Summary of 2004 Accomplishments
This year, the Department of Space Studies celebrated its 10th anniversary. We expanded onto a second floor of our building and hired eight new staff.
Below are figures from just a few of the accomplishments described here. Please see the full text that follows in the main section.
The day the Moon formed. Simulation of the first 24 hours after an impact of a Mars-sized planetesimal with the early Earth. Colors represent temperatures of 2000 K (blue) to >7000 K (red). -Robin Canup
Perspective view of the topography of some 3-4 billion-year-old "outflow channels" on Mars. The large amount of erosion requires more groundwater than can be regionally stored in the crust, implying that recharge and therefore an ancient hydrological cycle occurred. Numerical modeling suggests that the Tharsis rise was the most likely source region. -Keith Harrison and Bob Grimm
Sedna, the most distant known object in the Solar System, may have been initially scattered by the giant planets and then perturbed onto its current orbit by a passing star. Alternatively, this simulation shows the result of a dynamical simulation in which Sedna was captured from another stars protoplanetary disk during an encounter. -Hal Levison
This Hubble Space Telescope image of Ceres shows the motion of a surface feature as the asteroid rotates. The flattening of Ceres suggests a differentiated interior, perhaps into a rocky core and an icy mantle. -Joel Parker
Erika Barth worked on the development of a Titan general circulation model. She added microphysics routines which include the production of haze particles and the condensation of methane and ethane gases to form clouds.
Bill Bottke studied the size distribution of the main asteroid belt, a "fossil" left over from collision and dynamical processes taking place early in solar system history. By understanding main belt collisional processes, the work of Bottke and colleagues places new constraints on the nature of planet formation in the inner solar system. Bill worked on linking stony meteorites with their parent bodies in the near future. He used a collisional/dynamical evolution model to determine the formation time of Jupiter, the size of the primordial main belt, and the scaling law governing asteroid disruptions. Bottke and colleagues showed that Yarkovsky thermal drag forces constantly resupply main belt escape hatches with fresh debris. This explains the presence of small asteroids in chaotic resonances as well as the wide semimajor axis spreads of the Eos and Themis asteroid families. The work places constraints on the amount of asteroidal material that has been delievered to Earth over the last several Gy. They also used observations of asteroids from a recent breakup event in the main belt to determine the strength of the Yarkovksy thermal forces on 1-5 km asteroids.
Mark Bullock investigated the possibility of life in Venus' clouds, together with David Grinspoon and collaborators at the University of Texas, El Paso. At one time, Venus was wet and probably more Earth-like, and microbes that evolved on the surface could have migrated to the clouds (as they have appeared to do on Earth). Bullock and colleagues hypothesized that elemental sulfur, readily available in the clouds, could be used by bacteria as sunscreen to shield themselves from harmful UV radiation. Working with collaborators at the NASA Ames Research Center, Bullock has been performing experiments on the formation of salts on the Martian surface. They found that the synthetic Mars water has elemental abundances very similar to that of the soil measured by the Viking and Mars Pathfinder landers and, when evaporated, salts are left behind that show striking similarities to the salt beds found by the Mars rover Opportunity. Mark has produced synthetic images of the surface of Venus as it would be seen by a descent probe. He also collaborated with Eliot Young to observe the lower clouds of Venus using NASA's Infrared Telescope Facility in Hawaii.
Robin Canup completed the highest resolution and most physically realistic simulations yet of potential giant impacts with the early Earth, believed responsible for the origin of the Moon. She received the AGU's Macelwane medal in 2004, and was selected as one of Popular Science's "Brilliant 10" young scientists.
Clark Chapman published a comprehensive review of space weathering, which includes processes like micrometeorite bombardment that modify the spectral properties of sunlight reflected from the surfaces of airless bodies. In collaboration with Dan Durda, Bill Bottke, and others, Chapman continued to evaluate the hazard to Earth from asteroid impacts. He also worked with international colleagues on ways to improve the detection of potentially hazardous asteroids, on possible ways of deflecting a dangerous one from hitting the Earth, and on integration of the impact hazard into the larger scope of understanding and preparing for natural catastrophes. Clark and Bill Merline joined the rest of the MESSENGER team to view the successful launch of that spacecraft toward Mercury. Chapman and Merline are helping to devise the imaging and spectral mapping investigations of the surface of this closest planet to the Sun. Under supervision by Chapman and Merline, Beau Bierhaus completed his Ph.D. thesis on small-scale cratering of Europa, concluding that secondary cratering dominates the distribution of craters <1 km in size.
