Tag Archives: New Horizons

The Many Faces of Pluto and Charon

Reposted from https://blogs.nasa.gov/pluto/2016/02/12/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.

nh-pluto_four_faces_withwhitebox

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

nh-charon_six_faces_box

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.

Getting ready for the 2015 Pluto encounter. 2014 summer’s annual checkout brings high data payoff.

Reposted from http://pluto.jhuapl.edu/News-Center/Science-Shorts.php?page=ScienceShorts_07_11_2014.

You walk up to the Restaurant at the End of the Solar System, ready to try that slice of “Pluto on ice” that you heard amazing things about. The chef behind the counter asks, “So, how would you like your data? “ Without hesitation, you reply “Well calibrated.”

Pretty pictures or spectra make no sense “without context.” For images, we need to know how many kilometers map to a pixel and for each raw digitized value, a mapping from bits to energy units (like magnitude or ergs/cm^2/s). For spectra, we need to know how much spatial information is covered per pixel plus what each pixel’s response to wavelength and brightness is. For particle instruments, we need to what energy and from which direction that ion or dust grain came.

Before launch every New Horizons instrument underwent intensive laboratory characterization: “pre-flight calibration.” They were subject to spatial targets, integrating spheres, laser pulses, particle accelerators, to name a few good “known” sources, to get “translations” from bits stored to disk to “real” units like wavelength, flux energy, intensity, etc. After launch such “translations” were verified with “in-orbit” calibrations, where, for example, instead of a lab source, the instruments stared at stars or inspected Jupiter and its moons. Each year, the team executes an ACO, or Annual Check-Out, where instrument performances are trended and teams look for changes. Additional observations provide information to remove “unwanted artifacts” like hot-pixels, readout smearing, ghosts, etc.

Summer 2014 is ACO-8, our 8th annual checkout since launch. It showcases our last calibrations prior to the 2015 Pluto encounter. It’s jammed packed with observations that are done yearly for trending, but also some new ones to make sure the New Horizons instrument suite is “well calibrated.” Highlights include new radiometric calibrations for the LEISA IR spectrometer, a long stability test for the REX radio experiment, and a test for revised thresholds for PEPSSI, the high-energy particle detector. More calibration data is taken during the 2015 Pluto fly-by, and together, these data sets are placed in the data reduction pipeline to translate bits to “real” values. Resources and time aboard the spacecraft to execute these observations are limited, so a series of reviews and assessments are done prior to each checkout.

The team is eager to get the data from ACO-8. We wake up June 15th. After a similar series of spacecraft subsystem checkouts, the New Horizons payload calibrations begin and continue through August. It may not be the Pluto fly-by, but this summer’s data will play a big role in the science return from New Horizons next year!

jupiter-nh-calibrated

Demonstration of read-out smear removal, preserving the photon count, in LORRI’s calibration pipeline. The data in the smear is caused by imperfections in the CCD readout when illuminated by a lot of light. The source of the photons is from the object being imaged, so we need to correctly relocate the information. Data without good calibration is messy.

 

As a New Horizons deputy project scientist, Kimberly Ennico manages instrument readiness and calibration aspects of the mission. Her expertise includes instrument development, space qualification and calibration; optical/infrared astronomy; optical/infrared detectors, optics, cameras and spectrometers; and science communication.

The Pluto science community is rich and diverse, just like its target of study: the ever-fascinating Pluto and its satellite moons.

Reposted from https://blogs.nasa.gov/mission-ames/2013/07/27/the-pluto-science-community-is-rich-and-diverse-just-like-its-target-of-study-the-ever-fascinating-pluto-and-its-satellite-moons/.

This blog entry concludes my series of talk summaries for the July 22-26, 2013 Pluto Science Conference, “The Pluto System on the Eve of Exploration by New Horizons: Perspectives and Predictions.” You can read more about the conference and browse through the abstracts at the conference website.

