NASA's MESSENGER Mission Research Articles

Measuring the surface abundance of iron and nickel on the asteroid (16) Psyche in the presence of large solar particle events

This work investigates a novel signature for measuring the Ni/Fe ratio on the asteroid (16) Psyche that is robust against interference from large Solar Particle Events. NASA's Psyche mission launched on October 13th, 2023, and is headed to investigate this M-type asteroid. A primary science requirement for the Psyche gamma-ray spectrometer is to measure the absolute surface abundance of Ni and Fe. In particular, the Ni/Fe ratio will help test the hypothesis that (16) Psyche is a metal-rich body, possibly a remnant core from a failed planetesimal. However, Solar Particle Events can activate iron in the spacecraft, as well as the body of Psyche itself, disrupting the measurement of the surface abundance of iron for six months or more. Such an event happened during NASA's MESSENGER mission in orbit around Mercury on June 4, 2011, precluding further mapping of iron for the remainder of the mission. A similar event at Psyche could adversely affect mission science goals and/or prolong operation. Given the expected high abundance of Fe at Psyche, this paper proposes an alternative signature that relies on gamma rays from 54Fe rather than 56Fe. Although 54Fe has a lower natural abundance than 56Fe (5.8% vs 91.7%, respectively), 54Fe is much less susceptible to interference from activation and would allow measurements of the surface abundance of iron to resume within days after a large Solar Particle Event. In addition, 58Ni is shown not to be susceptible to interference from activation, thus making the 58Ni/54Fe ratio a robust alternative signature in the presence of Solar Particle Events.

Sulfides and hollows formed on Mercury's surface by reactions with reducing S-rich gases

The surface of Mercury is enriched in sulfur, with up to 4 wt.% detected by the NASA MESSENGER mission, and has been challenging to understand in the context of other terrestrial planets. We posit, that magmatic S was mobilized as a gas phase in volcanic and impact processes near the surface, exposing silicates to a hot S-rich gas at reducing conditions and allowing conditions for rapid gas-solid reactions. Here, we present novel experiments on the reaction of Mercury composition glasses with reduced S-rich gas, forming Ca- and Mg-sulfides. The reaction products provide porous and fragile materials that create previously enigmatic hollows on Mercury. Our model predicts that the gas-solid reaction forms Ca-Mg-Fe-Ti-sulfide assemblages with SiO2 and aluminosilicates, distinct from formation as magmatic minerals. The ESA/JAXA BepiColombo mission to Mercury will allow this hypothesis to be tested.

The Strangest Terrestrial Planet

NASA's MESSENGER mission previously revealed that Mercury has a volcanic crust; now it finds evidence for an inner “anticrust.”

Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2

The Mercury Laser Altimeter on the NASA MESSENGER mission has ranged to several ridges and lobate scarps during two equatorial flybys of the planet Mercury. The tectonic features sampled, like others documented by spacecraft imaging and Earth-based radar, are spatially isolated and have vertical relief in excess of 1 km. The profiles also indicate that the faulting associated with their formation penetrated to tens of kilometers depth into the lithosphere and accommodated substantial shortening. To gain insight into the mechanism(s) of strain accommodation across these structures, we perform analytical and numerical modeling of representative dynamic localization mechanisms. We find that ductile localization due to shear heating is not favored, given our current understanding of thermal gradients and shallow thermal structure of Mercury at the time of ridge and scarp formation, and is likely to be of secondary importance at best. Brittle localization, associated with loss of resistance during fault development or with velocity weakening during sliding on mature faults, is weakly localizing but permits slip to accumulate over geological time scales. The range of shallow thermal gradients that produce isolated faults rather than distributed fault sets under the assumption of modest fault weakening is consistent with previous models for Mercury’s early global thermal history. To be consistent with strain rates predicted from thermal history models and the amount of shortening required to account for the underlying large-offset faults, ridges and scarps on Mercury likely developed over geologically substantial time spans.

Mercury's surface and composition to be studied by BepiColombo

We describe the contributions that we expect the BepiColombo mission to make towards increased knowledge and understanding of Mercury's surface and composition. BepiColombo will have a larger and more capable suite of instruments relevant for determination of the topographic, physical, chemical and mineralogical properties of the surface than carried by NASA's MESSENGER mission. We anticipate that the insights gained into the planet's geological history and its current space weathering environment will enable us to understand the relationships between surface composition and the composition of different types of crust. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to better constraints on models for Mercury's origin and the nature of the material from which it formed.

