New Horizons continues to deliver the goods. Having sent back all of the data collected during its Pluto flyby in 2015, the spacecraft is still speeding along at a velocity of 14.32 kilometers per second relative to the Sun. That has allowed it to travel almost halfway between Pluto and its next target, a small Kuiper Belt object called 2014 MU69. By last Sunday, in fact, it had come to within two years of its flyby date—January 1, 2019.

At this point, mission managers are conducting operations on the fly (pun intended). That's because the Hubble Space Telescope only found the object in June, 2014, barely a year before New Horizons' flyby of Pluto. When NASA formally selected MU69 as the spacecraft's next target in late 2015, scientists were in the midst of downloading and analyzing data about the Pluto system.

But now the focus is shifting to the new object, and this has led to a flurry of planning as mission scientists must design, write, and test the spacecraft's command sequences for its second flyby. "For Pluto, that job took most of 2009 to 2013," New Horizon's principal investor, Alan Stern, recently explained. "But because the MU69 flyby is barely two years away, we have to compress all the planning into the next 18 months. Why? Because flyby operations for 2014 MU69 will begin in July 2018."

So what do scientists know about MU69? Not much. Based upon Hubble's observations, it measures between 25km and 45km across. This uncertainty is due to the fact that scientists aren't sure how bright it is. It could be as dark as fresh asphalt (albedo of 0.04) or a little bit brighter, like a dark forest canopy.

What scientists do know is that it's far away—about 44.3 astronomical units from the Sun on average, or 6.6 billion km. When New Horizons flies by MU69 in two years it will be the farthest world humans have ever explored. With its relatively small size, MU69 also represents a new class of objects for scientists to image, a midpoint between a typical comet nuclei and larger Trans-Neptunian objects like Pluto. What color will it be? Do objects like this have satellites? Will there be any surprises on its surface? Answers will be on offer in two years.

After the Pluto flyby, New Horizon's remaining fuel left a maneuvering budget of about 130 m/sec of delta-V. This left only a narrow slice of the Kuiper Belt within reach and the choice came down to two objects, MU69 and 2014 PN70. The former was chosen because, although it was less bright, it had the benefit of being more reachable. This should ensure that the spacecraft can make a closer flyby—likely much closer than the 12,500km New Horizons came within the surface of Pluto in 2015.