Mission Elapsed Time:
(1/19/06 19:00:00 UTC)
1538 Days (4.21 yrs.) 21 Hours 03 Minutes
Pluto Closest Encounter Operations Begin:
(4/12/15 00:00:00)
632 Days (1.73 yrs.) 20 Hours 34 Minutes
Pluto Closest Approach:
(7/14/15 11:49:59)
717 Days (1.96 yrs.) 08 Hours 24 Minutes
Charon Revealed!
New Horizons Camera Spots Pluto’s Largest Moon:
NASA’s Pluto-bound New Horizons spacecraft, using its highest-resolution telescopic camera, has spotted Pluto’s Texas-sized, ice-covered moon Charon for the first time. This represents a major milestone on the spacecraft’s 9½-year journey to conduct the initial reconnaissance of the Pluto system and the Kuiper Belt and, in a sense, begins the mission’s long-range study of the Pluto system.
For Photo :Pluto and Charon: New Horizons Long Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon, cleanly separated from Pluto itself. The frame on the left is an average of six different LORRI images, each taken with an exposure time of 0.1 second. The frame to the right is the same composite image but with Pluto and Charon circled; Pluto is the brighter object near the center and Charon is the fainter object near its 11 o’clock position. The circles also denote the predicted locations of the objects, showing that Charon is where the team expects it to be, relative to Pluto. No other Pluto system objects are seen in these images.
The largest of Pluto’s five known moons, Charon orbits about 12,000 miles (more than 19,000 kilometers) away from Pluto itself. As seen from New Horizons, that’s only about 0.01 degrees away. “The image itself might not look very impressive to the untrained eye, but compared to the discovery images of Charon from Earth, these ‘discovery’ images from New Horizons look great!” says New Horizons Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. “We’re very excited to see Pluto and Charon as separate objects for the first time from New Horizons.” The spacecraft was still 550 million miles from Pluto – farther than the distance from Earth to Jupiter – when its Long Range Reconnaissance Imager (LORRI) snapped a total of six images: three on July 1 and three more on July 3. LORRI’s excellent sensitivity and spatial resolution revealed Charon at exactly the predicted offset from Pluto, 35 years after the announcement of Charon’s discovery in 1978 by James Christy of the Naval Observatory.
New Horizons Course and Position in Three Dimensions:
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Pluto Science Conference:
July 22-26, 2013
Just two years before New Horizons’ historic flight through the Pluto system, scientists are gathered July 22-26 at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., to discuss the mission and its science plans – as well as make predictions about the science New Horizons will return from the planetary frontier. By the 1990s, it became clear that Pluto possessed multiple exotic ices on its surface, a complex atmosphere and seasonal cycles, and a large moon suggesting a giant impact origin for the pair. Also in the 1990s it became clear that Pluto was no misfit among the planets, as had long been thought; instead, it was revealed to be the largest and brightest body in the Kuiper Belt—a newly discovered “third zone” of our planetary system. More recently, observations have revealed that Pluto has an unexpectedly rich system of satellites and a surface that changes over time. It has even been speculated that Pluto may possess an internal ocean. For these and other reasons, the 2003 Planetary Decadal Survey ranked a Pluto Kuiper Belt mission as the highest priority mission for NASA’s newly created New Frontiers program. New Horizons is now 70% of the way along its journey to the Pluto system. It carries a sophisticated package with eight scientific instruments comprised of imagers, UV and IR spectrographs, plasma analyzers, a dust counter, and radio science. This payload was designed to reconnoiter the surfaces, atmospheres, interiors, and space environments of Pluto and its rich system of satellites, shedding light on the abundant new planetary class called ice dwarfs.
Comparative Compositions of Pluto and friends, even long-distant friends :
Bill McKinnon (Washington University) provided an engaging talk about implications for composition and structure for Pluto and Charon:
Where did Pluto Accrete (i.e. where was Pluto born -in this case distance from the Sun)? Pluto is not alone in its location on that a/e plot for Trans-Neptunian Objects (see previous posting). It’s part of an ensemble of bodies on the 2:3 resonance with Neptune, coined the group “Plutinos.” Was Pluto formed around 33 AU and then migrated outward? What does the Nice I Model which migrates the giant planets predict for the KBO population? The Nice I Model implies that for Pluto, Pluto could have formed at 20-29 AU (i.e. closer in) to allow it to achieve its high inclination. Then a subsequent model, Nice II, suggests Pluto may have formed in the 15-34 AU range. This is in okay-agreement with accretion models since Pluto, a 1000-km size body, would need 5-10 million years (i.e. within a nebular life) if it were formed in the 20-25 AU range. McKinnon’s Best guess: Pluto formed between 15-30 AU.
