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S L Murchie - One of the best experts on this subject based on the ideXlab platform.
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overview of Phobos deimos regolith ion sample mission prism concept
CubeSats and NanoSats for Remote Sensing II, 2018Co-Authors: Pamela Clark, A S Rivkin, Michael R. Collier, M. J. Schaible, William M. Farrell, David Folta, Kyle M. Hughes, John W. Keller, Ben Malphrus, S L MurchieAbstract:Far more definitive information on composition is required to resolve the question of origin for the Martian moons Phobos and Deimos. Current infrared spectra of the objects are inconclusive due to the lack of strong diagnostic features. Definitive compositional measurements of Phobos could be obtained using in-situ X-ray, gamma-ray, or neutron spectroscopy or collecting and returning samples to Earth for analysis. We have proposed, in lieu of those methods, to derive Phobos and Deimos compositional data from secondary ion mass spectrometry (SIMS) measurements by calibrating the instrument to elemental abundance measurements made for known samples in the laboratory. We describe the Phobos/Deimos Regolith Ion Sample Mission (PRISM) concept here. PRISM utilizes a high-resolution TOF plasma composition analyzer to make SIMS measurements by observing the sputtered species from various locations of the moons' surfaces. In general, the SIMS technique and ion mass spectrometers complement and expand quadrupole mass spectrometer measurements by collecting ions that have been energized to higher energies, 50-100 eV, and making measurements at very low densities and pressures. Furthermore, because the TOF technique accepts all masses all the time, it obtains continuous measurements and does not require stepping through masses. The instrument would draw less than 10 W and weigh less than 5 kg. The spacecraft, nominally a radiation-hardened 12U CubeSat, would use a low-thrust Solar Electric Propulsion system to send it on a two-year journey to Mars, where it would co-orbit with Deimos and then Phobos at distances as low as 27 km.
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composition of surface materials on the moons of mars
Planetary and Space Science, 2014Co-Authors: C M Pieters, S L Murchie, Nicolas Thomas, D T BrittAbstract:The two small asteroid-like bodies orbiting Mars, Phobos and Deimos, are low albedo and exhibit similar visible to near-infrared spectra. Determining the origin of these moons is closely tied to determining their composition. From available spectroscopic data Phobos exhibits two distinct types of materials across its surface, and data from both Mars Express and Mars Reconnaissance Orbiter have provided additional details about the properties of these materials and their spatial relation to one another. Although no prominent diagnostic absorptions have been detected, systematic weak features are seen in some data. An extensive regolith is observed to have developed on both moons with characteristics that may be unique due to their special environment in Mars orbit. Understanding the character and evolution of the regolith of Phobos and Deimos is central to interpreting the moons׳ physical and optical properties. The cumulative data available for compositional analyses across the surface of Phobos and Deimos, however, remain incomplete in scope and character and ambiguous in interpretation. Consequently the composition of the moons of Mars remains uncertain.
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analysis of disk resolved omega and crism spectral observations of Phobos and deimos
Journal of Geophysical Research, 2012Co-Authors: Abigail A. Fraeman, R. E. Arvidson, A S Rivkin, S L Murchie, J P Bibring, T Choo, B Gondet, D C Humm, R O Kuzmin, N ManaudAbstract:[1] Disk-resolved observations of Phobos acquired by OMEGA at a range of lighting and viewing geometries were fit with the Hapke photometric function to solve for the single particle phase function and single scattering albedos from 0.4 to 2.5 μm. Single scattering albedos were recovered from CRISM observations of Phobos using the OMEGA derived single particle phase function and are similar to those from OMEGA data. Both the ubiquitous red unit and the blue unit around the crater Stickney exhibit a smooth red-sloped spectrum, with a steeper continuum in the redder unit. Single scattering albedos retrieved from CRISM measurements of Deimos are similar to those for the red unit on Phobos. Retrieval of single scattering albedos from OMEGA data at 2.8 to 5.0 μm has greater uncertainty, but results in this wavelength range are also consistent with a smooth, red-sloped spectrum. Phobos' and Deimos' low reflectances, lack of mafic absorption features, and red spectral slopes are incompatible with even highly space weathered chondritic or basaltic compositions. These results, coupled with similarities to laboratory spectra of Tagish Lake (possible D-type asteroid analog) and CM carbonaceous chondrite meteorites, show that Phobos and Deimos have primitive compositions. If the moons formed in situ rather than by capture of primitive bodies, primitive materials must have been added to the Martian system during accretion or a late stage impact.