Alisdair Davey worked to develop a new method of reducing SUMER spectra data from the SOHO spacecraft. A series of SUMER observations of coronal holes have been analyzed, looking at characteristic differences between polar and equatorial holes and within the series of equatorial holes looking for morphological differences that lead to variations of the Ne VIII emission and its subsequent effect on the solar wind. He also worked on the Virtual Solar Observatory (VSO), a "one-stop shopping" service for solar physics data, with a team of people from, GSFC, Stanford, Montana State and NSO. Part of Alisdair's work on the VSO was dealing with the incorporation of scientific catalogs. This resulted in a collaboration with Meredith Wills-Davey in a comprehensive statistical study of SOHO-LASCO CME observations. Using these data, they were able to show that LASCO failed to observe a percentage of low-energy Earth-directed CMEs. These findings suggest that we may currently lack the capability to observe some geoeffective CMEs.
Craig DeForest published first results from SWAMIS, an artificial vision suite to track thousands of features simultaneously on the face of the Sun. He discovered a long-sought but previously undetected spectrum of high frequency waves in the solar chromosphere. Craig published first results from an internal research project to develop a new type of spectral imager (he is now proposing to NASA to build and fly one). Deforest also developed a new type of simplified global MHD model for tracing the solar wind into the heliosphere.
Dan Durda, working with Bill Bottke and David Nesvorny and collaborators at UC Santa Cruz and the University of Maryland, studied the distribution of fragment sizes resulting from numerical simulations of the collisional disruption of asteroids. Durda and collaborators conducted over 160 impact simulations in order to study the formation of asteroid satellites. They noted that the collection of debris fragments left over from the simulated collisions can be compared with actual observed 'families' of asteroids, recognized by planetary scientists as the evidence of catastrophic impacts in the main asteroid belt, in order to learn more about the impact processes that dominate the history of these small Solar System bodies.
Luke Dones, a member of the Cassini imaging team, analyzed ring images taken on approach to Saturn and during the first six months of operations after the spacecraft went into orbit on July 1, 2004. Along with other SwRI scientists and colleagues in France and Argentina, Luke investigated the collisional origin of families of irregular satellites and the effect of a close stellar encounter on the Kuiper belt. He also authored three papers on the dynamics of the Oort cloud of comets.
Bob Grimm collaborated with the Lunar and Planetary Institute and SwRI geologists to study Mars analog sites with ground-penetrating radar. Early results suggest that depths of investigation on Mars may be limited by simple geological scattering (fractures, structures, stratigraphy) in spite of the cold and dry nature of the uppermost crust. Grimm began a new project to measure the unfrozen water content of Mars-analog materials in order to understand its effect on radar sounding and microbe habitability. Bob revived his interest in meteorite parent bodies, with a new start to study the hydrogeological histories of carbonaceous chondrites and a pilot project on the coupled collisional and thermal histories of ordinary chondrites.
David Grinspoon continued his studies of the early climate evolution of Venus and Mars, and in collaboration with Mark Bulluck began more generalized studies of coupled surface/climate evolution on hypothetical Earthlike planets around other stars, geared at understanding the longevity of oceans on other worlds. He also continued to collaborate with Clark Chapman on modeling the early bombardment history of the Earth/Moon system, and conducted several astrobiology investigations into the possible metabolic bases for life in exotic places such as the clouds of Venus and the subsurface of Saturn's moon Titan
Keith Harrison extended his Martian groundwater modeling efforts in collaboration with Bob Grimm by developing a global aquifer model with spherical geometry. This will allow simulations of outflow channel discharge given recharge at Tharsis or the South Pole. Successful model testing has allowed a survey of the parameter space, including that spanned by recharge rates and aquifer permeabilities, to be initiated. A renewed focus on observational evidence of low-latitude recharge on Mars has produced promising initial results. Harrison and Grimm also began investigation of a hypothesis that an evolution in fluvial erosion on Mars from the Noachian to the Hesperian can be documented in the changing styles of valley networks and outflow channels.
