131 research outputs found
Dawn arrives at Ceres: Exploration of a small, volatile-rich world
On 6 March 2015, Dawn arrived at Ceres to find a dark, desiccated surface punctuated by small, bright areas. Parts of Ceres’ surface are heavily cratered, but the largest expected craters are absent. Ceres appears gravitationally relaxed at only the longest wavelengths, implying a mechanically strong lithosphere with a weaker deep interior. Ceres’ dry exterior displays hydroxylated silicates, including ammoniated clays of endogenous origin. The possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits, lobate flows of materials, and a singular mountain that appears to be an extrusive cryovolcanic dome. On one occasion, Ceres temporarily interacted with the solar wind, producing a bow shock accelerating electrons to energies of tens of kilovolts
On the Lense-Thirring test with the Mars Global Surveyor in the gravitational field of Mars
I discuss some aspects of the recent test of frame-dragging performed by me
by exploiting the Root-Mean-Square (RMS) orbit overlap differences of the
out-of-plane component N of the orbit of the Mars Global Surveyor (MGS)
spacecraft in the gravitational field of Mars. A linear fit of the full time
series of the entire MGS data (4 February 1999-14 January 2005) yields a
normalized slope 1.03 +/- 0.41 (with 95% confidence bounds). Other linear fits
to different data sets confirm the agreement with general relativity. The huge
systematic effects induced by the mismodeling in the martian gravitational
field claimed by some authors are absent in the MGS out-of-plane record. The
non-gravitational forces affect at the same level of the gravitomagnetic one
the in-plane orbital components of MGS, not the out-of-plane one. Moreover,
they experience high-frequency variations which does not matter in the present
case in which secular effects are relevant.Comment: LaTex2e, 8 pages, no figures, no tables, 17 references. It refers to
K. Krogh, Class. Quantum Grav., 24, 5709-5715, 2007 based on
astro-ph/0701653. Final version to appear in CEJP (Central European Journal
of Physics
Anomalies of Density, Stresses, and the Gravitational Field in the Interior of Mars
We determined the possible compensation depths for relief harmonics of
different degrees and orders. The relief is shown to be completely compensated
within the depth range of 0 to 1400 km. The lateral distributions of
compensation masses are determined at these depths and the maps are
constructed. The possible nonisostatic vertical stresses in the crust and
mantle of Mars are estimated to be 64 MPa in compression and 20 MPa in tension.
The relief anomalies of the Tharsis volcanic plateau and symmetric feature in
the eastern hemisphere could have arisen and been maintained dynamically due to
two plumes in the mantle substance that are enriched with fluids. The plumes
that originate at the core of Mars can arise and be maintained by the anomalies
of the inner gravitational field achieving +800 mGal in the region of plume
formation, - 1200 mGal above the lower mantle-core transition layer, and -1400
mGal at the crust.Comment: 9 pages, 5 figure
The Dawn Gravity Investigation at Vesta and Ceres
The objective of the Dawn gravity investigation is to use high precision X-band Doppler tracking and landmark tracking from optical images to measure the gravity fields of Vesta and Ceres to a half-wavelength surface resolution better than 90-km and 300-km, respectively. Depending on the Doppler tracking assumptions, the gravity field will be determined to somewhere between harmonic degrees 15 and 25 for Vesta and about degree 10 for Ceres. The gravity fields together with shape models determined from Dawn's framing camera constrain models of the interior from the core to the crust. The gravity field is determined jointly with the spin pole location. The second degree harmonics together with assumptions on obliquity or hydrostatic equilibrium may determine the moments of inertia
Dawn arrives at Ceres: Exploration of a small, volatile-rich world
On 6 March 2015, Dawn arrived at Ceres to find a dark, desiccated surface punctuated by small, bright areas. Parts of Ceres’ surface are heavily cratered, but the largest expected craters are absent. Ceres appears gravitationally relaxed at only the longest wavelengths, implying a mechanically strong lithosphere with a weaker deep interior. Ceres’ dry exterior displays hydroxylated silicates, including ammoniated clays of endogenous origin. The possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits, lobate flows of materials, and a singular mountain that appears to be an extrusive cryovolcanic dome. On one occasion, Ceres temporarily interacted with the solar wind, producing a bow shock accelerating electrons to energies of tens of kilovolts
Gravity Recovery and Interior Laboratory (GRAIL) Mission: Status at the Initiation of the Science Mapping Phase
The Gravity Recovery And Interior Laboratory (GRAIL) mission, a component of NASA's Discovery Program, launched successfully from Cape Canaveral Air Force Station on September 10, 2011. The dual spacecraft traversed independent, low-energy trajectories to the Moon via the EL-1 Lagrange point and inserted into elliptical, 11.5-hour polar orbits around the Moon on December 31, 2011, and January 1, 2012. The spacecraft are currently executing a series of maneuvers to circularize their orbits at 55-km mean altitude. Once the mapping orbit is achieved, the spacecraft will undergo additional maneuvers to align them into mapping configuration. The mission is on track to initiate the Science Phase on March 8, 2012