How long did accretion take and what are the implications (i.e. how-long did it take for to Pluto grow up)? If we have an accretion time (10’s of million years), there is time enough to form Aluminum-26, which is a form of heat through its decay. Heat then can melt ices and create a differentiated body (i.e., rocky core, icy mantle) and also drive water out. McKinnon’s Best guess: Pluto formed rapid and early. What are Pluto & Charon made of? They are understood to be made of rock+metal, volatile ices, and organics, with rock+metal more than ice, and ice more than organics. The rock will be some combination of hydrated & anhydrous silicates, sulfides, oxides, carbonates, condrules, CAIs (calcium-aluminum-rich inclusions), CHONPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur). We don’t really know what sort of composition these KBO volatile ices may have: will they be more like Jupiter Family Comets or Oort Comets? And we know even less about organic components: will the Nitrogen to Carbon ratio tell us whether KBO N2 (nitrogen) comes from organics rather than NH3 (methane)? Solar models (which lock up CO (carbon-monoxide) into carbon) can influence understanding of what rocks in the outer solar system are made of but their models are not in agreement with the best understanding of Pluto/Charon make-up. McKinnon’s Best guess: Rock/Ice nature of Pluto-Charon is 70/30.
Luke Burkhart (Johns Hopkins University) talked about his work on a “Non-linear satellite search around Haumea.” Haumea is another Trans-Neptunian Object (TNO) that has multiple satellite companion, like Pluto. Using HST (10 orbits) they observed the Haumea system and used a method of stacking & shifting to identify satellites. But this method fails to capture objects which are close in, moving fast, and on highly curved orbits. So they developed a new method using a non-linear shift-rate. Their approach, when applied to the Haumea system, had a null-result. However, this approach could be used on images of the Pluto system and other TNOs. Specifically, in answer to a question from the audience, Luke would be eager to use his technique on any of those long-range KBO targets the New Horizons project is currently investigating.
Photo here Family portraits of the eight largest Trans-Neptunian objects (TNOs). Pluto is shown with its 5 companions.
Small is the new big. Pluto’s family of small satellites sparks big discussions and new ideas.
Hal Weaver (APL) gave an introduction to “Pluto’s Small Satellites.” The Pluto system is rich. It has five confirmed moons, Charon (1978), Nix (2005), Hydra (2005), Kerberos (2011, formerly know as P4) and Styx (2012, formerly known as P5).
The Pluto system at a glance. Key top-level parameters of the satellites a=semi major axis (from the Pluto-Charon barycenter/center of mass) in kilometers, P=orbital period in days. The moons appear to be in orbital resonances Hydra:Kerberos:Nix:Styx:Charon = 6:5:4:3:1.
What about their albedo? Albedo is a measurement of a body’s reflectance, a reflection coefficient, where an albedo equal to 1 is “white” and an albedo equal to 0 is essentially “black” (e.g., dirty snowballs like comet nuclei has albedos ~0.04). It should be noted that albedo values can be functions of color (wavelength of light). We know that Pluto has an albedo ~0.5 and Charon has albedo ~0.35. Regolith exchange and dynamics agreements favor albedo ~0.35 for these small satellites, and assuming that density=1 (icy body). What are implications of these small satellite discoveries? These questions were posed: (1) Pluto system is highly compact and rich, so are there more satellites not yet discovered? (2) Was there a giant impact origin of Pluto System? (3) Could rings also form? (4) Could other large KBOs have multiple satellites? (We know Haumea has 2 companions. Could there be others?). What role will New Horizons bring? New Horizons will play a key role for small satellites, measuring their size and their shapes. Note: Additional occultation observations from Earth could reveal additional satellites and also provide measurements of their sizes, but not shapes. New Horizons best spatial resolution of the small satellites is: 0.46 km/pix (Nix), 1.14 km/pix (Hydra), 3.2km/pix (Kerberos), and 3.2 km/pix (Styx). Best estimates right now for the sizes of these bodies, assuming albedo 0.35, are Hydra 50km, Nix 40km, Kerberos 10km, Styx 4 km. That translates to roughly ~44, ~37, ~3, and ~1 pixels across Hydra, Nix, Kerberos, and Styx, respectively.
