The spacecraft’s Long Range Reconnaissance Imager (LORRI) photographed the dim KBO on August 16 from a distance of more than 100 million miles, surprising mission scientists, who did not expect any images of the object until September.
LORRI took a total of 48 images of the faint KBO against a dense background of stars, which it transmitted back to Earth via NASA’s Deep Space Network (DSN).
All previous images of Ultima Thule were either captured by the Hubble Space Telescope (HST) or obtained via ground-based telescopes when the KBO passed in front of a background star, casting a shadow.
Observations made between now and the January 1, 2019, flyby are of critical importance to the mission team, who will use them to refine the probe’s path to its closest approach, which will occur at 12:33 AM EST on New Year’s Day.
This initial detection confirms Ultima Thule is at the exact location where mission scientists expected it to be and indicates their calculations of its orbit are correct.
“Our team worked hard to determine if Ultima was detected by LORRI at such a great distance, and the result is a clear yes,” New Horizons principal investigator Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado, emphasized. “We now have Ultima in our sights from much farther out than once thought possible. We are on Ultima’s doorstep, and an amazing exploration awaits.”
Hal Weaver of the Johns Hopkins University Applied Physics Laboratory (JHUAPL), New Horizons project scientist and LORRI principal investigator, described the challenge mission scientists faced in directing the spacecraft to photograph Ultima Thule from such a great distance.
“The image field is extremely rich with background stars, which makes it difficult to detect faint objects. It really is like finding a needle in a haystack. In these first images, Ultima appears only as a bump on the side of a background star that’s roughly 17 times brighter, but Ultima will be getting brighter–and easier to see–as the spacecraft gets closer.”
Located around one billion miles beyond Pluto, Ultima Thule will be the most distant object ever visited by a spacecraft and the first small KBO studied up close. New Horizons will break its own record in the flyby, set when it explored Pluto in July 2015.
Other records set by the spacecraft include taking the most distant photo of the Sun, imaging a galactic open cluster, and capturing distant images of two remote KBOs.