Hubble To Search For Last Stop On Pluto Probe's Itinerary

By Scott Neuman

Published June 17, 2014 at 4:59 PM EDT

Artist concept of New Horizons spacecraft. The Hubble Space Telescope is being pressed into service to help scientists look for a post-Pluto target for the space probe.

The Hubble Space Telescope is being pressed into service to search for a post-Pluto "icy body" as a last stop for NASA's New Horizons probe.

The Baltimore-based committee that metes out observing time for the HST announced today that it is allotting time to look for a suitable Kuiper Belt object for New Horizons to flyby after it passes close to Pluto in July 2015.

As Nature explained last month before the New Horizons team secured time on Hubble: "A visit to a Kuiper belt object, or KBO, was always meant to be a key part of New Horizons' US$700-million journey, which began in 2006. But there is only a slim chance that astronomers will find a suitable KBO with their current strategy of using ground-based telescopes — and securing time on the orbiting Hubble Space Telescope is far from guaranteed."

But on Tuesday that guarantee came through. "Hubble is coming to the rescue of New Horizons, and we're very excited about it," says Alan Stern, principal investigator for the mission and a planetary scientist at the Southwest Research Institute in Boulder, Colorado.

The Kuiper Belt is a vast region of space just beyond the outer planets that's thought to comprise thousands of icy objects that formed along with the rest of the solar system. Pluto itself is thought to be a Kuiper Belt object.

NASA has yet to even approve funding for New Horizons to visit a KBO after Pluto, "but without a candidate KBO the question was moot. The problem has been how to pick out KBOs, which are far away and thus very faint, from the crowded background field of Milky Way stars against which the New Horizons probe is travelling," Nature says:

"Mission scientists began their ground-based search in earnest in 2011, but they've been stymied by bad weather at observing sites, and the fact, discovered only recently, that that there are actually fewer faint KBOs than one might expect given the number of bright ones. They have discovered more than 50 faint KBOs, but none are in the right region of space for New Horizons to make a close-up visit."