Scott Kenyon (Harvard SAO, by phone): “Formation of Pluto’s Low Mass Satellites.” He and his team looked at both the giant impact and capture formation paths for Pluto and Charon. They model a debris disk where viscous diffusion expands the disk, collisions circularize the orbits, particles experience migration, and satellites eventually grow. They found that lower mask disks take longer to reach equilibrium, do produce more satellites, and also produce the smaller satellites. Calculations with large seed planetesimals produce less satellites. Calculations also do predict 1-km size objects in large orbits (orbits beyond Hydra) in a diffuse debris disk.
Peter Thomas (Cornell University) and Keith Noll (NASA GSFC) provided a talk about “Pluto’s Small Satellites: What to Expect, What They Might Tell Us.:”
Small satellites of planets: variety and dynamics role. We have a small selection of satellites of 20-100km range (e.g. Metis, Amalthea, Thebe, Atlas, Prometheus, Pandora, Epimetheus, Janus, Hyperion, Phoebe and asteroids Mathilde, Eros, Ida). Best “comparatives” come from the Saturn family from amazing Cassini images, but these divided into two groups whether they are located within the ring arcs or not. Small satellites are irregular in shape, have high porosity (40-70% void space), weak (tidally fractured), crater morphology varies, regolith depths & distribution over surface, icy & rocky, and some have albedo markings.
Saturn’s moons may be useful “comparatives” for describing Pluto’s small satellites.
Predictions for New Horizons. Peter Thomas is excited to see New Horizons’ images of the small satellites. He predicts they will not look like egg-shaped. Thomas’ Best Guess: A Deimos/Hyperion hybrid morphology. KBOs and their satellites: variety and collision role. There are three multiple systems known in the Kuiper Belt: Pluto (6 components), Haumea (3 components) and 47171 1999 Tc36 (3 components). There are also 74 binary systems to date. The Pluto system is collisional. Unfortunately most of the KBO binaries have too low angular momentum to imply a collisional origin, but there is a subset of TNO binaries that could be a comparative set. Multiple collision systems in the Kuiper Belt could serve as possible analogs of the Pluto system.
Plutino binaries (above) are also “comparatives” images for describing Pluto’s small satellites. Other comparative bodies, which may have collisional origin could be Quaoar, 1998 SM165, Salacia, and Eris.
Predictions for New Horizons. New Horizons will tell us a lot about KBOs and test open theories about their formation and collisional history.
Mark Showalter (SETI): Talked about his preliminary work on “Chaotic Rotation of Nix & Hydra.” He started the presentation with a light curves for Hydra & Nix made the 2010-2012 HST data sets. They do not follow the expected “double sinusoidal.” When plotting phase angle vs. time, Hydra and Nix do get brighter with lower phase angle and he used this information to normalize their light curves. He found that Nix & Hydra’s brightness's do not correlate with their projected longitude on the sky. They are probably not in synchronous rotation. Also, he is not finding any single rotation period compatible with the data series he has. His premise is that Nix and Hydra are not following your typical rotation, and are very heavily influenced by the Charon-wobble. Best Guess: Hydra and Nix are in a state of “tumbling.” Bodies that not synchronous have no way to get to synchronous lock. Until now, Hyperion (one of Saturn’s moons) had been the only chaotic rotator. Not any more! It’s got company!
More predictions about Pluto’s changing atmosphere. And Charon may have a few surprises of her own.
