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ABSTRACT: We have compiled a global catalog of large lunar craters using LOLA
topography. The crater diameter and density data offer important
insights regarding the age of the lunar surface and the history of the
cratering flux in our solar system.
02/2011; 42:1006.
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M. T. Zuber,
D. E. Smith,
G. A. Neumann,
E. Mazarico,
M. H. Torrence, J. W. Head,
O. Aharonson,
O. W. Westbrook,
M. M. Sori,
M. J. Talpe,
I. Garrick-Bethell,
O. S. Barnouin-Jha,
T. C. Duxbury,
F. G. Lemoine,
J. Oberst,
P. G. Lucey
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ABSTRACT: The South Pole-Aitken basin is the largest and oldest impact structure
on the Moon and one of the largest impact basins in the solar system. As
such, it preserves the record of how major impacts disrupt early
planetary crusts and how topography on an airless planet is modified
throughout geologic history by subsequent impacts, volcanism, tectonics,
viscous relaxation and possible internal dynamics. While in the ~30 km x
200 km commissioning orbit of the Lunar Reconnaissance Orbiter, the
Lunar Orbiter Laser Altimeter (LOLA) has collected the
highest-resolution precision topographic data set yet assembled of the
southern hemisphere of the Moon. LOLA maps the lunar surface at a 28-Hz
rate with 5 beams that in the 50-km LRO mapping orbit result in 5-m
spots spaced 50-m apart along track with profiles along a given track
10-12 m apart. These observations enable the most detailed quantitative
morphologic characterization yet possible of a major impact basin. We
compare the structure of the basin floor with that of surrounding
highlands, including the geometric properties of craters within and
exterior to the basin. In addition, we map proposed ring remnants
possible ejecta distributions and characterize deviations from circular
symmetry, interpreting results in the context of basin formation and
modification. We also examine the depth/diameter relationships of
superposed craters to estimate the depth of post-SPA basin subfloor
sampling and mare fill thickness.
AGU Fall Meeting Abstracts. 11/2009; -1:06.
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D. E. Smith,
M. T. Zuber,
G. A. Neumann,
E. Mazarico,
M. H. Torrence,
O. W. Westbrook, J. W. Head,
O. Aharonson,
M. S. Robinson,
J. F. Cavanaugh,
X. Sun,
F. G. Lemoine,
O. S. Barnouin-Jha,
T. C. Duxbury,
J. Oberst,
P. G. Lucey
[show abstract]
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ABSTRACT: The Lunar Orbiter Laser Altimeter (LOLA) was turned on for the first
time in lunar orbit on July 3, 2009 and has been operating almost
continuously since July 13. In the eccentric (~30 km x 200 km)
commissioning orbit, LOLA acquired data over the entire southern
hemisphere and over part of the northern hemisphere during its first
month of operation. During the second month changes to the onboard
software enabled the instrument to operate out to near the apoapsis of
the commissioning orbit, ~190 km altitude, nearly four times higher than
its design specification. LOLA has 5 beams and each illuminates an ~5-m
spot on the lunar surface from the 50-km altitude orbit. The instrument
successfully tracks on the steepest of slopes (>45 degrees) and is
thus well suited for quantitative characterization of rough terrain,
such as crater walls and central peaks. The instrument has successfully
ranged with each of the two laser transmitters, which operate at 10-cm
single-shot precision and at 28 Hz on each of 5 beams. Subsequent to the
software changes to optimize performance in the commissioning orbit, the
instrument has been collecting of order 3.5 million valid topographic
measurements of the southern hemisphere per day with better spatial and
vertical resolution than achieved by any other lunar topographic
investigation. To attain LRO’s orbit determination requirement,
regular ranging from NASA’s Next Generation Satellite Laser
Ranging station (NGSLR) is taking place. Analysis of the Earth-based
laser ranges to LRO indicates a 48-cm single-shot rms range error, or 24
cm with refined calibration.
AGU Fall Meeting Abstracts. 11/2009; -1:05.
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ABSTRACT: Glaciers in Antarctica provide insight into the origin of debris-covered
glaciers on Mars. The Antarctic analogs suggest that the dichotomy
boundary was largely covered with plateau ice fields during parts of the
Amazonian.
