Vesta's Shape and Morphology Jaumann, R.; Williams, D. A.; Buczkowski, D. L. ...
Science (American Association for the Advancement of Science),
05/2012, Letnik:
336, Številka:
6082
Journal Article
Recenzirano
Vesta's surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass ...wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta's south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta's geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta's unique role as a transitional solar system body.
The Mars Science Laboratory Curiosity rover carries a basalt calibration target for monitoring the performance of the alpha particle X-ray spectrometer. The spectrum acquired on Sol 34 shows ...increased contributions from Mg, S, Cl and Fe relative to laboratory spectra recorded before launch. Mars Hand Lens Imager images confirm changes in the appearance of the surface. Spectra taken on Sols 179 and 411 indicate some loss of the deposited material. The observations suggest deposition of a surface film likely consisting of dust mobilized by impingement of the sky crane’s terminal descent engine plumes with surface fines during Curiosity’s landing. New APXS software has been used to model the thin film that coated the calibration target on landing. The results suggest that a film of about 100nm thickness, and containing predominantly MgO, Fe2O3, SO3, Cl and Na2O could give rise to the observed spectral changes. If this film is also present on the alpha particle sources within the APXS, then its effect is negligible and the terrestrial calibration remains appropriate.
A multispectral analysis of 21 discrete lunar mare deposits within the South Pole‐Aitken basin was undertaken in order to model the general mineralogical composition of farside mare deposits so that ...the near‐ and farside may be compared in terms of magma generation and emplacement. Determination of each deposit's mineralogy was based upon albedo, the 0.75/0.95 μm ratio indicating the presence of a 1.0 μm absorption band, and the strength and shape of that band. A combination of improved spatial resolution and the availability of the general multispectral signature for each pond allowed deposits to be examined for homogeneity in order to assess the nature and number of flows represented. FeO and TiO2 abundances were also estimated. Based upon the resultant data, 19 out of 21 ponds were determined to be mare deposits. Of these 19, 15 had spectra well‐defined enough to classify general mineralogy, nine having high‐Ca pyroxene signatures indicative of basalt and six showing low‐Ca signatures suggesting a substantial noritic component. We believe these noritic signatures can plausibly be attributed to vertical/lateral soil mixing processes for the smallest ponds, although a unique lithology cannot be ruled out for the largest pond. A majority of ponds in this study region have homogeneous spectral signatures, interpreted to represent individual eruptive phases. This indicates that very large volumes for these regions may be typical. Also, because such volumes are comparable to the largest terrestrial eruptions, they may have formed by a similar mechanism of emplacement. The vast majority of mature soils are spectrally redder (and thus have a lower estimated FeO abundance) than the Mare Serenitatis soil standard (MS‐2) in particular, and nearside basalts in general. These soils also average low to medium estimated TiO2 abundance, similar to Apollo 12 and 15, and Luna 24. The observations made here are consistent with a scenario in which basalts with low FeO and low to medium TiO2 contents were deposited during the lunar peak volcanic period that occurred in the Late Imbrian (3.80–3.20 Ga) and because of their small areal extent were more susceptible to mixing processes than nearside basalts.
The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, and operated by Malin Space Science Systems of San Diego, CA. They share common electronics and focal ...plane designs but have different optics. There are two Mastcams of dissimilar focal length. The Mastcam‐34 has an f/8, 34 mm focal length lens, and the M‐100 an f/10, 100 mm focal length lens. The M‐34 field of view is about 20° × 15° with an instantaneous field of view (IFOV) of 218 μrad; the M‐100 field of view (FOV) is 6.8° × 5.1° with an IFOV of 74 μrad. The M‐34 can focus from 0.5 m to infinity, and the M‐100 from ~1.6 m to infinity. All three cameras can acquire color images through a Bayer color filter array, and the Mastcams can also acquire images through seven science filters. Images are ≤1600 pixels wide by 1200 pixels tall. The Mastcams, mounted on the ~2 m tall Remote Sensing Mast, have a 360° azimuth and ~180° elevation field of regard. Mars Descent Imager is fixed‐mounted to the bottom left front side of the rover at ~66 cm above the surface. Its fixed focus lens is in focus from ~2 m to infinity, but out of focus at 66 cm. The f/3 lens has a FOV of ~70° by 52° across and along the direction of motion, with an IFOV of 0.76 mrad. All cameras can acquire video at 4 frames/second for full frames or 720p HD at 6 fps. Images can be processed using lossy Joint Photographic Experts Group and predictive lossless compression.
Key Points
The Mars Descent Imager, an f/3 9.7 mm, 2 M pixel color camera operated autonomously during landing taking a descent video at 4 frames/second
Mastcam‐34 f/8, 34 mm camera takes <1600 × 1200 pixel images in broad and narrowband color over a field 20° × 15° at a scale of 218 μrad/pixel
Mastcam‐100 f/10, 100 mm, f/10 takes <1600 × 1200 pixel images in broad and narrowband color over a field 6.8° × 5.1° at 74 μrad/pixel scale
Plain Language Summary
Paper describes the Mast cameras and Descent Imager on the Mars Science Laboratory Curiosity rover. Cameras take 2 megapixel color images that can be compressed in both JPEG lossy and predictive lossless format. One of the two Mastcams has a 34 mm lens, equivalent to a consumer camera 35 mm lens, and the other has a 100 mm lens, similar to consumer camera telephoto lens. The descent imager has a very wide angle lens (~90°) and takes wide angle pictures. The Mast cameras are mounted on an azimuth elevation mast so they can scan around the rover and into the sky. The Descent camera always points down. The Mast cameras have different filters to allow for scientific color imaging as well as standard color imaging as performed by consumer cameras.