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observations of Phobos deimos and bright stars with the imager for mars pathfinder
Journal of Geophysical Research, 1999Co-Authors: N Thomas, Kenneth E Herkenhoff, D T Britt, S L Murchie, Boris Semenov, H U Keller, P H SmithAbstract:The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to 1 μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm)−1 and 9.6(±0.6)% (100 nm)−1, respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10–15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement.
A S Rivkin - One of the best experts on this subject based on the ideXlab platform.
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overview of Phobos deimos regolith ion sample mission prism concept
CubeSats and NanoSats for Remote Sensing II, 2018Co-Authors: Pamela Clark, A S Rivkin, Michael R. Collier, M. J. Schaible, William M. Farrell, David Folta, Kyle M. Hughes, John W. Keller, Ben Malphrus, S L MurchieAbstract:Far more definitive information on composition is required to resolve the question of origin for the Martian moons Phobos and Deimos. Current infrared spectra of the objects are inconclusive due to the lack of strong diagnostic features. Definitive compositional measurements of Phobos could be obtained using in-situ X-ray, gamma-ray, or neutron spectroscopy or collecting and returning samples to Earth for analysis. We have proposed, in lieu of those methods, to derive Phobos and Deimos compositional data from secondary ion mass spectrometry (SIMS) measurements by calibrating the instrument to elemental abundance measurements made for known samples in the laboratory. We describe the Phobos/Deimos Regolith Ion Sample Mission (PRISM) concept here. PRISM utilizes a high-resolution TOF plasma composition analyzer to make SIMS measurements by observing the sputtered species from various locations of the moons' surfaces. In general, the SIMS technique and ion mass spectrometers complement and expand quadrupole mass spectrometer measurements by collecting ions that have been energized to higher energies, 50-100 eV, and making measurements at very low densities and pressures. Furthermore, because the TOF technique accepts all masses all the time, it obtains continuous measurements and does not require stepping through masses. The instrument would draw less than 10 W and weigh less than 5 kg. The spacecraft, nominally a radiation-hardened 12U CubeSat, would use a low-thrust Solar Electric Propulsion system to send it on a two-year journey to Mars, where it would co-orbit with Deimos and then Phobos at distances as low as 27 km.
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spectral absorptions on Phobos and deimos in the visible near infrared wavelengths and their compositional constraints
Icarus, 2014Co-Authors: Abigail A. Fraeman, Scott L. Murchie, R. E. Arvidson, R. V. Morris, A S Rivkin, Roger N. Clark, Faith VilasAbstract:Abstract Absorption features on Phobos and Deimos in the visible/near infrared wavelength region (0.4–3.9 μm) are mapped using observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Fe 2+ electronic absorptions diagnostic of olivine and pyroxene are not detected. A broad absorption centered around 0.65 μm within the red spectral units of both moons is detected, and this feature is also evident in telescopic, Pathfinder, and Phobos-2 observations of Phobos. A 2.8 μm metal–OH combination absorption on both moons is also detected in the CRISM data, and this absorption is shallower in the Phobos blue unit than in the Phobos red unit and Deimos. The strength, position, and shape of both of the 0.65 μm and 2.8 μm absorptions are similar to features seen on red-sloped, low-albedo primitive asteroids. Two end-member hypotheses are presented to explain the spectral features on Phobos and Deimos. The first invokes the presence of highly desiccated Fe-phyllosilicate minerals indigenous to the bodies, and the second invokes Rayleigh scattering and absorption of small iron particles formed by exogenic space weathering processing, coupled with implantation of H from solar wind. Both end-member hypotheses may play a role, and in situ exploration will be needed to ultimately determine the underlying causes for the pair of spectral features observed on Phobos and Deimos.
