The New Horizons spacecraft’s first images from its New Year's Day flyby of the outer solar system asteroid 2014 MU69 showed that the asteroid is two round lobes joined together in the middle: It looks a bit like a snowman.
Henry Throop, a member of the Corvallis High School class of 1990 and part of the New Horizons mission’s science team since 2001, said the asteroid likely formed like a snowman too — dust accreted over time into two separate balls and then the balls slowly collided, possibly at a speed of about a mile an hour.
“It’s not bashed up. It looks like a slow, gentle collision,” he said in an interview last week.
Throop said the structure of the asteroid, which is about 20 miles long and has been dubbed Ultima Thule, confirms what scientists have theorized about the outer solar system — that objects are so distant from the sun that its gravity doesn’t pull on them as hard as it does objects that are closer. So these distant objects move much more slowly.
“This is not a new thought about these collisions; this just illustrates it really dramatically,” said Throop.
The New Horizons spacecraft flew by Ultima Thule just after midnight Eastern Standard Time on Jan. 1. The object, which is past Pluto, is the farthest object from Earth that humanity has ever observed up close.
Throop, who was at the mission center at the Johns Hopkins University Applied Physics Laboratory in Maryland for the flyby, said the most tense moments of the flyby for the team came after it already had happened: the spacecraft was not communicating with Earth for four hours while it collected data near the asteroid, and then it took six hours for its communications to reach Earth after it passed the asteroid because it is so distant from the planet.
So for the team, the most dramatic moment came at around 10:30 a.m. EST Tuesday.
Throop said he was with around 1,000 other people who were gathered around to observe the 20 or so engineers working in the main control room. He said they were waiting on Missions Operation Manager Alice Bowman to announce the spacecraft’s status — and they finally heard the craft had executed its tasks perfectly.
“We were relieved and really excited,” he said.
Throop said unlike the New Horizons spacecraft’s previous flyby of Pluto, there weren’t really any surprises. While the Pluto flyby revealed that the dwarf planet is warmer and more geologically active than expected, the asteroid fit with all the predictions for what objects in the outer solar system should look like.
“This is in large part a confirmation that many of our models of the outer solar system are right ... which gives us the idea our other theories might be right.”
Throop said as data trickles back from the flyby over the next couple of years he will be analyzing data to look for evidence of rings around the asteroid, although he said he doesn’t expect to find rings around the asteroid, which are more common around celestial bodies that have had violent impacts.
Throop said the spacecraft is healthy and the mission team wants to find another object to explore in the outer solar system.
“It’s amazing to be part of this team," he said. "We’re proud to be part of this country that funds these missions to explore the universe for all of humanity."