The PI’s Perspective: On Final Approach to Ultima

set of images taken by the Long Range Reconnaissance Imager (LORRI) aboard New Horizons, Ultima Thule emerges from behind stars and grows brighter as the spacecraft approaches it.
In this set of images taken by the Long Range Reconnaissance Imager (LORRI) aboard New Horizons, Ultima Thule emerges from behind stars and grows brighter as the spacecraft approaches it. Image credit: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Laboratory/Henry Throop

The New Horizons spacecraft is healthy and on final approach to explore Ultima Thule in the Kuiper Belt. On New Year’s Eve and New Year’s Day, New Horizons will swoop three times closer to “Ultima” than we flew past Pluto!

On Saturday, Dec. 15, the New Horizons hazard watch team concluded its work, having found no moons or rings in the path of New Horizons on its planned closest approach to Ultima. With that information and a unanimous finding by our mission stakeholders team, I informed NASA that we are “go” to fly by Ultima on the trajectory that yields the best science. As a result, New Horizons will approach to within 3,500 kilometers (about 2,200 miles) of Ultima early on New Year’s Day. There is no longer any chance we will divert to a farther flyby distance with consequently lower-resolution images.

Just yesterday, New Horizons conducted another small trajectory correction engine burn to help us home in on Ultima. That 0.26 meter/second burn lasted only 27 seconds and was executed perfectly by the spacecraft, cancelling about 300 kilometers (180 miles) of estimated targeting error and speeding up our arrival time by about five seconds. We will continue to track and target the spacecraft toward our expected arrival location and time. If needed, we can transmit files to New Horizons as late as the day before arrival to correct for any offsets from our flyby design, but we cannot burn the engines any longer. This is because New Horizons will soon enter Encounter Mode, which does not allow for engine burns.

Encounter Mode (or EM) is designed to ensure the flyby science even if the spacecraft malfunctions. Normally, if New Horizons develops problems in flight – which is very rare – the bird halts its flight plan and calls Earth for instructions. But if that were to happen during flyby closest approach, we’d likely miss getting the goods on Ultima before our mission control on Earth could intercede. After all, the round-trip communications time from Ultima to Earth and back is now over 12 hours.

Encounter Mode is the solution to this dilemma. Once the spacecraft is in EM beginning on Dec. 26, it will use onboard software to correct problems and then resume its activities without instructions from Earth. We used Encounter Mode at Pluto, but fortunately, no problems came up during that period. At Ultima we want the same level of flyby protection.

But before we can enter Encounter Mode, we must first transmit the entire sequence of thousands of carefully choreographed spacecraft and instrument commands to New Horizons’ main computer. That radio transmission will take place Dec. 20, and will be verified by a technique known as “checksums” on Dec. 21. The load will engage on Christmas Day, Dec. 25.

We are flying by Ultima to see a Kuiper Belt object up close for the first time. Ultima is special for two reasons. First, based on its orbit type, we know that Ultima was formed way out where New Horizons is, 4 billion miles away. That means Ultima (officially named 2014 MU69) was formed in the middle of the Kuiper Belt, where temperatures are close to absolute zero.

Second, because of where it was formed and the fact that Ultima is not large enough to have a geologic engine like Pluto and larger planets, we expect that Ultima is the most well-preserved sample of a planetary building block ever explored. In effect, Ultima should be a valuable window into the early stages of planet formation and what the solar system was like over 4.5 billion years ago.

What will Ultima reveal? No one knows. To me, that is what’s most exciting—this is pure exploration and fundamental science!

And when will we see what Ultima is all about? Close approach images, composition spectra and other kinds of data will already start to flow from New Horizons on flyby day—Jan. 1! We expect to have an image with almost 10,000 pixels on Ultima by that night, ready for release on Jan. 2. By that first week of January we expect to have even better images and a good idea of whether Ultima has satellites, rings or an atmosphere.

Early next year, megapixel images will be sent, and if they contain the target – shooting at this resolution while speeding by at over 32,000 miles per hour is a stretch goal – they will reveal Ultima’s geology in exquisite detail.

This beautiful Ultima Thule flyby poster was created by artist-astronomer Tyler Nordgen.
This beautiful Ultima Thule flyby poster was created by artist-astronomer
Tyler Nordgen.

The Ultima Thule flyby is going to be fast, it’s going to be challenging, and it’s going to yield new knowledge. Being the most distant exploration of anything in history, it’s also going to be historic.

Fifty years before this flyby, at Christmas time 1968, I sat on my grandparents’ bed as a boy and watched Apollo 8 take off on the first human expedition to visit another world—our moon. That mission was also fast, it was challenging, and it yielded new knowledge. It was historic too. I will never forget it, nor the many talented people who made it possible and the three brave astronauts who flew aboard it.

The Apollo 8 mission happened 50 years ago this holiday season. Image credits: NASA.
The Apollo 8 mission happened 50 years ago this holiday season. Image credits: NASA.

Over all those years between Apollo 8’s December exploration and ours, NASA has made history by exploring farther and farther, oftentimes making what is very hard look very easy. Occasionally, missions stumbled. But most performed spectacularly, and as a result we have made Carl Sagan’s prediction that in just a generation or two the planets would be transformed from points of light to real and explored worlds. Equally important, NASA has shared the results of this exploration with people everywhere on this planet we call Earth, humankind’s cradle.

We on the New Horizons team are in awe of what Apollo 8 accomplished so long ago. With all the other missions of human and robotic exploration that came after, it opened up a solar system and a future that may soon see humans living on multiple worlds and robots exploring in new ways. The tradition of exploration is deep in homo sapiens; it sets us apart from other life here on Earth. Perhaps it’s something we may find in common with other spacefaring civilizations, if they exist.

Well, that’s my report for now. The flyby of Ultima Thule is literally now just days away. Onward now New Horizons, in the spirit of exploration, onward to 2019, and Ultima Thule!

And as always, keep exploring — just as we do!

-Alan Stern

There are many ways to follow New Horizons news and commentary on social media, such as these listed below. You can find others by searching the web.

p.s. You only have until midnight (EST) this Friday – Dec. 21 – to enter your name and a message to be radioed to Ultima Thule and New Horizons on flyby day at

You only have until midnight (EST) this Friday – Dec. 21 – to enter your name and a message to be radioed to Ultima Thule and New Horizons on flyby day at


The PI’s Perspective: Share the News—The Farthest Exploration of Worlds in History is Beginning!