Messenger: Volcanic Mercury

Mercury, while resembling the Moon, has much more volcanism apparent at the surface, and a rich collection of species in the plasma of its magnetosphere, according to first results from NASA's Messenger mission. And there's a mystery, too: there appears to be much less iron in these rocks than expected.

Impact of Ion Energy and Species on Single Event Effects Analysis

Experimental evidence and Monte-Carlo simulations for several technologies show that accurate SEE response predictions depend on a detailed description of the variability of radiation events (e.g., nuclear reactions), as opposed to the classical single-valued LET parameter. Rate predictions conducted with this simulation framework exhibit excellent agreement with the average observed SEU rate on NASA's MESSENGER mission to Mercury, while a prediction from the traditional IRPP method, which does not include the contribution from ion-ion reactions, falls well below the observed rate. While rate predictions depend on availability of technology information, the approach described here is sufficiently flexible that reasonably accurate results describing the response to irradiation can be obtained even in the absence of detailed information about the device geometry and fabrication process.

Venus atmospheric circulation: Known and unknown

After a pause of more than two decades, Venus' atmosphere is being explored again. Since April 2006, European Space Agency's Venus Express has been acquiring data, exploiting the near‐infrared windows that allow us to peer into the deep night‐side atmosphere. In June 2007, NASA's MESSENGER mission will fly past Venus on its way to Mercury, collecting useful data for a few weeks. Instruments and experiments on Venus Express are expected to provide a more comprehensive set of atmospheric observations over three and perhaps more Venus days. Venus Express observations are already providing clues about the processes that maintain the rapid circulation of Venus' atmosphere. The early observations show not only that the global circulation is organized into two hemispheric vortices centered over respective poles, but also that the vortex organization extends deep into the atmosphere. The limited Galileo NIMS near‐infrared observations in 1989 had revealed the deep circulation in the equatorial regions, but because of the spacecraft, flyby trajectory could not observe the high latitudes to elucidate the polar circulation and its organization. The long hiatus in systematic Venus observations has provided an opportunity to perform some new analysis of the previous Pioneer Venus observations. This paper presents a synopsis of the circulation measurements at high latitudes and an analysis of the solar thermal tides seen in the cloud motions and suggests some limitations of previous estimates of transport of angular momentum by eddies.

The BepiColombo Laser Altimeter (BELA): Concept and baseline design

The BepiColombo Laser Altimeter (BELA) has been selected for flight on board the European Space Agency's BepiColombo Mercury Planetary Orbiter (MPO). The experiment is intended to be Europe's first planetary laser altimeter system. Although the proposed system has similarities to the Mercury Laser Altimeter (MLA) currently flying on board NASA's MESSENGER mission to Mercury, the specific orbit and construction of the MPO force the use of novel concepts for BELA. Furthermore, the base-lined range-finding approach is novel. In this paper, we describe the BELA system and show preliminary results from some prototype testing.

Surface-Exosphere-Magnetosphere System Of Mercury

Mercury is a poorly known planet, since the only space-based information comes from the three fly-bys performed in 1974 by the Mariner 10 spacecraft. Ground-based observations also provided some interesting results, but they are particularly difficult to obtain due to the planet’s proximity to the Sun. Nevertheless, the fact that the planet’s orbit is so close to the Sun makes Mercury a particularly interesting subject for extreme environmental conditions. Among a number of crucial scientific topics to be addressed, Mercury’s exosphere, its interaction with the solar wind and its origin from the surface of the planet, can provide important clues about planetary evolution. In fact, the Hermean exosphere is continuously eroded and refilled by these interactions, so that it would be more proper to consider the Hermean environment as a single, unified system – surface-exosphere-magnetosphere. These three parts are indeed strongly linked to each other. In recent years, the two missions scheduled to explore the iron planet, the NASA MESSENGER mission (launched in March 2004) and the ESA cornerstone mission (jointly with JAXA) BepiColombo (to be launched in 2012), have stimulated new interest in the many unresolved mysteries related to it. New ground-based observations, made possible by new technologies, have been obtained, and new simulation studies have been performed. In this paper some old as well as the very latest observations and studies related to the surface-exosphere-magnetosphere system are reviewed, outlining the investigations achievable by the planned space-based observations. This review intends to support the studies, in preparation of future data, and the definition of specific instrumentation.