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.
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?
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!
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.
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!
Today’s blog is from Alan Stern of the Southwest Research Institute in Boulder, Colorado—principal investigator for NASA’s New Horizons mission.
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!
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.
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.
For news in the meantime, stay tuned to our websites and our social media channels!
Today’s blog is from Alan Stern of the Southwest Research Institute in Boulder, Colorado—principal investigator for NASA’s New Horizons mission.
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.
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.
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.
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!
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.
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!
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.
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.
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!
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.
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.
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?
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.
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!
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.
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.
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?
Today’s post is written by Alex Parker, a research scientist at the Southwest Research Institute in Boulder, Colorado, working on NASA’s New Horizons mission.
Nature is a common theme in Canadian literature, with desolate, remote landscapes often playing a role. It should come as no surprise, then, that Canada had a hand in writing the latest chapter in the story of Pluto, the most desolate and remote landscape ever explored.
To mark the first Canada Day (July 1) since the Pluto flyby, I wanted to share some of the ways that Canadian efforts have supported the New Horizons mission to Pluto and beyond.
A number of New Horizons team members are from Canada or were trained there in one way or another. I studied for my PhD at the University of Victoria in British Columbia; my PhD was in astrophysics, a field in which Canada is renowned as a global leader. Canada’s national partnership in the twin 8-meter Gemini observatories allowed me to pursue research in planetary astronomy, pushing the limits of what can be done with ground-based astronomical imaging without adaptive optics to explore the properties of binary systems in the Kuiper Belt. It was this work that prepared me for and eventually steered me toward the New Horizons mission, where I joined the team that discovered 2014 MU69, the post-Pluto target for a potential New Horizons extended mission.
Perhaps the most crucial Canadian contributions are in an area with a very long history: navigating a ship by the stars. During New Horizons’ approach to Pluto last year, it was a made-in-Canada star map that helped guide the way. National Research Council (NRC) of Canada scientists at the Canadian Astronomy Data Centre (CADC) in British Columbia used data collected from the Canada-France-Hawaii Telescope (CFHT) to assemble a detailed navigational star map for the mission, which was used by the Navigation and Hazards teams to keep the spacecraft on-course and safe from harm.
Dr. Stephen Gwyn and Dr. JJ Kavelaars, both at the NRC-CADC, have worked to support the New Horizons mission for years. JJ Kavelaars was my PhD supervisor, and both he and Stephen Gwyn taught me much of what I know about the astrometric and image processing techniques needed to find and track New Horizons’ potential post-Pluto target, 2014 MU69.
Gwyn developed and maintains MegaPipe, the data processing service that helps turn raw CFHT images into precisely-calibrated star maps, among other things. Using data collected from CFHT’s extremely well-calibrated MegaCam imager especially for the Pluto mission, Gwyn created a catalog the stars that would stand as a backdrop for Pluto during the flyby. The purpose of the catalog was to provide extremely precise locations and properties of the stars that would appear in New Horizons images on approach, so they could be used as navigational aids.
Frédéric Pelletier, a former Canadian Space Agency engineer from Quebec, was the KinetX Deputy Navigation Team Chief for the Pluto flyby. He and his team compared imagery from New Horizons to the CFHT star map to determine exactly the path that New Horizons was on with respect to Pluto, and adjust its course to achieve the planned flyby. The targeting was precise enough to fly New Horizons through the shadows of both Pluto and Charon. This allowed New Horizons to examine Pluto’s atmosphere backlit by the sun, and perform detailed analysis of its chemical makeup. The Atmospheres science team is led by Dr. Randy Gladstone at SwRI, who grew up in Canada and attended the University of British Columba.
Both Gwyn and Kavelaars are involved in our continued tracking of 2014 MU69, providing their expertise on matters of extremely high-precision astrometry of both stars and Kuiper Belt Objects. The CFHT star map is still in use for determining the precise orbit of 2014 MU69, and Kavelaars has led a Gemini Observatory program to track and refine the orbits of many other Kuiper Belt objects that New Horizons would study at long range during an extended mission.
If an extended mission is approved, these efforts will continue to help New Horizons find its way into the unknown as it flies to worlds in the outer solar system more distant than have ever been explored.
Today’s post is written by Alex Parker, a research scientist at the Southwest Research Institute in Boulder, Colorado, working on NASA’s New Horizons mission.
Pluto and its moons are the most distant worlds ever visited by any of humanity’s robotic explorers, but for how much longer will that remain true? New Horizons is outbound through the Kuiper Belt, and two years ago today we discovered a smaller, more distant world that we could send it to. Likely an icy relic left behind from the era of planet formation, this world lies nearly a billion miles further from the sun than Pluto. While it will eventually be named something befitting such a world, it is currently designated 2014 MU69, and if New Horizons’ extended mission is approved by NASA, it will become the new most distant world ever explored on Jan. 1, 2019.
