Thursday, January 27, 2005

Does an earthlike planet require a neighboring supernova? - A different 'Big Bang' may have saved Earth

I only see the USA Today when traveling. This morning I caught sight of this article. I expected to see some f/u in the New York Times, but USA Today seems to be ahead of the pack. On review I note that this is still a "controversial hypothesis", but a more technical article states some supporting evidence (atypical isotopes) will be published shortly.

This is tremendously interesting, though the journalist missed the key point of interest. The hypothesis is that earthlike planets, the only kind known to support sentience (one example), can only form when a supernova detonates very close (1 light year -- or closer than the current closest star) to a star with an early, very shortlived (few million years), planetary disk (disc). The supernova blows away parts of the disk and seeds the early solar system with heavy metals. Without the supernova effect any earth like planets get expelled or destroyed by careening gas giants early in solar system development -- or whacked by comets a bit later on.

Not to stretch an analogy, but the solar system is like an egg, and the supernova is like exploding ... ummmm ..... errrrr .... you know. If the supernova doesn't blow at precisely the right time and right distance -- the egg is sterile.

So what did Dan Vergano miss? This data should allow astronomers to estimate how common earth like planets are. One of the mysteries of our galaxy is that it's not swarming with little green men. There are several explanations of this; one explanation is that planets that support life, much less sentience, are very rare.

Supernovae are not all that common in our galaxy, though they were probably more common 4 billion years ago. If very proximal supernovae are required to produce "fertile" solar systems, then earth like planets may be quite rare. Since the galaxy is known to be a very violent place, many of those planets would be sterilized or destroyed before life could develop.

I'd be particularly interested to know if any "tweaks" to the fundamental parameters of physics (C, G, Planck's constant, etc) would change the equation to increase the number of "fertile" solar systems. It would be particulary interesting if small tweaks would change the frequency of "fertile" planets to either zero or many. If it turned out that the universe is "tuned" to produce an average of one sentience per spiral galaxy ... well ... that's interesting.

All fun stuff. I guess not everyone shares my hobby however!
Astronomers studying the planet-forming disks of dust that orbit young, distant stars are hoping to solve the mystery of our own solar system's youth. Why is our system so different in form and function from others they can see?

It's a difference that may have saved Earth, because the scientists suspect that Jupiter and Saturn would have collided with the planet — or slung it out of the solar system like a slingshot — if the disk surrounding our young sun hadn't been so damaged.

These "protoplanetary" disks were a hot topic at a recent meeting of the American Astronomical Society. "Something very bad happened to our solar system's disk in its early years," says Steve Desch of Arizona State University in Tempe.

An exploding star, or supernova, likely occurred within a light-year — about 5.9 trillion miles — of our sun in its infancy, he argues. (The closest star to our solar system now, Proxima Centauri, is about 4 light-years away)...

... A presentation at the meeting about a Hubble Space Telescope survey of 25 nearby stars, all youngsters less than 10 million years old, provides evidence that dust disks congeal into more compact bodies over only a few million years.

.... Only the eruption of a star 25 to 40 times bigger than our sun could have littered our solar system with the radioactive elements seen in meteorite surveys reported by Desch's team at the meeting.

Astronomers have seen just such explosions blasting protoplanetary disks in the Orion Nebula, a star-forming factory 1,500 light-years away. Rather than blowing away the disks, the supernova blasts appear to seed them with metals rocketed out of the heart of the exploding star.

The supernova that blasted our solar system may explain some of its other peculiarities:

•Planets in our solar system follow nearly circular orbits far from the sun. Most planets detected orbiting other, nearby stars follow either highly elongated orbits or circle incredibly close to their stars. Scientists suspect that a stellar explosion could have stopped these developments in our solar system.

•Dust disks seen orbiting nearby stars typically contain much more material, sometimes 100 times more, than our solar system. A Spitzer Space Telescope survey of 26 nearby sun-like stars known to have planets found evidence that six of them have comet belts. But all appear filled with about 100 times more comets than our own. [jf: comets can be very dangerous ...]

"There's good evidence the solar system had a stunted formation when the (supernova) injection happened," Desch says. And that may have been very good for Earth.

Many astronomers believe that Jupiter and Saturn formed deep in space, far beyond Pluto's orbit, and spiraled into the solar system. Why they stopped a safe distance from the sun and left Earth undisturbed — unlike the history of many other solar systems seen nearby — is the final mystery that disk studies may help answer..

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