Life on Mars? II. Physical restrictions.

The primary physical factors important to life's evolution on a planet include its temperature, pressure and radiation regimes. Temperature and pressure regulate the presence and duration of liquid water on the surface of Mars. The prolonged presence of liquid water is essential for the evolution and sustained presence of life on a planet. It has been postulated that Mars has always been a cold dry planet; it has also been postulated that early mars possessed a dense atmosphere of CO2 (> or = 1 bar) and sufficient water to cut large channels across its surface. The degree to which either of these postulates is true correlates with the suitability of Mars for life's evolution. Although radiation can destroy living systems, the high fluxes of UV radiation on the martian surface do not necessarily stop the origin and early evolution of life. The probability for life to have arisen and evolved to a significant degree on Mars, based on the postulated ranges of early martian physical factors, is almost solely related to the probability of liquid water existing on the planet for at least hundreds of millions to billions of years.     

The antarctic cold desert and the search for traces of life on Mars

The cryptoendolithic microorganisms that live inside rocks in the frigid Ross Desert of Antarctica can serve as a terrestrial model for what may have happened to life forms on Mars when the planet became dry and cold. Trace fossils of microbial rock colonization exist in Antarctica, and similar structures could ave formed on Mars. In some respects, such trace fossils could be an easier target for life-detection systems than fossils of cellular structures.     

Optical properties of dust and the opacity of the Martian atmosphere

Particulate component of the Mars atmosphere composed by micron-sized products of soil weathering and water ice clouds strongly affects the current climate of the planet. In the absence of a dust storm so-called permanent dust haze with τ ≈ 0.2 in the atmosphere of Mars determines its thermal structure. Dust loading varies substantially with the season and geographic location, and only the data of mapping instruments are adequate to characterize it, such as TES/MGS and IRTM/Viking. In spite of vast domain of collected data, no model is now capable to explain all observed spectral features of dust aerosol. Several mineralogical and microphysical models of the atmospheric dust have been proposed but they cannot explain the pronounced systematic differences between the IR data (τ = 0.05–0.2) and measurements from the surface (Viking landers, Pathfinder) which give the typical “clear” optical depth of τ ≈ 0.5 from one side, and ground-based observations in the UV–visible range showing much more transparent atmosphere, on the other side. Also the relationship between τ₉ and the visible optical depth is not well constrained experimentally so far. Future focused measurements are therefore necessary to study Martian aerosol.     

Spectroscopic observation of Mars

Visible and near-infrared reflectance spectroscopy has proven a powerful tool for exploring the geology of Mars. Most of this data has been obtained from Earth, but the technique is ideally suited to orbital application, as proposed for the U.S. Mars Geoscience/Climatology Orbiter mission. Spectral reflectance in the near-UV and visible is highly diagnostic of ferric-iron mineralogy, and has shown that Fe³⁺ in the ubiquitous bright dust and soil is amorphous or poorly-crystalline. Other iron-oxide minerals, indicative of other modes or episodes of crustal alteration, may be found in spatially localized deposits. Clay minerals (hydroxylated silicates) have diagnostic vibrational absorptions throughout the near-infrared. While some form of bound water and/or OH has been known on Mars for many years, a new result presented here is the identification of structural OH in a dilute or poorly crystalline magnesian clay. Salts such as carbonates, sulfates, and nitrates have not yet been detected in martian soils but have diagnostic spectral features in the 3- to 4-μm region, best suited to Mars-orbital observation. Analysis of reflectance spectra of low-albedo regions is a primary source of evidence for a basaltic or ultramafic crust, with identification of abundant clinopyroxene and possible detection of other mafic minerals. The distinctive near-infrared spectral shape of dark regions indicates that the dark materials commonly consist of relatively unaltered rocks or rock fragments very thinly coated by (or mixed with) bright oxidized material similar to the global dust. Visible and near-infrared reflectance spectroscopy is also a sensitive technique for detecting and analyzing water ice, as has been demonstrated on Mars by observations of the north polar cap.     

Hard X-ray and high-frequency decimetric radio observations of the 4 April 2002 solar flare

Hard X-ray and high frequency decimetric type III radio bursts have been observed in association with the soft X-raysolar flare (GOES class M 6.1) on 4 April 2002 (1532 UT). The flare apparently occurred 6 degrees behind the east limb of the Sun in the active region NOAA 9898. Hard X-ray spectra and images were obtained by the X-ray imager on RHESSI during the impulsive phase of the flare. The Brazilian Solar Spectroscope and Ondrejov Radio Telescopes recorded type III bursts in 800–1400 MHz range in association with the flare. The images of the 3–6, 6–12, 12–25, and 25–50 keV X-ray sources, obtained simultaneously by RHESSI during the early impulsive phase of the flare, show that all the four X-ray sources were essentially at the same location well above the limb of the Sun. During the early impulsive phase, the X-ray spectrum over 8–30 keV range was consistent with a power law with a negative exponent of 6. The radio spectra show drifting radio structures with emission in a relatively narrow (Δf ≤ 200 MHz) frequency range indicating injection of energetic electrons into a plasmoid which is slowly drifting upwards in the corona.     

