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Hubble to search beyond Pluto for New Horizons' next target

Jenny Winder, News Writer
Jun 18, 2014, 13:30 UTC

Sen—The Hubble Space Telescope has swung into action to search for an object that NASA's New Horizons mission could visit after it zips past Pluto in July 2015.

New Horizons is the fastest spaceprobe ever sent into space and it won't be able to hang around when it reaches the dwarf planet that is its initial target. Scientists need to prepare now for when it enters the outer reaches of the Solar System, a great void about which little is known.

The planned search will involve targeting a small area of sky in search of a Kuiper Belt object (KBO) for the outbound spacecraft to visit. Named after astronomer Gerald Kuiper who predicted its existence in the 1950s, the Kuiper Belt is a vast debris field of icy bodies left over from the Solar System's formation 4.6 billion years ago.

A KBO has never been seen up close because the belt is so far from the Sun, stretching out to a distance of 5 billion miles.

New Horizons’ lead scientist Alan Stern told Sen that the initial Hubble campaign to search for a KBO will last two weeks, or 40 orbits of the space telescope around the Earth.

If it is successful and finds one or more KBOs in that time, the New Horizons team will get use of the telescope for another 160 orbits to check for more.

They need to find a target by mid-August. If they don't find anything in the first observing session, which began on Monday night, then the search will be halted.

However, Stern said that, overall, computer models showed there is a 95 per cent chance that Hubble will be able to find a suitable target.

Matt Mountain, director of the Space Telescope Science Institute (STScI), said: "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." 

Hubble will scan an area of sky in the direction of the constellation Sagittarius to try and identify any objects orbiting within the Kuiper Belt. To discriminate between a foreground KBO and the clutter of background stars in Sagittarius, the telescope will turn at the predicted rate that KBOs are moving against the background stars. In the resulting images, the stars will be streaked, but any KBOs should appear as pinpoint objects.

If the test observation identifies at least two KBOs of a specified brightness, an additional allotment of observing time will continue the search across a field of view roughly the angular size of the full Moon.

Though Hubble is powerful enough to see galaxies near the horizon of the universe, finding a KBO is a challenging needle-in-haystack search. A typical KBO along the New Horizons' trajectory may be no larger than Manhattan Island and as black as charcoal.

Even before the launch of New Horizons in 2006, Hubble has provided consistent support for this edge-of-the-solar system mission. Hubble was used to discover four small moons orbiting Pluto and its binary companion object Charon, providing new targets to enhance the mission's scientific return.

And Hubble has provided the most sensitive search yet for potentially hazardous dust rings around Pluto. Hubble also has made a detailed map of the dwarf planet's surface, which astronomers are using to plan New Horizons' close-up reconnaissance photos.

"The planned search for a suitable target for New Horizons further demonstrates how Hubble is effectively being used to support humankind's initial reconnaissance of the solar system," said Mountain.

"Likewise, it is also a preview of how the powerful capabilities of the upcoming James Webb Space Telescope will further bolster planetary science. We are excited by the potential of both observatories for ongoing Solar System exploration and discovery."