NASA’s New Horizons probe has already made history several times. At launch, it was the fastest probe ever launched from Earth with a speed of more than 36,000 mph. It was also the first spacecraft to study the dwarf planet Pluto up close. Now, it’s on track for another first. In late 2018, New Horizons will encounter a Kuiper Belt object known as MU69. It turns out this object could be two or even three distinct bodies.
Because New Horizons had to reach such high speeds to arrive at Pluto in a reasonable amount of time, it could only perform a flyby of the dwarf planet. There was no way it could enter orbit of Pluto without a massive amount of fuel to counter all that speed. So, we only have several days of close-up observations from that phase of the mission. However, this also gave NASA a chance to check out more Kuiper Belt objects in the outer solar system.
After scanning for possible targets using the Hubble Space Telescope, NASA selected MU69 as the probe’s new destination. Two of the probe’s hydrazine thrusters fired for 16 minutes to bend New Horizons’ trajectory toward MU69. Astronomers have been observing the object in hopes of learning something about its composition before the probe gets there.
MU69 is between 19 and 28 miles across, which sounds large, but it’s too small and dark to be observed clearly from Earth. However, astronomers have been able to learn a bit about MU69 via occultation, when MU69 passes in front of a distant star. They report the main body of MU69 may actually be two distinct objects locked in orbit of each other (a binary system). There is also evidence for a third small moonlet that orbits the main body or bodies several hundred kilometers away.
It’s still possible MU69 is just one object that happens to be very “lumpy,” but even then, seeing it up close will be an important scientific achievement. New Horizons will get within 2,100 miles (3,500 km) of MU69. At that range, it can produce images with a resolution of 30 meters per pixel. MU69 will be the most distant and pristine object ever visited by a spacecraft — this is material that hasn’t changed since the formation of the solar system.
New Horizons will conduct nine days of extensive study as it nears MU69 on December 25, 2018. The closest approach should occur on January 1st, and images will be returned several days later.