New Horizons Journey through the Kuiper Belt
Spend your New Year’s Eve with NASA, as New Horizons conducts the first close-up exploration of any Kuiper Belt object and the farthest exploration of any worlds in space ever attempted — more than 4 billion miles from Earth and a billion miles beyond Pluto!

The New Horizons spacecraft is healthy and is now beginning its final approach to explore Ultima Thule — our first Kuiper Belt object (KBO) flyby target — about a billion miles beyond Pluto. And on New Year’s Eve and New Year’s Day, New Horizons will swoop three times closer to “Ultima” than we flew past Pluto three years ago!

As someone who follows New Horizons, let your friends and social media followers know about the upcoming exploration of Ultima and that New Horizons and NASA will make history at the holidays with this epic exploration.

Ultima Thule
There are many ways to follow New Horizons and its unprecedented exploration of the KBO Ultima Thule—from websites to NASA TV to social media to press articles! This beautiful artist’s conception of Ultima was created by Roman Tkachenko.

Ultima is 100 times smaller than Pluto, but its scientific value is incalculable. From everything we know, it was formed 4.5 or 4.6 billion years ago, 4 billion miles from the Sun. It’s been stored at that enormous distance from the Sun, at a temperature of nearly absolute zero, ever since, so it likely represents the best sample of the ancient solar nebula ever studied. Nothing like it has ever been explored.

Its geology and composition should teach us a lot about how these building blocks of small planets like Pluto were formed. The New Horizons mission team is excited too, and we can’t wait to see what we will find!

Will Ultima be an agglomeration of still smaller bodies formed at the birth of the solar system? Will it have an atmosphere? Will it have rings? Will it have moons? Any of that could be possible, and soon we’ll know the answers to these questions. So come along with New Horizons, spend your Christmas in the Kuiper Belt and your New Year’s with NASA – and join us for the Ultima flyby.

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

– Alan Stern

There are many ways to follow New Horizons news and commentary on social media, such as these listed below. You can find others by searching the web.
NASA’s New Horizons website
New Horizons mission website
• NASA New Horizons on Twitter
The PI’s “Inside View” on Twitter
New Horizons on Facebook
New Horizons E-News signup

The PI’s Perspective: Why Didn’t Voyager Explore the Kuiper Belt?

Voyager 1 and 2 spacecraft
NASA’s venerable Voyager 1 and 2 spacecraft made landmark explorations of the giant planets from 1979 to 1989. New Horizons is the next deep-space probe after the Voyagers, accomplishing the first exploration of Pluto and the Kuiper Belt beyond—our solar system’s third zone. Credit: NASA.

New Horizons is in good health and cruising closer each day to our next encounter, an end-of-the-year flyby of the Kuiper Belt object (KBO) 2014 MU69 (or “MU69” for short). Currently, the spacecraft is hibernating while the mission team plans the MU69 flyby. During hibernation, three of the instruments on New Horizons—SWAP, PEPSSI and SDC—collect data every day on the charged particle, ionized plasma and dust environment in the Kuiper Belt at a solar distance of 41-42 astronomical units (AU), where our spacecraft is traveling. (1 AU is the distance from the Earth to the Sun, about 93 million miles or 140 million kilometers; for comparison, Pluto is about 34 AU from the Sun, so we’re about 750 million miles farther out than Pluto now.)

A role of all NASA mission principal investigators is to communicate with the public. I typically give 20 to 30 public New Horizons talks per year, and a question I used to get a lot is whether Voyager could have explored Pluto. I addressed that really interesting question in this column in June 2014, shortly before our Pluto encounter began — have a look!

Now people often ask why the Voyagers didn’t explore the Kuiper Belt, since both Voyager 1 and 2 clearly transited this region after passing the giant planets. That’s a really good question with a number of facets, so I thought I’d address it in this PI Perspective.

Our New Horizons extended mission to explore the Kuiper Belt and KBOs runs to mid-2021, when the spacecraft will be at a distance of 50 AU. This mission consists of three primary scientific investigations: studying the ionized plasma and dust environment of the Kuiper Belt with our charged-particle and dust sensors, studying numerous KBOs in the distance with our Long Range Reconnaissance Imager (LORRI), and exploring one ancient KBO (2014 MU69) in a close flyby.

Voyager carried many spectacular instruments through the Kuiper Belt, including imagers, spectrometers, magnetometers and charged-particle detectors. Those instruments have contributed a lot to our understanding of the Sun’s heliosphere and the Kuiper Belt plasma environment, even though the Kuiper Belt wasn’t discovered until 1992, when Voyager 1 was almost all the way across the region and Voyager 2 was deep within it. So even though the Voyager team didn’t know their spacecraft was in the Kuiper Belt until 1992, the Voyagers themselves collected a lot of data about the region. Now, New Horizons is transiting the region with more advanced charged particle spectrometers and a dust detector, making new and more sensitive studies of this aspect of the Kuiper Belt’s environment.

Regarding the images we’re taking of KBOs our spacecraft passes in the distance, however, Voyager’s imagers would have not been able to do what New Horizons can—such as search for KBO satellites, or determine KBO rotation periods and shapes. Why not? First, with very few known KBOs at the time, and certainly no small ones known close to Voyager’s trajectory, it would have been impossible to put together a Kuiper Belt target observing list. But even had the team been able to somehow craft such a list, Voyager’s cameras used older-technology Vidicon detectors instead of the charge-coupled devices (CCDs) that LORRI uses (and are found in most digital cameras). As a result, Voyager’s imagers were not anywhere near as sensitive as those aboard New Horizons, and they could not have detected faint KBOs like the telescopic LORRI can.

But, perhaps most important is the question: could Voyager have flown by a small KBO as New Horizons will do this December and January? Again, regrettably, the answer is no, for a number of reasons. First, even once the Kuiper Belt had been detected in 1992, the Hubble Space Telescope (the only telescope capable of finding such distant flyby targets, even today) hadn’t been repaired to properly focus light. That repair didn’t occur until December 1993. By then, Voyager 1 was exiting the Kuiper Belt near 55 AU, and Voyager 2 was near 42 AU. But even after its repair, the Hubble wasn’t sensitive enough to detect KBOs as small and common as MU69, so there would have been no way to find a flyby target—that capability only came in 2009, when a more advanced and sensitive wide-field camera was placed aboard the Hubble during a servicing mission.

