It’s no simple matter to reach the outer solar system, so NASA is making the most of the opportunity it has with the New Horizons probe. After successfully completing its Pluto flyby in 2015, the agency redirected the spacecraft to visit an even more distant object known as Ultima Thule. New Horizons got up close and personal with this frozen chunk of rock on January 1st, but New Horizons has only just beamed back high-resolution images.
NASA launched New Horizons in 2006 when Pluto was still considered a planet. By the time the spacecraft reached its target, Pluto was merely a dwarf planet. That didn’t make the accomplishment any less significant, though. New Horizons provided the first images of Pluto sharp enough to reveal surface details like vast plains of frozen nitrogen and methane dunes.
The nature of New Horizons’ mission provided NASA with a unique opportunity to explore more of the outer solar system after the 2015 main event. Because Pluto is so far away, New Horizons had to get moving at a phenomenal speed to get there in a reasonable amount of time. It was the fastest spacecraft ever launched at the time (only recently supplanted by NASA’s Parker solar mission), and the fifth manmade object to reach solar escape velocity. Therefore, it wasn’t practical for New Horizons to enter orbit of Pluto. After it coasted through, NASA selected Ultima Thule as the next observational target and set a course.
The initial “bowling pin” image.
New Horizons passed within 2,200 miles (3,500 kilometers) of Ultima Thule, which lies in the Kuiper Belt some four billion miles from Earth. Shortly after the encounter, New Horizons beamed back a handful of initial images showing a bowling pin-shaped object. New Horizons is so far away it can only send data at about 2,000 bits per second, so it took time to get the new, higher-quality images.
The fuzzy bowling pin from that first data stream has been replaced by the new snowman version. This image confirms that Ultima Thule (official designation (486958) 2014 MU69) is a “contact binary” object, the first one ever explored up close. That means its two lobes are separate objects that have joined together. Ultima Thule is about 20 by 10 miles (32 by 16 kilometers) in size, but its composition is still unknown. Some of the data acquired by New Horizons might shed light on that.
The images we have of the object currently show no obvious impact craters, but there are hills and ridges. NASA is also interested in getting a closer look at the “neck” region of Ultima Thule, which appears much lighter in color than the rest of the surface. It has a reddish color, most likely due to long-term exposure to radiation. More data on Ultima Thule is streaming back to NASA at this very moment, so expect additional announcements in the coming days.
NASA currently expects New Horizons’ mission in the Kuiper Belt to run through 2021 at least. The Team hopes to set a course for new objects in the near future.