Pluto New Horizons

Today’s blog post is from Oliver White, a postdoctoral researcher in planetary science at NASA Ames Research Center in Mountain View, California. He studies the geomorphology and surface processes of planetary bodies in the outer solar system.

Looking at the surface of a planet or moon for the first time can be bewildering, particularly when confronted by a variety of terrains and landforms. This is certainly what NASA’s New Horizons team felt when we received the first close-up pictures of Pluto after the flyby in July 2015. None of us were expecting to see such a diverse range of landforms like mountains and glaciers of exotic ice on such a small, cold and distant world.

After flyby our challenge was to piece together the geological history of Pluto’s surface—that is, to determine what processes have formed and modified each terrain, and when these processes occurred relative to one another.

In order to accomplish this, planetary scientists create geological maps of the surfaces of distant bodies. The New Horizons spacecraft flew past Pluto at a range of several thousand miles/kilometers. As such, creating a geological map of a planetary surface like Pluto’s is more challenging than creating a map for one on Earth. Of course, we’re unable to walk around on Pluto and pick up samples in order to analyze what they are and how they have been processed. Instead, we must rely entirely on spacecraft images and other remote sensing data to create a Pluto map. For example, compositional data provided by the Ralph/Multispectral Visible Imaging Camera (MVIC) and the Linear Etalon Imaging Spectral Array (LEISA) are extremely useful for mapping Pluto. Knowing the composition of a unit helps constrain what physical properties it has and, therefore, how it likely formed and was modified over time. The compositional data are the closest we have to possessing an ice sample from each of the different terrains on Pluto.

The colored map shown above is just such a map that I have created for the region of the encounter hemisphere on Pluto that covers the huge nitrogen ice plains informally named Sputnik Planum and the terrain immediately surrounding it. The map shows New Horizons imagery of this area, overlaid with colors that represent different geological terrains, or units. The black and white image below shows the New Horizons imagery, along with latitude and longitude lines and a scale bar.

I have studied this area in great detail, and have defined each unit based on its texture and morphology—for example, whether it is smooth, pitted, craggy, hummocky or ridged. How well a unit can be defined depends on the resolution of the images that cover it. All of the terrain in my map has been imaged at a resolution of approximately 1,050 feet (320 meters) per pixel or better, meaning textures are resolved such that I can map units in this area with relative confidence.

By studying how the boundaries between units crosscut one another, I can also determine which units overlie others, and assemble a relative chronology (or timeline) for the different units; this work is aided by crater counts for the different terrains that have been obtained by other team members. I caution that owing to the complexity of the surface of Pluto, the work I’ve shown is in its early stages, and a lot more is still to be done.

My mapping project, which began only a few days after the flyby, is currently expanding across the rest of Pluto’s encounter hemisphere. Mapping a place as interesting as Pluto has been a highly engaging, thought-provoking and fun experience. When I was an undergraduate studying planetary science, filling in my first planetary geological map of a region on Mars with coloring pencils, I never imagined that a decade later I would be making the first geological map of this world that had been a tantalizing enigma for so long!

Today’s blog post is from Ross Beyer, a planetary scientist with the Carl Sagan Center at the SETI Institute and NASA Ames Research Center in Mountain View, California. He studies surface geomorphology, surface processes, remote sensing and photogrammetry of the solid bodies in our solar system.

I’ve always loved maps, and I’ve always loved planets and space, and the idea of exploring new places – so getting a doctorate in planetary sciences seemed to flow naturally from my interest in space, planets and exploring. My job as a research scientist, exploring the solar system vicariously through robotic spacecraft for the last two decades, has been a joy. But it wasn’t until later that I realized my work with planetary images was also connected to my love of maps. And all of these things have come together with my work on New Horizons.

