Randy McDonald (rfmcdpei) wrote,
Randy McDonald

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[BRIEF NOTE] Brown Dwarf Planetary Systems

Will Baird's The Dragon's Tales is a superlative place to go for many things: cute baby pictures, notes about Ukraine's development, militaria and geopolitics, space travel and astronomy. Yesterday, he made an interesting posting about brown dwarves. To wit, via Yahoo News:

A NASA telescope has detected for the first time the building blocks of planets around brown dwarfs, suggesting that such failed stars probably undergo the same planet-building process.

Until now, the microscopic crystal building blocks that eventually collide to form planets have only been seen around stars and comets — considered the remnants of the solar system.

NASA's Spitzer Space Telescope recently spotted the tiny crystals and dust grains circling five brown dwarfs located 520 light years away in the Chamaeleon constellation. The crystals, composed of a green mineral commonly found on Earth known as olivine, are thought to be the building blocks of planets.

Brown dwarfs, like stars, form from thick clouds of gas and dust. But they collapse under their own weight and are considered the older and dimmer cousins to stars.

"We are learning that the first stages of planet formation are more robust than previously believed," said Daniel Apai, an astronomer at the University of Arizona, Tucson.

Astronomers believe planets were born out of disks of dust that surround young stars and brown dwarfs. The particles that make up the disk eventually crystallize and clump together to form planets.

It's worth noting that these planets might not be Earthlike. Saturn has a single planet-sized moon, Titan, approximately the size of (though with a lower density than) Mercury. Jupiter, three and a half times as massive as Saturn, does not have a single much larger moon, instead hosting the Galilean moons, four planet-sized moons each slightly smaller than Titan. Would a brown dwarf massing ten times as much as Jupiter host (say) ten or so dense planet-sized objects, or just ten times as many Galilean worlds?

More critically, brown dwarves--unlike main-sequence stars--fade continuously over time. They are brown dwarves simply because they lack the mass needed to permanently turn on their stellar ignitions, cooling quickly. This won't prevent life from forming, or being seeded--in Karl Schroeder's 2002 novel Permanence, where the planet-sized worlds of brown dwarfs are illuminated and heated by superconducting cables--but it will limit the number of Earthlike worlds, with middling-density nitrogen-oxygen atmospheres, around. Think instead worlds with dense greenhouse atmospheres, of methane and carbon dioxide, or of frozen worlds with warm subsurface water and ammonia-water oceans.

These provisos aside, this is brilliant news. I can't wait to be proven wrong by the discovery of the first gas-giant world in orbit around a brown dwarf, the closer the better.
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