Not long after the ball dropped in New York City, NASA’s New Horizons spacecraft — the one made famous by flying past Pluto — visited a rock called MU69, or “Ultima Thule.” And at 4 billion miles from the sun, it’s the farthest object humanity has ever explored up close.
And now, New Horizons has sent back the first detailed photos of its encounter. Behold:
You can see that the 21-mile-long object is oddly shaped. It looks like two potatoes smashed together, or a two-tiered snowman. This is a black-and-white photo. In color, Ultima Thule takes on a reddish hue.
Astronomers call this a “contact binary” — basically, it’s two asteroids that have been fused together. Scientists are excited to study it because it’s possibly a remnant of the original rocks and debris that formed our solar system more than 4.5 billion years ago. Many of the planets and moons in the solar system may have been formed from objects like Ultima Thule being smashed and stuck together.
#UltimaThule used to be 2 separate objects. It likely formed over time as a rotating cloud of small, icy bodies started to combine. Eventually, 2 larger bodies remained & slowly spiraled closer until they touched, forming the bi-lobed object we see today: https://t.co/ZuxLDtzW9c pic.twitter.com/FwWDAaAdey— NASA (@NASA) January 2, 2019
“We expect that Ultima is the most well-preserved sample of a planetary building block ever explored,” Alan Stern, the principal investigator of New Horizons, wrote in a blog post. NASA reports it will take around 20 months for all the data collected during the flyby to be sent back to Earth. They’ll be making deep studies of the composition of the object, how it moves, and how the two lobes of the object stick together.
Ultima is located in the Kuiper belt, a vast region of the solar system beyond Neptune that’s filled with small, icy objects and dwarf planets like Pluto. Because Ultima is in such a cold, remote, and quiet region of the solar system, it’s probably been orbiting the sun undisturbed for nearly the entire age of the solar system.
After New Horizons flew past Pluto in 2015, its mission scientists chose MU69 as its next stop in the Kuiper belt, mainly because New Horizons had the ability to reach it with its remaining fuel. Kuiper belt objects are very faint and are really hard to spot amid a background of bright stars. It took a lot of painstaking work to discover MU69 and chart New Horizons on a course to get there.
The nickname “Ultima Thule” means “beyond the known world.” But the name also has some uncomfortable Nazi connections. As Newsweek’s Meghan Bartels points out, “Ultima Thule” is the mythical origin land of the Aryan race (though the phrase is older than the Nazi movement). NASA appears to be sticking with the nickname.
New Horizons was launched in 2006 and reached Pluto in 2015. It will continue its mission exploring the Kuiper belt until at least 2021, when funding for the mission is currently set to expire.