Don Hassler won two major new programs this year, a NASA sounding rocket program and an energetic particle spectrometer to fly on the next NASA Mars rover in 2009. The purpose of the sounding rocket program, called RAISE (Rapid Acquisition Imaging Spectrograph Experiment), is to build and fly a next generation ultraviolet spectrograph in order to validate new instrumental and observational techniques. The Mars rover instrument, called RAD (Radiation Assessment Detector), will be the first instrument to characterize the radiation environment at the surface of Mars in preparation for future human exploration of the planet.
Kandis Lea Jessup analyzed ultraviolet observations of Io's active plumes obtained with the Hubble Space Telescope. By observing the absorption of light as Io passes in front of Jupiter, the amount of sulfur dioxide and sulfur gases within Io's volcanic plumes were measured. With these measurements Kandis Lea will be able to determine the chemical make-up of the magma supplying each volcano and hence the eruption temperature. These findings relate directly to the formation of Io itself.
Dave Kaufmann continued work on symplectic numerical integrators used to study the formation and dynamical evolution of planetary systems. This work involved not only the NASA-sponsored improvement of Hal Levison's Swift package, but also an effort to develop an entirely new symplectic integrator with support from SwRI internal research funds. Hal Levison, Bill Bottke, David Nesvorny and Dave studied the evolution of dust particles released from Jupiter family comets in an effort to understand their contribution to the micrometeoroid environment of the inner Jovian system. Together with Panos Patsis of the Academy of Athens, Kaufman completed a preliminary study of a new family of orbits that exists in models of galaxies with thin bars. These new orbits - called "propeller" orbits on account of their shapes - may be important in providing the backbone structure of these types of bars.
Hal Levison continued his research into the origin and dynamical evolution of the outer Solar System. Included in this work was a detailed study into the origin of Sedna's orbit. Of the many scenarios studied, he and his collaborators found that only ones involving a passing star can reproduce the observations. In particular, Sedna probably was initially being scattered out of the Solar System by the giant planets and was perturbed onto its current orbit by a passing star. Another intriguing idea is that Sedna was captured from another star's proto-planetary disk during an encounter. Levison also worked on the migration of the giant planets as they cleared their neighboring proto-planetary disk. He and his collaborators found that the best way to get Neptune to its current orbit is for the original proto-planetary to be truncated at 30 AU.
Scott McIntosh and colleagues are developing new data analysis methods and a suite of instruments capable of measuring small changes in the Sun's thermodynamic and magnetic structure, with a view to understanding how the Sun' outer atmosphere is heated. McIntosh and colleagues demonstrated a correlation between chromospheric structure and the composition and speed of the nascent solar wind. This suggests that the magnetic environment and thermodynamic structure of the chromosphere are important factors in the driving and support of the solar wind. Members of the solar physics group have made large strides in connecting variations in the extreme ultraviolet emission from the Sun's corona to the convectively driven micro-turbulence over the entirety of the current magnetic cycle. The understanding gained will provide insight into the turbulent driving of small-scale magnetic fields and eventual magnetic reconnection in the Sun's corona. Such knowledge will give a critical foothold to the understanding the variations in the Sun's EUV radiation on many time scales.
Paul Meade adapted a terrestrial cloud microphysics simulation code to model the formation of sulfuric acid clouds on Venus.
Bill Merline continued to lead an international team to search for and study moons of asteroids. The team includes participation by SwRI researchers Clark Chapman, Peter Tamblyn, Dan Durda, and David Nesvorny. Last year they reported discovery of moons around asteroids (4674) Pauling, (22899), and (17246) . The latter two are the smallest main-belt asteroids known to have companions. The observational data are being used to calibrate computer models of formation of these binaries by simulation of asteroid collisions, led by Durda. Bill and analyst Brian Enke, in collaboration with the Jet Propulsion Lab, are attempting to optimize these simulations using Active Learning, an artificial intelligence technique. Merline was Visiting Scientist at the European Southern Observatory in Santiago, Chile, working with Christophe Dumas on binary asteroids and imaging of asteroid surfaces to determine shape and surface features using adaptive optics. With his SwRI colleagues, Bill is studying various physical properites of very young asteroids using ground- and space-based telescopes.