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analysis of disk resolved omega and crism spectral observations of Phobos and deimos
Journal of Geophysical Research, 2012Co-Authors: Abigail A. Fraeman, R. E. Arvidson, A S Rivkin, S L Murchie, J P Bibring, T Choo, B Gondet, D C Humm, R O Kuzmin, N ManaudAbstract:[1] Disk-resolved observations of Phobos acquired by OMEGA at a range of lighting and viewing geometries were fit with the Hapke photometric function to solve for the single particle phase function and single scattering albedos from 0.4 to 2.5 μm. Single scattering albedos were recovered from CRISM observations of Phobos using the OMEGA derived single particle phase function and are similar to those from OMEGA data. Both the ubiquitous red unit and the blue unit around the crater Stickney exhibit a smooth red-sloped spectrum, with a steeper continuum in the redder unit. Single scattering albedos retrieved from CRISM measurements of Deimos are similar to those for the red unit on Phobos. Retrieval of single scattering albedos from OMEGA data at 2.8 to 5.0 μm has greater uncertainty, but results in this wavelength range are also consistent with a smooth, red-sloped spectrum. Phobos' and Deimos' low reflectances, lack of mafic absorption features, and red spectral slopes are incompatible with even highly space weathered chondritic or basaltic compositions. These results, coupled with similarities to laboratory spectra of Tagish Lake (possible D-type asteroid analog) and CM carbonaceous chondrite meteorites, show that Phobos and Deimos have primitive compositions. If the moons formed in situ rather than by capture of primitive bodies, primitive materials must have been added to the Martian system during accretion or a late stage impact.
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near infrared spectrophotometry of Phobos and deimos
Icarus, 2002Co-Authors: A S Rivkin, J F Bell, R H Brown, David E Trilling, J PlassmannAbstract:Abstract We have observed the leading and trailing hemispheres of Phobos from 1.65 to 3.5 μm and Deimos from 1.65 to 3.12 μm near opposition. We find the trailing hemisphere of Phobos to be brighter than its leading hemisphere by 0.24±0.06 magnitude at 1.65 μm and brighter than Deimos by 0.98±0.07 magnitude at 1.65 μm. We see no difference larger than observational uncertainties in spectral slope between the leading and trailing hemispheres when the spectra are normalized to 1.65 μm. We find no 3-μm absorption feature due to hydrated minerals on either hemisphere to a level of ∼5–10% on Phobos and ∼20% on Deimos. When the infrared data are joined to visible and near-IR data obtained by previous workers, our data suggest the leading (Stickney-dominated) side of Phobos is best matched by T-class asteroids. The spectral slope of the trailing side of Phobos and leading side of Deimos are bracketed by the D-class asteroids. The best laboratory spectral matches to these parts of Phobos are mature lunar soils and heated carbonaceous chondrites. The lack of 3-μm absorption features on either side of Phobos argues against the presence of a large interior reservoir of water ice according to current models of Phobos' interior (F. P. Fanale and J. R. Salvail 1989, Geophys. Res. Lett. 16 , 287–290; Icarus 88 , 380–395).
J F Bell - One of the best experts on this subject based on the ideXlab platform.
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near infrared spectrophotometry of Phobos and deimos
Icarus, 2002Co-Authors: A S Rivkin, J F Bell, R H Brown, David E Trilling, J PlassmannAbstract:Abstract We have observed the leading and trailing hemispheres of Phobos from 1.65 to 3.5 μm and Deimos from 1.65 to 3.12 μm near opposition. We find the trailing hemisphere of Phobos to be brighter than its leading hemisphere by 0.24±0.06 magnitude at 1.65 μm and brighter than Deimos by 0.98±0.07 magnitude at 1.65 μm. We see no difference larger than observational uncertainties in spectral slope between the leading and trailing hemispheres when the spectra are normalized to 1.65 μm. We find no 3-μm absorption feature due to hydrated minerals on either hemisphere to a level of ∼5–10% on Phobos and ∼20% on Deimos. When the infrared data are joined to visible and near-IR data obtained by previous workers, our data suggest the leading (Stickney-dominated) side of Phobos is best matched by T-class asteroids. The spectral slope of the trailing side of Phobos and leading side of Deimos are bracketed by the D-class asteroids. The best laboratory spectral matches to these parts of Phobos are mature lunar soils and heated carbonaceous chondrites. The lack of 3-μm absorption features on either side of Phobos argues against the presence of a large interior reservoir of water ice according to current models of Phobos' interior (F. P. Fanale and J. R. Salvail 1989, Geophys. Res. Lett. 16 , 287–290; Icarus 88 , 380–395).
