NASA's New Horizons was launched to study Pluto but scientists behind the mission are apparently eyeing to study not just the dwarf planet but also other celestial bodies beyond it.

Scientists behind the New Horizons mission have in fact spent about four years looking for targets that the space probe may just be able to explore after it goes past the Pluto System.

The team has considered the possibility of an extended mission that involves New Horizons exploring another object in the Kuiper Belt, a region in the Solar System beyond the orbit of Neptune, where Pluto lies along with other Kuiper Belt objects (KBOs, which are believed to be the remnants of the birth of the solar system.

"These are objects that are much smaller than Pluto, and probably much more primitive in terms of their chemistry and their appearance," explained New Horizons principal investigator Alan Stern. "These are objects the size of counties, for example, not the size of planets. They're very faint."

The New Horizons team initially used some of the biggest ground-based telescopes in 2011 but out of the dozens of KBOs they found, none seemed to be reachable given the New Horizons' fuel supply. The scientists then turned to NASA's Hubble Space Telescope for help.

Using the Hubble, the scientists scouted for objects that the New Horizons can explore after it flies by Pluto in July 14 next year and finally last Wednesday, NASA revealed that the telescope has helped spot three KBOs that the spacecraft could potentially explore after its Pluto flyby.

"We started to get worried that we could not find anything suitable, even with Hubble, but in the end the space telescope came to the rescue," said New Horizons science team member John Spencer. "There was a huge sigh of relief when we found suitable KBOs; we are 'over the moon' about this detection."

KBOs vary in sizes. Two of the KBOs that the Hubble spotted are about 34 miles across and the third one is about 15 miles across. The objects lie about a billion miles beyond the location of Pluto.

Pluto was still categorized as a planet when the New Horizons was launched from Florida in 2006 but it has since been downgraded as a dwarf planet.

"Pluto was considered a planet until 2006," NASA said. "The discovery of a similar-sized worlds deeper in the distant Kuiper Belt sparked a debate that resulted in a new official definition of a planet that did not include Pluto."