Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
169
result(s) for
"MESSENGER Spacecraft"
Sort by:
Mercury : the view after Messenger
A study of the planet Mercury, particulary after the Messenger mission. The spacecraft was launched in 2004, orbited Mercury 2008-2015, and crashed onto the surface of Mercury in 2015.
Book
Clouds and Hazes of Venus
More than three decades have passed since the publication of the last review of the Venus clouds and hazes. The paper published in 1983 in the Venus book summarized the discoveries and findings of the US Pioneer Venus and a series of Soviet Venera spacecraft (Esposito et al. in Venus, p. 484,
1983
). Due to the emphasis on in-situ investigations from descent probes, those missions established the basic features of the Venus cloud system, its vertical structure, composition and microphysical properties. Since then, significant progress in understanding of the Venus clouds has been achieved due to exploitation of new observation techniques onboard Galileo and Messenger flyby spacecraft and Venus Express and Akatsuki orbiters. They included detailed investigation of the mesospheric hazes in solar and stellar occultation geometry applied in the broad spectral range from UV to thermal IR. Imaging spectroscopy in the near-IR transparency “windows” on the night side opened a new and very effective way of sounding the deep atmosphere. This technique together with near-simultaneous UV imaging enabled comprehensive study of the cloud morphology from the cloud top to its deep layers. Venus Express operated from April 2006 until December 2014 and provided a continuous data set characterizing Venus clouds and hazes over a time span of almost 14 Venus years thus enabling a detailed study of temporal and spatial variability. The polar orbit of Venus Express allowed complete latitudinal coverage. These studies are being complemented by JAXA Akatsuki orbiter that began observations in May 2016. This paper reviews the current status of our knowledge of the Venus cloud system focusing mainly on the results acquired after the Venera, Pioneer Venus and Vega missions.
Journal Article
Dipolarization Regions in Mercury's Magnetosphere: Observation of Flux Pileup and Formation of a Substorm Current Wedge
At the end of its mission, the MESSENGER spacecraft's orbit intersected Mercury's nightside magnetic equator at low altitudes below 420 km, enabling the first in situ observations of this region, where the magnetic field strength is typically sub‐dipolar. We present 5 events from these orbits where MESSENGER encountered Earth‐like dipolarization regions characterized by enhanced field strengths up to 20 nT above the intrinsic planetary field, and an average ≃23% $\\simeq 23\\%$ decrease and ≃44% $\\simeq 44\\%$ increase in plasma proton density and temperature, respectively, for 1–2 min periods, comparable to Hermean substorm timescales. The events span local times of 1.5 hr pre‐ and post‐midnight, and are present from the magnetic equator up to magnetic latitudes of at least 12° $12{}^{\\circ}$ north. Supported by estimates of decreased flux tube entropy during these events, we suggest these dipolarization regions are formed by the pileup of dipolarization fronts and formation of a substorm current wedge.
Journal Article
Calibration, Projection, and Final Image Products of MESSENGER’s Mercury Dual Imaging System
We present an overview of the operations, calibration, geodetic control, photometric standardization, and processing of images from the Mercury Dual Imaging System (MDIS) acquired during the orbital phase of the MESSENGER spacecraft’s mission at Mercury (18 March 2011–30 April 2015). We also provide a summary of all of the MDIS products that are available in NASA’s Planetary Data System (PDS). Updates to the radiometric calibration included slight modification of the frame-transfer smear correction, updates to the flat fields of some wide-angle camera (WAC) filters, a new model for the temperature dependence of narrow-angle camera (NAC) and WAC sensitivity, and an empirical correction for temporal changes in WAC responsivity. Further, efforts to characterize scattered light in the WAC system are described, along with a mosaic-dependent correction for scattered light that was derived for two regional mosaics. Updates to the geometric calibration focused on the focal lengths and distortions of the NAC and all WAC filters, NAC–WAC alignment, and calibration of the MDIS pivot angle and base. Additionally, two control networks were derived so that the majority of MDIS images can be co-registered with sub-pixel accuracy; the larger of the two control networks was also used to create a global digital elevation model. Finally, we describe the image processing and photometric standardization parameters used in the creation of the MDIS advanced products in the PDS, which include seven large-scale mosaics, numerous targeted local mosaics, and a set of digital elevation models ranging in scale from local to global.
