NASA has directed the Hubble Space Telescope to scan the outer frontier of the solar system for a second destination for the New Horizons space probe after it records historic first-time views of Pluto on a flyby next year.

This is an artist's rendering of the New Horizons spacecraft encountering a Kuiper Belt object -- a city-sized icy relic left over from the birth of our solar system. Credit: JHUAPL/SwRI
 
The famed orbiting observatory will try to do a job ground-based telescopes were unable to accomplish since the launch of the New Horizons mission in 2006.

With the rough dimensions and shape of a grand piano, the New Horizons spacecraft is on a trajectory to fly by Pluto and continue into a realm of the outer solar system harboring numerous icy worlds in a zone called the Kuiper Belt.

New Horizons is coasting toward a July 14, 2015, encounter with Pluto, its moon Charon and at least four other small satellites. Scientists will harvest unprecedented up-close images of Pluto from the first-ever flyby, along with fresh data on the environment in the unexplored reaches of the solar system.

But what comes next for New Horizons is undecided.

When scientists proposed the New Horizons mission, they sold the $728 million project partially on its ability to fly beyond Pluto, scouting a region of the solar system never before visited by a manmade spacecraft.

The probe has enough propellant to slightly change its path after the Pluto flyby to approach an object in the Kuiper Belt, a donut-shaped ring of icy worlds lying beyond the orbit of Neptune. Scientists consider Pluto itself a resident of the Kuiper Belt, along with dwarf planets like Eris, Makemake and other worlds detected in the last few years billions of miles from the sun.

But officials planning the New Horizons mission have not found a suitable object close enough to the probe's flight path, prompting a last-ditch request for observing time on the Hubble Space Telescope to search for a potential target after next year's visit to Pluto.

The request faced stiff competition for precious access to Hubble, but a board responsible for allocating observing time approved the proposal from the New Horizons team.

"I am pleased that our science peer-review process arrived at a consensus as to how to effectively use Hubble's unique capabilities to support the science goals of the New Horizons mission," said Matt Mountain, director of the Space Telescope Science Institute in Baltimore, Md.

Hubble began surveying a patch of the cosmos in the direction of the constellation Sagittarius this weekend, scanning across the sky at the predicted rate objects in the Kuiper Belt would move against a background field of stars.

Astronomers can detect Kuiper Belt objects, or KBOs, moving across a relatively unchanging canvas of stars and galaxies because the icy bodies are much closer to Earth.

"If the test observation identifies at least two KBOs of a specified brightness it will demonstrate statistically that Hubble has a chance of finding an appropriate KBO for New Horizons to visit," NASA said in a press release. "At that point, an additional allotment of observing time will continue the search across a field of view roughly the angular size of the full moon."

The trial phase of the Hubble observations, comprising 40 orbits of the telescope, will end next week, according to Alan Stern, lead scientist on the New Horizons mission from the Southwest Research Institute of Boulder, Colo.

If the initial observations go well, the full data set will be available by Aug. 15, Stern said in an email to Spaceflight Now.

Stern said a New Horizons flyby is possible from 2016 to 2021, with the most likely timeframe between 2018 and 2020.

Assuming Hubble finds a target, the New Horizons team will submit a proposal for review by NASA to win funding to continue operating the probe for a Kuiper Belt object flyby, Stern said.

The New Horizons spacecraft woke up from hibernation Sunday for a 12-week checkout of the probe's primary and backup systems, along with its seven science instruments, according to the mission's website.

The craft will also get a navigational fix on Pluto to help ground controllers guide New Horizons toward its flyby.

It will go back into sleep mode later this summer before New Horizons awakes for the last time in December to prepare for the Pluto encounter next year.

Follow Stephen Clark on Twitter: @StephenClark1.