02/2009; 40:2355.
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ABSTRACT: Gully fan morphology indicates multiple periods of depositional activity
with date-able secondary craters from a nearby rayed-crater emplaced
during an intermediate period in deposition, which provides a maximum
age for recent activity of this gully.
02/2009; 40:1677.
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ABSTRACT: The internal magnetic field at Mercury is overwhelmingly of core origin,
although small-scale fields of crustal origin may yet be shown to exist.
None of the craters profiled during the MESSENGER flybys exhibit any
magnetic signature.
02/2009; 40:1277.
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L. M. Prockter,
C. R. Chapman,
R. W. Gaskell,
S. C. Solomon,
S. L. Murchie,
O. S. Barnouin-Jha,
M. S. Robinson,
D. T. Blewett,
T. R. Watters, J. W. Head,
J. J. Gillis-Davis
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ABSTRACT: During its first flyby of Mercury in January 2008, MESSENGER viewed a
large portion of the surface of the planet not previously seen by
spacecraft. From high-resolution images obtained during the flyby we are
investigating the geology of the Raditladi basin, a ~~250-km diameter
impact feature located west of the Caloris basin and centered at
27°N, 119°E. On the basis of impact crater density,
approximately an order of magnitude less than is found on smooth plains
to the west of Caloris, Raditladi is thought to be one of the youngest
impact basins on Mercury, with an age of 1-2 Ga or less. Raditladi
contains an interior peak-ring structure ~~125 km in diameter, and its
floor is filled with smooth plains material that clearly embays the
central peak ring. The basin walls have undergone modification, with
terraces most pronounced within the north and west sides of the rim. The
plains are smoother on the eastern and southern side of the basin and
appear to have covered more of the underlying material. This difference
suggests that the fill may be slightly deeper there than elsewhere in
the basin. The plains within the basin floor contain a number of
discontinuous, arcuate, flat-floored troughs, interpreted to be graben.
The graben are arranged in an approximately circumferential pattern
about 70 km in diameter, centered ~~10 km south of the basin center. The
graben represent the only major extension identified on Mercury to date
outside of the Caloris basin. It is likely that the troughs formed as
the result of uplift and extension of the basin floor, but defining the
source of uplift at a relatively recent stage in Mercury's history when
interior cooling models predict a thick, strong lithosphere presents an
interesting challenge. The fill within Raditladi may have a volcanic
origin, as appears to be the case for plains in the nearby Caloris
basin, but an alternative interpretation is that the fill consists of
impact melt. Color analyses are underway to help understand the origin
of the plains material, and further studies of the cratering record,
topography, and geology will elucidate the history of this enigmatic
basin.
AGU Fall Meeting Abstracts. 11/2008; -1:0020.
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N. L. Chabot,
L. M. Prockter,
S. L. Murchie,
M. S. Robinson,
N. R. Laslo,
H. K. Kang,
S. E. Hawkins,
R. M. Vaughan, J. W. Head,
S. C. Solomon,
MESSENGER Team
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ABSTRACT: During MESSENGER's second flyby of Mercury on October 6, 2008, the
Mercury Dual Imaging System (MDIS) will acquire 1287 images. The images
will include coverage of about 30% of Mercury's surface not previously
seen by spacecraft. A portion of the newly imaged terrain will be viewed
during the inbound portion of the flyby. On the outbound leg, MDIS will
image additional previously unseen terrain as well as regions imaged
under different illumination geometry by Mariner 10. These new images,
when combined with images from Mariner 10 and from MESSENGER's first
Mercury flyby, will enable the first regional- resolution global view of
Mercury constituting a combined total coverage of about 96% of the
planet's surface. MDIS consists of both a Wide Angle Camera (WAC) and a
Narrow Angle Camera (NAC). During MESSENGER's second Mercury flyby, the
following imaging activities are planned: about 86 minutes before the
spacecraft's closest pass by the planet, the WAC will acquire images
through 11 different narrow-band color filters of the approaching
crescent planet at a resolution of about 5 km/pixel. At slightly less
than 1 hour to closest approach, the NAC will acquire a 4-column x
11-row mosaic with an approximate resolution of 450 m/pixel. At 8
minutes after closest approach, the WAC will obtain the
highest-resolution multispectral images to date of Mercury's surface,
imaging a portion of the surface through 11 color filters at resolutions
of about 250-600 m/pixel. A strip of high-resolution NAC images, with a
resolution of approximately 100 m/pixel, will follow these WAC
observations. The NAC will next acquire a 15-column x 13- row
high-resolution mosaic of the northern hemisphere of the departing
planet, beginning approximately 21 minutes after closest approach, with
resolutions of 140-300 m/pixel; this mosaic will fill a large gore in
the Mariner 10 data. At about 42 minutes following closest approach, the
WAC will acquire a 3x3, 11-filter, full- planet mosaic with an average
resolution of 2.5 km/pixel. Two NAC mosaics of the entire departing
planet will be acquired beginning about 66 minutes after closest
approach, with resolutions of 500-700 m/pixel. About 89 minutes
following closest approach, the WAC will acquire a multispectral image
set with a resolution of about 5 km/pixel. Following this WAC image set,
MDIS will continue to acquire occasional images with both the WAC and
NAC until 20 hours after closest approach, at which time the flyby data
will begin being transmitted to Earth.