Richard French (Wellesley College): presented a talk on “A Comparison of Models of Tides in Pluto’s Atmosphere and Stellar Occultation Observations:” We have come to understand that Pluto’s atmosphere is cold & tenuous, has a long radiative time constant, shows weak diurnal variations, indicates seasonal transport of volatiles with long term variations of atmospheric mass, and seems to be convectively stable. Current Pluto general circulation models (GCMs) predict smooth T(P) profiles reveal mean circulation and thermal structure. But there are problems. GCMs predictions (with these smooth T(P) profiles) are inconsistent with stellar occultation data, which imply much more complex T(P) profile. The other challenge to this mystery is that stellar occultations are spatial constrained (i.e., map across a particular lat/long swath of Pluto surface at the time of event). Are there waves in Pluto’s atmosphere? This is one proposition to explain the structures (spikes) seen in the Pluto occultation data. Tidal models they have built make predictions for large scale and small-scale structures. Also they can predict temperature profiles with altitude. Next steps are to apply this model to other occultation geometries. He showed a comparison of a tidal model against occultation data from an event on Aug 21, 2002 and they showed qualitative agreement. Richard French’s predictions for New Horizons fly-by: When New Horizons provides a true frost pattern, they can input this into their models and generate large-scale and small-scale structures for comparison with actual New Horizons atmosphere measurements. Their tidal models do generate regionally variable, latitude dependent thermal changes.
There was a dual Pluto & Charon occultation event on 4 June 2011. Pluto and Charon each pass in front of the star (at different times). Look at curve shapes. Charon’s curve sharply drops, indicative of no atmosphere, unlike Pluto’s curve, which has not-as-steep ingress/egress that indicates the presence of an atmosphere.
Using the light curve data, Sicardy and his team use a temperature vs. altitude model to fit the light curve depth, width and ingress/egress slope. Then with the temperature, they can derive a pressure. He presented results from the most recent Pluto occultation that was observed May 4, 2013. Good data and good fit.
Pluto, the Orange Frosty, served with a dash of Nitrogen, a pinch of Methane, and smidgen of Carbon Monoxide
Dale Cruikshank (NASA Ames) set the stage with a spectra-rich presentation and gave an overview talk about the “Surface Compositions of Pluto and Charon.” Putting it in context, even 45 years after Pluto was discovered, we did not know much about Pluto only where it was in the sky and its rotation period. That rapidly changed when Dale and colleagues saw strong evidence for solid methane on Pluto in 1976. Jim Christy discovered the companion moon Charon in 1978, and repeated observations of Pluto and Charon in the 1980s. Spectroscopy, the technique which spreads light into different wavelengths, has been a powerful diagnostic tool for the identification of molecular species, and therefore tells us the composition of the object. Low-resolution (R~100-500) spectra is sufficient to identify ice-solid features which are characterized by wide features, but higher resolution (R~1,000-10,000s) helps constrain models that determine temperature also. New Horizons’ LEISA spectrometer covers the 1.25-2.5micron spectral band, with resolution R~240, and a mode of R~550 between 2.10-2.25 microns, making it ideal for identifying solid features. It’s proximity to Pluto during the July 2015 fly-by provides unprecedented spatial resolution. Compared to ground-based & Hubble spectral measurements which can only provide full-disk (~1500km/pix) measurements (because Pluto appears only in a few pixels), New Horizons’ LEISA will provide the true “first look” at the composition of Pluto at 6.0km/pix (global) with some patches at 2.7 km/pixel.
Pluto’s Near Infrared Spectrum is rich in identifiable diagnostic solid materials, Nitrogen (N2), Methane (CH4) and Carbon Monoxide (CO). A comparison with Triton’s spectrum over the same wavelength is shown. Carbon dioxide (CO2) is suspiciously absent from Pluto’s atmosphere.
Pluto’s mid-infrared show a series of methane bands. The gap at 4.2 um is due to CO2 absorption from the Earth’s atmosphere.
Pluto’s UV Spectrum from HST also indirectly supports the presence of organics.
Geometric albedo (measure of reflectivity) of Pluto as a function of wavelength. See how red it looks?
The Surface of Charon. Charon has an intriguing different kind of surface than Pluto. There is water ice, perhaps crystalline ice, and ammonia (NH3) hydrate. But there are no CO, CO2, N2 or CH4, all which are present (or predicted) for Pluto. The nature and source of the ammonia is under debate. Could it come from below the surface and diffuse up or come from cryo-volcanism?
