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NASA NTRS2000

A Network Mission: Completing the Scientific Foundation for the Exploration of Mars

Despite recent setbacks and vacillations in the Mars Surveyor Program, in many respects the exploration of Mars has historically followed a relatively logical path. Early fly-bys provided brief glimpses of the planet and paved the way for the initial orbital reconnaissance of Mariner 9. The Viking orbiters completed the initial survey, while the Viking landers provided our first close-up look at the surface. Essentially, Mars Pathfinder served a similar role, giving a brief look at another place on the surface. And finally, Mars Global Surveyor (and the up-coming orbital mission in 2001) are taking the next step in providing in-depth, global observations of many of the fundamental characteristics of the planet, as well as selected high-resolution views of the surface. With this last step we are well on our way to acquiring the global scientific context that is necessary both for understanding Mars in general, its origin and evolution, and for use as a basis to plan and execute the next level of focused investigations. However, even with the successful completion of these missions this context will be incomplete. Whereas we now know a great deal about the surface of Mars in a global sense, we know very little about its interior, even at depths of only a meter or so. Also, as most of this information has been acquire by remote sensing, we still lack much of the bridging knowledge between the global view and the processes and character of the surface environments themselves. Thus, in many ways we lack sufficient fundamental understanding to intelligently cast the critical investigations into important questions of the origins and evolution of Mars in general, and in particular, life. The next step in building our understanding of Mars has been identified by several previous groups who were charged with creating a strategy for Mars exploration (e.g., COMPLEX, MarSWG, Planetary Roadmap Team). This is a so-called "network" mission, which places a large number of science platforms simultaneously on the surface.

W. B. Banerdt↗

NASA NTRS1973

Cartographic products from the Mariner 9 mission

Simultaneous acquisition of geodetic, cartographic, geologic, and other scientific data on Mars from Mariner 9 required extensive modification of conventional methods of mapping. Preliminary evaluation of all data simultaneously generated an inordinately large number of interim cartographic products for a final cartographic atlas of Mars. The selection of the scales at which Mars would be mapped, the projections to be used, and the way the planet would be divided into quadrangles was based on the resolution of Mariner 9 pictures and upon the resources available over the lifetime of the Mariner Mars 1971 Project.

Batson, R. M.↗

DOE OSTI2020

A giant planet candidate transiting a white dwarf

Astronomers have discovered thousands of planets outside the Solar System1, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. During the red giant phase, any close-orbiting planets will be engulfed by the star2, but more distant planets can survive this phase and remain in orbit around the white dwarf3,4. Some white dwarfs show evidence for rocky material floating in their atmospheres5, in warm debris disks6,7,8,9 or orbiting very closely10,11,12, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted13. Recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets14 demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. So far, no intact planets have been detected in close orbits around white dwarfs. Here we report the observation of a giant planet candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4 days. We observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. The planet candidate is roughly the same size as Jupiter and is no more than 14 times as massive (with 95 per cent confidence). Other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. In this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. Instead, our findings for the WD 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

The Martian atmosphere - Mariner 9 television experiment progress report.

Atmospheric phenomena appearing in the Mariner 9 television pictures are discussed in detail. The surface of the planet was heavily obscured by a global dust storm during the first month in orbit. Brightness data during this period can be fitted by a semi-infinite scattering and absorbing atmosphere model with a single-scattering albedo in the range 0.70-0.85. This low value suggests that the mean radius of the particles responsible for the obscuration was at least 10 microns. By the end of the second month, this dust storm had largely dissipated, leaving a residual optical depth of about 0.1. Much of the region north of 45 deg N was covered by variable clouds comprising the north polar hood.

Leovy, C. B.↗

NASA NTRS1973

Verification of performance of the Mariner 9 television cameras.

The large volume of picture data produced by the Mariner 9 Television Experiment, in addition to providing a description of the planet Mars, emphasizes the need for in situ verification of camera performance. Such data provide the basis for initial quantitative image interpretation by confirmation of the relevance of preflight measurement. This information must be the result of planned calibration sequences rather than extraction from nominal mission photography. A lack of sufficient numbers of frames restricted Mariner camera verifications to only limited operational modes under optimal conditions and required significant extrapolation over the duration of the mission. The evidence does suggest that measurable photometric changes occurred, whereas agreement with preflight data is observed for other parameters.

Thorpe, T. E.↗

NASA NTRS1984

Questions for the geologic exploration of Venus

Venus is the last terrestrial planet to be mapped in the Solar System. This is an indication not of its relative importance for comparative planetary studies but of the previous lack of demonstrated, affordable technology. Venus is, in fact, the most important planet to study for improving our understanding of global terrestrial processes such as plate tectonics. The next NASA mission to Venus, in 1988, will map the planet at a resolution comparable to that of the Mars Mariner 9 mission. The objective is 70 percent coverage at 1 km per line pair or better. This is the minimum resolution that will allow analysis of tectonic, volcanic, aeolian, meteorite impact and other features. An altimeter will provide a global map of topography that will considerably improve our data base and, together with gravity field measurements, provide better interior geophysical models.

