Scientists are keen to study Ultima Thule as it lives in a region that has been relatively untouched since the formation of the solar system, which in turn helps them better understand planetary formation. The spacecraft "has brought us back to the very beginning of solar system history".
The shape of Ultima Thule had been the subject of speculation for years leading up to the flyby. A distant object now actually feels real to everyone here on Earth. That supports the idea that billions of years ago, amid the swirling chaos of the early solar system, matter collected in larger and larger clumps until their gravity was strong enough to develop into planets and moons. "These are the only remaining basic building blocks".
Alan Stern, principal investigator for New Horizons, said: "It is only really the size of something like Washington DC and it is about as reflective as garden variety dirt".
The last time we saw Utlima Thule, it was a blur against the blackness of space, something not almost convincing enough of its existence.
The celestial body was nicknamed Ultima Thule - meaning "beyond the known world" - before scientists could say for sure whether it was one object or two.
"Everything that we're going to tell you [today] is just the tip of the iceberg", Dr Stern said. The new images revealed that the object is in fact a contact binary, consisting of two spheres that measure 31 km (19 mi) from end to end. Data that New Horizons collected as it approached its target suggested that Ultima Thule was bowling-pin-shaped and spinning like a propellor. In 2015, the spacecraft passed Pluto, providing the first images of a world once considered our ninth planet.
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Before today, it wasn't known if Ultima Thule was a single object or two objects orbiting one another.
Scientists have ascertained that the object takes about 15 hours to make a full rotation.
Scientist Jeff Moore says that the two spheres formed when small, icy pieces coalesced in space billions of years ago.
So gentle was the initial contact between the two lobes of MU69 that Mr. Moore related it to getting into a fender bender vehicle accident that produces no damage; you wouldn't bother filling out the insurance claim. Stern said the thing that was most surprising about the experience was "picking a Kuiper Belt object out of a hat" and then finding out that the team had picked a victor.
On Wednesday, NASA officials said they "could not be happier" with the latest image of the "snowman", which it said were "separate objects now joined together". "This is exactly what we need to move the modeling work on planetary formation forward". They could not see any large craters on its surface, though they said some could be revealed in images taken from different angles.
The New Horizons team was also able to pin down Ultima Thule's size more accurately.
New Horizons's encounter with Ultima Thule happened so far away that it took six hours for signals traveling at the speed of light to reach Earth. It is more than a billion kilometres past Pluto, and 6.4 billion kilometres from Earth.