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mars pathfinder spectral measurements of Phobos and deimos comparison with previous data
Journal of Geophysical Research, 1999Co-Authors: Scott L. Murchie, Kenneth E Herkenhoff, D T Britt, J F BellAbstract:The Imager for Mars Pathfinder (IMP) acquired four spectra of parts of the sub-Mars hemispheres of Phobos and Deimos. The measured region of Phobos is expected to be a mixture of the two spectral units identified on that satellite from Phobos 2 data, and the IMP spectra of Phobos are intermediate to the two units as expected. The derived geometric albedo is consistent with the value for that part of Phobos determined from Viking imagery. The IMP spectrum of Deimos is generally consistent with previous measurements acquired from the ground and from the Hubble Space Telescope (HST), but the signal-to-noise ratio is lower than that of the Phobos data. The spectral contrast between the two moons is similar to that seen in HST and Phobos 2 data. Mars Pathfinder measurements therefore substantiate recent results which indicate that Phobos and Deimos are not, as previously believed, analogous to C-type asteroids. They also provide some indications for an absorption near 700 nm, perhaps like that seen in other low-albedo asteroids. Both Martian moons are redder than most asteroids, and most closely resemble two analog materials believed to have undergone very dissimilar histories: primitive D-like asteroids, and highly space-weathered, mafic-rich assemblages, such as are present in lunar mare soils.
M H Acuna - One of the best experts on this subject based on the ideXlab platform.
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search for Phobos and deimos gas dust tori using in situ observations from mars global surveyor mag er
Icarus, 2010Co-Authors: M Oieroset, D A Brain, Erin Simpson, David L Mitchell, T D Phan, J S Halekas, R P Lin, M H AcunaAbstract:Abstract More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible signatures of solar wind interaction with dust or gas escaping from the moons. A total of 1246 solar wind disturbance events were identified and their distribution was examined relative to Phobos, the Phobos orbit, and the Deimos orbit. We find that the spatial distribution of solar wind perturbations does not increase near or downstream of Phobos, Phobos’ orbit, or Deimos’ orbit, which would have been expected if there is significant outgassing or dust escape from the martian moons. Of the 1246 magnetic field perturbation events found in the MGS data set, 11 events were found within 2000 km of the Phobos orbit, while three events were found within 2000 km of the Deimos orbit. These events were analyzed in detail and found to likely have other causes than outgassing/dust escape from the martian moons. Thus we conclude that the amount of gas/dust escaping the martian moons is not significant enough to induce detectable magnetic field perturbations in the solar wind. In essence we have not found any clear evidence in the MGS magnetic field data for outgassing or dust escape from the martian moons.
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martian shock and magnetic pile up boundary positions and shapes determined from the Phobos 2 and mars global surveyor data sets
AGU Fall Meeting Abstracts, 2004Co-Authors: J G Trotignon, C Mazelle, C Bertucci, M H AcunaAbstract:Abstract A great many Martian bow shock and magnetic pile-up boundary crossings have been identified in the Phobos 2 and Mars Global Surveyor, MGS, data. From these observations the positions and shapes of the bow shock and magnetic pile-up boundary, MPB, have been derived and modelled, using curve-fitting techniques. The models thus derived separately from the Phobos 2 and MGS data sets do not differ drastically, despite the different time and space data coverages. The purpose of the paper is therefore to show the results obtained from the mixing of the Phobos 2 and MGS data bases and to compare the derived bow shock and MPB models with the ones obtained previously. The underlying objective was to see whether it was possible to determine improved bow shock and MPB models or not. The answer is definitely yes, and particularly for the MPB, thanks to the complementary nature of the observations. The boundaries crossed close to the subsolar direction or mostly far downstream by Phobos 2 indeed allow a better coverage of the Martian space environment to be considered. Nevertheless, in order to reduce the domination of the overabundant MGS data set and/or the crossings that are close to Mars (x>−4 RM, i.e. x>−13 562 km) weighting factors have been introduced.