基于分层介质模型的HF雷达高度计火星回波仿真研究

火星次表层中的水探测是当前深空探测领域中的热门问题之一. 高频(HF)雷达高度计具有较强的穿透能力, 且能同时实现距离和功率测量, 是火星次表层探测的重要手段. 介绍了高频雷达高度计系统的原理和设计, 通过分析高度计电磁脉冲与多层光滑介质之间的相互作用, 得出其回波功 率随时间变化的模型, 并考虑了表面粗糙度对表面回波功率的影响. 选用典型的火星分层介质模型, 对其介电常数特性和高度计回波波形 进行了仿真. 仿真结果表明, 采用高频雷达高度计系统可实现对火星次表 层介电特性垂直廓线的反演, 对火星中水的识别具有重要 作用.      

The implantation of life on Mars: feasibility and motivation.

Environmental conditions on Mars are extremely hostile, and would be destructive to any organisms which might arrive there unprotected to-day. However, it is a biocompatible planet. Its unalterable astrophysical parameters would allow the maintenance of a much thicker, warmer carbon dioxide atmosphere than that which currently exists. Though very cold (averaging about -60 degrees C), highly oxidizing and desiccated, Mars may possess substantial quantities of the materials needed to support life--in particular, water and carbon dioxide. A general scenario for implanting life on Mars would include three main phases: (1) robotic and human exploration to determine whether sufficiently large and accessible volatile inventories are available; (2) planetary engineering designed to warm the planet, release liquid water and produce a thick carbon dioxide atmosphere; and (3) if no indigenous Martian organisms emerge as liquid water becomes available, a program of biological engineering designed to construct and implant pioneering microbial communities able to proliferate in the newly clement, though still anaerobic, Martian environment. The process of establishing an ecosystem, or biosphere, on a lifeless planet is best termed 'ecopoiesis.' This new word, derived from Greek, means 'the making of an abode for life.' It is by no means clear whether ecopoiesis on Mars is scientifically possible or technologically achievable. Thus we urge that it be one of the objectives of space research during the next century to assess the feasibility of ecopoiesis on Mars.     

Scientific objectives and payloads of Tianwen-1, China’s first Mars exploration mission

This paper describes the scientific objectives and payloads of Tianwen-1, China’s first exploration mission to Mars. An orbiter, carrying a lander and a rover, lifted-off in July 2020 for a journey to Mars where it should arrive in February 2021. A suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of Mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. The mission will also investigate Mars climate history. It is expected that Tianwen-1 will contribute significantly to advance our scientific knowledge of Mars.     

γ-ray spectroscopy in Mars orbit during solar proton events

Understanding the evolution of Mars requires determining the composition of the surface and atmosphere of the planet. The European Space Agency’s ExoMars rover mission, which is expected to launch in 2016, is part of the Aurora programme. The instruments on the rover will search for evidence of life on Mars and will map a sub-section of the Martian surface, extracting compositional information. Currently our understanding of the bulk composition (and mineralogy) of Mars relies on orbital data from instruments on-board satellites such as 2001 Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express, in addition to in-situ instrumentation on rovers such as Spirit and Opportunity. γ-ray spectroscopy can be used to determine the composition of Mars, but it has yet to be successfully carried out in-situ on Mars. This study describes some of the results obtained from the γ-ray spectrometer on 2001 Mars Odyssey during solar proton events and discusses whether the increased emissions are useful in γ-ray spectroscopy. The study shows that although increased γ-ray emissions were expected from the Martian surface during a solar proton event, they were not detected from orbit probably due to insufficient signal-to-background. However, this does not preclude the possibility of measuring changes in γ-ray flux corresponding to changes in solar activity on the surface of the planet.     

火星探测的微波遥感技术

从微波遥感的角度出发,综述目前国际上对火星的探测现状,列出对微波遥感探测有影响的火星表层土壤、岩层的结构、分布及其介电特性等参数的已有研究结果,分析对火星地壳表层水(或冰)存在可能性及其分布状态的研究动向.结合地球表面微波遥感技术的最新进展,提出用主动与被动微波遥感探测火星表面浅层土壤物质状态和分层结构的可行性分析,初步研讨了火星表层是否有水(或冰)存在的探测方案.      

Phosphorus as a potential guide in the search for extinct life on Mars.

