Pluto’s Not So Alone Out There, It Appears

Two Caltech astronomers using an aging telescope to scan the fringes of the solar system have found an object half the size of Pluto--a distant, icy sphere they have dubbed Quaoar.

The scientists say the dark, reddish object is the largest body discovered in the solar system since Pluto was spotted in 1930. Although precise measurements are impossible to make from Earth, Quaoar (pronounced KWA-wahr) is estimated to be about 780 miles across, the size of Pluto’s moon, Charon. It dances near the edge of the solar system 1 billion miles beyond Pluto, 4 billion miles from Earth.

The find by Mike Brown and Chad Trujillo, two Caltech astronomers who have worked in relative obscurity to survey the outer reaches of the solar system, was announced Monday at a meeting of planetary scientists in Birmingham, Ala.

Quaoar joins a handful of other strange, large objects recently found in Pluto’s neighborhood, the Kuiper Belt, a swath of icy cosmic residue that extends from Neptune to the solar system’s outer limits.

Its discoverers say Quaoar is too small to be a planet, although they note it is quite planet-like in its behavior and acts far more like a planet than Pluto--the smallest planet in the solar system, with a diameter of 1,400 miles. That finding immediately revived a simmering debate among astronomers about whether Pluto should be stripped of its designation as a planet, and is forcing astronomers to reconsider even basic notions about the solar system as a whole.

“There’s a whole zoo of things out there that we ought to be exploring but haven’t even been able to fit into our conceptual framework,” said David Jewitt, an astronomer at the University of Hawaii who with Jane Luu discovered the first object in the Kuiper Belt in 1992.

Other Plutonian peers found in recent years include Varuna, a 550-mile-across object named for the Vedic god of the oceans; Ixion, an object estimated to be nearly as large as Quaoar, named for the mythical Greek king who fathered the Centaurs; and Rhadamanthus, a smaller object named for one of three judges of the underworld in Greek mythology.

Quaoar takes its name from the creation myth of the original inhabitants of the Los Angeles Basin, the Tongva Indian tribe, also known as the Gabrielenos. According to tribal elder Mark Acuna, Quaoar is the formless, genderless creation force that sang into existence the other deities--Sky Father, Earth Mother and Grandfather Sun.

In this age of eagle-eyed space telescopes that can locate some of the most distant objects in our universe, the discovery of these startlingly large objects so close to home is something of a wake-up call. Even veteran astronomers are calling it “awesome,” “spectacular” and “cool.”

Quaoar orbits in a region of space so cold and dark that our blindingly bright sun appears there only as another star in the night sky. Until recently, most astronomers thought the region was a boring stretch of emptiness containing only Pluto, its moon and a long-sought entity called Planet X, whose theorized existence eventually was disproved.

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Billions of Objects

“People didn’t study [the area] because they didn’t know anything was there,” Jewitt said.

Astronomers since have realized that the Kuiper Belt is swarming with unexpected objects. In the 10 years since Jewitt’s discovery, scientists have found about 600 Kuiper Belt objects, or KBOs. Models suggest that there could be 10 billion of the objects there. Depending on the vagaries of their orbits and the linguistic predilections of astronomers, they are called “plutinos,” “trans-Neptunian objects,” “scattered objects” and “cubewanos” for the first KBO, a 175-mile-diameter object officially cataloged as QB1 despite Jewitt’s proposed name of “Smiley.”

The objects are a motley collection that defy stereotype. Some objects have such distant, looping orbits that they remain invisible from Earth for hundreds, if not thousands, of years. Except for Pluto with its reflective ice surface, the objects found so far are all dark, their carbon-rich surfaces scorched by a constant bombardment of cosmic rays. Some give off a faint, reddish glow. At least seven waltz with satellites nearly their own size. None appear to have atmospheres. And as large as Quaoar is, scientists expect it will soon be surpassed.

“I think this is spectacular,” said Alan Stern, an astronomer at the Southwest Research Institute who leads the Pluto-Kuiper Express, a NASA mission proposed to start journeying toward the Kuiper Belt in 2006. “But I would not be surprised if we found objects substantially larger than Pluto--the size of Mars or even Earth.”

