The science behind the vision for U.S. space exploration: the value of a human–robotic partnership

The Vision for U.S. Space Exploration offers new opportunities for aggressively increasing the pace of scientific discoveries across the Solar System by empowering an on-site partnership between humans and robotics, enhanced by new technology-enabled capabilities. In particular, the early emphasis of this new Vision will be on development of new scientific activities on the Moon, and later on Mars. Integration of in situ traditional science activities with creative new types of applied scientific research on the Moon and Mars is a key ingredient in the US Vision. The Apollo era record of achievement involving human exploration is particularly informative, as it demonstrates the accelerated pace of scientific discovery and understanding that resulted from human “on site” activities, however briefly, on planetary surfaces. An example of how integrated human and robotic exploration can enable breakthrough science on the planet Mars is provided in order to illustrate these points. The scientific opportunities associated with the Vision for US Space Exploration are many, and with the incorporation of human-based capabilities on the Moon and Mars, an accelerated pace of discovery and understanding will be possible.     

In Situ Biological Contamination Studies of the Moon: Implications for Planetary Protection and Life Detection Missions

NASA and ESA have outlined visions for solar system exploration that will include a series of lunar robotic precursor missions to prepare for, and support a human return to the Moon, and future human exploration of Mars and other destinations, including possibly asteroids. One of the guiding principles for exploration is to pursue compelling scientific questions about the origin and evolution of life. The search for life on objects such as Mars will require careful operations, and that all systems be sufficiently cleaned and sterilized prior to launch to ensure that the scientific integrity of extraterrestrial samples is not jeopardized by terrestrial organic contamination. Under the Committee on Space Research’s (COSPAR’s) current planetary protection policy for the Moon, no sterilization procedures are required for outbound lunar spacecraft, nor is there a different planetary protection category for human missions, although preliminary COSPAR policy guidelines for human missions to Mars have been developed. Future in situ investigations of a variety of locations on the Moon by highly sensitive instruments designed to search for biologically derived organic compounds would help assess the contamination of the Moon by lunar spacecraft. These studies could also provide valuable “ground truth” data for Mars sample return missions and help define planetary protection requirements for future Mars bound spacecraft carrying life detection experiments. In addition, studies of the impact of terrestrial contamination of the lunar surface by the Apollo astronauts could provide valuable data to help refine future Mars surface exploration plans for a human mission to Mars.     

The Scientific Case For A Human Spaceflight Infrastructure

I argue that science stands to benefit from the infrastructure developed to support a human space programme. By infrastructure I mean all those facilities and capabilities which purely scientific budgets could never afford to develop, but which nevertheless act to facilitate scientific research which would not otherwise take place. For example, the human presence on the Moon during the Apollo Project resulted in the acquisition of scientific data which would not have been obtained otherwise, and the same is likely to hold true for future human missions to both the Moon and Mars (and indeed elsewhere). In the more distant future, an important scientific application of a well-developed human spaceflight infrastructure may be the construction of interstellar space probes for the exploration of planets around other nearby stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

TOWARDS AN INTEGRATED SCIENTIFIC AND SOCIAL CASE FOR HUMAN SPACE EXPLORATION

I will argue that an ambitious programme of human space exploration, involving a return to the Moon, and eventually human missions to Mars, will add greatly to human knowledge. Gathering such knowledge is the primary aim of science, but science’s compartmentalisation into isolated academic disciplines tends to obscure the overall strength of the scientific case. Any consideration of the scientific arguments for human space exploration must therefore take a holistic view, and integrate the potential benefits over the entire spectrum of human knowledge. Moreover, science is only one thread in a much larger overall case for human space exploration. Other threads include economic, industrial, educational, geopolitical and cultural benefits. Any responsibly formulated public space policy must weigh all of these factors before deciding whether or not an investment in human space activities is scientifically and socially desirable.     

An Overview Of The Origin Of Life: The Case For Biological Prospecting On Mars

Studies of the Earth's earliest biosphere have suggested a close coupling between the evolution of early life forms and the physical and chemical evolution of the planetary surface. From a biological perspective there were many similarities between early Earth and early Mars. This has led to the idea that an origin of life event may have occurred on Mars, leading to the development of microbial life. Various theories have been advanced to explain the origin of life on Earth, and these are reviewed with relevance to Mars. If traces of past or present biogenic activity are to be found on Mars, then the most likely place to prospect is several kilometers below the surface where liquid water might be stable. Such prospecting may best lend itself to human exploration. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Moon and the New Presidential Space Vision

The new US Vision for Space Exploration is briefly described, with particular emphasis on the place of lunar exploration. The value of humans in the exploration of the Moon is discussed, and it is argued that people offer significant advantages over robots for the purposes of scientific exploration. The Vision provides a new rationale for space activities, one aimed at both broadening our knowledge base and, in the longer term, of increasing prosperity by providing access to the material and energy resources of the Solar System.     

