Pluto’s ‘Snakeskin’ Terrain: Cradle of the Solar System?

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.

The Bladed Terrain of Tartarus Dorsa
The Bladed Terrain of Tartarus Dorsa. Credits: NASA/JHUAPL/SwRI

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!

Orkan Umurhan
Orkan Umurhan
Credits: NASA/ARC/Carrie Chavez

The Polygons of Pluto

Pluto’s Al-Idrisi Montes
Close up of Pluto’s Al-Idrisi Montes—an example of chaotic polygon-shaped terrain as captured by NASA’s New Horizons spacecraft on July 14, 2015. Credits: NASA/JHUAPL/SwRI

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.

Pluto's Sputnik Planum
Sputnik Planum is the bright, western half of the heart shaped region near the middle of this enhanced view of Pluto. The Al-Idrisi mountains are adjacent to Sputnik’s northwestern edge. Credits: NASA/JHUAPL/SwRI

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.

Pluto’s Al-Idrisi Montes
Close up of Pluto’s Al-Idrisi Montes-and example of how blocks are traced. Credits: NASA/JHUAPL/SwRI

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!

Katie Knight
Katie Knight

Where’s My Data? Keeping Track of New Horizons’ Treasure of Information

Pluto
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.

data screen
New Horizons DataTrack Interface

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!

Emma Birath
Emma Birath / Credit: Michael Soluri

 

The Many Faces of Pluto and Charon

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.

Four Faces of Pluto
Four faces of Pluto in black-and-white and color. From left to right, the central sub-observer longitudes are ~180, 240, 360 and 60 degrees East Longitude. The Pluto “Encounter Hemisphere” (indicated by the white box) is most recognizable by the “heart” feature of the informally-named Tombaugh Regio. This is also the hemisphere that today never faces Charon, as Charon is “tidally locked” to Pluto, similarly to how the Earth only sees one face of our moon. Pluto’s “Charon-facing” side is the second column from the right. Pluto’s north pole is up in all these images. The top row contains LORRI grey-scale images taken on July 13, July 12, June 27 and July 3rd, when Pluto was 620, 189, 24 and 36 LORRI pixels across, respectively. The bottom row shows MVIC “enhanced-color” images made by combining the near infrared, red and blue filters. They were taken on July 13, July 12, July 10 and July 9, when Pluto was 163, 56, 26 and 21 MVIC color pixels across, respectively. All these images surpass what we had previously seen from Hubble Space Telescope imagery where Pluto’s disk was only about 12 pixels across. Of course, New Horizons was only millions of miles from Pluto—Hubble is over 3 billion miles away! Credits: NASA/JHUAPL/SwRI
Six faces of Charon
Six faces of Charon. Central sub-observer longitudes: top, from left to right, 350 (B&W), 2 (color), 32 (color); Bottom, from left to right, 67 (color), 86 (B&W), and 180 (color) degrees East Longitude. The side that faces Pluto is highlighted by the inset box. From left to right, the top row images were taken July 14, 14 and 13, 2015, with Charon spanning 523 (LORRI), 81 (MVIC), and 43 (MVIC) pixels. The bottom row images were captured from July 12, 12 and 10, 2015, with Charon spanning 28 (MVIC), 96 (LORRI), and 13 (MVIC) pixels. Charon remains a mainly neutral greyish color all around, with a distinct red northern polar cap appearing from all sides. Credits: NASA/JHUAPL/SwRI

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.

Kimberly Ennico
Kimberly Ennico and Pluto, Clark Planetarium, Salt Lake City, Utah

Pluto: Ultraviolet Amazement

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.

First detection of Pluto with the Alice UV spectrometer. Credits: SwRI/Eric Schindhelm
First detection of Pluto with the Alice UV spectrometer. Credits: SwRI/Eric Schindhelm

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!

Eric Schindhelm
Eric Schindhelm with the Alice imaging spectrometer. Credits: NASA/Kim Ennico-Smith

 

Pluto Flyby: Through the Eyes of an Early Career Scientist

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.

Left to right: Marcus Piquette, New Horizons Principal Investigator Alan Stern, Mihály Horányi, and former SDC students Jamey Szalay and David James. Credit:  JHUAPL
Left to right: Marcus Piquette, New Horizons Principal Investigator Alan Stern, Mihály Horányi, and former SDC students Jamey Szalay and David James. Credit: JHUAPL

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.

New Horizons Team
Some members of the New Horizons team enjoy ice cream after a science team meeting in Boulder, Colorado. Credits: SwRI/Rayna Tedford

 

Marcus Piquette
Marcus Piquette
Credits: SwRI/Con Tsang

 

Studying Pluto from 3 Billion Miles Away

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.

Pre-flyby maps of Pluto
Before: This is an example of the best pre-flyby maps of Pluto, made from images from the Hubble Space Telescope in 2002 and 2003, published in 2010. Credits: NASA/JHUAPL/SwRI/Marc Buie
Map of Pluto
After: Map of Pluto from New Horizons. Credits: NASA/JHUAPL/SwRI

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.