After the February 2007 Jupiter flyby, I helped the mission team plan the Pluto encounter. New Horizons was going to fly through the Pluto system, as if the spacecraft was on a rail moving out from the sun. We couldn’t do loop-de-loops or any other complicated motions at Pluto; we were just moving through. However, we could pivot and point our instruments at Pluto and its moons Charon, Nix, Hydra, Styx and Kerberos, so we had to figure out that sequence of events. Our mission had to satisfy numerous specific scientific objectives, so we had to lay out a sequence of observations that used our time wisely as we zipped past. I was just one of the many, many people involved in that effort. It was hard work, frustrating at times, but ultimately very educational and also fun, as we tried (and I think succeeded in) arriving at a plan that captured a wonderful series of observations from all seven science instruments on New Horizons. Of course, I was most interested in the pictures that we were going to take!

When New Horizons flew by Pluto and Charon last July, it snapped many pictures of these new worlds for the first time. As a geologist and a photogrammetrist (someone who measures things from images), it is important for me to understand correspondences between the images: where do the higher resolution images belong amongst the images taken from farther away that show more area? How is one image related to the next? To answer these questions and more, we make something called a control network, and from that we can make maps.

A control network is made from finding control points between images. So if we have two images of Pluto, and we can identify the same feature in both images – say, a crater – then we mark a spot on the crater rim in the same place in each image, and that is a control point. We do that for lots of features in each image, and then try to find those same features in other images. As you can imagine, we quickly run up a lot of points, and having a computer program to help us select and track all of these points is important.

Once we have a rich control network made up of points from all of the images we can measure, we can use a computer to perform something called a “bundle adjustment solution.” This action takes those points, and some information from the spacecraft about approximately where it was and where it was pointing when it took each image, and creates a “solution” for each image that correctly places it. This allows us to create mosaics and maps from the images. That is the key to knowing that image A is next to image B, for example, or that image C is higher resolution than either of them and is located within image A.

This kind of map allows us to not only make sense of all the images, it also allows us to combine data from the black-and-white camera and the color cameras, as well as other instruments. It helps all of the scientists on the team put their data together and tell a complete story about these amazing worlds that we have now explored!

Today’s blog post is from Orkan Umurhan, a mathematical physicist currently working as a senior post-doc at NASA Ames Research Center. He has been on the New Horizons Science Team for over two years. He specializes in astrophysical and geophysical fluid dynamics, and now works on a variety of geophysical problems, including landform evolution modeling as applied to the icy bodies of the solar system. He is a co-author of a graduate-level textbook on fluid dynamics coming out late this spring.

Greetings and salutations. In this week’s New Horizons blog entry, I want to share with you the exciting possibility that some of Pluto’s surface features may record conditions from the protosolar nebula from which the solar system formed.

A case in point is the image below. It’s what geologists call ‘bladed’ terrain in a region known as Tartarus Dorsa, located in the rough highlands on the eastern side of Tombaugh Regio. (Note that all names used here are informal.) A moment’s study reveals surface features that appear to be texturally ‘snakeskin’-like, owing to their north-south oriented scaly raised relief. A digital elevation model created by the New Horizons’ geology shows that these bladed structures have typical relief of about 550 yards (500 meters). Their relative spacing of about 3-5 kilometers makes them some of the steepest features seen on Pluto.

Now, here comes the puzzle. Spectroscopic measurements of this region made by New Horizons’ Linear Etalon Imaging Spectral Array (LEISA) instrument show that this region of Pluto’s surface has a predominance of methane (CH4)—with a smattering of water as well. Naturally, one then would ask, “Can pure methane ice support such steep structures under Pluto’s gravity and surface temperature conditions over geologic time?”

The answer is a meek “maybe.” To date, there are only two known published studies examining the rheological properties (i.e., how much a material deforms when stresses are applied to it) of methane ice in the extreme temperature range of Pluto—a bitterly cold -300 to -400 degrees Fahrenheit. According to one study, the answer is a definite ‘no,’ because methane ice of those dimensions would flatten out in a matter of decades. Yet in another study, methane ice may maintain such a steepened structure if the individual CH4 ice grains constituting the collective ice are large enough. Which study is right? Or is there a way to reconcile them? This is something we simply do not know at the moment.