In his closing comments, Alan Stern (SwRI), the lead scientist (Principal Investigator) for NASA’s New Horizons fly-by mission to Pluto, told us about the last time a scientific discussion gathering specifically about Pluto occurred. It was twenty years ago, a 3-day meeting in July 1993, in Flagstaff, Arizona. The talks and presentations from that workshop led to ten contributed papers in a special issue in 1994 in Icarus (Vol 108, Issue 2) and, in 1997, the publication of a book entitled “Pluto and Charon” by The University of Arizona Press.

When the group gathered in 1993, the 1989 Voyager 2 fly-by of Neptune’s moon Triton’s was still “fresh data”, the prime Pluto-Charon “Mutual Events Period” of the 1985-1990 had just ended, and the Hubble Space Telescope (HST) would be soon coming back on-line with its fixed optics (the 1st HST servicing mission would occur in December 1993). It was a busy time for the Pluto science community.

Some attendees at the open workshop meeting on Pluto & Charon in July 1993, Flagstaff, Arizona.

This five-day July 2013 meeting has demonstrated that the quest to better understand Pluto and its environment is a very rich and diverse field of study. With each new data set about Pluto and its companions, surprises are uncovered and new questions are posed. When the New Horizons spacecraft reaches the Pluto system in July 2015, a true “first encounter experience,” its on-board suite of modern instruments will transform our current-best resolution ~800 km/pixel (from Hubble observations) to a resolution of 0.46 km/pix (hemisphere) with 0.09 km/pix (regional) resolution with the LORRI instrument. You can be certain there will be a lot more surprises in store. Combining this with new and unique data sets from New Horizons’ particle & dust instruments and the UV and IR spectrometers, our understanding of the Outer Solar System will find a new grounding.

With 103 oral talks + 30 posters + 13 “topical sessions” this was a jammed pack week of sharing old information, sharing new data from the past few years, sharing “hot off the press data” (it’s Pluto observing season right now and during the conference attendees were doing observations of Pluto & Charon with IRTF, Keck and other telescopes, remotely or with their colleagues at the telescopes), identifying what computations or experiments are needed before the 2015 encounter, and in some cases, providing predictions of what might be detected at Pluto and Charon. Several papers presented at this conference will be submitted to the Icarus journal.

Attendees at the “The Pluto System on the Eve of Exploration by New Horizons: Perspectives and Predictions,” held July 22-26, 2013, in Laurel, MD. The topical sessions covered Atmospheres, Charon, Dust & Rings, Interiors, Kuiper Belt Context, Laboratory Studies, Magnetosphere, New Horizons Mission, Origins, Satellites, Surface Composition, Surface Geology, and Surface-Atmosphere Interactions.

The stage is set for a summer 2017 Pluto Science Conference. New Horizon’s flyby of the Pluto System is on July 14, 2015, but it will take a bit over a year for all the data to come down losslessly (i.e. without compression). Deliveries to the NASA’s Planetary Data System are planned in 2016 and early 2017.

I hope you enjoyed this blog series reporting on these intriguing topics. You can follow the New Horizons mission status at any time by visiting the New Horizons Mission Website at http://pluto.jhuapl.edu/ and http://www.nasa.gov/mission_pages/newhorizons/main/index.html.

To Pluto and Beyond!!!!

Pluto Exotica. Atoms. Pick Up Ions. Bow Shocks. Suprathermal Tails. X-Rays. UV airglow.

Reposted from https://blogs.nasa.gov/mission-ames/2013/07/27/pluto-exotica-atoms-pick-up-ions-bow-shocks-suprathermal-tails-x-rays-uv-airglow/.

The morning of the last day of this week’s July 22-26, 2013, Pluto Science Conference opened up the discussion with outer atmosphere (far out) and magnetosphere (really far out) talks.