Journal Article
Observational evidence of ring current in the magnetosphere of Mercury
The magnetic gradient and curvature drift of energetic ions can form a longitudinal electric current around a planet known as the ring current, that has been observed in the intrinsic magnetospheres of Earth, Jupiter, and Saturn. However, there is still a lack of observational evidence of ring current in Mercury’s magnetosphere, which has a significantly weaker dipole magnetic field. Under such conditions, charged particles are thought to be efficiently lost through magnetopause shadowing and/or directly impact the planetary surface. Here, we present the observational evidence of Mercury’s ring current by analysing particle measurements from MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft. The ring current is bifurcated because of the dayside off-equatorial magnetic minima. Test-particle simulation with Mercury’s dynamic magnetospheric magnetic field model (KT17 model) validates this morphology. The ring current energy exceeds
5
×
10
10
J during active times, indicating that magnetic storms may also occur on Mercury.
Ring currents have been observed in the magnetospheres of Earth, Jupiter, and Saturn. Here, the authors show observational evidence of Mercury’s ring current that is bifurcated because of the dayside off-equatorial magnetic minima.
Journal Article
Low-altitude magnetic field measurements by MESSENGER reveal Mercury's ancient crustal field
Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.
Journal Article
Rationale for BepiColombo Studies of Mercury’s Surface and Composition
BepiColombo has a larger and in many ways more capable suite of instruments relevant for determination of the topographic, physical, chemical and mineralogical properties of Mercury’s surface than the suite carried by NASA’s MESSENGER spacecraft. Moreover, BepiColombo’s data rate is substantially higher. This equips it to confirm, elaborate upon, and go beyond many of MESSENGER’s remarkable achievements. Furthermore, the geometry of BepiColombo’s orbital science campaign, beginning in 2026, will enable it to make uniformly resolved observations of both northern and southern hemispheres. This will offer more detailed and complete imaging and topographic mapping, element mapping with better sensitivity and improved spatial resolution, and totally new mineralogical mapping.
We discuss MESSENGER data in the context of preparing for BepiColombo, and describe the contributions that we expect BepiColombo to make towards increased knowledge and understanding of Mercury’s surface and its composition. Much current work, including analysis of analogue materials, is directed towards better preparing ourselves to understand what BepiColombo might reveal. Some of MESSENGER’s more remarkable observations were obtained under unique or extreme conditions. BepiColombo should be able to confirm the validity of these observations and reveal the extent to which they are representative of the planet as a whole. It will also make new observations to clarify geological processes governing and reflecting crustal origin and evolution.
We anticipate that the insights gained into Mercury’s geological history and its current space weathering environment will enable us to better understand the relationships of surface chemistry, morphologies and structures with the composition of crustal types, including the nature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models for Mercury’s origin including the nature and original heliocentric distance of the material from which it formed.
Journal Article
The Global Magnetic Field of Mercury from MESSENGER Orbital Observations
Magnetometer data acquired by the MESSENGER spacecraft in orbit about Mercury permit the separation of internal and external magnetic field contributions. The global planetary field is represented as a southward-directed, spin-aligned, offset dipole centered on the spin axis. Positions where the cylindrical radial magnetic field component vanishes were used to map the magnetic equator and reveal an offset of 484 ± 11 kilometers northward of the geographic equator. The magnetic axis is tilted by less than 3° from the rotation axis. A magnetopause and tail-current model was defined by using 332 magnetopause crossing locations. Residuals of the net external and offset-dipole fields from observations north of 30°N yield a best-fit planetary moment of 195 ± 10 nanotesla- ${\\mathrm{R}}_{\\mathrm{M}}^{3}\\phantom{\\rule{0ex}{0ex}}$ , where R M is Mercury's mean radius.