The Origin and Evolution of the Atmospheres of Venus, Earth and Mars

The chemical compositions of the primordial atmospheres of Venus, Earth and Mars have long been a topic of debate between the experts. Some believe that the original atmospheres were a product of outgassed volatiles from the newly accreted terrestrial planets and that these atmospheres consisted primarily of carbon dioxide, nitrogen, water vapor and residual hydrogen and helium (e.g., Lewis and Prinn, <it>Planets and their Atmospheres,</it> Academic Press, Orlando, FL, 1984, pp. 62–63, 81–84, 228–231, 383). Still others think the earliest atmospheres were composed of the gas components of the solar nebula from which the solar system formed (i.e., hydrogen, helium, methane, ammonia and water). I consider the latter to be the correct scenario. Presented herein is a proposed mechanism by which the original atmospheres of Venus, Earth and Mars were transformed to atmospheres rich in carbon dioxide and nitrogen. An explanation is proposed for why water is so common on the surface of Earth and so scarce on the surfaces of Venus and Mars. Also presented are the effects the “great impact” (single cataclysmic event that was responsible for producing the Earth–Moon system) had upon the early atmosphere of Earth. The origin, structure and composition of the impacting object are determined through deductive analyses.     

Habitability: from stars to cells

To determine where to search for life in our solar system or in other extrasolar systems, the concept of habitability has been developed, based on the only sample we have of a biological planet—the Earth. Habitability can be defined as the set of the necessary conditions for an active life to exist, even if it does not exist. In astronomy, a habitable zone (HZ) is the zone defined around a sun/star, where the temperature conditions allow liquid water to exist on its surface. This habitability concept can be considered from different scientific perspectives and on different spatial and time scales. Characterizing habitability at these various scales requires interdisciplinary research. In this article, we have chosen to develop the geophysical, geological, and biological aspects and to insist on the need to integrate them, with a particular focus on our neighboring planets, Mars and Venus. Important geodynamic processes may affect the habitability conditions of a planet. The dynamic processes, e.g., internal dynamo, magnetic field, atmosphere, plate tectonics, mantle convection, volcanism, thermo-tectonic evolution, meteorite impacts, and erosion, modify the planetary surface, the possibility to have liquid water, the thermal state, the energy budget, and the availability of nutrients. They thus play a role in the persistence of life on a planet. Earth had a liquid water ocean and some continental crust in the Hadean between 4.4 and 4.0 Ga (Ga: billions years ago), and may have been habitable very early on. The origin of life is not understood yet; but the oldest putative traces of life are early Archean (~3.5 Ga). Studies of early Earth habitats documented in the rock record hosting fossil life traces provide information about possible habitats suitable for life beyond Earth. The extreme values of environmental conditions in which life thrives today can also be used to characterize the “envelope” of the existence of life and the range of potential extraterrestrial habitats. The requirement of nutrients by life for biosynthesis of cellular constituents and for growth, reproduction, transport, and motility may suggest that a dynamic and rocky planet with hydrothermal activity and formation of relief, liquid water alteration, erosion, and runoff is required to replenish nutrients and to sustain life (as we know it). The concept of habitability is very Earth-centric, as we have only one biological planet to study. However, life elsewhere would most probably be based on organic chemistry and leave traces of its past or recent presence and metabolism by modifying microscopically or macroscopically the physico-chemical characteristics of its environment. The extent to which these modifications occur will determine our ability to detect them in astrobiological exploration. Looking at major steps in the evolution of life may help determining the probability of detecting life (as we know it) beyond Earth and the technology needed to detect its traces, be they morphological, chemical, isotopic, or spectral.     

Biochip for astrobiological applications: Investigation of low energy protons effects on antibody performances

Antibody-based micro-arrays instruments are very promising tools for the search for biomarkers in planetary exploration missions. Since such instruments have never been used in this context, it is important to test their resistance to space constraints. In particular, cosmic particles might be deleterious. In the present study, we have investigated the effect of low energy protons (2 MeV) on antibody performances with fluences levels much greater than expected for a typical mission to Mars. We show that these particles do not alter significantly the antibody recognition capability for both free (in solution) and grafted (covalently bound to the support) freeze–dried antibodies. Details of the freeze–dried drying process used to optimize antibody performances during our experiments are also presented.     

