Follow-up destinations considered for New Horizons
BY STEPHEN CLARK
Posted: August 31, 2014
Speeding through the outer solar system nearly 2.8 billion miles from Earth, NASA's New Horizons spacecraft was put into hibernation mode Friday for the last in a series of power-saving sleeps as scientists on Earth prepare for a make-or-break encounter with Pluto next summer.
The craft's appointment with Pluto is set for July 14, 2015, when it will zoom about 6,200 miles from the icy world's unmapped surface for a one-shot chance to explore Pluto's geology and atmosphere.
New Horizons passed the orbit of Neptune on Aug. 25, the first spacecraft to reach such distances in a quarter-century.
"It's going to be a bonanza for science in so many ways, and we're going to take you along for all of this journey," said Alan Stern, principal investigator for the New Horizon mission from the Southwest Research Institute in Boulder, Colo.
Stern said the New Horizons science team will use some of the three-month downtime to fish out new destinations for the probe, which has enough fuel to fly by one of the thousands of icy worlds in the Kuiper belt, a zone of Pluto-like objects that lies beyond the orbit of Neptune.
Kuiper Belt Objects, or KBOs, are a recent discovery. Astronomers only confirmed the existence of this new frontier of the solar system two decades ago, challenging assumptions about the boundaries of Pluto, and eventually relegating Pluto off the solar system's official list of planets.
NASA advertised the $700 million mission's capability to visit multiple destinations when New Horizons launched in January 2006, assuming new targets for the probe could be found in time.
"To explore them, we first have to find them," Stern said. "They're very faint. They're very far away. These are objects that are much smaller than pluto and probably much more primitive in terms of their chemistry and their appearance. These are objects the size of counties, for example, not the size of planets."
But the search for a follow-up target for New Horizons has, so far, come up empty.
In a last-ditch effort, NASA tasked the Hubble Space Telescope to search for another destination for New Horizons when ground-based surveys failed to find one.
"Hubble has done a spectacularly good job and yielded literally hundreds of images of that part of the sky, from which we've found some candidates," Stern said. "We don't know if any of them, though, are in our fuel reach and we won't still for some months."
Scientists need repeated observations of each object to measure their orbits and determine if they are within the spacecraft's reach. New Horizons carries a limited amount of fuel, so any decision on a targeted Kuiper Belt Object must account for the probe's capabilities.
Stern said a New Horizons flyby is possible from 2016 to 2021, with the most likely timeframe between 2018 and 2020.
"We hope to know before the year is out, and we will keep you posted as soon as we've made a determination of whether there are reachable objects," Stern said. "We certainly hope so."
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