It took years of effort from a dedicated team to find somewhere that New Horizons could visit after Pluto. We scoured the southern skies with Earth-bound and space-borne observatories, battling poor weather, unforeseeable hardware faults, and the endless interference of the dense star fields of Sagittarius, at the very center of our home galaxy itself. That search discovered over 50 new Kuiper Belt objects, and culminated with the discovery of New Horizons’ potential post-Pluto target, 2014 MU69.
What follows is a brief look back at that search, the discovery of 2014 MU69, and what it portends for the future of New Horizons and outer solar system exploration.
The Search Begins
Finding New Horizons a post-Pluto target in the Kuiper Belt was a long-standing mission goal. It was even included as a component of the original mission proposal in 2001 that New Horizons have the capacity for exploring a more distant Kuiper Belt object, should one be found that it could reach.
That last bit was the catch — at the time that New Horizons was designed, assembled, and launched, there were no suitable Kuiper Belt objects known near enough to the path that it would take out of the solar system for it to reach one after Pluto. Given that the first decade of the 21st century saw the peak rate of new Kuiper Belt object discoveries in all of history to date, why weren’t more known in the region of sky around Pluto?
Because that area of sky is one of the hardest to search for Kuiper Belt objects. It lies in front of the center of our galaxy and is packed full to brimming with background stars. For every Kuiper Belt object as faint as 2014 MU69 in our images, there were tens of thousands of stars far brighter.
Additionally, there was a quirk to the search that made waiting preferable: the longer we waited, the less sky we would have to search. You can imagine the swarm of possible Kuiper Belt objects that New Horizons could reach, all orbiting the sun on different paths with one common feature — those paths intersect with the path of New Horizons. As you go backward in time from the period during which New Horizons is passing through the Kuiper Belt, the paths of these Kuiper Belt objects diverge from one another, and they spread out like a dissipating cloud across the sky. The earlier we performed the search, then, the more sky we would have to cover in order to find these Kuiper Belt objects.
The first searches for a post-Pluto target were performed in 2004 at the Subaru observatory. At the time, the swarm of Kuiper Belt objects was quite spread out, so the search was performed over a relatively large area of sky without spending too long in any one area. These data were a large part of what was searched by the IceHunters citizen science effort, and a number of relatively bright Kuiper Belt objects were discovered in it, though none were within reach of New Horizons.
I came into the project in 2011, with our first Magellan observatory survey. The twin Magellan telescopes are situated adjacent to one another atop Las Campanas in Chile. While slightly smaller telescopes than Subaru, their site delivered us some of the best atmospheric conditions of the entire search. Since it was later than the first Subaru search, we did not have to search as much sky to cover the full swarm of targetable Kuiper Belt objects. This meant we could spend more time on each area, and see fainter Kuiper Belt objects.
But the challenge of the Milky Way remained. Above is an example of what just a portion of one of our raw images looks like. Every star you can see in this image is many times brighter than the other Kuiper Belt objects we were looking for.
I joined the search as a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics in 2011. There I was working on ways to suppress the stars in our images while leaving behind any and all objects that move like Kuiper Belt objects. These methods also had to compensate for the constantly-shifting blurring caused by the Earth’s atmosphere.
With lots of nights at the telescopes in Hawaii and Chile, lots of algorithm and code development, lots of CPUs crunching through the data, and lots of time spent scrubbing through the results manually to make sure nothing was missed, we turned up dozens of new KBOs between 2011 and 2013. Yet, while many of them came close to New Horizons’ path, still none of them were quite within reach of its fuel supply.
Taking The Search To Space
Time was growing tight, and we had to make a decision. We needed to not only find a targetable KBO, but we also needed to track its orbit over a long enough period of time that we could predict where it would be with the accuracy needed to target New Horizons for a hair-raising few-thousand-kilometer flyby. The longer we waited, the easier the search was to do, as the diffuse swarm of potentially-targetable KBOs slowly collapsed into a tight spot on the sky as the encounter dates approached. However, the time remaining for accurate follow up and orbital measurement got ever shorter.
2014 balanced both of these needs. It was the last year in which enough time remained to accurately measure any KBOs’ orbits well enough to target them with New Horizons, and it was late enough that the area of sky covered by potential targets had shrunk to the point that Alan Stern, the principal investigator of New Horizons, indicated that it was time to consider using our weapon of last resort: NASA’s Hubble Space Telescope.
Hubble has unrivaled sensitivity, and since it orbits above the Earth’s atmosphere, its unobscured view would permit us to search for KBOs hiding in front of our galaxy. The millions of background stars we had been contending with would be far less trouble for Hubble’s sharp vision.
That said, we knew that the survey we were asking for had no precedent. It would be the largest dedicated search for solar system objects ever conducted with Hubble. It would need to be designed with the utmost care, it would need to execute flawlessly, and the solar system would need to cooperate with us. And we would need to convince a panel of reviewers that this survey’s potential value outweighed the risk of coming up empty after investing so much of Hubble’s time.
As you might imagine, a request for the amount of Hubble time we needed could not be taken lightly, and the proposal was not a slap-dash affair. We painstakingly developed a risk-mitigating strategy that would both ensure our best chance of success while minimizing the amount of precious telescope time that would be wasted if the solar system did not cooperate by providing us with a targetable Kuiper Belt object.