Charon occultation from 2005
Charon occultation from 2005. The map New Horizons made of Charon is overlaid with new data. I’m looking to see if any of the measurements of Charon’s size were affected by the topography seen by New Horizons. Credits: NASA/JHUAPL/SwRI/Michael Person/Amanda Zangari

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.

Dr. Amanda Zangari
Amanda Zangari
Credit: Kyle Cassidy

 

Probing the Mysterious Glacial Flow on Pluto’s Frozen ‘Heart’

“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.

A nearly top-down view of Pluto’s icy plains
A nearly top-down view of Pluto’s icy plains, showing dark lanes reminiscent of glacial moraines. Credits: NASA/JHUAPL/SwRI
Flow patterns from the lower right of the image, extending to the center of Pluto’s informally-named Sputnik Planum.
This low incidence angle indicates flow patterns from the lower right of the image, extending to the center of Pluto’s informally-named Sputnik Planum. Credits: NASA/JHUAPL/SwRI

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.

Digital Elevation Model (DEM)
Credits: Paul Schenk, Ross Beyer and Orkan Umurhan

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.

Stereo imaging of Pluto’s surface with vertical relief on the order of .6 miles
Credits: Orkan Umurhan

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!

Orkan Umurhan
Orkan Umurhan

Pluto through a Stained Glass Window: a Movie from the Edge of Our Solar System

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.

As New Horizons flew by Pluto, it recorded spectacular images of the icy world’s surface using the LORRI and MVIC cameras. It recorded the plasma and dust environments with the PEPSSI, SWAP, and SDC instruments. But one instrument, designed to measure the composition of Pluto and Charon’s surfaces, did something you might not expect: it recorded the first movies from the edge of our solar system.

Recorded with a 256 x 256 pixel camera at under two frames per second, they are not exactly HDTV. However, they are movies. And they are in color. Sort of.

The instrument is LEISA, New Horizons’ infrared imaging spectrometer. It is an extremely clever instrument; it takes 2-D images just like a normal camera, but it takes them through a linearly-varying filter. One side of the camera can only see light of one specific wavelength of infrared light (light that has longer wavelengths than can be seen by our eyes), and each row of pixels can see a subtly different wavelength.

This linear filter allows light with wavelengths as short as 1.25 microns (a micron is one millionth of a meter; human eyes can perceive light with wavelengths as short as 0.39 microns to long as 0.7 microns) to fall on one side of the image sensor, and smoothly changes to allow light with wavelengths as long as 2.5 microns to fall on the far side of image sensor. This wavelength range was selected because many ices and other materials that exist on the surface of Pluto that have spectral features in this wavelength range that can uniquely identify them, like a fingerprint. We use this instrument to map the distribution of these ices and other materials across Pluto and its moons. A second linear filter to one side of the imager is designed to provide a finer measurement of the spectrum in a region of particular interest between wavelengths of 2.1 to 2.25 microns.

A simplified schematic of the how the LEISA instrument works
Figure 1: A simplified schematic of the how the LEISA instrument works. As the scene (in this case, Pluto) moves by along the scan direction, the imager records many frames of video in sequence, imaging each part of Pluto though each segment of the linear filter and building up a spectral map of the entire object. Credits: NASA/JHUAPL/SwRI/Alex Parker

The effect is much like looking through a stained glass window designed for infrared eyes. By scanning this image sensor with its linear filter across a scene and quickly recording many images during the scan (like a movie), LEISA builds up a two-dimensional map of the scene in front of the camera with a measurement of the infrared spectrum (the brightness versus wavelength) at every location in the image. It makes this complex measurement with exactly zero moving parts — highly reliable for deep-space operations.

The side-effect of collecting this scientifically-important data set, capable of measuring the composition of every location on the surface of Pluto and Charon that is imaged, is that LEISA collected low frame rate infrared color movies of Pluto and Charon as seen by New Horizons during its flyby.

Pluto Through Stained Glass: A Movie from the Edge of the Solar System. This colorful movie drifting across Pluto by was recorded by New Horizons’ LEISA infrared imaging spectrometer during the July 14 closest approach. The movie has been sped up approximately 17 times from its raw frame rate, and the infrared colors that LEISA sees have been translated into visual colors. Credits: NASA/JHUAPL/SwRI/Alex Parker

The animation shown here is one such movie collected by New Horizons during its flyby of Pluto. Each pixel is colored to show the relative wavelength of light that each pixel was allowed to see by LEISA’s linear filter. However, since LEISA sees in infrared light, the colors LEISA can see have been re-mapped for this video onto the human visual spectrum — the rainbow. The video has been sped up from its raw frame rate to show the motion smoothly.

In this animation, Pluto drifts by outside the spacecraft as New Horizons scans LEISA across the surface. As Pluto slides beneath the camera, you can see it nod back and forth from the top of the frame to the bottom — these changes in direction are due to New Horizons thrusters firing during the recording of the movie.

This is what you would have actually seen if you were on board the New Horizons spacecraft on July 14, looking out at Pluto through a stained glass window with infrared eyes.