Fran Bagenal (University of Colorado) started the session with a talk on “The Solar Wind Interaction with Pluto’s Escaping Atmosphere.” Pluto’s interaction with the solar wind was first suggested in 1981 by Larry Trafton. There are two generally predicted regimes of what this interaction might look like: (1) Venus-like (small escape rate) and (2) Comet-Like (high escape rate). A key parameter distinguishing the two is what the atmospheric escape rate might be, that is, how many atmospheric molecules (assumed to be nitrogen) are escaping from Pluto, no longer being bound by gravity. Current estimates for the escape rate, based on a number of approaches, notably a recent one by Darrell Strobel (2012), have this number at 2-5×1027molecules/sec.  This is large enough to suggest Pluto will appear to be “comet-like” in its interaction with the solar wind. However, we need to wait until 2015 for the New Horizons fly-by with their in-situ particle instruments SWAP & PEPSSI to make the interaction measurements.

When describing the Pluto System in terms of solar wind interaction, Fran Bagenal showed this image, which superimposed one of Darrell Strobel’s atmospheres (characterized with an exobase at 12 Pluto radii). Pluto becomes a “large object” for interaction with the solar wind.

When solar wind particles (protons) interact with the Pluto atmosphere, their path through space is bent along the magnetic field lines, and to convert momentum, pickup ions (neutral hydrogen atoms from the heliosphere that undergo a collisional charge-exchange interaction with solar wind protons, get ionized, are “picked up” by the solar magnetic field) get tossed onto new trajectories. Those ions are charged and will begin to rotate and follow electrical field lines. Where do the ionized particles go? A weak magnetic field will create large gyro-radii of pick-up ions which can extend millions of kilometers upstream of Pluto.  This is best modeled with a kinetic interaction.

Peter Delamere (University of Alaska, Fairbanks) spoke in greater detail about “The Atmosphere-Plasma Interaction: Hybrid Simulations.” Plasma interaction is an atmospheric diagnostic tool. Neutral gases are not easily picked up, but ions and how they interact with the solar wind can be detected with in-situ instruments such Hew Horizons’ SWAP and PEPSSI. He discussed his model plasma interaction mode, which was validated using Comet 19P/Borrelly that had been visited by Deep Space 1 on Sept 22, 2001.

Example of Comet 19B/Borelly environment time vs. energy reveals the structure of the interaction between a comet and the solar wind. The X-axis is time from closes approach, with the Y-axis energy. The color code is the number of particles counted by the PEPE instrument aboard Deep Space 1. This is similar to what the data is expected to look at for Pluto when New Horizons reaches it in 2015, however, the solar wind at 33 AU may be more extended and more diffuse and therefore the signal strength (in terms of counts) will be much less.

If we can understand where the bow shock forms, this becomes a diagnostic of the atmosphere, and if indeed the exosphere extends out to 10 Pluto radii as suggested by recent work by Darrell Strobel (2012) and other models, then this is a sizable ‘obstacle.’ But is it inflated enough to form a bow shock? Peter Delamere thinks so. He stepped us through a variety of simulations. One of the simulations predicts a partial bow shock. If you increase Qo (the escape rate parameter, predicted to be in the 2-5×1027 N2 molecules) or increase magnetic field strength you can create a full bow shock. Future work includes adding the pickup part of the solar wind model as input.  If there is a very slow momentum transfer, perturbed flow could extend out to an AU.

Simulations predict all sorts of shock structures (Mach cones, bow shocks), but these structures depend on the escape rate parameter.

Example of a plasma interaction mode for three escape rates, decreasing from right to left. This is a slide in space of plane vs. distance from.  The white lines are sample solar wind proton trajectories. The color scale indicates ion density. The solar wind (and hence, the direction from the sun) is incident from the left. Pluto is at (0,0).

Predictions at Pluto. He anticipates significant asymmetry. The predicted bow show could be as far as 500 Pluto radii.

Heather Elliot (SwRI, San Antonio) in her talk “Analysis Techniques and Tools for the New Horizons Solar Wind around Pluto” described the New Horizons SWAP instrument and the different rate modes (sampling rate and scan types) it will be using during the 2015 encounter.

