Challenges ahead

In October and November 2015, shortly after our exploration of Pluto, we fired the engines aboard New Horizons to retarget its trajectory to intercept MU69. That flyby will take place January 1, 2019, less than a year from now. That flyby date will set yet another record: the shortest time between the discovery of an object and its exploration by spacecraft (4.5 years). That’s barely 1 percent of an MU69 orbital period from discovery to exploration!





The flyby presents many challenges. One is simply hunting down MU69 to perform the intercept. Because it is so faint, no ground-based telescope has ever seen MU69; only Hubble has. And it is too faint for New Horizons to detect until about 100 days before we fly past, so we must rely on Hubble for all our tracking until fall 2018 when we are on final approach.





To determine MU69’s orbit, we combine the accurate astrometric measurements of MU69 from Hubble with the incredibly precise stellar positions delivered by the European Space Agency’s (ESA) Gaia astrometry satellite. Using these two sources and optical navigation data that New Horizons will obtain in 2018’s final months, we plan to target our spacecraft to a closest approach just 2,175 miles (3,500 km) above MU69 — about four times closer than we flew past Pluto. This means we’ll get images with about four times higher resolution!





Another challenge is that MU69 might be a binary. Scientists have found many binaries among the more than 1,500 known KBOs, and the number of cold classical KBOs that are binary tops 30 percent. But even Hubble cannot detect close binaries at MU69’s great distance. As I noted earlier, however, we did receive tantalizing hints that this might be the case July 17, 2017, when MU69 passed in front of a distant star. Ground-based observations of this occultation show it is either a close binary, two objects in contact with each other, or a single, highly elongated object with a big chunk taken out of it. We likely won’t confirm whether MU69 is a binary until New Horizons is on its final approach.





The object’s possible binary nature challenges us to plan searches for any other moons on approach, and to include in our flyby plans observations of those moons we might discover. If MU69 does have moons, their gravity may create a noticeable wobble in the position of our main target that can help us determine MU69’s mass and density.





Yet another challenge involves the possibility of hazards caused by rings or other orbiting debris that MU69 may have. Such debris would destroy New Horizons as it whips through at almost 33,000 mph (53,000 km/h). The recent discoveries of rings around the former KBO Chariklo, which now orbits among the giant planets, and the KBO Haumea make us all the more aware of this risk.





On top of these challenges, during the flyby we will have to operate the spacecraft with a 12-hour round-trip light-travel time (compared with nine hours at Pluto). This means that any ground-control intervention due to anomalies or the need for course corrections can only occur 12 hours or more after we determine the need for such actions.