rethinking the solar system
  POSTED 4 JUNE 1998. Are we alone in the universe? The answer depends on how many planets exist, since only planets allow the conditions for life to exist -- at least as we can envision it.

 
  new planet potential In the past couple of years, scientists have detected faint gravitational signs of more than half-a-dozen planets outside our solar system.

This NASA Hubble Telescope image of newborn binary stars shows a long thin nebula pointing to a faint object. Is this the first extrasolar planet to be imaged directly? Susan Terebey, Extrasolar Research Corp., and NASA.

big blue marble
  Now, a group of scientists think they've located an actual portrait of a planet in a picture from the Hubble Space Telescope.

Granted, it's heavy, gaseous, and probably hotter'n blazes. But actually seeing planet among the vast heavens could signify that they are fairly common.

End of preparatory blather.
The planet -- we'll call it that, even though the finding is preliminary -- appeared on a photo made last August of a pair of young stars in the constellation Taurus, about 450 light years from Earth. The planet was said to be two or three times as massive as Jupiter, and about 130 billion miles from its parent stars. At the rate it's leaving those stars, it will escape orbit and may wander perpetually through space.

The parent stars live in a star-forming region of the Milky Way, and they're young to be having babies -- perhaps just a few hundred thousand years old. The discovery was made by a team lead by Susan Terebey of Extrasolar Research Corp. of Pasadena, Calif., using the Near Infrared Camera and Multi-Object Spectrometer on the space telescope.

The instrument actually sees heat that the object generates internally, not reflected light. "This "planet" does not 'know' it's a planet because it now has the same temperature and luminosity as a low luminosity star," says Ben Zuckerman, professor of physics and astronomy at the University of California at Los Angeles.

Any strings attached?
Several.
First
, this planet could actually be a star that's light years away its supposed parent stars. "Just because you have an image near a star doesn't mean it's actually near the star," says Zuckerman. The object could be many light-years in front of, or behind, the parent stars.

Second, it could be a brown dwarf -- a small, dim star whose nuclear fusion never started fully cooking.

Third, if the object is a planet, it's probably a gas planet like Jupiter or Saturn -- not a rocky one like Earth. Since gas planets probably cannot harbor life, the new finding -- even if correct -- may say little about the formation of Earth-like planets.

Fourth, there's almost literally a string attached -- a streak of dust, gas, or to all appearances a giant leash -- linking the planet to its parents. It was this peculiar feature that prompted Terebey to examine the image more closely.

Cosmic streaker
Although the streak makes the planet look like a yo-yo, it is probably not restraining the planet. Yet Terebey says it may provide clues about how the planet formed.

once again Terebey says that the streak could be a tunnel burrowed by the planet through the dust cloud as it left the parent stars. This tunnel, she says, could serve as a "light tube" which channels light out from the stars cloaked in their dusty cocoon.

Another view of the possible planet and the binary "parent" stars. Susan Terebey, Extrasolar Research Corp.

But that explanation for the streak, which is what first distinguished the "planet," is controversial.

   
  If stars cut such tubes while passing through dust, Zuckerman argues that we'd probably have seen them. There are plenty of stars in dusty regions, he says. "Do we see light pipes around the orbits of these stars?" Furthermore, he says, the tubes would not last forever. "How long would it take for material from the surrounding dust cloud to fill it in from pressure and squeeze off the tube?"

What does it tell us about planet formation?
If correct, the finding could upset the traditional view of how planets are created or provide an alternative creation story for some planets. The standard view is that planets -- like stars -- coalesce from disks of interstellar crud -- mainly gases and some heavy elements.

Since these planets form from spinning disks, they are orbiting around the star from the start. In contrast, the new planet is said to have been flung rather directly away from its parent stars. Thus the mechanism that created these planets may say little about how Earth-like planets were created.

But for now, the best advice may be "first things first." Like the skeptics who prefer "found object" to "planet," The Why Files awaits further results. Perhaps most convincing, Zuckerman says, would be a photo taken in a year or two, showing that the object's path began at the binary stars that supposedly spawned it.


-- David Tenenbaum

The Why Files covered the search for extra-solar planets in more detail.
Here's the press release on the discovery.
And here's a page from Extrasolar Research Corp., on the "candidate protoplanet."


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