In contrast to the search for extant organisms, the quest for fossil remains of life on Mars need not be guided by the presence of water and organic compounds on the present surface. An appropriate tracer might be the element phosphorus which is a common constituent of living systems. Utilizing terrestrial analogues, it should preferentially exist in the form of sedimentary calcium phosphate (phosphorites), which would have readily resisted changing conditions on Mars. Moreover, higher ratios of P/Th in phosphorites in comparison to calcium phosphates from magmatic rocks give us the possibility to distinguish them from inorganically formed phosphorus deposits at or close to the Martian surface. Identification of anomalous phosphorus enrichments by remote sensing or in situ analysis could be promising approaches for selecting areas preferentially composed of rocks with remains of extinct life.     

Spectra and time variability of black-hole binaries in the low/hard state

We propose a jet model for the low/hard state of galactic black-hole X-ray sources which explains the energy spectra from radio to X-rays and a number of timing properties in the X-ray domain such as the time lag spectra, the hardening of the power density spectra and the narrowing of the autocorrelation function with increasing photon energy. The model assumes that (i) there is a magnetic field along the axis of the jet, (ii) the electron density in the jet drops inversely proportional to distance, (iii) the jet is “hotter” near its center than at its periphery, and (iv) the electrons in the jet follow a power-law distribution function. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5–2 and cutoff at a few hundred keV, power-law time lags versus Fourier frequency with index 0.8, and an increase of the rms amplitude of variability and a narrowing of the autocorrelation function with increasing photon energy as they have been observed in Cygnus X-1. The spectrum at long wavelengths (radio, infrared, optical) is modeled to come from synchrotron radiation of the energetic electrons in the jet. We find flat to inverted radio spectra that extend from the radio up to about the optical band. For magnetic field strengths of the order 10⁵–10⁶ G at the base of the jet, the calculated spectra agree well in slope and flux with the observations.     

Planetary protection and the search for life beneath the surface of Mars.

The search for traces of extinct and extant life on Mars will be extended to beneath the surface of the planet. Current data from Mars missions suggesting the presence of liquid water early in Mars' history and mathematical modeling of the fate of water on Mars imply that liquid water may exist deep beneath the surface of Mars. This leads to the hypothesis that life may exist deep beneath the Martian surface. One possible scenario to look for life on Mars involves a series of unmanned missions culminating with a manned mission drilling deep into the Martian subsurface (approximately 3Km), collecting samples, and conducting preliminary analyses to select samples for return to earth. This mission must address both forward and back contamination issues, and falls under planetary protection category V. Planetary protection issues to be addressed include provisions stating that the inevitable deposition of earth microbes by humans should be minimized and localized, and that earth microbes and organic material must not contaminate the Martian subsurface. This requires that the drilling equipment be sterilized prior to use. Further, the collection, containment and retrieval of the sample must be conducted such that the crew is protected and that any materials returning to earth are contained (i.e., physically and biologically isolated) and the chain of connection with Mars is broken.     

Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3 Å resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860 Å range of the far ultraviolet. A few nearby stars were observed in the 415–912 Å range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman (1216 Å) and the Lyman limit (912 Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.     

A space radiation shielding model of the Martian radiation environment experiment (MARIE)

The 2001 Mars Odyssey spacecraft was launched towards Mars on April 7, 2001. Onboard the spacecraft is the Martian radiation environment experiment (MARIE), which is designed to measure the background radiation environment due to galactic cosmic rays (GCR) and solar protons in the 20–500 MeV/n energy range. We present an approach for developing a space radiation-shielding model of the spacecraft that includes the MARIE instrument in the current mapping phase orientation. A discussion is presented describing the development and methodology used to construct the shielding model. For a given GCR model environment, using the current MARIE shielding model and the high-energy particle transport codes, dose rate values are compared with MARIE measurements during the early mapping phase in Mars orbit. The results show good agreement between the model calculations and the MARIE measurements as presented for the March 2002 dataset.     

火星探测无人机任务规划与建模分析

利用无人机进行火星探测, 具有探测范围广、可看到地形变化等优点. 介绍了火星探测无人机总体任务规划的情况, 讨论了探测无人机在火星与地球上飞行的区别, 建立了火星探测无人机纵向非线性模型, 并在平衡点对非线性模型进行泰勒展开, 得到线性化模型. 通过对线性模型的进一步分析, 掌握了火星探测无人机的稳态性能及飞行特点.      