So before we try to explain how the bladed shapes came to be, we have to make sure we have developed a detailed and controlled laboratory understanding of the behavior of both pure methane ice and methane-hydrate ice. If there were ever an example of why we need further laboratory work, this is it!

But what if it turns out that pure methane ice is always too ‘mushy’ to support such observed structures? Because water is also observed in this region, perhaps the material making up the bladed terrain is a methane clathrate. A clathrate is a structure in which a primary molecular species (say water, or H2O) forms a crystalline ‘cage’ to contain a guest molecule (methane or CH4, for example.). Methane clathrates exist on the Earth, namely at the bottoms of the deep oceans where it is sufficiently cold to maintain clathrate ice. Under those terrestrial conditions, however, methane clathrates are relatively unstable to increases in temperature, causing their cages to open and release their guest methane molecules. This poses a real problem for terrestrial climate stability, since methane is a potent greenhouse gas.

However, under the cold conditions typical of the surface of Pluto, methane clathrates are very stable and extremely strong, so they might easily mechanically support the observed bladed structures. While there is no direct and unambiguous evidence of methane clathrates on the surface of Pluto, it’s certainly a plausible candidate, and we are actively considering that possibility too.

If the Tartarus Dorsa bladed region is comprised of methane clathrates, then the next question would be, “how were the clathrates placed there and where did they come from?” Recent detailed studies (see Mousis et al., 2015) strongly suggest that methane clathrates in the icy moons of the outer solar system and also in the Kuiper Belt were formed way back before the solar system formed – i.e., within the protosolar nebula – potentially making them probably some of the oldest materials in our solar system.

Might the material comprising the bladed terrain of Tartarus Dorsa be a record of a time before the solar system ever was? That would be something!

Today’s blog is from Katie Knight, an undergraduate student at Carson-Newman University in Jefferson City, Tennessee. She works with the New Horizons team to help map some of the unusual terrain on Pluto, seeking patterns and estimating sizes and shapes of some of its unusual features.

Hello! My name is Katie Knight, and I’m here to talk about Pluto’s unusual geological features known as polygonal blocks. If you look to the upper left of Pluto’s “heart,” informally-named Sputnik Planum, you will see some chaotic terrain that is very different than the almost smooth terrain of the icy plains. These are the Al-Idrisi Montes, and they are filled with blocks measuring miles to tens of miles across.

The blocks within even a very small region can be very different. Some are really distinct and appear to be taller – without any other blocks touching them – while others get a bit more complicated. It’s my job to try to separate out which is which.

For example, I analyze them to try to see if these blocks might actually be one big block with some variation in height or if they are separate blocks themselves. The high resolution photos New Horizons took detail the surface with amazing clarity, but they can only show so much.

To look at the size and shape of the blocks, I trace them. The goal is to trace around the base of the blocks, including all the visible sides. Since the blocks cast shadows, some sides are very difficult to see. I am looking to see if there is an area range that is most common or potentially if there is a common shape. It can get complicated, since some blocks seem to blend together. The shadows that the sun casts on the blocks further complicates this analysis, but a lot can be distinguished. The blocks significantly vary in size and shape, but there may be some similarities between them that can be determined.

After this first look at size and shape, there are a lot of things we can also analyze. Topography can tell us about the height of blocks and indicate if they not only have some similar area but also a similar height. I am using gray-scale images from New Horizons to analyze the basics of the blocks, though the color pictures can tell us even more about the surface, so later I will analyze those too.

Learning the basics of these blocks will contribute to our knowledge about how the ice blocks formed. There are several theories and studying blocks on another planet will tell us even more. Chaos terrains like these on Pluto, while very different, can be compared to chaos on Mars and Europa to see what is common between all three of these and what that can tell us about the surface of all of these bodies.

The area I am looking at may be relatively small, but there is a lot we can learn from these blocks and I can’t wait to see more of what Pluto has to offer!