Saunders, R. S.↗

NASA NTRS1987

The Magellan mission to Venus

The Magellan mission will be the next NASA mission to Venus. This paper describes the mission as it is currently planned, showing how the design of the science payload, the spacecraft, and the mission satisfies the science objectives and requirements as well as other programmatic constraints. The Magellan mission is dedicated to obtaining SAR images of at least 70 percent of the surface of Venus at a resolution of 1 km per line-pair, or better, which is comparable to the coverage and resolution of the Mars Mariner 9 mission. Other investigations will study the geophysical characteristics of the planet using altimetric data and gravity field measurements, and measurements to determine global surface emissivity.

Dallas, S. S.↗

NASA NTRS1972

Viewing Phobos and Deimos for navigating Mariner 9.

A new on-board optical navigation data technique has been successfully demonstrated on Mariner 9. Science TV pictures of Phobos and Deimos against star fields were used in the real time navigation process to insert Mariner 9 into orbit about Mars. Real time and post flight evaluation results have shown that the satellite/star data taken by Mariner 9 was more accurate than preflight analysis indicated. In fact the orbital insertion phase of the mission could have been achieved using only optical data to determine encounter parameters. The use of a science TV camera to obtain this data was successfully demonstrated. Stars as dim as 9th magnitude were detected and measurement accuracies of 3 arc sec (1 sigma) were achieved. The success of the optical navigation techniques developed for Mariner 9 has placed a new class of demanding missions (e.g., multiple outer planet, satellite tour, etc) within realized navigation capability.

Duxbury, T. C.↗

NASA NTRS1974

Comparison of the far ultraviolet spectra of Venus and Mars

Both Venus and Mars have largely CO2 atmospheres and as a result should be similar above the turbopause. Thus it is of interest to compare the far ultraviolet spectra of the two planets, both for similarities and for differences. A comparison between the Mariner 9 ultraviolet spectra of Mars and a spectrum of the total disk of Venus obtained from a sounding rocket is described. Data in the 1240- to 1800-A were used. Both the absolute and the relative intensities were compared.

Moos, H. W.↗

NASA NTRS1974

Salt weathering on Mars

Mariner 9 photographs of Mars indicate that significant erosion has occurred on that planet. Although several possible erosion mechanisms have been proposed, most terrestrial weathering mechanisms cannot function in the present Martian environment. Salt weathering, believed to be active in the Antarctic dry valleys, is especially suited to Mars, given the presence of salts and small amounts of water. Volcanic salts are probably available, and the association of salts and water is likely from both thermodynamic and geologic considerations.

Malin, M. C.↗

NASA NTRS1984

The Venus radar mapper mission

The Venus Radar Mapper (VRM) Mission, in 1988, will be the next NASA mission to Venus. This paper describes the mission as it is currently planned, showing how the design of the science payload, the spacecraft, and the mission satisfies the science objectives and requirements as well as other programmatic constraints. The VRM mission is dedicated to obtaining Synthetic Aperture Radar (SAR) images of at least 70 percent of the surface of Venus at a resolution of 1 km per line pair or better (comparable to the coverage and resolution of the Mars Mariner 9 mission). Additional investigations will study the interior geophysical characteristics of the planet using altimetric data and gravity field measurements of the planet.

Dallas, S. S.↗

NASA NTRS1960

The Limiting Sizes of the Habitable Planets

The astrobiological problem of the occurrence of life in the universe is discussed from the standpoint of the size and nature of planets upon which living organisms might arise. The conclusion is tentatively drawn that the most likely radius of a habitable planet lies between 10(exp 8) cm and 2 x 10(exp 9) cm. Conditions of temperature and density also bear upon the occurrence of life; thus the moon and Mercury, although both fall within the range of favorable radii, are nevertheless believed uninhabited by indigeneous life.

Huang, Su-Shu↗

NASA NTRS1994

Periodic Comet Shoemaker-Levy 9 (1993e)

Jupiter will be bombarded by the debris of P/Shoemaker-Levy 9 that populated the comet's west-southwestern trail.

