Ultima Thule

The new year came in with a bang as the New Horizons spacecraft flew by the snowman-like icy body nicknamed Ultima Thule. This is the most distant exploration of any world in history. Scientists will need to wait 20 months to receive the several gigabytes of data collected from the flyby, since it is being transmitted at a rate of only about 1,000 bit per second. Nevertheless, scientists have already learned a lot about it, as summarized below.

Ultima Thule was discovered on June 26, 2014 by astronomers (led by former Lowell Observatory scientist Marc Buie) using the Hubble Space Telescope. This culminated the search for a Kuiper belt object — icy bodies that inhabit the outer solar system in a disc known as the Kuiper belt — that the New Horizons spacecraft could fly by after its successful passing of Pluto in 2015. The scientists cataloged the body as (486958) 2014 MU69, a precise enough name but pretty clunky and uninspiring.

When New Horizons team members designated this body as the target for the spacecraft flyby, they realized a simpler nickname was in order. They chose Ultima Thule after considering multiple possibilities. This term dates back hundreds of years to classical times and means “beyond the borders of the known world.”

Scientists describe Ultima Thule as a bi-lobate contact binary, a solar system body consisting of two roughly spherical bodies pulled together by gravity until they touch.

The bonded pair rotates on its axis every 15 hours and revolves the Sun once every 300 years or so.