Tim Michaels collaborated with scientists from Arizona State University to correlate surface aeolian geology seen by Spirit (MER-A) with modeled winds, as well as to correlate complex wind streak fields seen from orbit with atmospheric model winds. He continued mesoscale model development, and microscale and mesoscale investigation of Mars' atmosphere (dry air, water vapor, dust and water-ice aerosols).
David Nesvorny and colleagues showed that colors of asteroid surfaces become increasingly 'redder' with age and measured the rate of these spectral changes. This result has important implications for asteroid geology and the origin of meteorites that we collect at the Earth. Nesvorny and colleagues investigated the possibility that orbital groupings of irregular moons formed via collisions between large parent moons and stray planetesimals during Solar System formation. This constrains the mass of the residual planetesimal disk. The acceleration produced by anisotropic thermal mission (Yarkovsky effect) was directly detected in the main asteroid belt by David and his collaborators. This provides important parameter constraints on theoretical models of the dynamical evolution of asteroids, and on their thermal properties. Nesvorny and colleagues also showed that thermal torques arising from differential solar heating are major contributors to the modification of asteroid rotations, perhaps more important than collisions.
Cathy Olkin began analyzing a spectrum of Pluto spanning 2.8 to 3.7 microns. The data were recorded using the NIRSPEC spectrograph on the Keck II. The wavelength range encompasses a strong methane ice band at 3.3 microns.
Joel Parker studied the distribution of high-mass stars in the Magellanic Cloud galaxies, finding that isolated "orphan" massive stars are not be escapees from nearby star clusters as previously thought, and are significant contributors to the volume of the warm ionized gas in galaxies. Using the Hubble Space Telescope, Parker and colleagues determined the shape and rotation of Ceres, the largest asteroid; they discovered that the flattening of Ceres is less than expected, which may imply that Ceres has differentiated into a rocky core and water-ice rich mantle. Parker began a long-term program using ground-based telescopes to detect and measure the orbits of Kuiper-belt objects. He also was appointed as the Operations Project Manager for the Alice ultraviolet spectrometer on the Rosetta spacecraft, which launched in March 2004, and he has developed the data processing pipelines that will be used for the Alice instruments on three different missions: Rosetta, New Horizons, and Lunar Reconnaissance Orbiter.
Scot Rafkin focused his effort last year on providing critical simulations of Mars' atmosphere in support of Phoenix, the first Mars Scout mission. Together with Tim Michaels, Rafkin – a Phoenix science collaborator – simulated the local conditions at high latitude potential landing sites. The resulting model data is used by the Phoenix project to identify wind conditions hazardous to entry, descent, and landing operations, and as input to optimize system and science instrument performance. Scot provided similar meteorological simulations for the Mars Exploration Rovers.
John Spencer used three years of infrared observations to demonstrate that Io's sulfur dioxide atmosphere is more stable than previously expected, but is ten times denser on the side that faces away from Jupiter. Spencer co-led planning and analysis for icy satellite observations using the Composite Infrared Spectrometer on the Cassini spacecraft, which entered Saturn orbit in summer 2004. John also planned observations of the Jupiter system for the New Horizons flyby in early 2007, and led the search for Kuiper belt objects (KBOs) that could by targets after the spacecraft's Pluto encounter. Spencer supervised a large KBO survey with the Japanese Subaru telescope, searching for moving objects down to a limiting magnitude of 25.7.
Alan Stern Alan Stern supervised the successful space commissioning and calibration of the Rosetta-Alice ultraviolet imaging spectrometer. After initial commissioning, Alice observed comet Linear-T7 during cruise. Alan continued to lead the APL-SWRI New Horizons Pluto-Charon mission toward its hoped for January, 2006 launch as the first mission in NASA's New Frontiers program. Department research and engineering staff played major roles in payload and science operations center development. Stern continued as the PI of the SwRI SwIM Mars research initiative, and led a team that was selected to provide a UV spectrometer called LAMP for NASA's new Lunar Reconnaissance Orbiter mission, set for launch in late 2008. LAMP will search for evidence of exposed water ice at the poles, map landforms in the permanently shadowed regions of the Moon, and study the lunar atmosphere. Alan's final BDPR suborbital rocket mission, to examine the reflectance spectrum of Mercury, flew early in 2004. Alan's research activities included studies of the origin of the distant, large KBO named Sedna, the UV nightglow of Mars, the surface appearance of Ceres, and the evolution of comets in the Oort Cloud.