AGU Fall Meeting Abstracts. 11/2008; -1:0014.
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S. C. Solomon,
R. L. McNutt,
B. J. Anderson,
W. V. Boynton,
D. L. Domingue,
L. G. Evans,
R. E. Gold, J. W. Head,
S. M. Krimigis,
S. L. Murchie,
R. J. Phillips,
J. A. Slavin,
M. T. Zuber
[show abstract]
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ABSTRACT: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging
(MESSENGER) spacecraft, developed under NASA's Discovery Program, will
be the first probe to orbit the planet Mercury in March 2011. Launched
in August 2004, MESSENGER successfully completed the first of three
flybys of Mercury in January 2008. The Mercury Dual Imaging System
acquired an 11-color mosaic of part of the hemisphere not seen by
Mariner 10, including the entire Caloris basin; several large monochrome
mosaics at a range of resolutions; a series of color frames designed
for photometric analysis; and inbound and outbound movies. The Mercury
Atmospheric and Surface Composition Spectrometer obtained the first
high-resolution spectral reflectance measurements (at ultraviolet to
near-infrared wavelengths) of surface composition, conducted limb scans
of exospheric species, and mapped the composition and structure of the
tail region. The Magnetometer measured Mercury's internal field at low
latitudes and documented the major plasma boundaries of Mercury's
magnetosphere. The Energetic Particle and Plasma Spectrometer made the
first measurements of low-energy ions in Mercury's magnetosphere. The
Mercury Laser Altimeter carried out the first space altimetric profile
of the planet. Other instruments in the payload provided baseline
measurements that will aid in the interpretation of data from the
mission orbital phase. Together, the MESSENGER flyby observations have
begun to advance our understanding of the innermost planet.
AGU Spring Meeting Abstracts. 04/2008; -1:01.
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ABSTRACT: Fluvial sedimentary features (meander loops, scroll bars, point bar
sequences, and epsilon cross-bedding) indicate a stable delta plain
environment persisted within the Jezero crater lacustrine system during
an interval of the Noachian.
02/2008; 39:1354.
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ABSTRACT: We compare topographic roughness of typical terrains on Mercury, Venus,
the Earth, the Moon, and Mars at the spatial scales from 30 to 200 km.
We specifically discuss differences in heavily cratered terrains on the
Moon, Mercury and Mars.
02/2008; 39:1472.
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ABSTRACT: The first flyby of Mercury by the MESSENGER spacecraft allowed a
near-global assessment of the tectonics of the planet and provided new
constraints on the magnitude and timing of deformation.
02/2008; 39:1300.