What allows a planet to be both within a potentially habitable zone and sustain habitability over long geologic time? With the advent of exoplanetary astronomy and the ongoing discovery of ...terrestrial-type planets around other stars, our own solar system becomes a key testing ground for ideas about what factors control planetary evolution. Mars provides the solar systems longest record of the interplay of the physical and chemical processes relevant to habitability on an accessible rocky planet with an atmosphere and hydrosphere. Here we review current understanding and update the timeline of key processes in early Mars history. We then draw on knowledge of exoplanets and the other solar system terrestrial planets to identify six broad questions of high importance to the development and sustaining of habitability (unprioritized): (1) Is small planetary size fatal? (2) How do magnetic fields influence atmospheric evolution? (3) To what extent does starting composition dictate subsequent evolution, including redox processes and the availability of water and organics? (4) Does early impact bombardment have a net deleterious or beneficial influence? (5) How do planetary climates respond to stellar evolution, e.g., sustaining early liquid water in spite of a faint young Sun? (6) How important are the timescales of climate forcing and their dynamical drivers? Finally, we suggest crucial types of Mars measurements (unprioritized) to address these questions: (1) in situ petrology at multiple units/sites; (2) continued quantification of volatile reservoirs and new isotopic measurements of H, C, N, O, S, Cl, and noble gases in rocks that sample multiple stratigraphic sections; (3) radiometric age dating of units in stratigraphic sections and from key volcanic and impact units; (4) higher-resolution measurements of heat flux, subsurface structure, and magnetic field anomalies coupled with absolute age dating. Understanding the evolution of early Mars will feed forward to understanding the factors driving the divergent evolutionary paths of the Earth, Venus, and thousands of small rocky extra solar planets yet to be discovered.
In an effort to characterize individual eruptive phases and events, 86 isolated mare deposits (ponds) in the lunar South Pole‐Aitken and Orientale regions were analyzed to obtain information on ...areas, volumes, and other characteristics. Deposits likely to represent single eruptive episodes have area mean values of ∼2000 km2 in the South Pole‐Aitken Basin and ∼1100 km2 in the Orientale Basin. Pond volumes range from 35 to 8745 km3, with a mean value of 860 km3 for South Pole‐Aitken, and 10 to 1280 km3, with a mean value of 240 km3 for the Orientale region. No evidence was found for shallow crustal magma reservoirs. The relatively common occurrence of sinuous rilles in Orientale is consistent with very high effusion rates, and the large volumes of individual eruptive episodes (tens to many hundreds of km3) are comparable to flood basalt eruption volumes on Earth. Pond morphologies are consistent with extrusion from deep, probably subcrustal reservoirs. Distribution of deposits suggests that many ponds may be derived from single reservoirs. Comparison of ponds in both basins shows a higher areal density and average volume of lava ponds in the South Pole‐Aitken basin relative to the Orientale area. This is plausibly attributed to the extreme depths of the South Pole‐Aitken basin and the correspondingly thinner crust there relative to the Orientale region. These observations are consistent with magma ascent and eruption mechanisms that are strongly dependent on the overpressurization of deep‐seated source regions, the subsequent propagation of dikes, and the thickness of the intervening lunar crust through which these dikes must rise.
•We introduce the geologic mapping of Vesta Special Issue/Section of Icarus.•A geologic mapping campaign for Vesta was included as part of the Dawn Nominal Mission.•Geologic mapping of small airless ...bodies presents challenges not found on other planets.•We review the papers submitted for this Special Issue/Section.•We include a list of lessons learned from the mapping of Vesta, applicable to future missions.
The purpose of this paper is to introduce the Geologic Mapping of Vesta Special Issue/Section of Icarus, which includes several papers containing geologic maps of the surface of Vesta made to support data analysis conducted by the Dawn Science Team during the Vesta Encounter (July 2011–September 2012). In this paper we briefly discuss pre-Dawn knowledge of Vesta, provide the goals of our geologic mapping campaign, discuss the methodologies and materials used for geologic mapping, review the global geologic context of Vesta, discuss the challenges of mapping the geology of Vesta as a small airless body, and describe the content of the papers in this Special Issue/Section. We conclude with a discussion of lessons learned from our quadrangle-based mapping effort and provide recommendations for conducting mapping campaigns as part of planetary spacecraft nominal missions.
The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument onboard NASA’s
Perseverance
rover. SHERLOC combines imaging ...via two cameras with both Raman and fluorescence spectroscopy to investigate geological materials at the rover’s Jezero crater field site. SHERLOC requires
in situ
calibration to monitor the health and performance of the instrument. These calibration data are critically important to ensure the veracity of data interpretation, especially considering the extreme martian environmental conditions where the instrument operates. The SHERLOC Calibration Target (SCT) is located at the front of the rover and is exposed to the same atmospheric conditions as the instrument. The SCT includes 10 individual targets designed to meet all instrument calibration requirements. An additional calibration target is mounted inside the instrument’s dust cover. The targets include polymers, rock, synthetic material, and optical pattern targets. Their primary function is calibration of parameters within the SHERLOC instrument so that the data can be interpreted correctly. The SCT was also designed to take advantage of opportunities for supplemental science investigations and includes targets intended for public engagement. The exposure of materials to martian atmospheric conditions allows for opportunistic science on extravehicular suit (i.e., “spacesuit”) materials. These samples will be used in an extended study to produce direct measurements of the expected service lifetimes of these materials on the martian surface, thus helping NASA facilitate human exploration of the planet. Other targets include a martian meteorite and the first geocache target to reside on another planet, both of which increase the outreach and potential of the mission to foster interest in, and enthusiasm for, planetary exploration. During the first 200 sols (martian days) of operation on Mars, the SCT has been analyzed three times and has proven to be vital in the calibration of the instrument and in assisting the SHERLOC team with interpretation of
in situ
data.
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