Last summer’s historic flyby of Pluto and its moons generated a wealth of science data, capturing this new world which had never before been explored. Thousands of high resolution images, spectra and particle data were recorded on the spacecraft’s two solid state recorders as the spacecraft flew by its targets. It was a fast flyby, with the spacecraft traveling at 9 miles (14 kilometers) per second. To maximize the amount of time gathering data, very limited time was spent with an Earth-pointed spacecraft during the encounter itself, and thus only a select few images were transmitted back to Earth during the flyby. The rest of the data remained on the spacecraft waiting for the commands to be executed that would compress, packetize and transmit the bits to the ground.

My name is Emma Birath and I work on the Science Operations team at Southwest Research Institute in Boulder, Colorado. We operate the science instruments onboard the spacecraft; for the encounter it was our job to build observations that accomplished the scientists’ objectives, while also satisfying spacecraft and navigation constraints. In addition to commanding the science instruments, it is also our responsibility to write the command sequences for the compression of the science data, and the transmission of the compressed science data to NASA’s Deep Space Network of radio receivers on Earth.

Due to very low downlink rates with a spacecraft that is 3 billion miles away (and counting), it will take more than a year to get every bit down from the Pluto encounter sequence. Today – about 7 months after the encounter – more than half of the data is still on the spacecraft! Because of the long duration downlink period, it is important that this work is done as efficiently as possible.

To facilitate the playback of New Horizons’ encounter data, I led an effort to build a piece of software, called DataTrack. DataTrack consists of a web-based user interface, with a MySQL database backend. It allows us to schedule and sequence playbacks for each command load sent to the spacecraft. It helps us keep track of all data sets from the encounter load, and at what stage they are in the downlink process. It also helps us track the processes of mathematical data compression on New Horizons, which is necessary to maximize how much data we can get back to the ground each week and month. Has a data set been compressed already? What compression type was used? What is the estimated data volume, and will it fit in an upcoming downlink track? It flags errors that may be introduced in a playback sequence, and ensures efficiency and optimization.

Flying a spacecraft is risky, and at any time something could happen in which we lose contact and any information that hasn’t already made it to the ground, so the prioritization of the data sets by the science team is critical. DataTrack allows us to keep track of what’s been sent to the ground, what’s scheduled to be sent, and what’s left to plan for; it also lets us track what data has been compressed.

Another important purpose of the software is to provide the science team with information on when a particular data set is expected to reach the ground. It has greatly improved communication across team boundaries.

Working on this team has been an incredible, once-in-a-lifetime experience. Seeing years of hard work and patience come to fruition has been exhilarating and very rewarding. I have to pinch myself from time to time, reminding myself how lucky I am to work in this field and to be part of the exploration of the solar system!

 

Today’s blog post is from Kimberly Ennico, a member of the New Horizons’ Composition Theme Team and one of the deputy project scientists. She works at NASA’s Ames Research Center in Moffett Field, California, and has been on detail to the Southwest Research Institute in Boulder, Colorado.

No one can doubt the beauty of Pluto and Charon—amazing worlds revealed by the images from NASA’s New Horizons mission. From Pluto’s mountains, glaciers, ice-volcanoes, blue skies, and layered colorings to Charon’s vast tectonic structures and enigmatic red-colored pole, these pictures and associated spectra are rich puzzles waiting to be solved.

The July 14, 2015 Pluto flyby gave us an initial look at one side of Pluto, with its iconic heart-shaped feature. But I’m interested in the full planetary perspective, finding the “other sides” of Pluto to be every bit as fascinating as the encounter hemisphere. We must remember that a flyby is a moment in time lasting a few hours. In contrast, Pluto and Charon each rotate about its axis every 6.4 Earth days. This means that when New Horizons flew through the Pluto system it captured one hemisphere of each body in incredible detail.

