Guess what? Earth isn't a real planet, either. It's just a ball of rocky left-overs that didn't get its fair share of gas when the accretion disk was still swirling. Indeed, the same goes for Mars, Venus, and Mercury. These tiny rocks (Earth, the largest, is barely a thousandth the mass of Jupiter) orbit in the wrong damn place, far to close to their primary star to have any hope of hanging onto a volatile envelope of hydrogen and a bit of helium. In fact, I think it's about time the IAU bit the bullet and admitted that these dwarfish rocky cores are just that, and introduced a new category, "failed planetary nuclei", to define the rocky Earthlike bodies of the inner solar system.

Given that the "Plutonoids" are believed to be mostly condensed gassy stuff, we can (subject to confirmation) then redesignate them as "failed planetary atmosphere fodder". The asteroids and small KBOs can then be allocated to one group or the other, or a fourth, catchment category: "irritating little shit". And the rationalization of the solar system is done.

It'll be so much easier to teach kids the names of the planets when we've pruned them back to four!



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This page is an archive of entries in the News category from August 2006.

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