And even if those limitations weren’t the case, it might have been hard to find a KBO along the Voyagers’ paths. That’s because both Voyagers 1 and 2 traveled far out of the plane of the solar system, on which the heart of the Kuiper Belt resides. Unlike New Horizons, which is traveling directly through the densest region of the Kuiper Belt, the Voyagers were literally a billion or more miles above (Voyager 1) or below (Voyager 2) most of the KBO population; they were closer to the fringes of the population where there are fewer flyby candidates. Of course, had the Kuiper Belt been known in the 1980s, the Voyagers could have been targeted to fly through its heart, but that would have adversely affected the targeting of and scientific return from their final flybys at Saturn and Neptune, respectively, something I doubt the science teams would have favored because their prime objectives were to study the giant planets and their satellites.

Illustration of the Kuiper Belt
New Horizons is the fifth spacecraft to traverse the Kuiper Belt, but the first to conduct a scientific study of this mysterious region beyond Neptune. Credit: NASA/JHUAPL/SwRI/Magda Saina

It’s too bad, because their cameras and spectrometers and other instruments could have made very nice observations of a flyby target had they been able to find one. But alas, there’s wrinkle to that too: Voyager’s cameras also weren’t sensitive enough to navigate to a close flyby the way New Horizons can, snapping pictures to home in on MU69 even from distances of over 100 million miles (or 160 million kilometers), so it would have been very difficult to target a close flyby using Voyager. In sum, a Voyager KBO flyby was simply not in the cards, given the lack of knowledge of the Kuiper Belt back then, the Hubble’s capabilities when Voyager crossed the region, the spacecraft trajectories and their onboard optical imaging and navigation limitations.

So, all in all, practical limitations meant that Voyager really could not have done the Kuiper Belt exploration mission New Horizons is now performing. But no matter, New Horizons is exploring the Kuiper Belt, and the Voyagers left an amazing legacy of truly opening our eyes to the giant planets and their rings, satellites and magnetospheres—both amazing outcomes!

I wonder when the next, even farther explorations will take place out in the Kuiper Belt, and how will people compare those future missions to what we accomplish with New Horizons?

Fans of New Horizons
I recently ran into John deBoer and his mother, Corrie, on a flight across New Zealand. John said how much he loved New Horizons! It’s amazing to see people so far away from America appreciating what NASA does. In an email John sent me a few days later, he said, “Thanks for really opening up some new horizons for us all, and for the sustained vision and efforts it took to achieve those results.” John, your sentiments make all the work we do on New Horizons worth it! Credits: Alan Stern/SwRI

Well, that’s my update for now. For more mission news, stay tuned to the many websites and social media channels listed below.

I’ll write again around the time we wake up New Horizons in early June. Until then, 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.
NASA’s New Horizons website
New Horizons mission website
NASA New Horizons on Twitter
The PI’s View on Twitter
New Horizons on Facebook
New Horizons E-News signup

The PI’s Perspective: Wrapping up 2017 En Route to Our Next Flyby

2019 New Horizons Close Flyby of a KBO
New Horizons will fly by its next exploration target, a distant Kuiper Belt object called 2014 MU69, on Jan. 1, 2019. Credit: Roman Tkachenko

New Horizons is in good health and cruising closer each day to its next encounter: a flyby of the Kuiper Belt object (KBO) 2014 MU69 (or “MU69” for short). If you follow our mission, you likely know that flyby will occur on New Year’s Eve and New Year’s Day 2019, which is just barely over a year from now!

As I write this, New Horizons is wrapping up an active period that began when the spacecraft emerged from hibernation mode in September. But soon, on Dec. 21, we’ll put the spacecraft back in hibernation, where it will remain until June 4, 2018. After June 4 the spacecraft will stay “awake” until late in 2020, long after the MU69 flyby, when all of the data from that flyby have reached Earth.

But before we put New Horizons into hibernation this month, we have some important work ahead. We’ll observe five more KBOs with the onboard LORRI telescope/imager to learn about their surface properties, satellite systems and rotation periods. This work is part of a larger set of observations of 25-35 Kuiper Belt objects from 2016 to 2020 on this extended mission. Learning about these KBOs from close range and at angles that we cannot observe from Earth makes will give us key context for the more detailed studies we’ll make of MU69 from a thousand times closer than we can study any other KBO. In addition to that LORRI imaging of these objects, we’re continuing our nearly round-the-clock observations of the charged particle and dust environment of the Kuiper Belt—both before and while New Horizons hibernates.

Also right ahead is a 2.5-minute engine burn planned for Dec. 9 (yes, a Saturday). This maneuver will both refine our course and optimize our flyby arrival time at MU69, by setting closest approach to 5:33 Universal Time (12:33 a.m. Eastern Standard Time) on Jan. 1, 2019. Flying by at that time provides better visibility by the antennas of NASA’s Deep Space Network, which will attempt to reflect radar waves off the surface of MU69 for New Horizons to receive. If it succeeds, that difficult experiment will help us determine the surface reflectivity and roughness of MU69 at radar wavelengths—something that has been successfully applied to study asteroids, comets, planetary satellites and even some planets, including Pluto, which New Horizons observed the same way in 2015.

Our Pluto observation set a record for the most distant object ever studied with radar —shattering the previous record by over 300 percent! If our radar experiment is successful on the much-smaller MU69 (which is perhaps 30 kilometers [19 miles] in diameter—tiny compared to Pluto’s almost 2,400-kilometer [1,480-mile] diameter), then we’ll break our own record, something unlikely to be surpassed for decades.

Since hibernating, New Horizons requires less attention from mission control than when we’re in active operations. This will allow our mission team to focus fully on planning the detailed sequences that will tell New Horizons how to make every scientific observation of MU69 during its close-range pass in the days surrounding Jan. 1, 2019.

People at the MU69 flyby planning meeting.
MU69 flyby planning meetings, like this small one recently held in at Southwest Research Institute in Boulder, Colorado, are well under way. Credit: Alan Stern/SwRI

The year ahead will also include many observations of other KBOs, more study of the Sun’s heliosphere with our dust and plasma instruments — SDC, PEPSSI, and SWAP, and our Alice ultraviolet spectrometer — as well as all the remaining flyby planning for MU69.

