The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described

Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere

Exploring the smallest terrestrial planet: Dawn at Vesta

Dawn maps the surface of Vesta and Ceres and probes their internal density distributions, during one year of orbital operations at each body. Dawn carries a framing camera, a visible and infrared spectrometer (VIR), a gamma ray and neutron spectrometer (GRaND), and determines their gravity fields. The camera maps the surface in color, and obtains stereo data to derive global topography models. VIR determines the mineral composition of the surface and GRaND determines the elemental composition. Dawn maps from three science orbits at altitudes of ~2700 km, ~700 km, and ~200 km. Thus far, we have surveyed for moons around Vesta, accurately determined Vesta’s mass, refined the rotation axis, and have preliminary information on surface features and composition. The existence of abundant meteorites on Earth that came from Vesta or Vesta-derived material provides deep insight into geochemistry of Vesta, albeit without geologic context. We expect our Vesta data to provide that missing geologic context for the Howardite, Eucrite and Diogenite (HED) meteorites. According to the ages of the HED meteorites, Vesta formed in the solar system’s first few million years. Vesta likely accreted close to the time of a supernova explosion that provided short-half-life radionuclides supplying sufficient heat to melt Vesta, drive off the water and allow differentiation and formation of an iron core. Vesta is the second most massive asteroid in the main belt. It is thought to have a large impact structure surrounding its south pole. Initial observations with Dawn are not inconsistent with this hypothesis, but the terrain is unlike other impact basins. Outside this structure, the surface is heavily cratered. Vesta’s albedo is higher than most other asteroids, the Moon and Mercury. Vesta’s compositional diversity is more similar to the Moon and Mercury than other asteroids and it possesses a global 1-micron spectral feature due to ferrous iron absorption, which appears only locally on other airless bodies, and in stark contrast to Mercury where it is absent. In this and the following talks, we discuss current understanding of this complex body and what it teaches us about the earliest days of the solar system

Exploring the smallest terrestrial planet: Dawn at Vesta

The Dawn mission is designed to map Vesta and Ceres from polar orbit for close to one year each. The ion-propelled Dawn spacecraft is illustrated in Figure 1. Dawn carries a framing camera with clear and color filters, a visible and infrared mapping spectrometer, a gamma ray and neutron spectrometer, and obtains radiometric data on the gravity field. The camera obtains stereo imagery from which a global shape and topography model are derived. The mapping spectrometer determines the mineral composition of the surface and the gamma and neutron spectrometer determines the elemental composition. As Dawn approaches Vesta, as illustrated in Figure 2, it measures the rotational characteristics of the body to determine the orientation of the rotation axis. This in turn determines when solar illumination reaches the north pole and when mapping can be completed. As shown in Figure 3, there are three science orbits: Survey at a radial distance of 3000 km and a period of 69 hr; high-altitude mapping at a radial distance of 950 km and a period of 12.3 hr; and low-altitude mapping at a radius of 465 km and a period of 4 hours. Vesta is the ultimate source of the HED meteorites from which much has been learned about their parent body. By the time of this presentation we will have surveyed the region around Vesta for moons, determined a much more accurate mass and rotation axis for Vesta, and have preliminary information on surface features and composition from the survey orbit

Dawn Discovery Mission: A journey to the beginning of the solar system

In December 2001, NASA announced the selection of the Dawn mission to Vesta and Ceres as the next mission to be undertaken in the Discovery series. Dawn examines the role of size and water content in planetary evolution, contrasting the primitive and apparently wet protoplanet, Ceres, with its dry and highly evolved neighbor, Vesta. Dawn maps the surface in visible and infrared wavelengths to determine its mineralogical composition and crustal properties, uses gamma ray and neutron spectroscopy to determine its elemental composition and magnetometry and radio science to probe the interior and laser altimetry to provide precise topography. Dawn is a partnership between UCLA, representing the science team members, the Jet Propulsion Laboratory, Orbital Sciences Corporation, the German Aerospace Center, DLR and the Italian Institute for Space Astrophysics, IAS. The mission uses ion propulsion to fly to Vesta, orbit it at a variety of altitudes for close to a year, leave Vesta orbit, fly to Ceres and orbit it similarly. The spacecraft carries a framing camera provided by DLR’s Institute of Space Sensor Technology and Planetary Exploration in Berlin; a mapping spectrometer provided by the Istituto di Astrofisica Spaziale in Roma, a gamma ray and neutron spectrometer provided by the Los Alamos National Laboratory, a laser altimeter provided by NASA’s Goddard Space Flight Center and a magnetometer provided by UCLA. This paper summarizes the mission goals, and the trajectory, orbits, and instruments that enable the mission to attain those goals

DAWN : A journey to the beginning of the solar system

Dawn, NASA's ninth Discovery mission, is scheduled to launch on May 27, 2006 on a journey that will take it into orbit about the two most massive asteroids 4 Vesta and 1 Ceres. Dawn's goal is to understand the conditions and processes present at the solar system's earliest epoch, and the role of water content and size in planetary evolution. To this end Dawn carries a framing camera, a mapping spectrometer, a laser altimeter, a gamma-ray/neutron spectrometer, a magnetometer and a gravity investigation. Dawn uses solar arrays to power its xenon ion engine that provides thrust at an efficiency that is ten times greater than chemical rockets provide. Dawn is a partnership between UCLA, JPL, and the American, German and Italian space agencies

