The most-distant object we have ever visited with a spacecraft is finally coming into focus. NASA鈥檚 New Horizons spacecraft flew by the distant rock called 2014 MU69, nicknamed Ultima Thule, on New Year鈥檚 Day this year, and the data from that speedy fly-by shows that it must have formed in a slow-motion collision.
The first results that arrived from the spacecraft showed Ultima Thule to be shaped a bit like a snowman. Later images, however, revealed that the rock鈥檚 two lobes are not spheres 鈥� they are flat like a pair of pancakes stuck together on the pan. The New Horizons team presented new data on 18 March at the Lunar and Planetary Science Conference in Houston, Texas.
Analyses show that the larger of the lobes, nicknamed Ultima, is lumpy. The lumps are all fairly geologically similar, but they may have started out as smaller rocks that slowly collided, said team member Jeff Moore from NASA Ames Research Center in California.
Advertisement
Both lobes are almost entirely covered in organic compounds that give them a red hue. Their surfaces show signs of water ice, organic materials and methanol, a compound of methane and oxygen, said team member Silvia Protopapa at the Southwest Research Institute in Texas. They also share three types of bright area: small round spots, larger bright areas and thin stripes. It聽isn鈥檛聽clear exactly how any of these shiny features formed, said team lead Alan Stern.
The shape of the final object, with both lobes aligned along the same plane, suggests that they orbited one another closely in a slow dance before merging, said team member Bill McKinnon at Washington University in Missouri.
A lack of large cracks or rubble suggests that when the two objects merged, they probably hit each other at just 2 or 3 metres per second. 鈥淚f you take a brisk walk into a wall, you will find out what that [sort of collision] is like,鈥� said McKinnon.
New Horizons will continue downloading data for more than a year, which will help the team figure out how MU69 formed and what it is made of. It is the oldest and most pristine planetary building block we have ever visited, Stern said, so it may help us understand how planets in our solar system form.