What do we know about the “other sides” of Pluto and its largest moon? In the three weeks before the flyby, the Long Range Reconnaissance Imager (LORRI) and Multispectral Visible Imaging Camera (MVIC) imaged Pluto and Charon every day, sometimes two or three times a day to gather as much coverage across the bodies as New Horizons closed in. LORRI is New Horizons’ primary camera, an 8-inch telescope outfitted with an unfiltered charge-coupled device (CCD) – like you’d find in your own digital camera – sensitive to visible light. MVIC is a separate instrument with multiple CCDs, for which several are outfitted with color filters. The highest resolution images of the “other sides” of Pluto and Charon were observed 3.2 Earth days earlier, around July 10-11.

Working with a subset of the data (as not all these images have been sent to Earth from New Horizons yet), we’ve received our first glimpse of these “non-encounter” hemispheres below.

What strikes me most about the new Pluto color images is that the latitudinal (horizontal) banding identified on the encounter hemisphere is evident all around Pluto. Specifically, the northern polar region has a distinctive color from adjacent latitudes. The darkest region, which spans the equator, also appears to continue around Pluto, showing distinct variations on the side facing Charon, which have yet to be understood.

Why is this interesting? Coloring on Pluto is thought to have been the result of hydrocarbons called tholins that have formed in the atmosphere and have been “raining” down on Pluto’s surface over the millennia. We’re investigating whether Pluto’s colored terrains are primarily due to changes in or movements of its surface ices, specifically whether they have been undergoing seasonal effects –changing in temperature over time from the amount of cumulative sunlight – which could display itself as horizontal banding. The presence of that vast reservoir of methane, nitrogen and carbon monoxide ices in Pluto’s “heart” complicates the picture and could serve as a visible marker to trace changes.

Over the next few months, as more of this late-approach imagery gets downlinked from the spacecraft’s recorders, we will continue to piece together this colorful story of Pluto and Charon – from all sides.

Eric Schindhelm is a research scientist at the Southwest Research Institute in Boulder, Colorado. He supported the Pluto system encounter in summer 2015 as part of the Atmospheres team for New Horizons.

I was very fortunate to participate in the New Horizons Pluto encounter last summer, supporting the Atmospheres science theme team.

I arrived at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland—home of New Horizons mission operations—a few weeks before the historic July 14 Pluto flyby. My job was to prepare to analyze data from the Alice instrument, a sensitive ultraviolet imaging spectrometer designed to probe the composition and structure of Pluto’s atmosphere. While a spectrometer separates light into its constituent wavelengths (like a prism), an “imaging spectrometer” like Alice separates the different wavelengths of light and produces an image of the target at each wavelength – so we were really looking forward to some incredible and valuable data.

Over the following weeks, as we approached the Pluto system, the Ralph and Long Range Reconnaissance Imager (LORRI) instruments returned increasingly amazing images and spectra. From the cracked and cratered surface of Pluto’s largest moon, Charon, to clear compositional differences across Pluto itself, these icy worlds at the edge of our solar system were turning out to be even more interesting than we expected. To be honest, I was starting to get a little jealous of the results pouring in from LORRI and Ralph. When would we get to see Pluto appear in Alice data?

The challenge was that at far-ultraviolet wavelengths (550 to 1,850 Angstroms), Pluto and Charon are only visible in reflected sunlight, and the sun is particularly faint at those wavelengths. By contrast, the sun is much brighter at the visible and infrared wavelengths that LORRI and Ralph use. We made some calculations about when we should get our first glimpse of Pluto in Alice data and the result turned out to be on Sunday July 12, just two days before closest approach!

When that Sunday evening came I kept checking the server to see if the data had reached the ground and gone through the data-reduction pipeline. Before too long I saw the data and downloaded it to my computer with anticipation. I used an adjacent row on the detector to determine the background to subtract, producing the plot below with an obvious surplus of photons at higher wavelengths.