Vesta: Exploration, Predictions, and Surprises

Introduction: The Dawn mission (led by PI Chris Russell) has been selected for implementation and will launch in 2006. It will arrive at Vesta in July 2010 and explore that protoplanet in detail for about a year before leaving for Ceres. Although samples believed to have originated from Vesta (HEDs) have been well studied in Earthbased laboratories, this is the first time in history we will have the opportunity to actually test what we think we have learned from these stones from the sky. Certainly some predictions will prove to be wrong, and overlooked and unexpected details will surprise us. In order to sharpen our skills in preparation for the year at Vesta it is worthwhile to examine and re-examine what we “know” and what we might find. Examples are given here, but we hope the community will be motivated to seriously probe ongoing and new issues. Ancient Differentiated Body: We naturally expect to find some of the oldest basalt flows of the solar system (4.5 Ga). We may also find source areas to be volcanoes or rifts. Alternatively, the closest basaltic analogue may turn out to be the heavily cratered southern highlands of Mars. Large craters and basins (such as at Vesta’s south pole) will have exposed the lower crust and perhaps mantle, thus providing the stratigraphy of this differentiated protoplanet. Such a geologic context will resolve with certainty the relationship between Eucrites and Diogenites. More importantly, it will identify and characterize other (unsampled?) rock types that constrain Vesta’s geologic evolution. Predictions are welcomed. Remanent Magnetic Field: Vesta is expected to have a core that also formed early. Although a currently active dynamo is not likely, any remanent magnetic signature frozen in by the quickly cooled protoplanet will certainly be detected. Assuming the 4.5Ga age of ALH84001 represents the age of the ancient Martian crust, then the crust of Vesta and Mars are roughly contemporaneous, and Vesta presents an exceptional laboratory with which to study early magnetization processes. Fresh Surface: The strong ferrous absorption bands observed in Vesta’s optical spectrum have long been interpreted to indicate the surface is relatively fresh, or unweathered by the solar wind and space environment. This is hard to reconcile with the growing evidence that significant spaceweathering has occurred on other, smaller asteroids (Eros, Gaspra). If a recent large impact event has resurfaced the upper few millimeters of the surface, such an event will be readily apparent from orbit. Alternatively, if an unexpectedly strong magnetic field is observed, it might protect the surface from interaction with much of the solar wind. Moons of Vesta: Given the suite of small Vestoids associated with Vesta (Binzel and Xu., Science,260,1993, 186), it is possible, if not probable, that several moonlets will be seen as we approach the protoplanet. Larger moonlets conceivably might be detected prior to arrival at Vesta using adaptive optics with modern large telescopes

A Strategy for Exploring the Asteroid Belt with Ion Propulsion: Status of the Dawn Mission

The largest asteroids are survivors from the earliest days of the formation of the solar system and by and large have escaped the heavy bombardment period largely unscathed. Moreover, these largest bodies should have remained closest to their points of origin. Thus a strategy of visiting the largest bodies in the main belt could tell us much about the original compositional gradient in the solar system and hence the temperature and pressure gradient that produced it. The Dawn mission explores the two most massive main belt asteroids 4 Vesta and 1 Ceres at 2.34 and 2.77 AU respectively. These bodies are very different. Vesta has an equatorial diameter of about 520 km and is covered with basaltic flows whereas Ceres is close to 1000 km in diameter and has a shape and density consistent with a rocky core covered by a thick ice (˜100 km) shell. The third most massive main belt asteroid, 2 Pallas, lies at the same distance as Ceres with the same size of Vesta but a much lower density. However, since it orbits at a high inclination it is quite inaccessible. The fourth most massive asteroid is 10 Hygiea at 3.12 AU. Much less is known about Hygiea than the other three asteroids but it is sufficiently further out that we might expect as much a difference between Hygiea and Ceres as we see between Ceres and Vesta, perhaps indicating how organic molecules were radially distributed. Another significant body in this region is 16 Psyche that appears to be the iron core of a much larger original body. This too would make an attractive target for an asteroid mission. In fact it is possible using the latest advances in ion engines to design a mission like Dawn that could visit both these bodies

Exploring the asteroid belt with ion propulsion: Dawn mission history, status and plans

In this report, we describe the journey Dawn has taken in the recent past, its present status, and its future mission. The overall objective of Dawn is to explore backward in time via its observations of the primitive bodies, Vesta and Ceres. Thus Dawn embarks on three journeys. The first is its tumultuous temporal terrestrial trek during development. The second is its soon-to-be voyage in space to 4 Vesta, the second most massive asteroid in the main belt, and to 1 Ceres, the most massive. The third is its journey backward in time to infer the conditions as the solar system was formed. Finally, we discuss how it is possible to go back even further in time, beyond the horizon of the Dawn mission to obtain “pre Dawn” observations at 10 Hygiea, the fourth most massive asteroid, and one more primitive than Vesta and Ceres