Astronomers have found a mini-Pluto that's neither a moon nor a planet. It's a plutino -- an object that orbits the Sun in the same amount of time as Pluto, but is too small to be called a planet.

Take Plutino Home

Starry Night users! Follow these steps to download a Starry Night datafile to add Plutino to your own personal solar system! 1)

2) When asked where you want to save it, navigate to the "Starry Night Data" folder in your Starry Night folder. Save the file there. 3) Next time you start up Starry Night, you'll see "Asteroid 2000 EB 173 Plutino" under Asteroids in your Planets window.

Don't have Starry Night yet? Now's a great time to download the demo .The Plutino data file will work just as well with the demo as with the full version!

The object, 2000 EB173, was found in March using data collected by a 39-inch (1-meter) telescope at the CIDA Observatory in Venezuela. The space rock is estimated at about one-quarter the size of Pluto and joins a club of more than 300 other "trans-Neptunian objects," small bodies that orbit the Sun beyond Neptune.

"This is the biggest and brightest that has been seen so far," said Charles Baltay, a Yale University physicist who headed up the investigation. Baltay and his co-authors plan to report their finding in Astronomical Journal Letters.

"We believe that this thing has been orbiting since the formation of the solar system. So it's the primordial stuff, and it's bright enough that we can study it in detail."

The object appears to be dark red, suggesting it is covered with ancient organic chemistry, Baltay said, but more data will reveal better facts.

The size of the object has been estimated but it actually could range from 185 to 435 miles (300 to 700 kilometers), said Gareth Williams, associate director of the International Astronomical Union's Minor Planet Center (MPC). All discoveries of this type are made to the MPC in Cambridge, Massachusetts.

"We can't see it directly," he said of EB173, but astronomers estimated its size based on its brightness. The object orbits the Sun every 240 years.

An observer with a 12- to 16-inch (305- to 405-millimeter) telescope could locate the object but it's invisible to the naked eye or even binoculars.

There are two primary places for asteroids in our solar system; the Main Belt between Mars and Jupiter is home to some 40,000 to 50,000 objects and a belt that extends beyond Neptune's orbit.

The discovery of EB173 brings back the argument of whether Pluto, discovered after a long search by Clyde Tombaugh in 1930, ought to be called a planet, Williams said. "If it were discovered today it would get a minor planet designation," he said -- that is -- not a planet.