Kenneth E Herkenhoff - One of the best experts on this subject based on the ideXlab platform.
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spectral heterogeneity on Phobos and deimos hirise observations and comparisons to mars pathfinder results
Planetary and Space Science, 2011Co-Authors: Nicolas Thomas, Kenneth E Herkenhoff, R Stelter, Anton Ivanov, N T Bridges, A S McewenAbstract:Abstract The High-Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to observe Phobos and Deimos at spatial scales of around 6 and 20 m/px, respectively. HiRISE ( McEwen et al., JGR, 112, CiteID E05S02, DOI: 10.1029/2005JE002605, 2007 ) has provided, for the first time, high-resolution colour images of the surfaces of the Martian moons. When processed, by the production of colour ratio images for example, the data show considerable small-scale heterogeneity, which might be attributable to fresh impacts exposing different materials otherwise largely hidden by a homogenous regolith. The bluer material that is draped over the south-eastern rim of the largest crater on Phobos, Stickney, has been perforated by an impact to reveal redder material and must therefore be relatively thin. A fresh impact with dark crater rays has been identified. Previously identified mass-wasting features in Stickney and Limtoc craters stand out strongly in colour. The interior deposits in Stickney appear more inhomogeneous than previously suspected. Several other local colour variations are also evident. Deimos is more uniform in colour but does show some small-scale inhomogeneity. The bright “streamers” ( Thomas et al., Icarus, 123, 536–556,1996 ) are relatively blue. One crater to the south-west of Voltaire and its surroundings appear quite strongly reddened with respect to the rest of the surface. The reddening of the surroundings may be the result of ejecta from this impact. The spectral gradients at optical wavelengths observed for both Phobos and Deimos are quantitatively in good agreement with those found by unresolved photometric observations made by the Imager for Mars Pathfinder (IMP; Thomas et al., JGR, 104, 9055–9068, 1999 ). The spectral gradients of the blue and red units on Phobos bracket the results from IMP.
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mars pathfinder spectral measurements of Phobos and deimos comparison with previous data
Journal of Geophysical Research, 1999Co-Authors: Scott L. Murchie, Kenneth E Herkenhoff, D T Britt, J F BellAbstract:The Imager for Mars Pathfinder (IMP) acquired four spectra of parts of the sub-Mars hemispheres of Phobos and Deimos. The measured region of Phobos is expected to be a mixture of the two spectral units identified on that satellite from Phobos 2 data, and the IMP spectra of Phobos are intermediate to the two units as expected. The derived geometric albedo is consistent with the value for that part of Phobos determined from Viking imagery. The IMP spectrum of Deimos is generally consistent with previous measurements acquired from the ground and from the Hubble Space Telescope (HST), but the signal-to-noise ratio is lower than that of the Phobos data. The spectral contrast between the two moons is similar to that seen in HST and Phobos 2 data. Mars Pathfinder measurements therefore substantiate recent results which indicate that Phobos and Deimos are not, as previously believed, analogous to C-type asteroids. They also provide some indications for an absorption near 700 nm, perhaps like that seen in other low-albedo asteroids. Both Martian moons are redder than most asteroids, and most closely resemble two analog materials believed to have undergone very dissimilar histories: primitive D-like asteroids, and highly space-weathered, mafic-rich assemblages, such as are present in lunar mare soils.
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observations of Phobos deimos and bright stars with the imager for mars pathfinder
Journal of Geophysical Research, 1999Co-Authors: N Thomas, Kenneth E Herkenhoff, D T Britt, S L Murchie, Boris Semenov, H U Keller, P H SmithAbstract:The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to 1 μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm)−1 and 9.6(±0.6)% (100 nm)−1, respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10–15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement.