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April 15, 2020

The PI's Perspective: Probing Farther in the Kuiper Belt

New Horizons is healthy and performing perfectly as it flies deeper and deeper into the Kuiper Belt! Recently we conducted an engineering review of the spacecraft to "trend" how it was working compared to when it was launched. The result was amazing: Every system and science instrument aboard New Horizons is working as well as it did when we lifted off, more than 14 years and almost 5 billion miles ago. As mission principal investigator I could not be prouder — the men and women who designed, built and tested New Horizons literally created a masterpiece of American workmanship that will likely be able to perform and explore for many more years and many more miles!

Before I update you on mission news, I want to highlight something cool on our mission website, https://pluto.jhuapl.edu/. There's a crazy amount of detail there for anyone interested in knowing more about the New Horizons mission and our scientific discoveries, but we've also posted a file to create 3D spacecraft models. With this file anyone with access to a 3D printer can create their own New Horizons to have at home or at work!

The New Horizons mission website is filled with information; visit it at https://pluto.jhuapl.edu/

Now for some mission happenings, starting with a cool public engagement project we're doing this month and next. As I mentioned, New Horizons is almost 5 billion miles from Earth. That is so far away, that the very closest stars appear in different positions in the sky than they do from Earth. This is due to the different perspective New Horizons has of these stars from its far away perch. On April 22 and 23, New Horizons will image two of the closest stars, Proxima Centauri and Wolf 359. Here on Earth, astronomical observatories and amateur observers will simultaneously take images of the same stars. Using software to combine imagery from the spacecraft and the ground, we'll be able to produce stereo images of these star fields showing each star "popping out" because of the "parallax," or changed perspective, between Earth and New Horizons.

Nothing like this has ever been accomplished before! We'll release these 3D images in May, so stay tuned. But in the meantime, details on how you can take part in this experiment are on the mission website.

My first mission news update is that this summer, we'll be using a trio of the largest telescopes on Earth, specifically, the Japanese Subaru telescope, and the U.S. Gemini and Keck telescopes to discover new Kuiper Belt objects (KBOs) for New Horizons to study. We expect to literally find hundreds of new KBOs! Most of these will be too far to study from New Horizons, but a few dozen will be close enough for the spacecraft to image. Although the objects will just be points of light in the distance, millions or even tens of millions of miles from our spacecraft, New Horizons images will be valuable for studying their surface properties, their satellite systems, their shapes and their rotations in ways that cannot be accomplished from Earth -- owing to their great distance and our limited viewing angles from the inner solar system.

New Horizons has been conducting studies of KBOs like this since 2016, but we've only been able to find and study about 20 so far. With discoveries from the Gemini, Subaru and Keck telescopes, we hope to triple or even quadruple that number, greatly enhancing our scientific return from the Kuiper Belt.

This graphic illustrates the concept of the New Horizons stellar parallax project, which is happening this month. For the first time, a spacecraft will image stars from so far from Earth that the stars 'shifted position is large enough to create 3D images of them! See the mission website for more details and how you can get involved. Credit: Pete Marenfeld, NSF's National Optical-Infrared Astronomy Research Laboratory)

We will also scour the set of newly discovered KBOs for any that New Horizons might be able to fly by, as we did with the KBO Arrokoth early last year. Computer models indicate the probability of finding another close flyby target is small, because we have so little fuel on board to divert toward such a flyby -- but that won't stop us from looking! Our fondest hope is that we get lucky and have the opportunity for one more close flyby of a KBO. After all, no other spacecraft is exploring (or ever has explored) the Kuiper Belt, and none are on the drawing board to do so. This is humankind's best chance to get such a close up of another KBO for decades to come!

This 1,000-plus page technical compendium of everything learned about Pluto and its moons by the New Horizons flyby in 2015 will be published late this year or early next.

I also want to update you on another cool development for the mission: We are looking at how to increase the capabilities of New Horizons' instrument payload through software upgrades. The team is evaluating several cost and capability- increase options for six of the seven instruments, and we expect to decide which ones to implement in May. By about this time next year, these "flight software" changes will be made, tested and sent to New Horizons for us to begin using those new capabilities. Later this year, once we've selected which enhancements to implement, I'll describe each of them.

I'll close with some scientific news. First, I want to announce the forthcoming publication late this year or early next of a 1,000-plus page technical research volume called The Pluto System After New Horizons. This book, to be published in the distinguished University of Arizona Space Science Series, will contain 24 chapters detailing essentially every aspect of what was learned about Pluto and its moons from the historic first-ever flyby exploration of Pluto, which New Horizons conducted in July 2015. All 24 chapters are now written, each by a team of scientific experts. Some have already completed review by other scientists to improve them, while others are undergoing that step. By May or June, we expect all 24 chapters to be in production for publication. The book should then be published about six months later.

New Horizons discoveries about the Kuiper Belt object Arrokoth filled the pages of the "headliner" research journal Science in both May 2019 (shown above) and February 2020. (Credit: AAAS/Science)

The other science news I want to relay is about a blockbuster discovery this mission made as a result of its close flyby of the Arrokoth. We published the first indications of this discovery in the esteemed research journal Science in 2019; a much deeper analysis confirming the early results was published in Science this February. The discovery is about how Arrokoth, and by inference most other primordial "planetesimals" (or planetary building blocks), came into existence.

For many years, two competing mathematical models of planetesimal formation existed. The data from New Horizons shows, definitely, that only one of these models -- variously called the "streaming instability" or "pebble cloud collapse" model -- can produce an object like Arrokoth. Our evidence? The detailed shape, geology and alignment of the two halves, or "lobes" of Arrokoth. The New Horizons images, compositional spectra, and color data on Arrokoth all point to this model being how Arrokoth formed. We summarized this discovery in a Feb. 13 press release. This may be the single most impactful discovery of the entire New Horizons mission so far, pointing to how planets got their start while settling what has literally been a decades-long computer modeling duel between competing theories.

And with that big news, I'll conclude this report. I'll write again this summer. Meanwhile, I hope you'll keep on exploring — just as we do!

–Alan Stern

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