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September 5, 2018

The PI's Perspective: Tally Ho Ultima!

New Horizons has crossed almost all of the billion miles separating our July 14, 2015, flyby of Pluto and our upcoming January 1, 2019, flyby of the Kuiper Belt object (KBO) nicknamed Ultima Thule.

More than 12 years after launch, New Horizons continues to be healthy, perform well, and speed across the outer solar system at a clip of nearly 1 million miles per day!

Since I last wrote, earlier this year, our flight team has been incredibly busy operating our spacecraft and planning for our next flyby. That work includes conducting mission simulations and preparing contingency plans for handling more than 250 separate possible anomalies on the spacecraft or in mission control that could jeopardize flyby success.

Planning meetings like this one, sometimes involving more than two-dozen New Horizons scientists, flight controllers, engineers and mission planners, take place almost daily as we prepare for the upcoming flyby of Ultima Thule, our first KBO target.

Now, as September opens, our journey from Pluto to our next flyby target, a Kuiper Belt object nicknamed "Ultima Thule" (a Latin phrase, pronounced "ultima toolee" and meaning "beyond the farthest frontiers") is 90 percent complete. Ultima, as we call our next exploration target for short, is believed to be a building block of small planets like Pluto, making it incredibly scientifically valuable for understanding the origin of our solar system and its planets. Our flyby and exploration of Ultima will culminate as we pass closest to the object on New Year's Eve and New Year's Day 2019, less than four months from now!

But that's not our big news. The big news is that as of August 16, we've spotted Ultima using the LORRI telescopic imager onboard New Horizons! It wasn't easy, but we did it! Ultima is still 100 times fainter than Pluto is as seen from Earth, and over a million times fainter than the naked eye can see. But LORRI is an amazing machine, capable of detecting pinpoints of light that faint, and even a little fainter.

Since New Horizons ended its last hibernation cruise phase in early June, it has been busy – undergoing tests, loading new fault protection software, and sending us valuable data about the Kuiper Belt. Once all that work was complete, on August 13, the spacecraft transitioned from its cruise spin-stabilized mode, to a pre-flyby mode that allows it to point to any place in the sky with its cameras and spectrometers. Less than three days later, on its first attempt, New Horizons spied Ultima for the first time!

Those detection images were radioed back to Earth on the weekend of August 18-19. Scientists on our team in Maryland, Arizona, and Colorado jumped right onto those data, carefully processing them to remove background stars and other artifacts — and out popped Ultima, a faint beacon, dead ahead, in just the very pixel our navigation crew had predicted it would show up!

New Horizons spotted Ultima Thule for the first time on August 16, near the center of the red circle in this LORRI image of the dense Milky Way star field where Ultima lies.

We had long expected the detection of Ultima from New Horizons to be possible in September, but decided about a year ago to try to find it in August, because an earlier detection would help us begin homing in on it even farther out (and save fuel); and it worked! More regular imaging of Ultima to refine our course will begin this month and continue through the flyby. Based on the tracking of both New Horizons and Ultima we've done so far, we are already planning to execute a small course correction on October 3 of about 3 meters per second (7 miles per hour) to tune up our flyby arrival time and position.

But the detection from New Horizons wasn't our only big news about Ultima Thule in August. We also detected Ultima from Africa, when it passed in front of a star, making the star briefly blink out in what is called a stellar occultation. You might recall that we captured a similar stellar occultation in July 2017 from Argentina. These rare events have allowed us to refine our knowledge of Ultima's exact position and also to search for debris that might be orbiting it and pose a hazard for our flyby of it. Fortunately, neither of the two occultations we observed revealed any debris, though much more sensitive searches will be possible November and December as New Horizons closes in and can use LORRI to scan for debris at closer range.

This fall, in addition to hazard searches, ongoing navigation imaging of Ultima and several possible additional course-correction maneuvers, New Horizons will collect data on a half-dozen other Kuiper Belt objects and the plasma and dust environment way out there in the Kuiper Belt, nearly 4 billion miles from Earth. Also, our flight team will be finalizing the software loads to drive the spacecraft's close-up flyby observations of Ultima and its environment, from geology to composition, to searches for moons, rings and any atmosphere Ultima may sport.

Spend your New Year's Eve with NASA as New Horizons conducts the first close-up exploration of any Kuiper Belt object in history, and the farthest exploration of any body in space ever attempted, more than 4 billion miles from Earth!

Our science team will be busy with that planning too, as well as conducting flyby simulations, and reporting new results on the Pluto system at the annual American Astronomical Society's Division of Planetary Sciences meeting in October. In fact, we have two-dozen research papers presenting new results in the hopper for that meeting!

But make no mistake, the highlight and the centerpiece of our current Kuiper Belt extended mission is the flyby of Ultima, and we hope you will help spread the word as we undertake the most distant exploration of any object ever seen in space. Tell your relatives, coworkers and friends that they can be a part of it, spending their Christmas in the Kuiper Belt and their New Year's with NASA, as Ultima Thule is revealed by New Horizons!

Well, that's my update for now. For more New Horizons mission news, stay tuned to the websites and social media channels listed below. I'll write again around the time we begin intensive flyby operations in late November.

Until then, I hope you'll keep exploring—just as we do!

–Alan Stern
New Horizons Mission PI


There are many ways to follow New Horizons news and commentary on social media! You can find others by searching on the Web.