What strange object is named after a mythical, far-northern island in medieval literature and has its own rock anthem performed by Queen guitarist Brian May?
Ultima Thule (pronounced TOO-lee).
“This is truly the most primitive object ever encountered by a spacecraft,” said Hal Weaver, project scientist at the Johns Hopkins Applied Physics Laboratory.
Ultima Thule lies in the Kuiper Belt, a vast cosmic disc left over from the days when planets first formed. Astronomers sometimes call it the “attic” of the solar system.
Scientists did not even know the Kuiper Belt existed until the 1990s. The Kuiper Belt begins some 4.8 billion km beyond the Sun, past the orbit of Neptune which is the furthest planet from the Sun.
“It is teeming with literally billions of comets, millions of objects like Ultima which are called planetesimals, the building blocks out of which planets were formed, and a smattering – a handful of dwarf planets the size of continents, like Pluto,” said Alan Stern, principal investigator on New Horizons.
“It is important to us in planetary science because this region of the solar system, being so far from the Sun, preserves the original conditions from four and a half billion years ago. So when we fly by Ultima, we are going to be able to see the way things were back at the beginning.”
The New Horizons spacecraft sped through space at 51,500 km per hour, travelling almost 1.6 million km per day. At that pace, if it hits a piece of debris as small as a rice pellet, the spacecraft could be destroyed instantly.
“We don’t want that to happen … [and the fly-by] “requires extremely precise navigation,” said Stern. Ultima Thule was first discovered by the Hubble Space Telescope in 2014, and now that the world has its first images of the space rock, Stern hopes this won’t be the end for New Horizons, which launched in 2006 and is powered by plutonium.
“We hope to hunt down one more KPO (Kuiper Belt Object), making an even more distant fly-by in the 2020s,” Stern said.