The variation of counts from 1,300 to 1,500 Angstroms gives you an idea of how ‘noisy’ the data was at the time, but longward of 1,500 Angstroms there was clearly a signal from Pluto. Pluto’s ultraviolet signal was rising out of the noise! While spectra are not as immediately aesthetic as images, there was a certain beauty to these data – these were the first far-ultraviolet photons from Pluto ever to be detected by humans. This cannot be done from Earth with the tools anyone has available – the signals are too faint. You have to send a spacecraft to Pluto to get data like this, which are useful for determining the composition of Pluto’s surface and atmosphere. And that requires quite a bit of teamwork to design, build, and launch a spacecraft to fly all the way to the outer solar system. When I saw this on my computer, I knew that the New Horizons team had succeeded and recorded the first far ultraviolet spectra of Pluto!

A few minutes later, a large group came back from dinner, and among them was Annette Tombaugh Sitze, daughter of Clyde Tombaugh – the man who discovered Pluto in 1930. They were at our hotel (where I was working) to socialize, but I just had to show off New Horizons’ latest find. Annette was excited to see her father’s planet in the far ultraviolet for the first time, and related how he used to teach her about astronomy when she was a child. At the time, my wife was pregnant with our first child, and I was struck by a great sense of continuity in the human experience of exploration and understanding. It was fascinating to see the New Horizons spacecraft turn the Pluto system from a few points of light into a complex and dynamic system of worlds. I’m grateful to have been a part of that and can’t wait to tell my new son about it when he grows up.

Before I go, I want to mention that –in addition to the New Horizons data –we were awarded time on the Hubble Space Telescope to look at the same side of Pluto and Charon that New Horizons viewed as it flew past, using the Space Telescope Imaging Spectrograph to obtain mid-ultraviolet spectra from 1,850 to 3,200 Angstroms. The sun is much brighter here than at the far-ultraviolet wavelengths, so Hubble is capable of seeing Pluto in this wavelength range all the way from Earth — 3 billion miles away. The Hubble data bridge a gap of spectral coverage between what Alice and Ralph cover, allowing us to check close-up spectra obtained by New Horizons against those observed at Earth. The spectral signatures due to Pluto and Charon’s surfaces should be consistent across all wavelengths. Stay tuned for those results!

 

Today’s post is from Marcus Piquette, a third-year graduate student in the Astrophysical and Planetary Sciences Department at the University of Colorado, Boulder. Marcus is a part of the Particle and Plasmas Theme Team working on the Student Dust Counter aboard New Horizons.

Hello, I’m a Ph.D. student at the University of Colorado in Boulder; I recently took over as the lead graduate student for the Student Dust Counter (SDC) aboard New Horizons. SDC is an instrument that measures the distribution of dust in our solar system, providing information about the structure and evolution of bodies in the Kuiper Belt.

Being a fifth student generation to work on the instrument, I feel compelled to thank those who have come before me. Dozens of students spanning nearly 15 years came together to design, build, and now operate SDC—providing not only important scientific contributions, but also an unprecedented opportunity for young scientists and engineers to work on an interplanetary space mission. Their work has created a student legacy, led by the instrument’s principal investigator, Dr. Mihály Horányi, which exemplifies hard work and a team driven attitude, an attribute shared throughout the entire New Horizons mission.

Even though my interaction with the New Horizons team outside SDC has been limited to email or phone calls, I was able to see them in action during the Pluto encounter. In July 2015, I traveled to the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland to partake in the Pluto flyby events and to share in the momentous achievement. In the moments leading up to the Pluto flyby, I could feel the excitement in the team, the nation and even the world. Family members and friends were constantly asking for updates and information, as New Horizons flew ever closer to Pluto. The world was abuzz with wonder.

Due to a nearly 4 ½-hour light travel time between Earth and Pluto, operations aboard New Horizons including slews, observations, and communication were handled autonomously via a pre-loaded sequence of commands. On the morning of closest approach, starting around 5:30 AM EDT, scientists gathered to view initial images of Pluto showcasing details of the dwarf planet never before seen. As the day marched on, operations aboard New Horizons focused on crucial observations of the Pluto system and did not communicate with Earth until the following day. Unaware of the success or failure of the flyby proved to be stressful. Later that evening, the spacecraft called back to Earth to inform us of its survival and successful observations with a roaring response from the crowd.

