5,602 research outputs found
A Side of Mercury Not Seen By Mariner 10
More than 60,000 images of Mercury were taken at ~29 deg elevation during two
sunrises, at 820 nm, and through a 1.35 m diameter off-axis aperture on the
SOAR telescope. The sharpest resolve 0.2" (140 km) and cover 190-300 deg
longitude -- a swath unseen by the Mariner 10 spacecraft -- at complementary
phase angles to previous ground-based optical imagery. Our view is comparable
to that of the Moon through weak binoculars. Evident are the large crater
Mozart shadowed on the terminator, fresh rayed craters, and other albedo
features keyed to topography and radar reflectivity, including the putative
huge ``Basin S'' on the limb. Classical bright feature Liguria resolves across
the northwest boundary of the Caloris basin into a bright splotch centered on a
sharp, 20 km diameter radar crater, and is the brightest feature within a
prominent darker ``cap'' (Hermean feature Solitudo Phoenicis) that covers the
northern hemisphere between longitudes 140-250 deg. The cap may result from
space weathering that darkens via a magnetically enhanced flux of the solar
wind, or that reddens low latitudes via high solar insolation.Comment: 7 pages, 4 PDF figures, pdfLaTeX, typos corrected, Fig. 2 modified
slightly to add crater diameters not given in published versio
SkyMapper Southern Survey: First Data Release (DR1)
We present the first data release (DR1) of the SkyMapper Southern Survey, a
hemispheric survey carried out with the SkyMapper Telescope at Siding Spring
Observatory in Australia. Here, we present the survey strategy, data
processing, catalogue construction and database schema. The DR1 dataset
includes over 66,000 images from the Shallow Survey component, covering an area
of 17,200 deg in all six SkyMapper passbands , while the full area
covered by any passband exceeds 20,000 deg. The catalogues contain over 285
million unique astrophysical objects, complete to roughly 18 mag in all bands.
We compare our point-source photometry with PanSTARRS1 DR1 and note an
RMS scatter of 2%. The internal reproducibility of SkyMapper photometry is on
the order of 1%. Astrometric precision is better than 0.2 arcsec based on
comparison with Gaia DR1. We describe the end-user database, through which data
are presented to the world community, and provide some illustrative science
queries.Comment: 31 pages, 19 figures, 10 tables, PASA, accepte
The three-dimensional structure of Saturn's E ring
Saturn's diffuse E ring consists of many tiny (micron and sub-micron) grains
of water ice distributed between the orbits of Mimas and Titan. Various
gravitational and non-gravitational forces perturb these particles' orbits,
causing the ring's local particle density to vary noticeably with distance from
the planet, height above the ring-plane, hour angle and time. Using
remote-sensing data obtained by the Cassini spacecraft in 2005 and 2006, we
investigate the E-ring's three-dimensional structure during a time when the Sun
illuminated the rings from the south at high elevation angles (> 15 degrees).
These observations show that the ring's vertical thickness grows with distance
from Enceladus' orbit and its peak brightness density shifts from south to
north of Saturn's equator plane with increasing distance from the planet. These
data also reveal a localized depletion in particle density near Saturn's
equatorial plane around Enceladus' semi-major axis. Finally, variations are
detected in the radial brightness profile and the vertical thickness of the
ring as a function of longitude relative to the Sun. Possible physical
mechanisms and processes that may be responsible for some of these structures
include solar radiation pressure, variations in the ambient plasma, and
electromagnetic perturbations associated with Saturn's shadow.Comment: 42 Pages, 13 Figures, modified to include minor proof correction
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