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ABSTRACT: Sedimentary deposits that are clearly related to valley networks on Mars
are relatively unusual and have been recognized in only a few locations
on Mars. However, such sediments have the potential to preserve an
excellent record of the surface environment at the time of their
emplacement, including data on the potential habitability of the
surface, which makes them important targets of study for both orbital
and landed missions. An exceptional example of valley network-derived
sedimentary deposits is located in Jezero crater, a ~40-km diameter
impact crater, northwest of the Isidis Basin near the Nili Fossae
(centered at 77.6 E and 18.4 N). Two valleys debouch into this crater
from the west and north, and each valley appears to have deposited a
sedimentary fan. On the eastern end of the crater, an outlet valley is
observed, and based on the elevation of the outlet valley, Jezero crater
must have contained a sizeable lake at one time, with a volume of at
least 250 km3, of comparable volume to terrestrial Lake Tahoe (V ~ 160
km3). The fan deposits have been interpreted as deltaic sediments,
deposited into this lake. New data from MRO and other recent missions
has motivated the reexamination of Jezero crater and its sedimentary
deposits. Meter-scale layering is commonly observed on fan deposits in
HiRISE data. Layers appear to dip gently (<10-15°) and outcrop
in sinuous patterns. Many unconformities are discernable between
packets of the layered material. We interpret these sediments as having
been deposited via lateral accretion during meander migration, with
observed unconformities resulting from numerous channel switching events
on the fan. CRISM visible/near-infrared observations of the fan
materials indicate that where these light- toned, finely-layered packets
of sedimentary material are exposed, they commonly have spectra
consistent with iron-magnesium phyllosilicate. Phyllosilicates are also
found on the Jezero crater interior off the margins of the primary
deposits. Given both the unique geological setting and mineralogy of
the Jezero crater fan materials, it is a prime target for future landed
missions, such as MSL.
AGU Fall Meeting Abstracts. 11/2007; -1:1562.
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ABSTRACT: We present stratigraphic, topographic, and textural relationships
between lineated valley fill (LVF) and lobate debris apron (LDA)
morphological units in Nilosyrtis Mensae as evidence of multiple stages
of glacial overprinting during the recent Amazonian.
02/2007; 38:1384.
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ABSTRACT: We review possible effects of volatile S species under cold climate
conditions. They include surface and sub-ice runoff of aqueous solutions
of sulfuric acid, and, for very cold climate, sulfur dioxide glaciers
and liquid sulfur dioxide runoff.
02/2007; 38:1510.
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ABSTRACT: Gully analogs (Antarctic Dry Valleys) show that top-down melting of
trapped windblown snow is a major water source; meltwater soaks into the
hyporheic zone and travels along the top of the ice table, providing
insight into the origin of Mars gullies.
02/2007; 38:1728.
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ABSTRACT: Most valley networks on Mars appear to have been formed during the
Noachian. However, there are a few locations where valleys incise
younger surfaces, including the Hesperian-aged volcanoes Ceraunius
Tholus and Hecates Tholus (Gulick and Baker, 1990). Both of these
volcanoes are characterized by numerous small radial valleys on their
flanks (widths <~500 m). Ceraunius Tholus also has a set of large
canyons on its north flank that appear qualitatively different from the
smaller features (width ~2 km). The largest of these canyons
originates near the lowest part of the caldera, continues 40 km down the
north flank, and debauches into Rahe Crater (an oblique impact crater)
where it formed a depositional fan. We have been exploring the origin
of these relatively young valley features to help constrain valley
formation mechanism on Mars. Recent study of climate change on Mars
suggests that many low-latitude regions (especially large volcanic
edifices) were periodically the sites of snow accumulation, likely
triggered by variations in spin-axis/orbital parameters. As with
earlier work on Hecates Tholus (Fassett and Head, 2006), numerical
modeling suggests that conductive cooling from intrusions of plausible
geometry within Ceraunius Tholus would provide sufficient surface heat
flux to melt snowpack of a few hundred meters in thickness on these
volcanoes. We interpret this process to have formed the radial valleys.
