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A little planet's big impact

These three panels show the first detection of the faint distant object dubbed "Sedna." Imaged on November 14th from 6:32 to 9:38 Universal Time, Sedna was identified by the slight shift in position noted in these three pictures taken at different times. Subsequent observations at longer time intervals provided the information necessary to deduce the nature of Sedna's 10,500 year orbit around the Sun. The field of view of each frame is 3.4 arcminutes square, and each pixel is 1.0 arcsecond. NASA/Caltech Image Data - SpaceDaily Gif
 By Phil Berardelli
 Washington (UPI) March 16, 2004
Back in 1930, when Clyde W. Tombaugh peered through the telescope at the Lowell Observatory in Flagstaff, Ariz., and discovered the planet that eventually was named Pluto, our solar system, our galaxy and our universe were much, much simpler places.

We had the sun, the moon and the five visible planets -- Mercury, Venus, Mars, Jupiter and Saturn. We had the other two gas giants, Uranus and Neptune, which had been observed telescopically in the 18th century. We had the asteroid belt, a few neighboring galaxies and assorted comets.

Aside from some tantalizing preliminary findings -- made the previous year at Lowell by an astronomer named Edwin Hubble -- suggesting that most other galaxies seemed to be speeding away from the Milky Way, for all intents and purposes the universe was a relatively peaceful, predictable place.

Astronomers felt relatively comfortable in their basic theories about the solar system's formation -- how the sun, planets and smaller bodies coalesced billions of years ago out of a giant cloud of dust. They had been assembled painstakingly over the previous 420 years, ever since Galileo looked through his rudimentary telescope, saw what appeared to be four moons circling Jupiter, and shook to its core the widely held belief the Earth was the center of the universe.

In such a context, the discovery of a new planet that fit comfortably into the clockwork of existence was big news, but not particularly surprising.

Now, flash forward to November 2003, when Mike Brown and colleagues at the California Institute of Technology compared three time-lapsed images of the night sky and found the unmistakable motion of a solar system object the size of a very small planet.

Not only was this object much, much farther away than anything ever seen before, it also was discovered at a time when our fundamental concepts about the solar system are being cast anew.

Given the unofficial name Sedna -- for an Inuit goddess who created all sea life -- the planetary object currently is about 8 billion miles from the sun, or nearly three times farther away than Pluto.

"The sun appears so small from that distance that you could completely block it out with the head of a pin," Brown told reporters Monday at a news briefing on the discovery. Despite its remoteness, Sedna was detected as part of a six-year-long sky survey being conducted by Brown and colleagues. The same survey detected another planetoid, called Quaoar, in 2002. Quaoar resides amid a swarm of objects called the Kuiper Belt, which extends from the orbit of Neptune out well beyond Pluto.

Sedna is a different animal altogether. Its location, orbit and probable composition are unlike anything ever seen before, meaning it could not possibly accommodate the clockwork model.

It is the first object to be confirmed within a distant zone called the Oort Cloud, the theoretical home of perhaps trillions of comets. A few of these dirty snowballs occasionally are disturbed enough to send them plunging toward the sun, locking them into periodic orbits such as the one producing the appearance of Comet Halley every 76 years.

Sedna cannot be a comet, however. For one thing, it is too large -- somewhere between 800 and 1,100 miles in diameter, or about three-fourths Pluto's size. Most cometary diameters are smaller than 25 miles.

For another, Sedna's surface seems to be red, like the planet Mars and Jupiter's volcanic moon, Io.

There is evidence Sedna has a moon of its own. Brown told United Press International the little planet rotates about once every 40 days. When a body that large has a rotation that slow, it almost always is due to the gravitational tug of a satellite, he said.

Sedna's strangest aspect, however, is its orbit. In a sense, its discovery was highly serendipitous. Despite its extreme distance from the sun, at the moment it is closer -- and therefore more "visible" -- than it has been during all of recorded history. Sedna is heading back out to a distance that eventually will reach 84 billion miles in a circuit that requires about 10,500 years to complete.

This strange, astounding orbit has supplied astronomers with several important clues about the origins of the solar system -- clues that, if confirmed, will shatter a number of assumptions.

What seems to have happened, Brown said, is Sedna originally inhabited the solar system somewhere in or around the Kuiper Belt. At some point, it interacted gravitationally with one of the gas giant planets -- probably Neptune -- and was ejected into outer space at high speed.

Technically, Sedna should have kept on going, but somehow its trajectory was altered by another gravitational force, which guided it into its hugely elliptical orbit.

As Brown explained, the likely explanation for this development is Sedna must have been influenced by a nearby star.

"The star would have been close enough to be brighter than the full moon and it would have been visible in the daytime sky for 20,000 years," he said.

The only problem is there are no stars around to have played this role, so the only plausible scenario involves how our sun was formed in the first place. Instead of a solar-system-sized dust cloud that produced our sun and the planets, astronomers now think the primordial dust cloud, itself the remnant of a giant exploding star called a supernova, was big enough to have formed several stars -- perhaps dozens.

During the early years of the solar system, when collisions and gravitational interactions occurred almost continually, chances are other formative stars were close enough to influence local celestial developments, such as parking Sedna and other Oort Cloud residents in their current orbits.

Only further research will confirm this, which is why, Brown said, Sedna's discovery is likely to spur a more intensive search for its neighbors. Meanwhile, the venerable Hubble Space Telescope will be pointed at the planetoid to snap its first real photograph.

All rights reserved. Copyright 2004 by United Press International. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by United Press International. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of by United Press International.

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