Measurement of the solar wind taken with the SWAP instrument aboard New Horizons during the last 6 years of cruise. This data set covers AU=10 (Saturn distance) out to AU=23 in 2012. The solar wind is mostly protons (H+). The second most abundant species are alphas (He++). The colors are the intensity of species. The vertical axes are energy per charge units and the horizontal axis is time.

Fitting the SWAP data to a solar wind model requires making adjustments for view angle and during the hibernation period, when they do not have attitude information, they have modeled the Sun-probe-Earth angle to estimate the attitude and this works well to fit their data.

John Cooper (NASA Goddard) spoke about the  “Heliospheric Irradiation in Domains of Pluto System and Kuiper Belt.”  He is interested in computing the “radiolytic” dosage onto bodies in the outer solar system (that is, the effect of how molecules break down or change molecular band structure due to the influence of radiation, such as by cosmic rays, particles, UV, etc.). For this he needs measurements of the particle flux at large AU.  New Horizons joins its cousins Voyager 1 & 2, Pioneer 10 & 11 and Ulysses in exploring the outer solar system.

spacecraft_outersolar

Location of the NH spacecraft (orange on the left, purple on the right) for two different views of the solar system. Also plotted are deep space missions Voyager and Pioneer, among many. The left view is s top down view of the solar system with the Sun at (0,0), the axes are in AU, where 1 AU (Astronomical Unit) is the distance between the Earth and Sun. The right is a view of time vs. latitude for the crafts. Comparative data sets to New Horizons, which travels along the solar ecliptic, are Pioneer 10 and early Voyager 2 data.

He showed computations of irradiation dosage when applying those particle rates measured by New Horizon’s PEPSSI instrument and instruments aboard Voyager 2 and Pioneer 10.

He maintains a database of all particle instrument flux measurements at the Virtual Energetic Particle Observatory http://vepo.gsfc.nasa.gov.

Thomas Cravens (JHU/APL) with ”The Plasma Environment of Pluto and X-Ray Emission: Predictions for New Horizons,” asked “What happens when you get to within 1000 km of Pluto?“  Pluto is anticipated to be “Comet-Like” in its interaction with the solar wind, however when you get closer to Pluto (around 1000 km), it may more closely resemble “Venus-like” interaction. He is trying to compute where the charge-exchange boundary could be, probably around r~5000km. This is boundary between the kinetic (r>5000km) and fluid (r<5000 km) regimes, essentially probing the ionosphere regime of Pluto.

Switching to slightly lower energies, Casey Lisse (JHU/APL) gave a talk on “Chandra Observations of Pluto’s Escaping Atmosphere in Support of New Horizons.” X ray interactions (charge exchange, scattering and auroral precipitation) require an extensive neutral atmosphere, which is what is expected at Pluto. Interaction of solar wind with comets has consistently shown X-ray emission. He expects to see X-ray emission from Pluto. If detected it would tell us about the size and mass of Pluto’s unbound atmosphere. The best time to look for x-rays at Pluto is about 100 days after a large CME (corona mass ejection) event, which is about the time it takes for CME to get to Pluto at 33 AU.

He and his colleagues applied for, and got, time on NASA’s Chandra X-ray telescope. On Chandra, Pluto & Charon will appear to fill one Chandra pixel using the Chandra HRC instrument.  He ended his talk suggesting that looking at background counts with the LORRI and RALPH CCDs might serve as a poorman’s x-ray detector. It is also possible that PEPSSI background counts could be used to infer presence of lower X-rays.