Predictions for New Horizons. It will be hard to find HCN with LEISA due to its spectral resolution as there is a strong methane band nearby. Dale Cruikshank thinks it will be challenging as well to find alkenes. The mystery of the missing CO2 on Pluto remains. Carbon dioxide is seen on Triton (see above), whose spectra is very similar to Pluto. Dale Cruikshank looks to NASA’s JWST (James Webb Space Telescope, a 6.5 m diameter visible infrared space telescope) as the proper tool to make this detection. New Horizons LEISA instrument has probably too low a resolution to detect CO2 features around 2 microns.
Jason Cook (SwRI) presented a talk on “Observations of Pluto’s Surface and Atmosphere at Low Resolution.” Intrigued by the ethane (C2H6) detection, he got the new idea to look for it this in old data he took in 2004 using the Gemini-N NIRI instrument, with R~700 (low resolution) spectroscopy. In his analysis, he had to include the C2H6 ice contribution to make a fit of ice abundances to the data. He was able to fit multiple methane bands and derive comparable amounts that agrees with other published methane detections at higher resolution.
Bryan Butler (NRAO) talked about “Observations of Pluto, Charon and other TNOs at long wavelengths.” As you go to longer wavelengths, you are less affected by solar reflection. You become dominated by the thermal emission from the body itself. But the emission at these wavelengths will be weak such that building highly sensitivity instruments is key, such as ALMA (in Chile) or updated VLA, called the EVLA (in New Mexico). They have been using ALMA and EVLA to observe Pluto and Charon in 2010-2012 and they had to remove the background contribution as Pluto had been moving through the galactic plane in this period.
The path of Pluto is shown with the green line that appears to make loops. This is the path of Pluto projected against the sub-millimeter. The enhanced horizontal signal is strong sub millimeter thermal emission from the plane of the Milky Way. This caused an undesired extra background signal that needed to be removed from data taken in the 2010-2012 time frame.
What’s Next? They wish to use ALMA to study Pluto & Charon and also attempt to detect Nix & Hydra, if they fall on the larger size. ALMA will be used to observe TNOs and will have the capability to resolve the largest TNOs like Eris (size ~2400km diameter). They predict they can make high-SNR images of Pluto, but barely resolve Charon within a short observation time. To get high-SNR images of Charon would take more observatory time than they think would be awarded for a single object:
Playing Marbles at Pluto. Looking at the Dynamic Dust Environment. Generators, Sweepers, and Sweet-Spots.
Simon Porter (Lowell Observatory) began this part of the session with “Ejecta Transfer within the Pluto System.” He asked, “Where does the short lived dust go?” Having small satellites is not unusual in the solar system. Both Jupiter & Saturn have low number-density rings formed from short-lived dust particles ejected from small satellites. Their Hypothesis: Dust ejected from the small satellites is swept up by Pluto and Charon. Their Experiment: Simulate dust trajectories in a computer (N-body computation) starting randomly in the system (but constrained within the orbits of the small satellites) and map where they impact Pluto & Charon. Repeat this 10,000 times for a combination of parameters. Their Results: Dust particles do hit all the bodies in the Pluto System. For the Charon impacts, smaller particles survive longer, and those that hit Charon tend to have speeds around 50 m/s (like a fastball pitcher). If a particle were to hit Pluto, it would be happen with speeds in the 50-200 m/s range and occur much quicker (due to the fact that Pluto has a larger gravity mass than Charon). They found that lower speed particles would hit the Pluto’s trailing side, whereas the higher speed particles hit the Pluto’s leading side. They also found a slight northern preference for smaller particles due to radiation pressure. And they made an intriguing observation that the impacts they computed correlate well to bright albedo areas (high reflectivity) on the Pluto surface.
David Kaufman (SwRI) next talked about “Dynamical Simulations of the Debris Disk Dust Environment of the Pluto System.” He was interested in modeling where debris dust would exist in the Pluto System. The motivation was to evaluate the probability of whether New Horizons would encounter a large enough dust particle that could be catastrophic to the spacecraft. He described the dynamics: the Pluto System can be approximated by a “circular restricted three-body (Pluto-Charon-particle) problem,” but it’s far from simply three bodies. There are features such as the Charon Instability Strip, where the moon Charon sweeps away material. The Lagrange points are unstable. And the outer moon can significantly perturb (change) trajectories that cross their orbits. He mentioned that “unusual type orbits” can be sustained by the unique gravity and motion characteristics of the Pluto System. He’s done numerical simulations following the particles, governed by physics principles for the system, over a time period of 500 years, and derived that the debris disk is an expended three-dimensional and stable. The inner debris disk recreated the instability strip.
