Ultima Thule: an unexplored 'time capsule' of ancient past

NASA's New Horizons spacecraft's latest flyby target -- an object dubbed "Ultima Thule" -- may hold a well-preserved cache of secrets frozen in time from the ancient past of the solar system, scientists say.

The distant icy "worldlet" located four billion miles from the Sun is orbiting in the heart of our solar system's Kuiper Belt, far beyond Neptune.

Officially designated 2014 MU69, it was nicknamed "Ultima Thule," a Latin phrase meaning "a place beyond the known world," after a public call for name recommendations.

Objects in Kuiper Belt -- a collection of icy bodies ranging in size from dwarf planets like Pluto to smaller planetesimals like Ultima Thule (pronounced "ultima toolee") and even smaller bodies like comets -- are believed to be the building blocks of planets.

Ultima's nearly circular orbit indicates it originated at its current distance from the Sun. That means Ultima is an ancient sample of this distant portion of the solar system, NASA said in a statement.

Since temperatures this far from the Sun are barely above absolute zero -- mummifying temperatures that preserves Kuiper Belt objects -- they are essentially time capsules of the ancient past, the US space agency said.

Marc Buie, New Horizons co-investigator from the Southwest Research Institute (SwRI) in the US, and members of the New Horizons science team discovered Ultima using the Hubble Space Telescope in 2014.

The object is so far and faint in all telescopes, little is known about the world beyond its location and orbit. In 2016, researchers determined it had a red color.

In 2017, a NASA campaign using ground-based telescopes traced out its size -- just about 30 kilometers across -- and irregular shape when it passed in front of a star.

From its brightness and size, New Horizons team members have calculated Ultima's reflectivity, which is only about 10 per cent, or about as dark as garden dirt. Beyond that, nothing else is known about it -- basic facts like its rotational period and whether or not it has moons are unknown.

After the flyby, New Horizons will map Ultima and determine how many moons it has and find out if it has rings or even an atmosphere. It will also measure Ultima's temperature and perhaps even its mass.

"In the space of one 72-hour period, Ultima will be transformed from a pinpoint of light -- a dot in the distance -- to a fully explored world. It should be breathtaking!" said New Horizons Principal Investigator Alan Stern, of SwRI.