The mission is running out of time to discover a targetable object. To make the most of extremely limited fuel, the spacecraft must steer toward the post-Pluto target soon after the Pluto flyby. In order to navigate accurately enough to fly close by an object, we have to know its orbit. To know its orbit, we need to have two images of it taken close to a year apart. So we need to discover the object this summer. Only two months remain for the search to succeed. Based on what we now know about the Kuiper belt, the continuing search with such fabulous telescopes as Subaru, Magellan, and Keck -- on which the mission has been awarded 84 hours of search time in 2014 -- have only a 38% chance of finding at least one object.

Only the Hubble Space Telescope can save New Horizons' Kuiper belt mission now. The search team has calculated that using Hubble's Wide Field Planetary Camera 3 for the search would give the team a 94% chance of discovering at least one targetable object. The summer of 2014 is actually the best possible moment to use Hubble for the search, because the region of space that contains objects that New Horizons could reach is at its most compact this year, and the objects will be at opposition (and therefore brightest) in July. Even so, it would take close to 200 precious Hubble orbits. A typical Hubble year includes 3400 orbits. That's a lot of Hubble time.

The search team seems to have made their proposal for a lot of Hubble time more palatable by proposing a pilot search. Space Telescope Science Institute director Matt Mountain awarded 40 orbits of his "director's discretionary time" on Hubble to the New Horizons team. Those 40 orbits will supply two images each of 20 fields on the sky. The pilot program, which has already begun, is designed to check whether the search team's predictions for the structure of the Kuiper belt are correct, implying that using another 160 orbits of Hubble time will very likely yield a targetable object for New Horizons. "The more low-inclination objects we find in the pilot program....the more likely we are to find an accessible object in the full search....if we exactly reach our trigger threshold (2 cold Kuiper belt objects discovered in the pilot), we have an 85% probability of finding at least one accessible object in the full search. We estimate a 78% chance of reaching or exceeding this threshold in the pilot survey." They will find out within a couple of weeks whether the pilot search will pay out.

How were they able to get to work so fast after the acceptance of the proposal? Preparation, Alan Stern told me. Ordinarily, teams that propose to Hubble wait until after they have heard if their proposal has been accepted to do their "Phase 2" studies -- this is where they develop the specific technical instructions for the telescope. But with time being so limited, John Spencer and his team went ahead and performed the Phase 2 work in the hopes that their proposal would be accepted, taking the risk that all the work might be for nothing. For his part, Matt Mountain had instructed telescope schedulers to prepare two plans for Hubble in June, one including the New Horizons team's plans, and one without them, while the peer review of the proposal proceeded. Once the proposal was accepted, the New Horizons target search orbits went straight into the queue, and the team is already analyzing data.

Stern told me that they are now preparing the Phase 2 studies for the rest of the Hubble orbits. They won't wait for the completion of the 40 pilot orbits; as soon as they find two objects in the pilot program, they'll forward the discoveries to the Space Telescope Science Institute, and request the remaining 160 search orbits. Here is how those 160 orbits will appear on the sky, compared to a probability distribution of where they can hope to spot targetable objects: