WASHINGTON -- NASA has selected two teams to further study the feasibility of a mission to Pluto. The spacecraft would be dispatched in the 2004-2006 time frame to arrive at the distant world before 2020.

The mission would explore the only planet in our Solar System not yet visited by a spacecraft from Earth, as well as the Kuiper Belt of rocks orbiting beyond Pluto. But there's one catch.

While NASA has given the study monies, the President's fiscal year 2002 budget request does not contain development funding for a Pluto-Kuiper Belt (PKB) mission. Still Congress eventually could provide funding and one of the two design teams would get a go-ahead.

The two rival study teams are:

A team led by S. Alan Stern of Southwest Research Institute, also of Boulder, Colorado. Stern's group called their proposal, New Horizons: Shedding Light on Frontier Worlds.

The probe is managed by the Applied Physics Laboratory in Laurel, Maryland, with NASA Goddard Space Flight Center as a co-investigator on the mission.

"I'm euphoric," Esposito told SPACE.com. "It's a great opportunity for us and the country to develop two possible studies for getting to Pluto."

Esposito said studies have been under way for about a decade to develop a Pluto mission. "If feels good to get one step closer to the actual mission," he said. "It's a long and expensive mission, so in our study we are going to show NASA how we can lower risk and maximize the science."

Colleen Hartman, Pluto Program Director in NASA's Office of Space Science, said sending the PKB to look at the deep-freezer of a world will help scientists know how our Solar System evolved to what it is today, "including the precursor ingredients of life."

Each team will receive $450,000 to conduct a three-month concept study of a PKB mission. At the end of that three months, NASA will thoroughly evaluate the studies to determine if either proposal is selectable.

The two selected proposals were judged to have the best science value among five proposals submitted to NASA in April 2001, according to a NASA statement. Both address the major science objectives defined in the original announcement. Each proposal includes a remote sensing package that includes imaging instruments, a radio science investigation, and other experiments to characterize the global geology and makeup of Pluto and its companion, Charon, map their surface composition, and characterize Pluto's atmosphere.

Why go to Pluto in the first place?

Pluto is a different kind of planet. It is not a rocky planet like Earth, Mars, Mercury or Venus, or a gas giant like Jupiter, Saturn, Uranus or Neptune. It is a Kuiper Belt Object, a class of objects composed of material left over after the formation of the other planets, which has never been exposed to the higher temperatures and solar radiation levels of the inner solar system.

It is known that Pluto has large quantities of ices of nitrogen, and simple molecules containing combinations of carbon, hydrogen and oxygen that are the necessary precursors of life. These ices would be largely lost to space if Pluto had come close to the Sun. Instead they remain on Pluto as a representative sample of the primordial material that set the stage for the evolution of the Solar System as it exists today, including life.