After we welcome in the new year at midnight December 31, we’ll wake up (or stay up) to witness another milestone on the first day of 2019: the farthest planetary encounter in history. At 12:33 a.m., with many a New Year’s party still in progress, NASA’s New Horizons spacecraft will make its closest approach to asteroid 2014 MU69, nicknamed Ultima Thule , nearly 3½ years after its historic pass of Pluto.
Ultima is located a billion miles beyond Pluto in the Kuiper Belt, a region beyond Neptune home to countless icy asteroids. In medieval times, “Ultima Thule” referred to any far away place beyond the borders of the known world. Later, it was associated with Iceland and Greenland. After a public campaign and vote, the name was selected as the nickname for the target. A perfect fit, I think. A final name will be approved later by the International Astronomical Union.
This past week, engineers “woke” the spacecraft up to begin preparing it for the encounter. Cruising through the Kuiper Belt more than 3.7 billion miles (6 billion km) from Earth, New Horizons had been in energy-saving hibernation mode since Dec. 21. After a good yawn, the spacecraft was found to be in excellent health and operating normally.
The mission team is collecting navigation tracking data and sending commands to the onboard computers to being preparations for the flyby. In August, the team will use New Horizons’ camera to start taking pictures of Ultima, so they can refine the spacecraft’s course for a safe flyby of the object.
Since the July 2015 flyby of Pluto and its family of moons, New Horizons has sped on, measuring the properties of the heliosphere, the giant bubble of space centered on the sun and under its influence, as it beams toward Ultima Thule. New Horizons is now approximately 162 million miles (262 million km) or less than twice the distance between Earth and the Sun from Ultima, speeding along at 760,200 miles an hour.
As long as we had a spacecraft in the neighborhood after the Pluto flyby, mission planners got approval to tack on an additional flyby of an even more remote object, the asteroid 2014 MU69. The ~20-mile-wide reddish asteroid was discovered in June 2014 using the Hubble Space Telescope. The necessary maneuvers were and are being made, and if all goes smoothly, New Horizons will pass within 2,200 miles (3,500 km) of the object early on Jan. 1. Looks like many of us will be staying up after the ball drops.
Last July, Ultima Thule passed in front of a star and cast a brief shadow across Argentina and Africa in an event called an occultation. Astronomers strung along the path measured the duration and appearance of the shadow and discovered that the asteroid has very unusual shape or may even be two asteroids. It resembles a narrow football or a dog biscuit (with twin lobes) or two separate asteroids orbiting about their common center of gravity called a contact binary. Later this year, we’ll know for sure.
During the flyby, the spacecraft will to spot details as small as 230 feet (70 meters) across, almost 3 times better than at Pluto. Using all seven onboard science instruments, New Horizons will obtain photos, information on the object’s composition and search for an atmosphere and any moons.
New Horizons is presently nearly 3.8 billion miles (6.1 billion km) from Earth — a radio signal sent at light speed from the spacecraft takes 5 hours and 40 minutes to get here. NASA will keep the craft active until late 2020 after it’s transmitted all the data from the Ultima encounter back to Earth.