SF State astronomy students can expect a new and significant addition to their textbooks next year.

NASA scientists revealed today that astronomers have recently discovered a planet-like object that sits at the farthest reaches of our solar system, possibly making it the 10th planet. The planet, named Sedna, after the Inuit goddess who created the sea creatures of the Arctic, is three times farther from Earth than Pluto, the previously known outermost planet to revolve around the sun.

“The sun appears so small from that distance that you could completely block it out with the head of a pin,” said Dr. Mike Brown of California Institute of Technology, Pasadena in a news release.

Researchers at Caltech’s Palomar Observatory near San Diego first detected Sedna last November. It is the largest object found in our solar system since Pluto, the ninth planet, was discovered in 1930.

What’s particularly fascinating about this discovery, according to SF State research fellow Chris McCarthy, is that Sedna’s orbit is radically elliptical, unlike most planets’ orbits, which are more spherical.

“What’s interesting is it has a ridiculously eccentric orbit,” McCarthy said. “This makes it different from other planets in the solar system.”

McCarthy says that because of its elliptical orbit, Sedna, which is 8 billion miles away, was not previously close enough to Earth to be detected. This suggests, according to McCarthy, that there could possibly be other undetected planets within the solar system that are larger than Sedna, which is smaller than Pluto, but which have equally dramatic elliptical orbits that have allowed them to be undetected by researchers. In other words, there could be other planets in our orbit we aren’t aware of yet.

Already there is some debate about whether Sedna should technically be called a planet. McCarthy says astronomers generally define a planet as a mass that orbits around a star. But researchers also use other characteristics to classify something as a planet. For instance, some also take into account the size of the object or whether the object was formed into a sphere by its own gravity. For now, Sedna is being referred to as a planet or “planetoid,” since it indeed orbits the sun.

In any case, the Sedna’s sighting underscores the ever-evolving process of discovery just within our own solar system.

“I think it just reminds us that astronomy is an ongoing process of discovery,” McCarthy said. “We’re constantly rewriting the textbooks by the new discoveries that have been made.”

» E-mail Cassandra Braun @ cassbraun@yahoo.com