While the world was ringing in the New Year, NASA was celebrating a different milestone more than a billion miles beyond Pluto. The New Horizons probe successfully rendezvoused with Ultima Thule, a tiny world on the edge of the solar system. While the data will continue to stream in for months, the first images have now arrived, revealing a bowling pin-shaped object that spins like a propeller.
New Horizons buzzed Ultima Thule at 12:33 am EST on January 1, getting as close as 2,200 miles (3,500 km). Being four billion miles (6.4 billion km) from the Sun, this little rock is the most distant object ever explored by a spacecraft. The first signals of the mission's success came in at 10:29 am EST, confirming that the craft is functioning fine and had collected its fill of science data during its close approach.
The first blurry photos confirm earlier observations that Ultima Thule is either quite elongated and shaped like a bowling pin, or might be two objects orbiting each other very closely. Either way, the new data says it measures about 20 miles long and 10 miles wide at its thickest point (32 by 16 km).
While the science team hasn't yet been able to nail down how long each rotation takes, observations did show that it tumbles end over end, spinning like a propeller. The axis it spins around is pointing almost directly at New Horizons, which explains the first mystery: Why the team wasn't able to detect the object's light curve as the craft approached.
These first few images may be a little grainy and underwhelming for the general public, but this is just the beginning. Given that New Horizons can only transmit data at a trickle of 2 kB per second, it will take about 20 months for everything to reach Earth, so new details and clearer photos will continue to trickle in throughout 2019 and into 2020.
"New Horizons performed as planned today, conducting the farthest exploration of any world in history – 4 billion miles from the Sun," says Alan Stern, Principal Investigator of the New Horizons team. "The data we have look fantastic and we're already learning about Ultima from up close. From here out the data will just get better and better!"
Source: Johns Hopkins University Applied Physics Laboratory
I wonder whether this kind of dumbbell configuration will turn out to be a pretty common shape for objects too small to be crushed round by gravity. Any time you have two big rocks close enough and moving at low enough relative velocity, they'll eventually collide and stick. And the spin will be around their common center, because that's where the leftover angular momentum is. (And the odds of additional sticky collisions adding rocks 3, 4 etc are probably pretty low in most regions)