Dirk Terrell continued to research a variety of topics on close binary star systems. He and Mark Bullock were awarded an internal research grant to develop models of the climates of planets in binary star systems. He also completed software based on the Wilson-Devinney model to compute binary star observables from a set of binary parameters. Analysis of individual binaries continued with papers published on the overcontact binary AM Leonis, the early-type detached binary CX Canis Majoris, the early-type overcontact binary TU Muscae and the evolved, early-type binary MP Centauri. Work was also completed on the binary HD 23642, a member of the Pleiades cluster that was recently discovered to undergo shallow eclipses. Analysis of the data shows that the Hipparcos distance to the cluster is signifcantly in error, with implications for the cosmological distance scale and upcoming astrometry missions like GAIA. Terrell and amateur colleagues began a multi-year photometric survey of several bright open clusters with a fully automated observatory in Sonoita, AZ looking for both short and long period variables. Terrell also demonstrated a method to determine the mass ratio of a binary from photometric data alone.
Henry Throop explored the diversity of environments in which planets can form. Computer modeling performed in the division showed that some regions of space - called 'OB associations' for the massive, UV-bright stars of type O and B which populate them - may foster the rapid growth of planets under some circumstances. Previously, it had been assumed that such hot, violent environments allowed the formation of planets only under rare conditions. Henry further showed that such environments may allow for the rapid production of complex organic molecules that were precursors to life on Earth.
Bill Ward and colleague Doug Hamilton (Univ. Maryland) explained the comparatively large tilt of Saturn's spin axis as the result of gravitational perturbations by Neptune. A similarity between the precession period of Saturn's spin axis and the precession period of Neptune's slightly inclined orbit plane implies a resonant interaction between these planets as responsible for tilting Saturn from an initially more upright state. Ward and Hamilton make a case that Saturn was captured into this resonance during the erosion of the Kuiper belt, which decreased the rate of regression of Neptune's orbit plane. Penetrating the resonance pumped up Saturn's obliquity to its current value. The spin axis may also be librating in the resonance, which constrains Saturn's moment of inertia. Matching the current pole position to the predicted outcome may place new constraints on early solar system processes.
Meredith Wills-Davey spent most of her time developing a theoretical model for the large-scale pulse waves observed in the solar corona. She determined that the presence of closed magnetic field structures requires MHD solitons to travel more slowly than under other conditions. Such closed magnetic fields correspond to the structure of the solar corona, explaining why only slow solitons are observed. Meredith worked with Laurel Rachmeler to compile a catalog of TRACE observations of coronal pulse waves. They also discovered several unique wave phenomena, including a pulse wave that maintains coherence through an active region. In addition, Wills-Davey collaborated with Alisdair Davey in a comprehensive statistical study of SOHO-LASCO CME observations. Using these data, they were able to show that LASCO failed to observe a percentage of low-energy Earth-directed CMEs. These findings suggest that we may currently lack the capability to observe particularly geoeffective CMEs.
Eliot Young observed Titan from the Keck telescope at the same time as two Cassini flybys, and also enhanced HST images of Titan to detect its extended haze layer. He and Cathy Olkin produced new 3-3.6 micron spectra of Pluto with ten times better resolution than any best-published examples. Eliot is leading efforts to implement an image-improvement pipeline for NASA's IRTF telescope and he achieved first light with a new portable high-speed occultation telescope system. He also began a new project to use neural networks to classify spectra of distant solar system objects in order to determine surface characteristics from spectral features in water, methane, or nitrogen ices.
Leslie Young discovered unexpected variation in Triton's nitrogen frost, in collaboration Eliot Young and Will Grundy (Lowell Observatory). Near-infrared measurements showed that the absorption by nitrogen ice, the main ice on Triton's surface, was twice as deep on the side that faces Neptune as on the opposite side. One explanation is that the nitrogen frost has been subliming from the area around the sunlit south pole, leaving a nitrogen-rich equatorial collar that is larger on the sub-Neptune than anti-Neptune side.