Due to the geometry of the summit, meltwater would also have accumulated
in the summit caldera, forming a caldera lake of significant volume. It
appears that catastrophic drainage of this summit caldera lake may have
formed the large canyons, in a manner most akin to terrestrial
jökulhaups. The hypothesis that these canyons formed fluvially is
supported by comes from the similarity in the volume of material removed
from the valley and found in its depositional fan (both ~20 km3),
consistent with its formation by a mechanism that was predominantly
erosional. This similarity in volume is likely not what would be
expected if these canyons formed from a volcanic process (e.g., Li and
Robinson, 2001). The presence of both the large canyons and small
radial valleys on Ceraunius Tholus may be related to confluence of two
circumstances, summit snow deposition and volcanic activity, which may
explain why valley formation was occurs only on some volcanoes during
the Hesperian. References Fassett, C.I., Head, J.W., 2006. Valleys on
Hecates Tholus, Mars: origin by basal melting of summit snowpack.
Planet. Space Sci. 54, 370-378. Gulick, V.C., Baker, V.R., 1990. Origin
and evolution of valleys on Martian volcanoes. J. Geophys. Res. 95,
14,325-14,344. Li, H., Robinson, M.S., 2002. Modeling Channel Formation
on Ceraunius Tholus, Mars. AGU Spring Meeting, #P31A-13.
AGU Fall Meeting Abstracts. 11/2006; -1:03.
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ABSTRACT: The LOLA instrument design is similar to those of MOLA on Mars Global
Surveyor and MLA on MESSENGER in cruise to Mercury, but with five laser
beams and five receiver channels. The laser transmitter consists of a
single stage diode-pumped and Q-switched Nd:YAG laser at 1064-nm
wavelength, 2.7-mJ pulse energy, 6-ns pulse width, 28-Hz pulse rate, and
100 ?rad beam divergence angle. A diffractive optic element (DOE), made
of fused silica with an etched-in diffraction pattern, is used to split
the single incident laser beam into five slightly off pointed beams. The
reflected signal is collected by a 14-cm diameter telescope and a
5-optical-fiber array at the focal plane, each sees one of the five
laser spots on the lunar surface and delivers the signal to one of the
five avalanche photodiode (APD). The transmitted laser pulse and the
five received laser pulses are time stamped with respect to the
spacecraft mission elapsed time (MET) using a set of time-to-digital
converters (TDC) at <0.5 ns precision. LOLA also measures the
transmitted and the received pulse energy by integrating the pulse
waveforms. The on board science algorithm running on an embedded
microprocessor autonomously adjust the receiver detection threshold
levels, the detector gain, and to keep the range window tracking the
lunar surface returns. The instrument weighs 12.6 kg and 33 watts of
power. From the 50 km orbit of LRO the five laser beams illuminate 5
spots on the lunar surface, each 5 meters in diameter. The spots are
arranged in a cross-pattern within a 50-meter circle on the lunar
surface and the pattern is oriented such that the along- track motion of
the spacecraft produces 5 parallel profiles of spots approximately 50
meters apart.
AGU Fall Meeting Abstracts. 11/2006; -1:0826.
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ABSTRACT: A remnant of Taylor Glacier ice rests beneath a 40–80 cm thick layer of sublimation till in central Beacon Valley, Antarctica. A vapour diffusion model was developed to track summertime vapour flow within this till. As input, we used meteorological data from installed HOBO data loggers that captured changes in solar radiance, atmospheric temperature, relative humidity, soil temperature, and soil moisture from 18 November 2004–29 December 2004. Model results show that vapour flows into and out of the sublimation till at rates dependent on the non-linear variation of soil temperature with depth. Although measured meteorological conditions during the study interval favoured a net loss of buried glacier ice ([similar]0.017 mm), we show that ice preservation is extremely sensitive to minor perturbations in temperature and relative humidity. Net loss of buried glacier ice is reduced to zero (during summer months) if air temperature (measured 2 cm above the till surface) decreases by 5.5°C (from −7°C to −12°C); or average relative humidity increases by 22% (from [similar]36% to 58%); or infiltration of minor snowmelt equals [similar]0.002 mm day−1. Our model results are consistent with the potential for long-term survival of buried glacier ice in the hyper-arid stable upland zone of the western Dry Valleys.
Antarctic Science 08/2006; 18(03):421 - 428. · 1.56 Impact Factor
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[hide abstract]
ABSTRACT: A global equatorial geotraverse representing ~39% of the surface of
Venus was mapped to test directional and non-directional geological
evolution models. Major units showed global and generally continuous
lateral geological correlation.
02/2006; 37:1366.