Part of that strategy was a two-part search. We would perform a pilot project and prove that we could discover as many Kuiper Belt objects as our models predicted before proceeding with the larger main survey. We had a tight deadline to deliver this proof, with about two weeks to analyze this unprecedented new dataset, deliver our new discoveries, and pass the go-no go threshold for the full program.
With this strategy in place, we were awarded the time. And that was when things got really interesting.
In mid-June of 2014, we learned that our proposal had been selected, and that it was scheduled for immediate execution on Hubble. I quickly booked a flight to Boulder to join the rest of the team for the push to beat the tight demonstration deadline. I arrived in Boulder just as the first of the data was being collected by Hubble, orbiting somewhere far overhead.
I didn’t know it at the time, but the intense search effort that followed was a preview of what the following summer would be like as New Horizons flew by Pluto.
There was no good demonstration data to tune our tools on, which meant that we went in cold and had to write our analysis software on the fly. We were developing new software and refining the speed and sensitivity with which we could handle the data as it streamed down from space.
We had to convince energy-conscious building managers to keep the HVAC running late into the night and over the weekends to keep the offices and server rooms at livable temperatures during the summer Colorado heat. In parallel, there was another team on the East coast working to make sure that an independent and redundant pipeline was developed and running. We checked each teams’ performance by placing synthetic KBOs of known brightness in the data and determining how faint they could be before our software stopped finding them reliably.
It was exactly two years ago – on June 28, 2014 – that our search first bore fruit. Marc Buie alerted the Boulder team that he had spotted something in the data, and subsequent analysis by all the involved teams confirmed that it was a Kuiper Belt object. Eventually, this first discovery would be designated 2014 MU69.
We quickly found another Kuiper Belt object, and passed the go-no go. After all was said and done, we found five new extremely faint Kuiper Belt objects in this search data, with three candidates with promising orbits that might make them targetable.
The discovery observations alone were enough to suggest that 2014 MU69 might be targetable by New Horizons, but it would take further follow up to confirm it. In August of 2014, a batch of Hubble observations picked up 2014 MU69 again, and with those new observations my analysis of the orbit concluded that it was guaranteed to be targetable given New Horizons’ fuel reserves. Even if no others panned out, we had a world we could reach.
In the end, two of the five candidates withstood the test of subsequent observations. Of those two, it was still the first that we discovered that remained the best candidate, and so it was that 2014 MU69 was selected as the nominal target of a potential New Horizons extended mission.
But just discovering a targetable world was not enough.
Tracking, Targeting, And Understanding A New World
Pluto had been tracked for 85 years—well over a third of its orbital period, before New Horizons arrived. 2014 MU69 lives deeper in the Kuiper Belt than Pluto, and takes nearly 300 years to orbit the sun. We only discovered it two years ago. By the time we fly by it, we will have known about it for only one and a half of one percent of its orbital period. This short baseline of observations means that in order to predict the position of 2014 MU69 with sufficient accuracy and precision to fly a spacecraft by it, we would need exquisitely calibrated observations between now and the flyby.
Since its discovery, we have continued to track 2014 MU69 with Hubble. Once these extremely accurate observations are linked with the extremely precise GAIA astrometric network, we will have an orbit solution for 2014 MU69 that is unparalleled for the period of time that it has been tracked.
From its orbit, we have already learned that 2014 MU69 is a very intriguing kind of Kuiper Belt object. It belongs to the “Cold Classical” Kuiper Belt, a population that appears to be a surviving remnant of the disk of material from which the planets formed. The cold classicals seem to have escaped much of the violent processing that other kinds of minor planets were subject to. This makes 2014 MU69 the clearest window into the era of planet formation that we have ever had the chance to see up close.
All of our effort in finding 2014 MU69 opened the door to a potential extended mission for New Horizons. After the Pluto flyby in the summer of 2015, we and the spacecraft and navigation teams designed the largest spacecraft maneuver ever performed beyond Neptune. This maneuver would adjust New Horizons’ course to intersect the orbit of 2014 MU69 on Jan. 1, 2019. It would also be the largest series of engine burns New Horizons had ever attempted.
The maneuvers to do this began in October of 2015, and took several weeks to perform. After it was complete in November, New Horizons had 2014 MU69 in its sights. We were on our way.
The Extended Mission
New Horizons has targeted 2014 MU69, and we have proposed to NASA for an extended mission that would support the flyby of this distant world. This extended mission proposal is still under consideration. If approved, we will not only explore 2014 MU69, we will also study about 20 of the other Kuiper Belt objects that we discovered in our ground- and space-based searches. We won’t approach these worlds nearly as close as 2014 MU69, but New Horizons’ unique vantage point still makes it possible for us to examine them in more detail than is possible with any other facility.
Then, on Jan. 1, 2019, New Horizons will cruise over the surface of 2014 MU69, and the speck that we spotted in Hubble’s images two years ago will turn into a real world before our eyes.