Our First Interstellar Destination: A Brown Dwarf?

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We are on the verge of uncovering a “really cool” universe of potentially millions

of never before seen objects.

By “really cool” I’m not trying to sound hippy-dippy, but rather am talking about objects in space that are less than 1,000 degrees Fahrenheit.

And, this might lead us down the path to an interstellar mission to a cryoplanet where surface temperatures hover tens of degrees above

absolute zero.

This “cool” survey of the comparatively chilly universe will

be conducted by NASA’s WISE mission (Wide Infrared Survey Explorer). The

mission’s small cryogenic space telescope in a Thermos bottle is scheduled to

launch on Dec. 9 from Vandenberg Air Force Base in California. It will complete

making an all-sky infrared map by the middle of next year. The catalog is expected

to reveal the coolest stars, 100,000 asteroids, and some of the brightest

star forming galaxies that are shrouded in dust, among many other targets.

I’m predicting two potentially news breaking headlines from

WISE (and no doubt there will be other stories too). The first would be the

discovery of an entirely new class of dark astronomical object that has

previously escaped detection. Since I can’t imagine what that could be, there

isn’t much more I can say except to expect the unexpected.

The other headline would be the discovery of a brown dwarf that

is even closer to Earth than the nearest star, the Alpha Centauri system at 4.3

light-years. Brown dwarfs are objects that form along with stars but do not

have enough mass to trigger or sustain nuclear fusion. They are so cool and dim

very little is known about their distribution in the galaxy.

A survey of the local stellar neighborhood by Tod Henry of

Georgia State University leads him to estimate there is at best a 50/50 chance

of a brown dwarf being closer to Earth than Alpha Centauri. But within a year

we may have the answer from the WISE survey where astronomers predict finding

1,000 brown dwarfs.

As a hypothetical, let’s say a brown dwarf is found to be no more

than a couple light-years away. That’s roughly 120,000 times the distance

between Earth and the sun. There would certainly be talk of launching a mission to the dwarf. Today’s fastest interplanetary payloads would take 40,000 years to get there. A vastly advanced propulsion system, such as an interstellar laser, would push an ultra miniaturized

probe like a leaf caught in a jet of water from a garden hose. A transit time of

40 years would require blistering velocities of no less than 5 percent the

speed of light. That’s fast enough to travel from Earth to the moon in 30

seconds!

Why bother visiting the dwarf even if it is so close by? Simulations

predict that protoplanetary disks should form around brown dwarfs. In 2006, NASA’s

Spitzer Space Telescope surveyed 35 nearby browns dwarfs and found dusty disks

around a third of them. The remainder of the sample possibly had disks that are much fainter because they have already been cleared out by planets, say researchers.

“There should be enough material present to form terrestrial planets in the inner disks [of brown dwarfs], and therefore the closest brown dwarfs should be important targets for future planet searches,” wrote Danial Apai, of Stewart Observatory in Science magazine in 2005. What’s more, exoplanet candidates have

been found orbiting three brown dwarfs so far.

Any cryoworlds around a neighboring dwarf would be an unlikely place

to look for life. Brown dwarfs cool off quickly. The coolest found so far is at 700 degrees Fahrenheit. But if Jupiter’s moon Europa is any example, brown dwarf planets could have subsurface oceans kept warm by gravitational tidal interactions with the dwarf or other planets.

The flyby would last just a few hours. The encounter timeline would be crammed with a barrage of imaging and spectroscopic observations. No astrobiology experiments could be done. But imagine if there were tantalizing fleeting snapshots of water ice plumes erupting from a planet, like the geysers on Saturn’s frigid moon Enceladus.

The builders of the probe would have spent their entire professional career waiting for the close encounter. The public would be enticed by the prospect of the first interstellar mission that can be completed with a single lifetime. The biggest cultural impact from the mission would be a photograph of the dwarf, with our sun seen as merely a bright star among background constellations.

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