Silvia Giuliatti Winter (UNESP, Brazil) talked about “The Dynamics of Dust Particles in the Pluto-Charon System.” She is interested in the orbital evolution of small particles ejected form the surface of Nix and Hydra and what happens to them when dust particles from interplanetary meteoroids on these satellites. The goal is to place constraints on predictions for a ring in the Pluto System. They model 1um and 5-10um “dust particles” and track where they travel.
Othon Winter (UNESP Brazil) spoke about “On the Relevance of the Sailboat Island for the New Horizons Mission.” In investigating where particles would find stabile orbits, their modeling predicted a region where there was a cluster of orbits characterized by high eccentricity (e= 0.2 to 0.8) and located around 0.6 Pluto-Charon semi-major axis (i.e. between Pluto and Charon). They nicknamed it “Sailboat Island’ because on a eccentricity vs. distance- from the Pluto plot it looked like a sailboat.
The figure describes a family orbits called S-type that are stable. The plots are in d vs. e. where d, on the x axis is the Pluto-centric semi-major axis (how far from the Pluto barycenter) and e, on the y axis is the eccentricity. The “white” areas are orbit solutions that were found to be stable. Area ‘1’ is the “Sailboat Island” described in the talk. Left are prograde (inclination=0) orbits, right are retrograde (inclination=180 degrees) orbits.
Example of a particular family of orbits from the “Sailboat Island” parameter space in the full-family of stabile orbits.
Andrew Poppe (UC Berkeley) on “Interplanetary dust influx to the Pluto System: Implications for the Dusty Exosphere and Ring Production.” The three previous talks addressed what happened to particles in the Pluto system with time (i.e., their lifetime, where they impacted objects, what stable orbits they achieved). Here He asked, could the source of the dust come from interplanetary sources? For example, come from the Kuiper Belt being dragged into the Sun. Because Pluto’s orbit is highly inclined but our Solar Systems Kuiper Belt dust disk is mainly in the ecliptic plane and Pluto periodically passes through the thickness part of the dust disk. EKB = Edgeworth–Kuiper belt
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Computation of the dust flux (in particles/m^2/s) for Pluto over one Pluto orbit. The peaks are when Pluto crosses the ecliptic (expected). New Horizon’s Jul 2015 Pluto Fly-by (shown by the red dashed line) will be close to an ecliptic crossing.
Implications for Rings. They turn their “mass influx models” and do calculations on where rings could form. They predict optical depth tau < 10^-7 (in backscatter). They are working to refine their models to include larger grains. Open questions. We still do not really have a good handle on the amount of dust generated by “the Kuiper Belt residents”. This is an active area of study.
Henry Throop (SwRI at large) talked about putting “Limits on Pluto’s Ring System from the June 12, 2006, Stellar Occultation.” You can search for rings by direct limited (e.g., using HST) or using stellar occultations. Direct imaging is 2D but at coarse scales whereas stellar occultation give 1 D cuts at higher spatial resolution. He saw that although the Jun 12, 2006 occultation event was 61 seconds in duration, about 3 hours of data was taken over the entire event, so he started to look outside the main events in search for rings that would appear as shallower drops in the light curve.
Three hours of data taken around the Jun 12, 2006 Pluto occultation even. They did not see any rings or debris with this data set.
Looking back at the timing they realized that Nix was just missed by 1000km or so. So had their been a cosmic coincide that this occultation caught Nix, Nix would have been discovered 10 years earlier. Implications for New Horizons? This null results combined with other searchers for rings (e.g. recent HST observations) put limits on ring detection, but this dataset is the only data set looking for rings at scales < 1500km, the spatial resolution on HST. The New Horizons spacecraft on its fly-by through the Pluto system in July 2015 should detect a ring with its Student Dust Counter instrument, if such a ring exists.