That moment of excitement got me thinking about the mission as a whole. Never before had I seen such commitment and dedication over a shared goal. Even if it meant sacrificing holiday time, team members never faltered in their duties—giving everything they have. The flyby of Pluto was a culmination of everything that makes the hard work worth doing. Seeing the successful results is inspirational and provides hope for future exploration. As I venture further into my career, I will always remember my experience on the New Horizons team and what can be accomplished with the right set of goals, people and motivation.

I am thankful for those who came before me on SDC, the entire New Horizons team, and the friends I’ve made along the way.

 

 

Today’s blog post is from Amanda Zangari, a member of the New Horizons’ Geology, Geophysics and Imaging Team. She works at Southwest Research Institute in Boulder, Colorado.

My name is Amanda Zangari, and I’ve been a postdoc on the New Horizons mission for 2 ½ years. It’s been a wild ride, and it’s amazing how the time has flown by.

In the 85 years between Pluto’s discovery and the New Horizons flyby, we’ve learned enough about the Pluto system to fill a textbook and several scientific journals. Telescopes, cleverness, and lots and lots of math enabled us to figure out many of the basics of the Pluto-Charon system before New Horizons arrived, even if Pluto was just 11 pixels across in the best images taken from Earth. We knew that Pluto was brownish-red with dark and light patches, and that the surface was covered with nitrogen, methane and tholins—brown gunk made when UV light hits nitrogen and methane.

We also saw a patch of carbon monoxide at Pluto’s brightest spot, which turned out to be the area that forms the left side of Pluto’s ‘heart,’ which we informally call Sputnik Planum. We determined that Pluto’s moon Charon has a surface that is instead made of water ice and is gray in color. (Charon’s red “hair” at the north pole was a surprise!)  We confirmed that we’d found all of Pluto’s small satellites. We also knew that Charon did not have an atmosphere and Pluto did, and we’ve been studying it for over 25 years.

New Horizons finally brought Pluto and Charon into focus, and we got to see just how much of that patchy map — the result of measuring reflected light from Pluto at different angles — turned into mountains, ice flows and the bladed terrain that hasn’t been seen anywhere else in the solar system.

I like to think of the whole experience as getting to look at the answer in the back of the book. To extend the back-of -the-book analogy, like many textbooks, we are only getting half the answer. With Pluto, that missing element isn’t the even problems, but time. Our greatest images are from the July 14 closest encounter, and thus we only have one glimpse of one side of Pluto on one day. Yet these images show Pluto as an active world, undergoing volatile-ice transport and change.

One of my big interests is tying past ground-based observations together and comparing them to what has been seen by New Horizons. I’ve been working on several different projects to this effect.

The first project took place during New Horizons’ journey to Pluto. I compiled all the available research journal articles to gather what measurements had been taken, and catalogued what longitude and latitude scale had been used to make measurements. In 2009, the IAU reversed the direction of Pluto’s pole, reversing both the direction of longitude and latitude on Pluto. Without that change, Pluto’s ‘heart’ would be upside down! Even before the change, latitude and longitude had been expressed in multiple different formats, official or not.

The next project I’m working on involves comparing measurements of Pluto’s brightness taken by the New Horizons spacecraft between 2013 and 2015 against Hubble Space Telescope observations from 2002 and 2003. We’d like to see how Pluto’s surface has changed in that time, as there is already possible evidence of change on Pluto between the 90s and the early 2000s.

Finally, as you can see in the figure below, I’m looking at stellar occultations of Charon, using the Charon topography New Horizons imaged, to check if known features influenced these past results.

Making ground-based comparisons to New Horizons is extremely important. Until we go back to Pluto (I’d love to see an orbiter), the only way we’ll be able to watch Pluto evolve is from Earth-based telescopes.

If we’ve learned anything from the flyby, we’ve learned that Pluto is worth continuing to watch.

