Meet Ultima Thule (later designated 486958 Arrokoth.)
And “Ultima” and “Thule”, according to New Horizons‘ principal investigator Alan Stern at today’s NASA press briefing (later named “Wenu” and “Weeyo”), the informal names the team has given the two lobes of the red object out in the Kuiper Belt New Horizons spent New Year’s encountering. The contact binary connected by a neck of material indicates two objects that came together and stuck sometime in the distant past when these kinds of interactions were leading elsewhere in the solar system to accretions that would eventually form the planets and their moons.
Arrokoth is likely fairly pristine and as such represents a sample of the building blocks of our solar system. It consists of two objects that came together to ride out the billions of years since their creation while their surface material slowly becomes irradiated by the distant sun to turn red in color. The velocity of collision must have been really low, perhaps no faster than parking a car in a parking space. Scientists also think the spherical shape of the two lobes indicates their formation from even small chunks of primordial material accreting together at the same extremely low velocity.
Arrokoth is a dark object, reflecting no more light than dark gardening soil here on Earth. The neck stands out because it is brighter, reflecting 13% of light. Why is it brighter than the two lobes? Team scientists think the brightness is due to finer particles that have fallen downslope into the neck “ravine.”
There are even higher resolution images coming, including images with the sun at an angle and more shadows to give a better sense of Arrokoth’s topography. Another press briefing tomorrow will provide the public a sample of these data planetary scientists will be studying for years to come.