impact events Periodic Comet Shoemaker-Levy 9 Jupi↗

NASA NTRS2013

The Martian Dust Cycle: Observations and Modeling

The dust cycle is critically important for Mars' current climate system. Suspended atmospheric dust affects the radiative balance of the atmosphere, and thus greatly influences the thermal and dynamical state of the atmosphere. Evidence for the presence of dust in the Martian atmosphere can be traced back to yellow clouds telescopically observed as early as the early 19th century. The Mariner 9 orbiter arrived at Mars in November of 1971 to find a planet completely enshrouded in airborne dust. Since that time, the exchange of dust between the planet's surface and atmosphere and the role of airborne dust on Mars' weather and climate has been studied using observations and numerical models. The goal of this talk is to give an overview of the observations and to discuss the successes and challenges associated with modeling the dust cycle. Dust raising events on Mars range in size from meters to hundreds of kilometers. During some years, regional storms merge to produce hemispheric or planet encircling dust clouds that obscure the surface and raise atmospheric temperatures by tens of kelvin. The interannual variability of planet encircling dust storms is poorly understood. Although the occurrence and season of large regional and global dust storms are highly variable from one year to the next, there are many features of the dust cycle that occur year after year. A low-level dust haze is maintained during northern spring and summer, while elevated levels of atmospheric dust occur during northern autumn and winter. During years without global-scale dust storms, two peaks in total dust loading are generally observed: one peak occurs before northern winter solstice and one peak occurs after northern winter solstice. Numerical modeling studies attempting to interactively simulate the Martian dust cycle with general circulation models (GCMs) include the lifting, transport, and sedimentation of radiatively active dust. Two dust lifting processes are commonly represented in these models: wind-stress lifting (i.e., saltation) and dust devil lifting. Although the predicted patterns of dust lifting and atmospheric dust loading from these simulations capture some aspects of the observed dust cycle, there are many notable differences between the simulated and observed dust cycles. For example, it is common for models to predict one peak in global dust loading near northern winter solstice due to excessive dust lifting in the Hellas basin at this season. Additionally, it is difficult for models to realistically capture the observed interannual variability in global dust storms. New avenues of dust cycle modeling research include exploring the effects of finite surface dust reservoirs and the effects of coupling the dust and water cycles on the predicted dust cycle.

Kahre, Melinda A.↗

NASA NTRS1979

Mars gravity field model from Mariner 9, Viking 1 and 2 data

Earth artificial satellite methods are extended by means of two way Doppler data, to the computation of very accurate orbiter trajectories around another planet, and to the determination of its gravity field. It is reported that in the case of Mars, all observations collected by 10 Deep Space Network stations located at three different sites during the Mariner 9 and Viking 1 and 2 missions have been processed and used to compute a full twelfth degree and order spherical harmonic model of the gravitational potential. It is concluded that the aeroid derived from the model shows very large correlations with the Martian topography, raising questions as to the deep structure of the planet which cannot be interpreted on the basis of topographic and isostatic considerations alone.

Balmino, G.↗

NASA NTRS2005

NASA Strategic Roadmap Summary Report

In response to the Vision, NASA commissioned strategic and capability roadmap teams to develop the pathways for turning the Vision into a reality. The strategic roadmaps were derived from the Vision for Space Exploration and the Aldrich Commission Report dated June 2004. NASA identified 12 strategic areas for roadmapping. The Agency added a thirteenth area on nuclear systems because the topic affects the entire program portfolio. To ensure long-term public visibility and engagement, NASA established a committee for each of the 13 areas. These committees - made up of prominent members of the scientific and aerospace industry communities and senior government personnel - worked under the Federal Advisory Committee Act. A committee was formed for each of the following program areas: 1) Robotic and Human Lunar Exploration; 2) Robotic and Human Exploration of Mars; 3) Solar System Exploration; 4) Search for Earth-Like Planets; 5) Exploration Transportation System; 6) International Space Station; 7) Space Shuttle; 8) Universe Exploration; 9) Earth Science and Applications from Space; 10) Sun-Solar System Connection; 11) Aeronautical Technologies; 12) Education; 13) Nuclear Systems. This document contains roadmap summaries for 10 of these 13 program areas; The International Space Station, Space Shuttle, and Education are excluded. The completed roadmaps for the following committees: Robotic and Human Exploration of Mars; Solar System Exploration; Search for Earth-Like Planets; Universe Exploration; Earth Science and Applications from Space; Sun-Solar System Connection are collected in a separate Strategic Roadmaps volume. This document contains memebership rosters and charters for all 13 committees.

Wilson, Scott↗

NASA NTRS2006

Terrestrial Planet Finder Interferometer Technology Status and Plans

A viewgraph presentation on the technology status and plans for Terrestrial Planet Finder Interferometer is shown. The topics include: 1) The Navigator Program; 2) TPF-I Project Overview; 3) Project Organization; 4) Technology Plan for TPF-I; 5) TPF-I Testbeds; 6) Nulling Error Budget; 7) Nulling Testbeds; 8) Nulling Requirements; 9) Achromatic Nulling Testbed; 10) Single Mode Spatial Filter Technology; 11) Adaptive Nuller Testbed; 12) TPF-I: Planet Detection Testbed (PDT); 13) Planet Detection Testbed Phase Modulation Experiment; and 14) Formation Control Testbed.

Terrestrial Planet Finder (TPF)↗

NASA NTRS1974

Exploring the planets with spacecraft - Accomplishments to date

A summary of knowledge gained about Venus, Mars, Jupiter, and Mercury via spacecraft. Mariner and Venera probes returned data on Venus' size, atmospheric structure and composition, temperature profiles, and magnetic field. Knowledge of the clouds is still primitive. Mars and Mariner probes (especially Mariner 9) expanded knowledge of the Martian surface, atmospheric structure and dynamics, and magnetic field. Mars is now viewed as a very active planet, with the possibility of life not immediately ruled out. Pioneer 10 returned data on Jovian temperature profiles and magnetic field, Galilean satellite masses, and Io's atmosphere. Mariner 10 added to knowledge of Mercury's surface, magnetic field, atmosphere, and activity.

Rea, D. G.↗