Numerical simulations of the radiance from the comet 46P/Wirtanen in the various configurations of the measurements during “Rosetta” mission

The work we present deals with the spectrometric measurements of VIRTIS instrument of the Comet P/Wirtanen planned for the Rosetta mission. This spectrometer can monitor (VIRTIS M channel: 0.250μm – 0.980μm; Δκ=20cm⁻¹; 0.980 – 5.0 μm; Δκ = 5cm⁻¹; VIRTIS H channel: 2.0 μm – 5.0 μm; Δκ=2cm⁻¹) the nucleus and the coma in order to provide a general picture of coma's composition, the production of gas and dust, the relationship of coma production to surface composition and the structure and variation of mineralogy of the nucleus surface. During the mission the observation conditions of the spectroscopic investigation change due to different relative positions spacecraft/comet, and to the different illumination conditions of the surface at various distances of the comet to the Sun. The nucleus surface is continuously modified by the ice sublimation accompanied by gas and dust emission. Consequently the surface also its spectrophotometric properties changes and their monitoring can give a new insight. The important role of simulations is to predict the results of measurements in various experimental condition what, in the future, can help in interpretation of the measured data.

In this paper the first results of our simulation the radiance from the comet in the 0.25–5.0μm spectral range at two distances from the Sun (1AU and 3AU) are shown. The distance between the Rosetta orbiter and the nucleus surface as well as the sun zenith angles are taken into account according to the Rosetta mission phases. In fact the surface and coma properties vary along the comet orbit, and should be taken into account in our calculations. The optical parameters of the dust on the surface (e.g. reflectance) and in the coma (e.g. Q_ext) were calculated from optical constants of possible comet analogues. The thermodynamic parameters of the comet are taken from the models of comet evolution. Through this kind of modelling it is possible to identify the surface characteristics in spectra of the radiation from the surface of nucleus transmitted through the coma loaded with dust and gases.

Even if the “Rosetta mission” is postponed, with the consequence of a target change, we think that our idea and the method used for the simulations can be useful also for the new Rosetta target - the comet 67P/Churyumov Gerasimenko.     

Large-scale impact cratering on the terrestrial planets

Impact cratering as a geologic process on the terrestrial planets is addressed. The crater densities on the Earth and Moon form the basis for a standard flux-time curve, which can be used to date unsampled planetary surfaces and constrain the temporal history of endogenic geologic processes. The attached uncertainties and the shape of the flux curve (a rapid exponential decay for the period 4.6 – 4.0 by, followed by the establishment of a constant fluid by 3.5 – 3.0 by which continues more or less to the present) are such that only very old (3.8 by) and very young ( 1.0 by) surfaces can be dated with some confidence. Dating of intermediate-aged surfaces is more imprecise; a problem which is most significant for the geologic history of Mars.

The cratering mechanics of simple craters are fairly well understood. A transient cavity of roughly parabolic cross-section results from the combined excavation and displacement of the target rocks by the cratering flow-field, which can be approximated by the Z-model derived from shallow-buried explosive events. The walls of the transient crater are unstable and slump inwards, resulting in a final bowl-shaped crater partially filled by breccia. The formation process of larger, shallow complex structures is less well understood. Recent models favor the complete collapse of the initial cavity, with the dynamic uplift of the excavated cavity floor. Regardless of the driving force for uplift, yield strength of the target rocks must be drastically reduced during cavity modification by an, as yet, imprecisely known process.

The formation of large impact basins had a profound effect on planetary evolution. They define the basic tectonic and stratigraphic framework of the Moon and their secondary effects lasted for 10⁸ y. The evidence is less compelling from other planets, but a general feature appears to be the concentration of later endogenic activity in and around basins. On Earth, it is possible that basin-formation contributed to the establishment of the dichotomy between proto-continental and proto-oceanic crusts. The effects of impact continue into recent geologic history and may be linked to major biological changes on Earth, such as at the Cretaceous-Tertiary boundary.     

A mars communication constellation for human exploration and network science

This paper analyses the possibility of exploiting a small spacecrafts constellation around Mars to ensure a complete and continuous coverage of the planet, for the purpose of supporting future human and robotic operations and taking advantage of optical transmission techniques. The study foresees such a communications mission to be implemented at least after 2020 and a high data-rate requirement is imposed for the return of huge scientific data from massive robotic exploration or to allow video transmissions from a possible human outpost.     

Strategies for the future exploration of Mars

While the Viking mission yielded a wealth of scientific information about Mars, many intriguing new questions were raised about its chemical and physical environment. For many reasons, Mars thus continues to be an object of intense scientific interest. In addition, many scenarios for the further exploration of that planet have been advanced in recent years, and there is also keen public interest in future Mars missions. In looking ahead, one important aspect in planning a strategy for the exploration of Mars is whether or not to assume that Mars is a dead planet and also whether it is capable of supporting the growth of terrestrial organisms. Three very different mission strategies are presented here, depending upon how these assumptions are made.