Kandi Jessup (SwRI) gave a talk addressing the “14N15N Detectability at Pluto.” We care about14N15N because it can be used to determine the 15N to 14N isotropic fractionation. This can help tell us about the evolution of Pluto’s atmosphere. Learning about Pluto’s atmospheric evolution history also provides vital suggestions for the evolution of equivalent TNOs (Trans-Neptunian Objects) and other objects in the Kuiper Belt, and hence, the outermost parts of our Solar System

The measurement will be the UV spectral observations during the solar occultation of Pluto by the Alice instrument during the New Horizons fly-by. N2 is the dominant absorber between 80-100nm. To identify the molecule 14N15N they use an atmosphere model from Krasnopolsky & Cruikshank (1999). That model does not have a troposphere. Next they need absorption cross-sections (a parameter that quantifies the ability of a molecule to absorb a photon of a particular wavelength) for 14N2 and 14N15N. 14N2 is the more dominant species and they are trying to find a very small percentage for 14N15N. Using these simulations they anticipate the Alice instrument will be sensitive enough to detect at least a 14N15N to 14N2 ratio of 0.3%. They will be look at the UV spectrum between 88 and 90 nm where the 15N lines spectrally shifted from 14N line. 14N15N to 14N2 ratio has been measured on Mars (0.58%), Titan (0.55%), and Earth (0.37%). What ratio will Pluto have? New Horizons data will hopefully tell us.

Randy Gladstone (SwRI, San Antonio) spoke about “Ly-alpha at Pluto.” Pluto ultraviolet (UV) airglow line emissions will be very weak, except at HI Lyman-alpha (Ly-a). Ly-a at Pluto could have both a solar (Sun) and an interplanetary (IPM/interplanetary medium) source. Ly-a should be scattered by Hydrogen atoms in Pluto’s atmosphere.  He uses the Krasnopolsky & Cruikshank (1999) Pluto atmosphere model that predicts the number of Hydrogen atoms at altitude. There are several observations near Pluto closest approach planned with the New Horizons Alice instrument to measure Lyman-alpha emissions.  This data will provide information about the vertical distribution of H and CH4 in Pluto’s atmosphere. Observation of the IPM Lyman-alpha source will be unique and provide important information to model Pluto’s photochemistry, especially for the nightside and winter pole region.

Randy Gladstone (SwRI, San Antonio) ended the session with a talk about “Pluto’s Ultraviolet Airglow.” He presented a model by Michael Stevens (Naval Research Lab), which has been used to explain the Cassini UVIS (Ultraviolet Imaging Spectrograph) observation of UV airglow at Titan over the 80-190 nm wavelength, emissions arising from processes on N2 (Stevens et al 2011). The model is called AURIC, the Atmospheric Ultraviolet Radiance Integrated Code. This model will be used for interpreting Pluto atmosphere data taken at UV wavelength with the New Horizons Alice instrument.

If Pluto was not already an exotic place to visit with all the predictions about its formation, its interior, its surface, it surface-atmosphere interaction, its composition, etc., it certainly will prove to be an amazing place if any or all of these predicted upper atmosphere and mesosphere molecular species, ions, and high energy particles are measured with the New Horizons spacecraft!

Winds. Fog. Frost. Global weather predictions on Pluto.

Reposted from https://blogs.nasa.gov/mission-ames/2013/07/27/winds-fog-frost-global-weather-predictions-on-pluto/.

Talk summaries from the Pluto Science Conference held July 22-26, 2013 in Laurel, MD continues. This blog entry is about atmosphere presentations on July 26th.

Angela Zalucha (SETI) began the discussion with her talk entitled “Predictions of Pluto’s vertical temperature and wind structure from the MIT Pluto general circulation model.”

A general circulation model (GCM) solves conservation of momentum in 3D, conservation of mass, conservation of energy and equation of state (P=rRT). It can tell us some fundamental atmospheric properties such as composition (what is it made of), pressure (how much is there?), temperature (how hot is it?), and wind (how does it move?). In particular, understanding wind is one of the most important things a general circulation model gives you, because it is so hard to observe remotely.