Revised Thickness of the Lunar Crust from GRAIL Data: Implications for Lunar Bulk Composition
High-resolution gravity data from GRAIL have yielded new estimates of the bulk density and thickness of the lunar crust. The bulk density of the highlands crust is 2550 kg m-3. From a comparison with crustal composition measured remotely, this density implies a mean porosity of 12%. With this bulk density and constraints from the Apollo seismic experiment, the average global crustal thickness is found to lie between 34 and 43 km, a value 10 to 20 km less than several previous estimates. Crustal thickness is a central parameter in estimating bulk lunar composition. Estimates of the concentrations of refractory elements in the Moon from heat flow, remote sensing and sample data, and geophysical data fall into two categories: those with refractory element abundances enriched by 50% or more relative to Earth, and those with abundances the same as Earth. Settling this issue has implications for processes operating during lunar formation. The crustal thickness resulting from analysis of GRAIL data is less than several previous estimates. We show here that a refractory-enriched Moon is not require
Advancing Tests of Relativistic Gravity via Laser Ranging to Phobos
Phobos Laser Ranging (PLR) is a concept for a space mission designed to
advance tests of relativistic gravity in the solar system. PLR's primary
objective is to measure the curvature of space around the Sun, represented by
the Eddington parameter , with an accuracy of two parts in ,
thereby improving today's best result by two orders of magnitude. Other mission
goals include measurements of the time-rate-of-change of the gravitational
constant, and of the gravitational inverse square law at 1.5 AU
distances--with up to two orders-of-magnitude improvement for each. The science
parameters will be estimated using laser ranging measurements of the distance
between an Earth station and an active laser transponder on Phobos capable of
reaching mm-level range resolution. A transponder on Phobos sending 0.25 mJ, 10
ps pulses at 1 kHz, and receiving asynchronous 1 kHz pulses from earth via a 12
cm aperture will permit links that even at maximum range will exceed a photon
per second. A total measurement precision of 50 ps demands a few hundred
photons to average to 1 mm (3.3 ps) range precision. Existing satellite laser
ranging (SLR) facilities--with appropriate augmentation--may be able to
participate in PLR. Since Phobos' orbital period is about 8 hours, each
observatory is guaranteed visibility of the Phobos instrument every Earth day.
Given the current technology readiness level, PLR could be started in 2011 for
launch in 2016 for 3 years of science operations. We discuss the PLR's science
objectives, instrument, and mission design. We also present the details of
science simulations performed to support the mission's primary objectives.Comment: 25 pages, 10 figures, 9 table
Gravity, Geodesy and Fundamental Physics with BepiColombo’s MORE Investigation
open40siThe Mercury Orbiter Radio Science Experiment (MORE) of the ESA mission BepiColombo will provide an accurate estimation of Mercury’s gravity field and rotational state, improved tests of general relativity, and a novel deep space navigation system. The key experimental setup entails a highly stable, multi-frequency radio link in X and Ka band, enabling two-way range rate measurements of 3 micron/s at nearly all solar elongation angles. In addition, a high chip rate, pseudo-noise ranging system has already been tested at 1-2 cm accuracy. The tracking data will be used together with the measurements of the Italian Spring Accelerometer to provide a pseudo drag free environment for the data analysis. We summarize the existing literature published over the past years and report on the overall configuration of the experiment, its operations in cruise and at Mercury, and the expected scientific results.openIess L.; Asmar S.W.; Cappuccio P.; Cascioli G.; De Marchi F.; di Stefano I.; Genova A.; Ashby N.; Barriot J.P.; Bender P.; Benedetto C.; Border J.S.; Budnik F.; Ciarcia S.; Damour T.; Dehant V.; Di Achille G.; Di Ruscio A.; Fienga A.; Formaro R.; Klioner S.; Konopliv A.; Lemaitre A.; Longo F.; Mercolino M.; Mitri G.; Notaro V.; Olivieri A.; Paik M.; Palli A.; Schettino G.; Serra D.; Simone L.; Tommei G.; Tortora P.; Van Hoolst T.; Vokrouhlicky D.; Watkins M.; Wu X.; Zannoni M.Iess L.; Asmar S.W.; Cappuccio P.; Cascioli G.; De Marchi F.; di Stefano I.; Genova A.; Ashby N.; Barriot J.P.; Bender P.; Benedetto C.; Border J.S.; Budnik F.; Ciarcia S.; Damour T.; Dehant V.; Di Achille G.; Di Ruscio A.; Fienga A.; Formaro R.; Klioner S.; Konopliv A.; Lemaitre A.; Longo F.; Mercolino M.; Mitri G.; Notaro V.; Olivieri A.; Paik M.; Palli A.; Schettino G.; Serra D.; Simone L.; Tommei G.; Tortora P.; Van Hoolst T.; Vokrouhlicky D.; Watkins M.; Wu X.; Zannoni M
Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and End-Game Status
The Gravity Recovery and Interior Laboratory (GRAIL) [1], NASA s eleventh Discovery mission, successfully executed its Primary Mission (PM) in lunar orbit between March 1, 2012 and May 29, 2012. GRAIL s Extended Mission (XM) initiated on August 30, 2012 and was successfully completed on December 14, 2012. The XM provided an additional three months of gravity mapping at half the altitude (23 km) of the PM (55 km), and is providing higherresolution gravity models that are being used to map the upper crust of the Moon in unprecedented detail
- …