MU69 flyby operations will begin with distant navigation imaging to help us accurately home in on our target; that work will start in late August or September and will continue until literally 48 hours before flyby. Our navigation teams at KinetX and NASA’s Jet Propulsion Lab JPL will use those navigation images to compute the engine burns to further refine our course toward our planned closest approach point just 3,500 kilometers, or about 2,175 miles, from MU69. That’s more than three times as close as we flew by Pluto, which should make for spectacular MU69 images and other data!

Additionally, beginning in the final weeks of 2018, we’ll search for moons or dust structures around MU69 that could harm New Horizons if we were to collide with them during our 32,000-miles-per-hour flyby. If hazards that threaten the spacecraft are found, we can burn our engines to divert to a farther flyby, with a closest approach of 10,000 kilometers (about 6,200 miles), which should be safer.

Well, that’s my update for now. For more mission news, stay tuned to NASA websites, our own project website, and our social media channels, which are listed below so you can bookmark them.

I’ll write again early next year. Until then, I hope you have a safe and productive finish to 2017, a happy new year, and that 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.
NASA’s New Horizons website
New Horizons mission website
• NASA New Horizons on Twitter
PI Alan Stern on Twitter
New Horizons on Facebook
New Horizons E-News signup

No Sleeping Back on Earth!

Today’s blog is from Alan Stern of the Southwest Research Institute in Boulder, Colorado—principal investigator for NASA’s New Horizons mission.

image of 2 people standing under Pluto
Did this get your attention? It sure got mine! This provocative image of a scale model of Pluto “hanging” over a harbor was produced by the Griffith Observatory in Los Angeles and CuriosityStream.

Three weeks ago we put our New Horizons spacecraft into hibernation mode, the first time we’d done that since late 2014, before the Pluto flyby. By coincidence, that same day – April 7—was also the exact halfway mark on the calendar between our Pluto and Kuiper Belt object (KBO) flybys!

The hibernation period we’re in will last through mid-September. Every Monday between now and then, the spacecraft will check in with a health report, in which it sends one of seven possible “beacon tones” ranging from what we call “green” (meaning all’s well) to various shades of “red” (which mean something is amiss). On the way to Pluto we hibernated for a total of about 250 weeks during 2007-2014, and only saw a handful of red beacons over all those weeks. And so far in this hibernation, on all three Mondays, New Horizons has sent green beacons.

We’ve used spacecraft hibernation a lot since 2008. This mode turns off most onboard systems, but leaves the radios, main computer, power distribution and thermal control systems active. Our three space environment monitoring scientific instruments—SWAP, PEPSSI and SDC – also continue to operate. By turning off other electronics (like those for guidance and propulsion, and all backup systems) we save on time and, therefore, wear and tear on many spacecraft components, prolonging their life.

The other big advantage of hibernation is that our mission and science operations teams get a break from babysitting the bird and can concentrate on other things—in this case, detailed planning for that KBO flyby coming on Jan. 1, 2019. So while our spacecraft may be dozing, our team sure isn’t—they are as busy as can be with the many hundreds of flyby planning details that have to be completed this year, so we can finish testing the plan early next year during another hibernation. After all, flyby operations begin in July 2018, which is less than 15 months away!

Science Team Members
Science team members at the Southwest Research Institute in Boulder, Colorado, discuss MU69 flyby plans during a telecon with counterparts at the Johns Hopkins Applied Physics Lab in Laurel, Maryland. (Credit: Alan Stern)

Before we went into hibernation mode earlier this month, New Horizons finished downlinking all the data it took on distant KBOs in January. It also sent back the data we collected from January through March on Kuiper Belt dust distribution and the charged-particle radiation environment a half-billion miles past Pluto. Our science team is now analyzing these data, and we’re already finding some interesting results — including a wide range of dwarf planet surface properties. More on that in another PI Perspective…

Meanwhile, as New Horizons hibernates, the three scientific instruments I mentioned earlier will gather more data on the radiation and dust environment of the Kuiper Belt, something we can do much better than the Voyagers did in the 1990s. The reason why we can do so much better is simply that we have the first detector ever to fly in the Kuiper Belt and our radiation instruments were built in the 2000s, and are therefore highly advanced compared to their cousins on the venerable Voyagers that were built in the 1970s.

Illustration of pathway to MU69
Our pathway to MU69: This diagram depicts our path across 5 billion miles of space to reach Pluto and then fly by MU69 on the first day of 2019. The position of Pluto is not where it was when we flew past in 2015, but where it will be on MU69 flyby day, a billion miles sunward of MU69. (Credits: NASA/JHUAPL/SwRI)

In addition to planning the command sequences that will choreograph all seven of our scientific instruments and the relevant spacecraft operations during our KBO flyby, there are some other important, mission related events this summer:

  • Beginning May 1 and continuing across the summer, NASA’s Hubble Space Telescope will take images of our flyby KBO against star fields. We’ll use these images to refine our knowledge of the target’s orbit so we can assess the need for any engine burns – course corrections – as we home in. The next such burn opportunity is in early December.
  • In June, our science team will hold a major workshop to evaluate the trades (pros and cons) involved in choosing the best altitude for the flyby. Our goal is to get the best science with the highest probability of mission success, and a lot of factors are involved. Choosing that distance is more complex than just “go as close as we can,” since some objectives are better served with the spacecraft farther out, or at a more leisurely pace a more distant flyby that can fit more observations in while we’re very close to the target. The ultimate flyby distance will be somewhere between about 3,000 and 20,000 kilometers (1,875 to 12,500 miles). We’ll let you know later this summer what altitude came out on top.
  • On June 3, and then again on July 10 and 17, our flyby KBO—called 2014 MU69—will occult (block the light) from a different star on each date. No such “stellar occultation” of MU69 has ever been observed, so we’re pretty excited. If we’re successful in deploying telescopes to the occultation paths in South America and Africa and getting the goods, we will learn about MU69’s size, if it has rings or other hazardous debris in orbit around it, and maybe even something about its shape. All of that will help feed our flyby planning effort.
  • NASA’s Hubble Space Telescope will be pressed into service for us again in June and July – this time to measure how fast MU69 rotates and how strongly its brightness varies as it turns on its axis. Because MU69 is so faint, not even the world’s largest groundbased telescopes can make this measurement. But Hubble can, and we’ll use this information to better plan the exact timing and other details of the close flyby activities on Jan. 1, 2019.