None of this bodes very well for Pluto’s status as a planet.

Pluto was discovered in 1930 by Clyde Tombaugh and quickly deemed a planet. But with the discovery of so many other denizens in its neighborhood, its status has declined. Pluto is not like other planets in our solar system. Its orbit is not circular, but fiercely eccentric, at some points cutting in front of Neptune during a 248-year cycle. It is the only planet that does not lie in the same plane as the others.

In recent years, Pluto has become the Rodney Dangerfield of planets. New York’s Hayden Planetarium demoted Pluto when it included only eight planets in its depiction of the solar system. And now comes this latest blow.

“Quaoar definitely hurts the case for Pluto being a planet,” said Brown, the Caltech astronomer, who argues that if Pluto was discovered today, it would go down in history not as a planet, but as one whopper of a Kuiper Belt object.

Quaoar behaves far more like a planet than Pluto does. Its orbit is nearly as circular as Earth’s and it lies in the same plane as all the other planets--except Pluto.

Pluto’s defenders already are bristling. “You shouldn’t say Pluto’s not a planet because it’s surrounded by other things,” Stern said. “We don’t say Earth’s not a planet because it’s surrounded by asteroids.”

Stern has run calculations showing that any object up to 180 miles across is large enough to become round by gravitational forces and thus should be called a planet. He suggests that Pluto should remain in the pantheon of planets and Quaoar should be invited in too.

“I hate to sound politically correct,” Stern said, “but we need to be inclusive.”

The International Astronomical Union, a group charged with naming and cataloging astronomical objects, created a cosmic stink several years ago when it quietly tried to assign Pluto to the ranks of the “small bodies orbiting the sun.”

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Dual Status Proposed

“People get quite upset about Pluto,” said Brian Marsden, an astronomer at the Harvard-Smithsonian Center for Astrophysics and one of the IAU’s directors. He now proposes that Pluto enjoy “dual status” as a planet and a Kuiper Belt object.

Regardless of Pluto’s status, astronomers believe the little planet and its brethren within the Kuiper Belt hold a host of answers to the origins of our solar system. The region is a kind of refrigerator, holding in deep freeze the ancient dust, ice, rock and organic material, such as carbon, from which all planets formed.

Discovering the secrets of the Kuiper Belt is not easy, given that it is billions of miles away.

Here’s what they know about Quaoar: It takes 288 days to orbit the sun. It completes one rotation every nine hours. It’s not much brighter than a piece of charcoal and is somewhat red. It’s a magnitude 18.5 object--less than 1/100,000 the brightness of the faintest star visible to the human eye. One side is brighter than the other. It’s composed of some still unidentified dark material and water ice. It has no satellites.

Although it sounds basic, this is hard-won information. Distant objects that do not give off their own light are difficult to study, or even find, from the vantage point of Earth. The objects are so faint, they yield few clues even when studied by more powerful telescopes like the Hubble. Only the biggest objects yield much meaningful information at all.

Until recently, astronomers had to scan by eye large photographic plates of the night sky to look for distant objects. They sought faint dots of light that changed position in the sky over the course of the night. Computers now do most of the nastiest work, crunching through digital images looking for objects that have moved.

Graduate students and postdoctoral researchers such as Trujillo do the rest, peering at images the computer has selected, to see if there is indeed anything interesting there. “It’s tedious,” admitted Brown, an associate professor of planetary astronomy at Caltech who has been scanning the Kuiper Belt for five years using the Palomar Observatory’s 48-inch Oschin telescope in northern San Diego County.

Before computers, objects such as Quaoar were easy to miss. Quaoar itself was missed. After finding it in June, Brown went back to photos former Caltech astronomer Charlie Kowal took in 1982 in his search for Planet X. Quaoar was right there. Rather than a discovery, astronomers call a find like Quaoar, whose existence was recorded but not detected, a “precovery.”