The composition of Pluto makes itself apparent in the animation. Dark bands top-to-bottom correspond to absorption by specific chemicals on the surface of Pluto; many of the bands visible in this view are due to absorption from solid methane ice. However, as some terrains slide by, you can see that they do not become dark under those bands like other terrains; in these areas, the chemical responsible for that absorption is absent.

The discovery of water ice on Pluto was made using the data in this movie. The discovery of ammonia ice within the informally-named Organa crater was made using data from a similar movie of Charon. The New Horizons composition team is busy analyzing these and other movies taken by the LEISA instrument in order to further understand what the surface of Pluto and Charon are made of and how they might be changing with time.

But please — just take a moment and imagine you were on board our little robotic emissary to the farthest worlds ever explored, watching Pluto come into view through a colorful window on the side of the spacecraft. Sure, it might not be in HD, but I promise that you’ve never seen anything like this before!

Alex Parker
Alex Parker

Where Math Meets Pluto

Greetings and Salutations!   I’m Dr. Orkan Umurhan, a scientist on New Horizons’ Geology and Geophysics Investigation (GGI) Team.  This is my first blog entry about my experiences on this most excellent mission. Over the upcoming months and years I intend to share the scientific questions I work on pertaining to New Horizons, and I hope that you will find them as fascinating as I do.

But first, a little about myself:  Although I’m on the GGI Team, I actually have a background in astrophysics with particular emphasis on astrophysical flows. I’ve done a lot of work on turbulence in protoplanetary disk environments, the very places where planets are known to form and grow. I have a lot of experience with extracting physical insights from complex flows. I really see myself more as a mathematical physicist. Some of my colleagues jokingly refer to me as the team’s “applied math mercenary,” a description that is not too far from the truth.

Just over two years ago, I was invited to join the New Horizons science team—probably being the last person to board the mission. While being both thrilled and honored to be involved, I wondered about how a scientist like me, who then knew very little about geology (rocks are hard!), could contribute in a scientifically meaningful way to the mission. The answer I received from both Alan Stern (our fearless captain and leader) and Jeff Moore (GGI Team lead, aka “Our GGI Platoon Leader”) is a testament to the uniqueness of this mission, its openness, and the cutting edge manner in which we conduct scientific inquiry.

They explained that the Pluto-Charon system is a place where we expect to see things we’ve never seen before, involving the behavior of ices and (possibly) fluids at temperatures and pressures that have not been adequately examined in the laboratory—nor have they been observed in any natural terrestrial system. Because this was going to be a fresh encounter with Nature, Alan and Jeff explained to me that they were determined to assemble as diverse a scientific team as possible, having a very wide spectrum of viewpoints and expertise on hand to interpret and debate the puzzling and weird things likely to be encountered.

As you probably know, Pluto has turned out to be a spectacular, awesome, active low temperature physics laboratory, full of conundrums and outright weirdness that has kept us all busy, fulltime.

In hindsight, one wonders why we were so surprised. For instance, the triple point (the location on the temperature-pressure phase diagram in which a material can coexist as solid, liquid and gas) of both carbon monoxide and molecular nitrogen is in the vicinity of 63 Kelvin (- 346 Fahrenheit), a temperature that is achievable on Pluto, given its distance from the sun.  We know from the Earth that when a system is near its triple point (as in the case of water), interesting phases can manifest, such as flowing water, glaciers and vapor. This is one of the reasons why the Earth and its surface morphology is such a cool place—no pun intended.

Pluto’s Pattern of Pits
On July 14 the telescopic camera on NASA’s New Horizons spacecraft took the highest resolution images ever obtained of the intricate pattern of “pits” across a section of Pluto’s prominent heart-shaped region, informally named Tombaugh Regio. The image is part of a sequence taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) as the spacecraft passed within 9,550 miles (15,400 kilometers) of Pluto’s surface, just 13 minutes before the time of closest approach.
Credits: NASA/JHUAPL/SwRI

When we look at Pluto we see the informally-named Sputnik Planum (SP), which is probably a giant nitrogen ice sea, with a lot of methane and carbon monoxide to share the space. It has the texture of toothpaste and has flow timescales on the order of dozens of years.  We see in the surrounding mountain ranges evidence of glacier ice flowing into the basin of SP. The ice within the plains appears to be undergoing so-called “solid-state convection,” the overturning of the ice layer because it’s warmer below than above, which causes it to buoyantly rise to the surface. We see perplexing textures that look like pits and worms on various parts of SP, a phenomenon possibly due to the strong sublimation of nitrogen or possibly even methane. We see globules of glacier ice that look like coagulated jelly in various locations near the glacier flows.

Together with the other geologists and geophysicists in GGI, I work on aspects of all these odd-looking features and facets. I participate in debates over physical interpretation of the things we see but, more importantly, I bring my experience with flow modeling and dynamical evolution and apply them directly to setting up numerical mathematical models in order to evaluate the myriad of hypotheses we conjure up.

I’ll go into detail about some upcoming results in my next blog entry in early 2016, so stay tuned!

Orkan Umurhan
Orkan Umurhan