What I’ve just summarized, along with more Pluto science analysis of the Pluto system datasets we collected and just finished transmitting to the ground last October, will fill the next few months for the New Horizons project team. (In fact, two-dozen new Pluto system research papers are being published in the May 1 issue of the planetary science journal Icarus.)

One last thing I want to tell you is something I get asked a lot about. Yes, we’re going to give 2014 MU69 a real name, rather than just the “license plate” designator it has now. The details of how we’ll name it are still being worked out, but NASA announced a few weeks back that it will involve a public naming contest. Look for more information on that in the fall.

Planetary Scientist Mike Belton and his wife Anna
I was pleased to give retired planetary scientist Mike Belton, pictured here with his wife, Anna, this Pluto globe earlier this year. Mike chaired the 2003 National Academy planetary decadal report that placed the exploration of Pluto at the top of NASA’s new planetary mission priority list. Mike and his decadal survey committee of experts are unsung heroes of the exploration of Pluto! Credit: Tod Lauer)

For news in the meantime, stay tuned to our websites and our social media channels!

NASA’s New Horizons website
New Horizons mission website
NASA New Horizons on Twitter
New Horizons on Facebook
New Horizons E-News signup

Exploring Pluto and a Billion Miles Beyond

Today’s blog is from Alan Stern of the Southwest Research Institute in Boulder, Colorado—principal investigator for NASA’s New Horizons mission.  

Year of KBO image
New Horizons is on its way to a new flyby, where it will study an ancient building block of small planets like Pluto, on New Year’s Day 2019. Credit: Roman Tkachenko

As 2016 ends, I can’t help but point out an interesting symmetry in where the mission has recently been and where we are going. Exactly two years ago we had just taken New Horizons out of cruise hibernation to begin preparations for the Pluto flyby. And exactly two years from now we will be on final approach to our next flyby, which will culminate with a very close approach to a small Kuiper Belt object (KBO) called 2014 MU69 – a billion miles farther out than Pluto – on Jan. 1, 2019. Just now, as 2016 ends, we are at the halfway point between those two milestones.

During this phase between flyby operations, all of the systems and scientific instruments aboard New Horizons are healthy. In October, we completed the 16-month-long transmission of all Pluto flyby data to Earth. Our science team is now steadily analyzing those data, making new discoveries and writing reports to research journals like Science, Nature, Icarus, the Journal of Geophysical Research and the Astronomical Journal. Almost 50 scientific papers reporting new results about Pluto and its system of moons were submitted this year!

Additionally, our science and science operations teams have made two major Pluto submissions to NASA’s archive of all planetary mission data, the Planetary Data System (PDS). Two final submissions to the PDS will be made in 2017, wrapping up the archiving of Pluto data for others in the scientific community to use. Those upcoming submissions will include better-calibrated datasets resulting from the intensive, post-Pluto flyby calibration campaign we conducted this summer using all seven payload instruments aboard New Horizons and a series of “meta-products” like maps and atmospheric profiles created from New Horizons data.

The year ahead will begin with observations of a half-dozen KBOs by our LORRI telescope/imager in January. Those observations, like the ones we made in 2016 of another half-dozen KBOs, are designed to better understand the orbits, surface properties, shapes, satellite systems and frequency of rings around these objects. These observations can’t be done from any groundbased telescope, the Hubble Space Telescope, or any other spacecraft – because all of those other resources are either too far away or viewing from the wrong angles to accomplish this science. So this work is something that only New Horizons can accomplish.

The Astrophysical Journal Letters
This is the abstract of the first scientific paper reporting new results from the study of KBOs by New Horizons, and the first observations of KBOs from within the Kuiper Belt. The full paper can be found on the website for The Astrophysical Journal Letters. Credit: Astrophysical Journal Letters

Also in January, we’ll continue studying the dust and charged-particle environment of the Kuiper Belt using the SWAP, PEPSSI and SDC instruments, and we’ll use our Alice ultraviolet spectrometer to study the hydrogen gas that permeates the vast cocoon of space surrounding the sun called the heliosphere.

February is likely to begin with a small (about a half-meter per second) course correction maneuver to better target the close flyby of 2014 MU69. In March, once all the KBO data collected in January is back on Earth, we’ll put New Horizons in hibernation for the first time since 2014. That will last until September, when we’ll begin several more months of KBO observations using LORRI.

Kuiper Belt diagram
This diagram covers various aspects of our plan for observing almost two-dozen KBOs as we cross the Kuiper Belt between 2016 and 2020. Credit: JHUAPL/SwRI/John Spencer

While New Horizons “sleeps” through much of 2017, our spacecraft, mission operations, and science teams will be designing, writing and testing the spacecraft command sequences for the 2014 MU69 flyby. For Pluto that job took most of 2009 to 2013. But because the MU69 flyby is barely two years away, we have to compress all the planning into the next 18 months. Why? Because flyby operations for 2014 MU69 will begin in July 2018.

Coffee cup
Can’t get Pluto off your mind? Me neither – sometimes even when I’m not working on data or research papers, such as when I was served this cup of cappuccino one morning. Share any quirky reminders of Pluto or its moons you have on Twitter @NewHorizons2015 or @AlanStern. Credit: Alan Stern

When New Horizons reaches 2014 MU69 just under two years and two weeks from now, we’ll be setting another record – for exploring the farthest world ever explored, over 4 billion miles from Earth! Since there no planned mission after New Horizons to explore worlds in the Kuiper Belt, it’s anyone’s bet how long it will be before our record is eclipsed.

So, as 2016 ends and 2017 prepares to dawn, I want to wish you all the very best for the holidays and the coming year. I’m going to spend the holidays with family, thankful that our team has now successfully collected all of the data from the first exploration of Pluto and its moons, and is hard at work analyzing that gold mine!

Pluto: What a Journey!

This blog is from Hal Weaver, who joined the New Horizons team in May 2002, his first assignment after taking a job at the Johns Hopkins University Applied Physics Laboratory. He started out as the principal investigator for the LOng Range Reconnaissance Imager (LORRI) and in 2003 became the New Horizons project scientist.

