Solar system just became much larger

The big news from space this week is that our celestial neighborhood has suddenly gotten a whole lot bigger.

In case you missed it, astronomers announced Monday the discovery of a frozen sphere that is the most distant celestial body known to orbit our sun. Unofficially named Sedna, after the Inuit sea goddess who is said to live in the Arctic Ocean, the newfound object is the largest to be detected in the solar system since Pluto was spotted in 1930.

“There’s absolutely nothing else like it known in the solar system,” said Dr. Michael Brown, an astronomer at the California Institute of Technology who led the research team.

But while some scientists suggest that the red ball of rock and ice is a likely candidate to become our 10th planet, others insist it’s far too early to rewrite our science textbooks by adding Sedna to the familiar planetary grouping we first learned about as children.

“I certainly will not be calling it our 10th planet,” said Neil Comins, a University of Maine astronomer and author who expects the seventh edition of his popular textbook, “Discovering the Universe,” to be published in April. “It’s too small and has too elliptical an orbit for a planet, which typically has a more circular orbit around the sun.”

If nothing else, Comins said, the hoopla surrounding Sedna’s discovery is sure to reignite the debate over what constitutes a planet in the first place. One group of astronomers believes that Pluto is not a true planet, for example, but merely one of the largest of a vast number of minor objects, the so-called planetoids, that exist at the icy outer edges of the solar system. Another holds that Pluto is indeed a planet, although one made mostly of ice and rock like a comet, which could lend legitimacy to such a classification for Sedna, which may have a similar primordial composition, though of lesser mass.

“I am inclined to believe that more of these objects will be found,” Comins said. “And these new bodies, like Sedna, will absolutely demand that we rethink Pluto, too.”

The traditional solar system, he explained, is made of the sun, the nine planets, moons, comets, asteroids and smaller pieces called meteoroids. As early as the 1950s, however, it’s been conjectured that there are reservoirs of other stuff out there, too. One is called the Kuiper Belt, a doughnut-shaped region of cometary matter stretching from Neptune to just beyond Pluto.

“Since the 1990s, they have found in excess of 600 Kuiper Belt objects, about a dozen of them quite large,” Comins said. “They’re believed to be the sources of comets, the material that gets kicked our way as ice and rocky debris.”

Sedna travels an egg-shaped orbit that begins at the outer edge of the Kuiper Belt and extends to a vast distance, taking it 10,500 years to revolve around the sun. Some scientists suggest that Sedna could have been a part of the Kuiper Belt that was dislodged and sent on its widely eccentric orbit. It’s also possible, Comins said, that the Sedna planetoid is part of the Oort Cloud, a more distant repository of comets pulled toward the sun.

“If so, it would be the first Oort Cloud object we know of,” he said.

Whatever the icy body is called, and wherever it might have come from, Sedna’s far-ranging travels through space have scientists speculating over what it tells us about the breadth of our solar system.

“Sedna’s elliptical orbit has definitely stretched it out and made it much bigger,” Comins said.