Journal Article
Transport and Distribution of Sodium Ions in Mercury's Magnetosphere: Results From Multi‐Fluid MHD Simulations
Mercury is surrounded by a tenuous neutral exosphere composed primarily of sodium atoms, which can be continuously ionized. The production of sodium ions is concentrated on the dayside, and these ions can subsequently be transported to the magnetotail and flanks. MESSENGER spacecraft observations revealed dawn‐dusk asymmetric distributions of sodium ions Na+$N{a}^{+}$ . In this study, we investigate the Na+$N{a}^{+}$circulation, distribution, and its influence on global magnetospheric convection with a two‐fluid MHD model, which is coupled with an empirical sodium exosphere profile as the source of Na+$N{a}^{+}$ . In particular, we aim to investigate if the dawn‐dusk asymmetries in Na+$N{a}^{+}$distributions near the equator can be driven by internal mechanisms within the magnetosphere. Our findings indicate that (a) the observed dawn‐dusk asymmetric Na+$N{a}^{+}$distributions can be driven by the separation of H+${H}^{+}$and Na+$N{a}^{+}$flows, and (b) the Hall‐driven global convection preferentially transporting Na+$N{a}^{+}$ions to the morning sector. Plain Language Summary Mercury's weak magnetic field and proximity to the Sun make its magnetosphere much smaller and more dynamic than Earth's. With no substantial ionosphere, the magnetosphere is dominated by solar wind protons rather than planetary ions. However, Mercury has a tenuous sodium exosphere, and these neutral sodium atoms can become ionized on the dayside. This study uses a two‐fluid MHD model that couples magnetospheric plasma flows with Mercury's neutral sodium exosphere to study the transport and distribution of the sodium ions. It shows the Hall effect and the velocity separation between the proton fluid and sodium fluid can produce dawn‐dusk asymmetric distributions of sodium ions. Key Points Developed a multi‐fluid MHD model to study the dawn‐dusk asymmetric distributions of sodium ions in Mercury's magnetosphere Velocity separation between proton and sodium ion fluids can drive sodium ion dawn‐dusk asymmetric distributions Hall effects can transport more sodium ions to the morning sector
Journal Article
North–South Plasma Asymmetry Across Mercury's Near‐Tail Current Sheet
Among nearly 300 near‐Mercury tail current sheet crossings performed by the MESSENGER spacecraft, we identified 37 traversals of an asymmetric current sheet, wherein the lobe densities on opposite sides differ by a factor of three or more. These asymmetric current sheet crossings primarily occur on the dawnside. A global magnetohydrodynamic (MHD) simulation was found to be in excellent agreement with the observations. The results suggest that the north–south density asymmetry is caused by solar wind entering via an upstream‐connected window in one hemisphere. Furthermore, the Parker spiral interplanetary magnetic field (IMF) controls the near‐tail density asymmetries, whereas Mercury's offset dipole magnetic field controls those in mid‐ or distant‐tail regions. We propose that hemispheric asymmetries in Mercury's magnetospheric convection occur under strong IMF conditions. Plain Language Summary Mercury possesses a small magnetosphere owing to its weak planetary magnetic field and strong interactions with the solar wind in the inner heliosphere. The transport process of the solar wind mass and energy into its magnetosphere remains unclear. Previous MESSENGER observations suggest that although the Earth‐like plasma mantle is detected inside the near‐tail magnetopause in normal IMF magnitudes, it is not a permanent feature of Mercury's magnetosphere. Here we report, for the first time, that solar wind ions can enter deep into the near‐tail region via an upstream‐connected window in one hemisphere and form a density‐asymmetric current sheet under strong IMF conditions. Through MHD simulations, we revealed tail dawn–dusk asymmetries during the transport of solar wind plasma. Advanced data expected from BepiColombo will further improve our understanding of the solar wind–magnetosphere coupling. Key Points North–south asymmetries exist in Mercury's magnetotail Both the interplanetary magnetic field (IMF) BX polarity and intrinsic offset dipole magnetic field control the north–south density asymmetry in Mercury's tail The IMF Parker spiral results in a dawnside preference for the plasma asymmetric current sheet
Journal Article