Now that most of the New Horizons science data have been downlinked to Earth, it seems only fitting to reflect on the long journey that took us to the frontier of our solar system. Below are some personal memories I’d like to share about this incredible voyage of discovery.

The pre-launch years were a time of intense activity for the New Horizons project. As soon as New Horizons received its funding in 2002, the team worked feverishly to deliver the spacecraft to Kennedy Space Center in time for the earliest possible launch window and the shortest flight time to Pluto. As we struggled to deliver the systems and instruments to the spacecraft during the spring of 2005, the payload team started having Sunday morning telecons to stay on track. This was typical behavior across the New Horizons project—people doing whatever it took to meet the looming deadlines. A camaraderie developed that would sustain us throughout the entire mission, and I feel privileged to have worked with such an outstanding group of engineers, managers and scientists.

The New Horizons spacecraft was shipped to Kennedy Space Center/Cape Canaveral Air Force Station in September 2005, where various tests were run to demonstrate readiness for launch. We passed the Mission Readiness Review with flying colors on Dec. 13, 2005. But there was still some high drama during NASA’s Flight Readiness Review at the Cape in January 2006, when a launch vehicle technical issue threatened an indefinite delay. Fortunately, the NASA administrator ultimately decided it was safe to launch, and away we went on Jan. 19, the fastest spacecraft ever to leave the Earth! Watching the picture-perfect launch of New Horizons with the rest of the science team, and then hugging each other as we savored the moment, was one of my favorite experiences during the mission.

New Horizons Spacecraft launch
The left image shows the New Horizons spacecraft during testing at Kennedy Space Center in fall 2005. At right, New Horizons lifts off from Cape Canaveral Air Force Station on Jan. 19, 2006. Credit: NASA

The aperture door of the LOng Range Reconnaissance Imager (LORRI) was finally opened Aug. 29, 2006, and its first images of a star cluster looked great. But in early September, the New Horizons Guidance and Control system’s lead engineer appeared ashen-faced at my office door announcing that LORRI had accidentally been pointed at the sun. Anyone who has worked with telescopes knows that focusing sunlight on a sensitive detector can overheat and destroy the detector. Fortunately, the sun was only briefly slewed across the LORRI detector, and LORRI survived without any degradation in performance. This experience was a poignant reminder that constant vigilance would be needed to ensure a successful Pluto flyby.

The Pluto encounter in July 2015 was the highlight of the New Horizons mission, with enough memories to fill an entire book. But I truly will never forget the scene in my office just after midnight on July 13, when I displayed on my computer screen the last full-frame image of Pluto taken by LORRI, which had just been downlinked from the spacecraft. There were five other colleagues in my office – the team that produced the beautiful color images displayed for the world the next morning – and we all gasped at the iconic “heart” of Pluto and marveled at the diversity of the terrain surrounding it. During media interviews leading up to the encounter, I frequently stated that an important objective of the New Horizons mission was to transform Pluto from the pixelated view seen from Earth into a real world, with complexity and diversity. As the figure below demonstrates, mission accomplished!

The Pluto image to the left was taken by the Faint Object Camera of the Hubble Space Telescope in 1994 and is representative of the highest resolution achieved from Earth. The Pluto image to the right was taken by New Horizons just 16 hours before closest approach in July 2015. This LORRI image is the raw, compressed version seen by New Horizons scientists shortly after midnight on July 13, but it still clearly demonstrates the dramatic increase in science content available from a flyby mission. Credits: NASA/ESA/A. Stern and M. Buie (left image); NASA/JHUAPL/SWRI (right image)

I can’t believe a year has passed since NASA’s New Horizons spacecraft successfully executed its historic encounter with the Pluto system. People around the world have been captivated by the incredible new views of Pluto and its moons provided by New Horizons. As much as I love planetary astronomy and spacecraft missions, I love my family even more and want to thank them for their support while I indulged my scientific passions.

I’m deeply appreciative of the opportunity to participate in this grand adventure, and I’m looking forward to the January 2019 New Horizons encounter with the Kuiper Belt object 2014 MU69, which might be the most primitive body ever visited by a spacecraft.

Hal Weaver
New Horizons Project Scientist Hal Weaver
Credits: JHUAPL/Mike Buckley

Commanding the Eyes of New Horizons

This New Horizons blog is a team effort between Cathy Olkin, the co-principal investigator of the New Horizons Ralph instrument, and Ralph instrument engineer Eddie Weigle.

Just as it takes teamwork to fly a spacecraft to Pluto – even tasks like checking the commands that are sent to the spacecraft are done by a team – we decided to team up on this blog to take you behind-the-scenes of interplanetary spaceflight. Specifically, we’ll tell you how we check the commands for New Horizons’ Ralph instrument to make sure they will accomplish the desired science objectives.

New Horizons Ralph Instrument
The Ralph instrument is the main “eyes” of New Horizons and is charged with making the maps that show what Pluto, its moons, and other Kuiper Belt objects look like. The instrument is so named because it’s coupled with an ultraviolet spectrometer called Alice in the New Horizons remote-sensing package – a reference familiar to fans of “The Honeymooners” TV show. Credits: NASA/JHUAPL/SwRI

Cathy: A command load is a set of commands that are transmitted to the spacecraft’s computers from Earth – in our case, sent through NASA’s largest Deep Space Network antennas – which control the spacecraft’s activities. Sometimes the command load covers a short period of time – maybe four days, or a week – but in other instances a single command load can span months, such as when New Horizons was in hibernation mode for much of the journey to Pluto.

For the time around closest approach to Pluto, we had one command load that executed commands over a nine-day time span ranging from one week before closest approach to two days after. These command loads are built by the science and mission operations teams and are then checked by the spacecraft engineers and instrument teams. That’s where we come in. We check the command loads for the Ralph instrument, a color camera and near-infrared imaging spectrometer.

We had more than 20 versions of this nine-day command load. The command load had 30,124 lines that needed to be checked! We checked that the instruments would carry out the desired science observations and that nothing would harm the spacecraft or instruments.

The first step in checking a command load is to compare where the instrument is pointing with the desired location. The Ralph instrument builds up images by scanning the field of view of the instrument across the target and I check that the pointing of the instrument is right by looking at a visualization of the commands using a tool call the Satellite Tool Kit.