A Comparison of Feature Classification Methods for Modeling Solar Irradiance Variation

Physical understanding of total and spectral solar irradiance variation depends upon establishing a connection between the temporal variability of spatially resolved solar structures and spacecraft observations of irradiance. One difficulty in comparing models derived from different data sets is that the many ways for identifying solar features such as faculae, sunspots, quiet Sun, and various types of “network” are not necessarily consistent. To learn more about classification differences and how they affect irradiance models, feature “masks” are compared as derived from five current methods: multidimensional histogram analysis of NASA/National Solar Observatory/Kitt Peak spectromagnetograph data, statistical pattern recognition applied to SOHO/Michelson Doppler Imager photograms and magnetograms, threshold masks allowing for influence of spatial surroundings applied to NSO magnetograms, and “one-trigger” and “three-trigger” algorithms applied to California State University at Northridge Cartesian Full Disk Telescope intensity observations. In general all of the methods point to the same areas of the Sun for labeling sunspots and active-region faculae, and available time series of area measurements from the methods correlate well with each other and with solar irradiance. However, some methods include larger label sets, and there are important differences in detail, with measurements of sunspot area differing by as much as a factor of two. The methods differ substantially regarding inclusion of fine spatial scale in the feature definitions. The implications of these differences for modeling solar irradiance variation are discussed. K.L. Harvey and S.R. Walton are deseased, to whom this paper is dedicated.     

Full Causal Bulk Viscous LRS Bianchi I With Time Varying Constants

In this paper we study the evolution of a LRS Bianchi I Universe, filled with a bulk viscous cosmological fluid in the presence of time varying constants “but” taking into account the effects of a c-variable into the curvature tensor. We find that the only physical models are those which “constants” G and c are growing functions on time t, while the cosmological constant Λ is a negative decreasing function. In such solutions the energy density obeys the ultrastiff matter equation of state i.e. ω = 1.     

Coronal heating by magnetic reconnection

The theory of magnetic reconnection has advanced substantially over the past few years. There now exists a new generation of fast two-dimensional models known as almost-uniform reconnection and nonuniform reconnection, depending on the boundary conditions. Also, we are beginning to explore the uncharted region of three-dimensional reconnection, where regimes of “spine reconnection” and “fan reconnection” have been discovered. Furthermore, part of the coronal heating problem appears to have been solved with recent observational support for the Converging Flux Model in which heating is produced by coronal reconnection driven by footpoint motions.     

Mission design for Human Outer Planet Exploration (HOPE) using a magnetoplasma spacecraft

To send humans beyond Mars, a Human Outer Planet Exploration (HOPE) mission has been studied for new spacecraft concepts and technologies. In this paper, an interplanetary trajectory and a preliminary spacecraft design are presented for the HOPE visit to Callisto, one of Jupiter's moons. To design a round-trip trajectory for the mission, the characteristics of the spacecraft and its trajectories are analyzed. A detailed optimization approach is formulated to utilize a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine with capabilities of variable specific impulse, variable engine efficiency, and engine on-off control. It is mainly illustrated that a 30 MW powered spacecraft can make the mission possible in a 5-year round trip constraint around the year 2045. Trajectories with different power and reactor options are also discussed. The results obtained in this study can be used for formulating an overall concept for the mission.     

Spin evolution of neutron stars in binary systems

I review our understanding of the evolution of the spin periods of neutron stars in binary stellar systems, from their birth as fast, spin-powered pulsars, through their middle life as accretion-powered pulsars, upto their recycling or “rebirth” as spin-powered pulsars with relatively low magnetic fields and fast rotation. I discuss how the new-born neutron star is spun down by electromagnetic and “propeller” torques, until accretion of matter from the companion star begins, and the neutron star becomes an accretion-powered X-ray pulsar. Detailed observations of massive radio pulsar binaries like PSR 1259-63 will yield valuable information about this phase of initial spindown. I indicate how the spin of the neutron star then evolves under accretion torques during the subsequent phase as an accretion-powered pulsar. Finally, I describe how the neutron star is spun up to short periods again during the subsequent phase of recycling, with the accompanying reduction in the stellar magnetic field, the origins of which are still not completely understood.     

Digging Foundations for the ‘Royal Road’

H.N. Russell and Z. Kopal both liked the metaphor of the “Royal Road” to scientific discovery; I discuss which one used it first. I present some personal reminiscences of Professor Kopal and then consider his attitude to the determination of the elements of eclipsing binaries from their observed light changes, comparing it with that of Russell. This leads me to discuss Kopal’s work on the evolution of binary stars and his opposition to the prevailing belief in the importance of mass transfer between the components. Kopal’s attitudes on these matters puzzle me, but I suggest that at least part of his motivation was to act as a critic of “normal science” within the paradigm that most of us have accepted.     

Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies

The Galactic foreground contamination in CMBR anisotropies, especially from the dust component, is not easily separable from the cosmological or extragalactic component. In this paper, some doubts will be raised concerning the validity of the methods used until now to remove Galactic dust emission and will show that none of them achieves its goal. First, I review the recent bibliography on the topic and discuss critically the methods of foreground subtraction: the cross-correlation with templates, analysis assuming the spectral shape of the Galactic components, the “maximum entropy method”, “internal linear combination”, and “wavelet-based high resolution fitting of internal templates”. Second, I analyse the Galactic latitude dependence from WMAP data. The frequency dependence is discussed with data in the available literature. The result is that all methods of subtracting the Galactic contamination are inaccurate. The Galactic latitude dependence analysis or the frequency dependence of the anisotropies in the range 50–250 GHz put a constraint on the maximum Galactic contribution in the power spectrum to be less than ∼ 10% (68% C. L.) for an ∼ 1 degree scale, and possibly higher for larger scales. The origin of most of the signals in the CMBR anisotropies is not Galactic. In any case, the subtraction of the galaxy is not accurate enough to allow a “precision Cosmology”; other sources of contamination (extragalactic, solar system) are also present.     

Advanced Fresnel X-ray telescopes for spectroscopic imaging

We present an effective achromatic imaging technique for diffraction-limited X-ray telescopes. For a common focal length, independent optical sections of the aperture are dedicated to two or more spectral bands and optimized with respect to their efficiency. For this purpose, we introduce the “achromatic gain” of an X-ray hybrid lens. Large-scale segmented and nested apertures provide a promising implementation of that scheme. An optimized numerical example and astrophysical simulations prove its capabilities for an energy range between 6 and 16 keV.     

Atmospheric Losses Under Dust Bombardment in the Ancient Atmospheres

We have considered the new process of atmospheric losses - “sputtering” under bombardment by interplanetary dust. It is demonstrated that “sputtering” due to collisions with the interplanetary dust is an effective way of atmospheric gas loss (10^–4–10^–3 of the dust particles' accreting mass) and that it changes the composition of the atmospheric gases. In calculations we have taken that the dust particles collide elastically with the atoms and molecules of the atmosphere. Estimation of the effects of inelastic collisions was also considered. As a result of these collisions a part of the atmospheric atoms and molecules will have “upward” velocity and enough energy to escape. It was considered that escaping atoms can collide with the atoms of the “main” gas of the upper atmosphere. The atmospheric gas composition is assumed to be just as in the modern Martian atmosphere - the “main” gases in the upper atmosphere were taken to be O and CO₂. In our computations we pay particular attention to the abundance of noble gases in planetary atmospheres since these gases are very important for theories of atmospheric origin. We computed that under “sputtering” by the interplanetary dust, atmospheres were enriched by the “heavy” elements and isotopes in the wide range of the upper atmospheric parameters O/CO₂, T/g (O/CO₂– on the level of homosphere;T is temperature of the exosphere,g is gravitational acceleration). However the loss efficiency for “heavy” gases is relatively high compared to other known gas loss processes. In the case of noble gases for the specific parameters of the upper atmosphere (small T/g ratio; high O/CO₂ on the level of homosphere) we have got the unique result: despite the diffusion separation in the upper atmosphere the loss efficiency of Xe > Kr > Ar. The effect of “sputtering” of the planetary atmospheres was strongest during the early stages of the planetary evolution - when the rate of the dust accretion was intrinsically higher than now because of collisions of planetesimals. In light of the new escape process, the main peculiarities of the noble gases abundance in the planetary atmospheres could be explained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of Solar Wind Events Using Interplanetary Scintillation Remote Sensing 3D Reconstructions and Their Comparison at Mars

Interplanetary Scintillation (IPS) allows observation of the inner heliospheric response to corotating solar structures and coronal mass ejections (CMEs) in scintillation level and velocity. With colleagues at STELab, Nagoya University, Japan, we have developed near-real-time access of STELab IPS data for use in space-weather forecasting. We use a 3D reconstruction technique that produces perspective views from solar corotating plasma and outward-flowing solar wind as observed from Earth by iteratively fitting a kinematic solar wind model to IPS observations. This 3D modeling technique permits reconstruction of the density and velocity structure of CMEs and other interplanetary transients at a relatively coarse resolution: a solar rotational cadence and 10° latitudinal and longitudinal resolution for the corotational model and a one-day cadence and 20° latitudinal and longitudinal heliographic resolution for the time-dependent model. This technique is used to determine solar-wind pressure (“ram” pressure) at Mars. Results are compared with ram-pressure observations derived from Mars Global Surveyor magnetometer data (Crider et al. 2003, J. Geophys. Res. 108(A12), 1461) for the years 1999 through 2004. We identified 47 independent in situ pressure-pulse events above 3.5 nPa in the Mars Global Surveyor data in this time period where sufficient IPS data were available. We detail the large pressure pulse observed at Mars in association with a CME that erupted from the Sun on 27 May 2003, which was a halo CME as viewed from Earth. We also detail the response of a series of West-limb CME events and compare their response observed at Mars about 160° west of the Sun – Earth line by the Mars Global Surveyor with the response derived from the IPS 3D reconstructions.