 

“Since its discovery, Pluto has proven consistently troublesome to the theorist.”
– Sir Patrick Moore, The Observer’s Book of Astronomy (1971)

Written 45 years ago, these words are more appropriate today than Moore could have ever imagined. Greetings, I’m Dr. Orkan Umurhan, a scientist on New Horizons’ Geology and Geophysics Investigation (GGI) Team.

Pluto’s surface geology alone – from the bladed terrain of Tartarus Dorsa to the mysterious dark mound of Morgoth Macula (just to mention a few informally named features with perplexing geologies) – continues to stump all of us on the New Horizons Geology and Geophysics Investigation (GGI) team.

Over the last month, I’ve been examining numerous theoretical and modeling questions to attempt to explain the processes at work within Pluto’s frozen plains, known as Sputnik Planum (SP). In a separate, yet parallel vein, I’m also studying the nature of glacial flows onto SP from the highlands bordering its eastern shoreline. In this blog, I will talk about the glacial flow problem.

First, let’s look at some pictures of glacial flow on Pluto’s frozen plains.

These are two views of the same part of the eastern side of SP—one is a nearly overhead snapshot, while the other one is a very low-incidence angle image, dramatically displaying the relief of the landscape. In the overhead image you can see dark streaks emanating from the right leading onto the open plane tracing a lobate pattern – kind of like hot wax moving down an inclined plane. The dark materials are reminiscent of glacial moraines seen on Earth, but because this is Pluto, we have no idea what this dark material is, and whether or not the patterns we see are indeed moraines in the traditional terrestrial sense.

However, we do know what our colleagues on the New Horizons Composition team tell us: they have pretty solidly (ahem!) determined that the surface material on and in the near vicinity of SP is mainly made up of nitrogen, carbon monoxide, and methane ices, although their relative proportions are not yet determined.

In my initial considerations, I assume the flowing material is made of mostly nitrogen with some carbon monoxide, both of which have similar molecular bond structures. Based on what little lab work has been done on their properties under cold temperatures characteristic of Pluto’s surface (-390 degrees Fahrenheit or 38 Kelvin), these volatiles ought to flow more slowly than silly putty, but much faster than glacial water ice on Earth.

The response timescales appropriate for these volatiles with the scale and relief of the highlands seen around Sputnik Planum leads us to the geophysical insight that these high relief structures (icy mountains) are probably not made up of any of these pure volatile ices, because they would have flattened out a long time ago. Instead, we speculate that the highlands are more likely made of a very strong structurally rigid water ice “bedrock” covered by a very thin coating of nitrogen and/or carbon monoxide ice.

This is where I come in: I fold all of this laboratory information about the volatile ices, as well as various geophysical insights into a numerical simulation platform I built a year ago that models glacial flow. This tool is used to examine various scientific hypotheses from me and other members of the geology team.

For example, one task is to examine possible scenarios explaining how the observed lobate pattern (think hot wax) comes about, and whether or not a nitrogen glacial model can explain what we see. To accomplish this, I start with a Digital Elevation Model (DEM) seen above, using stereo imaging of Pluto’s surface with vertical relief on the order of .6 miles (1 kilometer). I use this model as my bedrock surface—then I add nitrogen ice and study the response.

To show you an example of the kind of response the model can exhibit, consider the figure above, where I take this surface bedrock and add glacial nitrogen ice, indicated by the red ellipse on the left figure. To this model I also add a feature representing the uniform accumulation of deposited nitrogen ice, in the amount of about one yard (one meter) per year. The outflow state is shown in the right panel. In this artificial example, I have put in nearly 400 yards (400 meters) of ice inside the circled red region. The final flow state – including nice frontal lobes – gets there in about 20 Earth years. This is fast! You can also see accumulation of nitrogen ice inside of craters; this is because the steady deposition of ice also runs down steep-sided slopes and collects inside.

In understanding complex Pluto, progress is slow, but we are making progress. Stick around for the next installment of my blog, in about a month, when I will have more cool results!