Now, I will turn it over to Eddie to tell you more about how we check the command loads.

Eddie: Now we get to the fun stuff: making sure the Ralph instrument is doing what the scientists want. Prior to creating the command load, the Ralph science team confers and debates over the best possible ways to use the instrument. There are several facets to consider when deciding on the science. These discussions for creating Science Activity Plans (SAPs) must take into account the Ralph operating mode, where and when to point the instrument, the observation target, memory requirements, the type of data compression, and downlink time. Each SAP the science team approves is broken down into one or more “observations.” Each observation has a single purpose, and consists of a particular target, operating mode, and time.

With all this information, the command load is built. The load contains commands not just for Ralph, but for all the other instruments and subsystems as well, including the spacecraft itself. These command loads may contain thousands of commands, so to check each version of each load manually would be extremely time-consuming. So to aid our team in verifying the loads, we developed a Python script to analyze the full file. The script verifies that all the necessary commands are there to properly execute each observation.

After all the subsystem leads check and approve the command script, we still need to make sure the commands work as they should. So we run each command load on the New Horizons Operations Simulator – or “NHOPS”—a fancy name for a set of electronics that functions just like the spacecraft itself. Understanding the full complexity of the entire spacecraft typically goes beyond any individual instrument team, so we conduct a dry run to ensure all resources are properly used. To analyze the results of each NHOPS run, the Ralph team developed a web-based tool called Ralph Activity Manager (RAM).

RAM provides the team with end-to-end coverage for the commanding of the instrument. It not only includes the command checker I described earlier, but also correlates the spacecraft telemetry, the telemetry from the simulator tests, the command loads, and the science objectives. This allows us to easily track and manage all of the science goals, from the time we decide what to observe, until the data from those observations are on the ground.

And that, in a nutshell, is how we confirm the commanding on New Horizons is accurate – and how the mission team was not only able to deliver the goods on one of the great planetary encounters of our time, but also how we’ll continue to explore the farthest reaches of the solar system!

NH team
Eddie Weigle (left) and Cathy Olkin with New Horizons teammate Allen Lunsford during Pluto flyby. Courtesy of Cathy Olkin

Pluto: Preparing for the Perfect Alignment

Today’s blog is from Anne Verbiscer, a research associate professor in the Department of Astronomy at the University of Virginia. On the New Horizons science team she studies the scattering properties and composition of icy surfaces in the Pluto system and the Kuiper Belt.

Every year, planets orbiting the sun beyond Earth’s orbit reach what astronomers call “opposition,” when they appear in the sky at the position opposite that of the sun. At opposition, the planet, or satellite or asteroid, and the sun line up with Earth between them. Pluto and its moons were at opposition this year on July 8, at 03:30 universal time. Sometimes these alignments are so precise that if you were standing on the surface of one of these bodies and looking back at Earth, you would see our planet transit (or move across) the solar disk.

Earth and Moon transit the solar disk
Earth and Moon transit the solar disk, seen from an outer planet during a “special” opposition when the planet is near the Line of Nodes. Credits: P. Molaro, et al., from arXiv 1509.01136, 2015

These “special” oppositions take place when the planet is near what is called the Line of Nodes at the time of opposition. The Line of Nodes is the intersection of the plane of the Earth’s orbit and a planet’s orbit. If the planet is near one of these intersection points at the time of opposition, it is in near-perfect alignment with the Earth and sun. Pluto was last near one of these intersection points in 1931 and will be again in 2018. After that, because of the eccentricity of Pluto’s orbit, it will be another 161 years until the next perfect alignment opportunity.

The Line of Nodes
The Line of Nodes is the intersection between the orbital plane of Pluto (purple) and that of Earth (white). Because Pluto’s orbit is significantly inclined relative to the ecliptic plane, node crossings are rare, and because Pluto’s orbit is eccentric, they occur in 87- and 161-year intervals. Credit: Anne Verbiscer

Pluto’s last node crossing was within one year of Clyde Tombaugh’s discovery in 1930. Did Tombaugh discover Pluto because it happened to lie right in the plane of the Earth’s orbit and the orbits of most of the other planets in the solar system in 1930? Probably. But did the fact that objects tend to be brighter, sometimes exceptionally so when they are near opposition, also increase Tombaugh’s chances of making his famous discovery? Perhaps. Pluto was definitely brighter at that time, but just how much brighter? And why was it brighter? To answer those questions, we need to investigate the “opposition effect.”

The Opposition Effect

The surfaces of airless bodies in the solar system all exhibit an “opposition effect.” This is the (sometimes dramatic) increase in reflected sunlight that occurs when a planet, moon, asteroid or comet is at opposition. The angle between the sun and Earth as seen from the planet is called the solar phase angle, or simply the phase angle. The opposition effect is the increase in brightness observed as the phase angle decreases to zero.

Saturn and its rings and moons had their node crossing in January 2005, and several of the world’s telescopes were watching. The 2.2-meter telescope at Calar Alto Observatory in Spain obtained the three images below at different phase angles. When Saturn was at opposition on the night of Jan. 13, 2005, the phase angle decreased to 0.02 degrees and the rings became stunningly bright, far brighter than they were at a larger phase angle in February and even brighter than they were just one night after opposition. Why did the rings get so bright? And why did Saturn not get bright?

Three views of Saturn
Three views of Saturn from Spain’s Calar Alto Observatory in 2005. On the night of Jan. 13, Saturn was very close to the Line of Nodes. Note how bright the rings appear. Only one night later (center) they are significantly dimmer, and even more diminished in brightness a month later (right). Credit: Calar Alto Observatory

The opposition effect is the product of two phenomena: particle shadow hiding and coherent backscatter. When a planetary surface or ring is at opposition, particles can hide their own shadows and contribute to an increase in brightness. Additionally, incident (or incoming) rays of sunlight can interfere constructively with sunlight reflected from the surface at opposition and increase the observed brightness. Atmospheres, however, do not exhibit dramatic opposition effects like the rings and moons do. Astronomers watching Saturn’s moons on the night of Jan. 13 were amazed to see Rhea, Saturn’s second largest moon, appear brighter than mighty Titan, Saturn’s largest moon which is covered by a thick atmosphere. Despite the fact that Rhea’s projected surface area is more than 11 times smaller than Titan’s, it was visibly brighter entirely due to the opposition effect.