She presented her model, based on the MIT (Massachusetts Institute of Technology) GCM that was originally designed as an ocean model. She turned it upside down to make it an atmosphere model. It has multiple layers, CH4 mixing ratio at 1%, CO mixing ratio at 0.05%, includes atmosphere models (Strobel et al 1996) and runs for a 15 year Earth integration rate (she notes that is probably not enough time to have the atmosphere equilibrate). She sets frost layers on the surface as a parameter, and explored different surface pressures (8 16, 24 microbars). She uses the Ecliptic North convention. One output from this model are curves of temperature vs. altitude, called a temperature profile. She reported the presence of a frost predicts a much colder atmosphere. Future work will be to investigate other ice distributions, put in a CH4 transport model, and improve surface model.

Example of a suite of temperature profile curves from the Pluto MIT GCM. Temperature in Kelvin is shown for a range of altitudes in kilometers. The MIT GCM has assumed a particular Pluto radius to set zero altitude.

Melanie Vangvichith (LMD, Paris) in her talk “A Complete 3D Global Climate Model (GCM) of the Atmosphere of Pluto” presented another general circulation model for Pluto, the LMD (Dynamic Meteorology Lab) GCM. For a thin atmosphere that is expected on Pluto, their model uses careful parametizations of the nitrogen condensation and sublimation surface-atmosphere processes, which they claim is key (Forget et al 1998). They also adopt a particular initial frost distribution, the distribution from Lellouch et al 2000.  Their model is run for 140 Earth years, starting with 1988 adopting initial conditions based on observations. Conclusions.When adopting a 20 MKS thermal inertia, the model is in agreement with occultation data to date, but this model does not predict a troposphere, just a “big stratosphere.”

Example of a wind prediction from the Pluto LMD GCM. The temperatures (in K) are represented by the color and the arrows represent the wind direction and speed at particular height. This is mapped onto a lat/long grid using the right-hand-rule (i.e. matches the Marc Buie convention).

In the previous entry, I had commented on thermal inertia and its role in atmosphere dynamics. To recap here, thermal inertia is a measure of the ability of a material to conduct and store heat. In the context of planetary science, it is a measure of the subsurface’s ability to store heat during the day and reradiate it during the night. This has natural consequences for deriving what happens to processes that require an exchange of heat. A GCM uses thermal inertia of the surface as a key parameter. There is a currently big disconnect in the community over what Pluto’s thermal inertia is. In E. Lellouch’s talk on Jul 23 he reported that Spitzer & Herschel have measured Pluto’s thermal inertia as 20-30 MKS (Lellouch et al 2011). However, Pluto atmosphere pressure models needed to match occultation data by C. Olkin & L. Young require Pluto have a much higher thermal inertia >1000 MKS to explain their occultation measurements (this meeting). Thermal inertia is usually quoted in MKS units, where MKS is an abbreviation for “J K-1 m-2 s-1/2.”

Anthony Toigo  (JHU/APL) with his talk “The Atmosphere and Nitrogen Cycle on Pluto as Simulated by the PlutoWRF General Circulation Model” presented a third general circular model. Their GCM is based on the terrestrial model used for Weather Research and Forecasting (WRF). It has been adopted for Mars, Titan and Jupiter, and they have adopted it for Pluto.  They ran their model for two extremes of thermal inertia, as this is a current open question in the community. They are just attempting to see what effect this has on the predictions.  They also looked at the effect of the nitrogen cycle adjusting amount of nitrogen ice. Conclusions. The model is in agreement with the increase in pressure derived from observations, supports large volatile abundances, and shows a pole-to-pole transport. Future work for Pluto includes constraining the volatile cycle and looking at surface wind relations.

The three modelers sparked a lively debate at the Pluto Science Conference. Sometimes they agree and in many cases they diverge greatly. It was neat to see how different groups tackle the same physics problem. It came down to the details and initial assumptions. GCMs have become such powerful tools to describe dynamics (changes) in atmospheres, but because there are still so many assumptions about Pluto’s surface and atmosphere, it will only be until New Horizons provides measurements to start anchoring down these models.