366 research outputs found
Librations and Obliquity of Mercury from the BepiColombo radio-science and camera experiments
A major goal of the BepiColombo mission to Mercury is the determination of
the structure and state of Mercury's interior. Here the BepiColombo rotation
experiment has been simulated in order to assess the ability to attain the
mission goals and to help lay out a series of constraints on the experiment's
possible progress. In the rotation experiment pairs of images of identical
surface regions taken at different epochs are used to retrieve information on
Mercury's rotation and orientation. The idea is that from observations of the
same patch of Mercury's surface at two different solar longitudes of Mercury
the orientation of Mercury can be determined, and therefore also the obliquity
and rotation variations with respect to the uniform rotation. The estimation of
the libration amplitude and obliquity through pattern matching of observed
surface landmarks is challenging. The main problem arises from the difficulty
to observe the same landmark on the planetary surface repeatedly over the MPO
mission lifetime, due to the combination of Mercury's 3:2 spin-orbit resonance,
the absence of a drift of the MPO polar orbital plane and the need to combine
data from different instruments with their own measurement restrictions. By
assuming that Mercury occupies a Cassini state and that the spacecraft operates
nominally we show that under worst case assumptions the annual libration
amplitude and obliquity can be measured with a precision of respectively 1.4
arcseconds (as) and 1.0 as over the nominal BepiColombo MPO lifetime with about
25 landmarks for rather stringent illumination restrictions. The outcome of the
experiment cannot be easily improved by simply relaxing the observational
constraints, or increasing the data volume.Comment: 30 pages, 6 figures, 2 table
On the eve of the 100th anniversary of IAU Commission 19/A2 âRotation of the Earthâ
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugĂ€nglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.IAU Commission 19 began in 1919 with the birth of the IAU at the Brussels Conference, where Standing Committee 19 on Latitude Variations was established as one of 32 standing committees. At the first IAU General Assembly in 1922, Standing Committee 19 became Commission 19 âVariation of Latitudeâ. In the beginning, the main topic of the Commission was the investigation of polar motion. Later, its activities included observations and theory of Earth rotation and connections between Earth orientation variations and geophysical phenomena. As a result, in 1964 at the XII IAU General Assembly, the Commission was renamed âRotation of the Earthâ. The investigation of Earth orientation variations is primarily based on observations of natural and artificial celestial objects. Therefore, maintenance of the international terrestrial and celestial reference frames, as well as the coordinate transformation between the frames and the improvement of the model of precession/nutation, have always been among the primary Commission topics. In 1987, the IAU through Commissions 19 and 31 âTimeâ established, jointly with the International Union of Geodesy and Geophysics, what is now known as the International Earth Rotation and Reference Systems Service. Commission 19 continued to work to develop methods to improve the accuracy and understanding of Earth orientation variations and related reference systems and frames as well as theoretical studies of Earth rotation. In 2015, Commission 19 was renewed as Commission A2 âRotation of the Earthâ continuing Commission 19âs functions and linking the astronomical community to other scientific organizations such as the International Association of Geodesy, International VLBI Service for Geodesy and Astrometry, International GNSS Service, International Laser Ranging Service and International DORIS Service. During its entire history, IAU Commission 19/A2 has always worked in close cooperation with these and other related services to improve the accuracy and consistency of the Earth orientation parameters and celestial and terrestrial reference frames
Universal-SBAS: A worldwide multimodal standard
This paper describes a generalisation of the aeronautical GNSS Space Based Augmentation System (SBAS) air interface, in a true worldwide multimodal standard named Universal S-BAS. Examples of usages of this multifrequency future standard are presented in the area of science and precise positioning, timing, security, robust positioning, maritime and reflectometry applications
Planetary Exploration Horizon 2061 Report, Chapter 3: From science questions to Solar System exploration
This chapter of the Planetary Exploration Horizon 2061 Report reviews the way
the six key questions about planetary systems, from their origins to the way
they work and their habitability, identified in chapter 1, can be addressed by
means of solar system exploration, and how one can find partial answers to
these six questions by flying to the different provinces to the solar system:
terrestrial planets, giant planets, small bodies, and up to its interface with
the local interstellar medium. It derives from this analysis a synthetic
description of the most important space observations to be performed at the
different solar system objects by future planetary exploration missions. These
observation requirements illustrate the diversity of measurement techniques to
be used as well as the diversity of destinations where these observations must
be made. They constitute the base for the identification of the future
planetary missions we need to fly by 2061, which are described in chapter 4.
Q1- How well do we understand the diversity of planetary systems objects? Q2-
How well do we understand the diversity of planetary system architectures? Q3-
What are the origins and formation scenarios for planetary systems? Q4- How do
planetary systems work? Q5- Do planetary systems host potential habitats? Q6-
Where and how to search for life?Comment: 107 pages, 37 figures, Horizon 2061 is a science-driven, foresight
exercise, for future scientific investigation
GENESIS: Co-location of Geodetic Techniques in Space
Improving and homogenizing time and space reference systems on Earth and,
more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy
of 1mm and a long-term stability of 0.1mm/year are relevant for many scientific
and societal endeavors. The knowledge of the TRF is fundamental for Earth and
navigation sciences. For instance, quantifying sea level change strongly
depends on an accurate determination of the geocenter motion but also of the
positions of continental and island reference stations, as well as the ground
stations of tracking networks. Also, numerous applications in geophysics
require absolute millimeter precision from the reference frame, as for example
monitoring tectonic motion or crustal deformation for predicting natural
hazards. The TRF accuracy to be achieved represents the consensus of various
authorities which has enunciated geodesy requirements for Earth sciences.
Today we are still far from these ambitious accuracy and stability goals for
the realization of the TRF. However, a combination and co-location of all four
space geodetic techniques on one satellite platform can significantly
contribute to achieving these goals. This is the purpose of the GENESIS
mission, proposed as a component of the FutureNAV program of the European Space
Agency. The GENESIS platform will be a dynamic space geodetic observatory
carrying all the geodetic instruments referenced to one another through
carefully calibrated space ties. The co-location of the techniques in space
will solve the inconsistencies and biases between the different geodetic
techniques in order to reach the TRF accuracy and stability goals endorsed by
the various international authorities and the scientific community. The purpose
of this white paper is to review the state-of-the-art and explain the benefits
of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS
Pre-mission InSights on the Interior of Mars
Abstract The Interior exploration using Seismic Investigations, Geodesy, and Heat Trans-
port (InSight) Mission will focus on Marsâ interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moonâs much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of 3â10Ă relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars
Atmospheric Science with InSight
International audienceIn November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP3), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous in situ missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSightâs sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both ânoiseâ to be decorrelated from the seismic signal and âsignalâ to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars
New constraints on Saturn's interior from Cassini astrometric data
This work has been supported by the European Communityâs Seventh Framework Program (FP7/2007-2013) under grant agreement 263466 for the FP7-ESPaCE project, the International Space Science Institute (ISSI), PNP (INSU/CNES) and AS GRAM (INSU/CNES/INP). The work of R. A. J. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. N.C. and C.M. were supported by the UK Science and Technology Facilities Council (Grant No. ST/M001202/1) and are grateful to them for financial assistance. C.M. is also grateful to the Leverhulme Trust for the award of a Research Fellowship. N.C. thanks the Scientific Council of the Paris Observatory for funding. S. Mathis acknowledge funding by the European Research Council through ERC grant SPIRE 647383
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