The Opposition Effect and Analyzing New Horizons Data

So what does the opposition effect tell us about a planetary surface? By carefully measuring the change in reflectance as phase angles get smaller and smaller, physical surface properties such as porosity, particle size and transparency can be discerned from the opposition effect.

The quantitative analysis of how light is scattered from a particulate surface requires looking at all viewing angles, not just at opposition or at “full moon,” but all the way to “thin crescent.” As New Horizons approached Pluto last year, the phase angle was about 15 degrees, and through the encounter, the phase angles at which New Horizons instruments viewed Pluto and its moons grew larger and larger until they were finally viewing these bodies backlit by the sun at phase angles near 170 degrees. But New Horizons never viewed Pluto or its moons at phase angles smaller than 8 percent, far larger than the phase angles attainable from Earth and at opposition. Because of the size of Earth’s orbit viewed from Pluto, Pluto and its moons can never be observed from Earth at phase angles larger than about 2 degrees.

By combining the data gathered by New Horizons at larger phase angles with data acquired from Earth-based telescopes, we can measure some physical properties of the surfaces in the Pluto system by studying the manner in which sunlight is scattered from them. Observations at larger phase angles tell us about surface roughness, while those at the smallest phase angles hold clues to the particle sizes and how tightly they are compacted, or the surface porosity.

Pluto and Charon
Pluto and Charon as seen by the New Horizons Long Range Reconnaissance Imager (LORRI) on July 8, 2015, at a phase angle of about 15 degrees. Credits: NASA/JHUAPL/SwRI

What will happen when Pluto and its moons cross their Line of Nodes on July 12, 2018? Charon is normally about half as bright as Pluto, but when is at opposition near the Line of Nodes, will it appear brighter than Pluto, like Rhea was brighter than Titan when Saturn crossed its Line of Nodes in 2005? Probably not, since Pluto’s atmosphere is much thinner than Titan’s. How much of a boost in reflectance did Pluto’s opposition effect give Clyde Tombaugh? We won’t know just how bright Pluto can get until 2018, but you can be sure we will be watching to find out, and to learn more about the fascinating surfaces of Pluto and Charon!

Anne Verbiscer
Anne Verbiscer
Credit: University of Virginia/
Dan Addison

26 Years and 3 Billion Miles to Pluto

Fran Bagenal is a research scientist at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, who is working on the New Horizons mission to Pluto and the Juno mission to Jupiter. Her main area of expertise is the study of charged particles trapped in planetary magnetic fields. She remembers a young Alan Stern walking into her office in 1989 and suggesting a mission to Pluto.

“Whatever units you use – Kelvin, Fahrenheit or Celsius – it’s bloody cold on Pluto!” I incant in my strongest English accent.

I love giving public talks about Pluto. The audience is dying to see the latest pictures. And the New Horizons mission is a great success story. I recently returned from Toronto, where Pluto was the centerpiece of an annual astronomy evening – as it has been in many towns this past year. The Canadians peppered me with questions well into the night.

Alan Stern and Fran Banenal
In this photo from a meeting of the Outer Planets Science Working Group in April 1991, Alan Stern (left) and Fran Bagenal (right) pitched the case for a mission to Pluto. Credit: Dale Cruikshank

Planetary exploration is a story of people. I start my talks showing how clever people in the mid-20th century used telescopes to pin down basic facts about Pluto (size, mass, temperature, composition, atmosphere, etc). With Voyager 2 completing its exploration of the outer planets in the fall of 1989, Alan Stern — then chairman of the Outer Planets Science Working Group — rallied support to go to Pluto. But in those days, when Pluto was a small, lonely misfit on the edge of the solar system, it was hard to convince people to send a mission just to Pluto. This all changed with the advent of digital photography that allowed the discovery of objects – now thousands of them – in the Kuiper Belt. Pluto became one of a class of objects that hinted at a much more complicated solar system history.

After a year of amazing pictures of Pluto’s complex surface from New Horizons, it feels bizarre to see the fuzzy pictures from Hubble and remember just how little we could see before. I scroll through the New Horizons’ images of convecting nitrogen ice, water ice mountains, puzzling pits, and the photochemistry of haze and tholins on the surface – repeating jokes about confused geologists that always seem to get a laugh.

Toronto audience takes in Paul Schenk’s cool 3-D images
Everyone loves 3-D! This Toronto audience takes in Paul Schenk’s cool 3-D images of Pluto during one of Fran Bagenal’s many public talks. Credit: Chris Sasaki

Sometimes the 3-D pictures are a great success, sometimes not so much. I guess there’s a huge range in human visual perception. But by now the questions are flowing. Some are basic: Why not land on Pluto? Because we preferred to take science instruments than the necessary fuel. Where next? NASA has just approved an extended mission to New Horizons’ next target: an object in the Kuiper Belt known as 2014 MU69. The science team has a running joke that the KBO’s name is “Jim Green”—a reference to NASA’s director of planetary science. This usually elicits chuckles from the group.

Some of the questions during my talks are basic science: Why does Pluto have an atmosphere but not Earth’s moon? Chemistry, location, temperature. What’s the heat source driving the convection? There’s enough heat from the rock inside. (I think.) Then there is the dreaded question: Why not carry a magnetometer? In Toronto, I was lucky to have Sabine Stanley — Toronto planetary physics professor — in the audience, who nodded in strong agreement when I said, “I’m pretty certain Pluto does not have a magnetic dynamo.”

Some questions are about the human side: What did you do for the 9.5 years to get to Pluto? Plan and work on other missions. How come there are so many women on the team? Good leadership (New Horizons Principal Investigator Alan Stern and Jim Elliott, MIT professor and planetary occultation expert) that fosters female participation. And Pluto’s fun!

The past 26 years have been a fantastic ride to Pluto. So much planetary science has emerged, with tons of new physics to study and a topic that engages the public. Yes, there have been ups and downs. But overall, what a great crew the New Horizons team is to work with. What’s next? Europa, Venus, Uranus, Quaoar…anyone?

Fran Bagenal
Fran Bagenal holds 3-D-printed models of the New Horizons spacecraft (left) and the Juno spacecraft (right). Juno successfully went into orbit around Jupiter on July 4 after an almost five-year journey. Credit: Chris Sasaki