Mars Observer Research Articles

TES Mapping of Mars' North Seasonal Cap

The Mars Global Surveyor thermal emission spectrometer has made observations of Mars' north polar region for nearly a full martian year. Measurements of bolometric emission and reflectance, as well as brightness temperatures in specific bands synthesized from thermal radiance spectra, are used to track the behavior of surface and atmospheric temperatures, the distribution of condensed CO 2 and H 2O, and the occurrence of dust storms. CO 2 grain size in the polar night is variable in space and time, and is influenced by atmospheric conditions. Some specific locations display concentration of H 2O frost and indicate the presence of long-term water-ice near the surface. Annual budgets of solid CO 2 range up to 1500 kg m −2; preliminary analysis suggests significant transport of energy into latitudes near 70°N during the polar night.

NASA. Goldin quits top space agency post, but his legacy lingers.

NASA. Goldin quits top space agency post, but his legacy lingers.

Tempe Fossae, Mars: A planetary analogon to a terrestrial continental rift?

Tempe Terra, the northeastern part of the Tharsis Region on Mars, is characterized by several extensional structures differing in style and age. The Tempe Fossae, a particularly well‐developed system of graben striking N45°E, have been studied for the first time in detail on the basis of Viking Orbiter imagery and Mars Observer Laser Altimeter (MOLA) topographic data. The graben system appears to be unique in the whole region because of its extent, the remarkable width and depth of the graben, the varying graben pattern, and the associated volcanism. Single graben can be up to 35 km wide and 120 km long, while their depth can reach nearly 3000 m. They typically show an asymmetric architecture, often in halfgraben or step fault style. The graben system widens and changes its style along strike from NE to SW from a single, very deep, and narrow graben to a complex set of several shallower, sinuous graben and halfgraben. Crustal extension was measured in the northeastern part from the observable throw and amounts to 2.5–3.1 km. Volcanic structures can be found at several locations along the graben. In the SW the graben system seems to be connected with the Tempe Terra volcanic province marked by flood basalts and plains volcanism. Craters were counted on volcanic units unaffected by extensional tectonics. Crater statistics indicate an absolute crater model age for the upper end of the extensional deformation of ∼3.5 Ga. The dimensions and the characteristics of the mapped graben system resemble those of terrestrial continental rifts, and a comparison between them and the Kenya Rift reveals striking similarities. Therefore the Tempe Fossae are interpreted as a Martian analog to a continental rift associated with an underlying mantle plume. This hypothesis seems to be supported by recent geophysical models based on topography and gravity data from Mars Global Surveyor which indicate regional uplift for Tempe Terra.

Planetary research in Kazakhstan

The history of planetary research in Kazakhstan is recounted from the 1940s up to now. The beginning of this research effort may be traced back to two renown astrophysicists, V.G. Fessenkov and G.A. Tikhov. For the most part, observational and theoretical programs have been directed towards the study of the major planets, especially Jupiter and Saturn. Occasionally, observations of Mars, the Moon, and of various phenomena of interest in the solar system have also been carried out. During the last few decades, planetary research—as well as research on many other astrophysical topics—has been actively developed at the Fessenkov Astrophysical Institute.

HF radio wave attenuation due to a meteoric layer in the atmosphere of Mars

In the atmosphere of Mars, the effect of an ionospheric layer of meteoric origin on an HF radio wave propagation is investigated. We consider the putative magnesium ion layer which results from the ablation of sporadic meteors from a work recently published. To account for day‐night variability, two electron profiles are considered in an altitude range around 80 km. First we argue that there may be some observational evidence of this magnesium layer in early Mars observations that were not noticed before. Then we study the effect of this ionospheric layer on the attenuation of HF waves. For a propagation path through the ionosphere as envisaged for HF subsurface sounding on future Mars missions, the one‐way attenuation may range from up to 360 dB's at 1.8 MHz and up to 18 dB's at 9 MHz.

Latent outflow activity for western Tharsis, Mars: Significant flood record exposed

Observations permitted by the newly acquired Mars Observer Laser Altimeter data have revealed a system of gigantic valleys northwest of the huge Martian shield volcano, Arsia Mons, in the western hemisphere of Mars (northwestern slope valleys (NSVs)). These features, which generally correspond spatially to gravity lows, are obscured by veneers of materials including volcanic lava flows, air fall deposits, and eolian materials. Geologic investigations of the Tharsis region suggest that the system of gigantic valleys predates the construction of Arsia Mons and its extensive associated lava flows of mainly late Hesperian and Amazonian age and coincides stratigraphically with the early development of the outflow channels that debouch into Chryse Planitia. Similar to the previously identified outflow channels, which issued tremendous volumes of water into topographic lows such as Chryse Planitia, the NSVs potentially represent flooding of immense magnitude and, as such, a source of water for a northern plains ocean.

The water vapor vertical distribution on mars from millimeter transitions of HDO and H 218O

Millimeter observations of Mars were performed in April 1997, near opposition, using heterodyne spectroscopy with the IRAM 30-m antenna at Pico Veleta (Spain). During the observations, the northern latitude of the sub-Earth point was about 24°. The planetocentric longitude of the Sun ( L s) was close to 100°, which corresponds to the beginning of Martian northern summer, when the water vapor abundance is expected to be maximum at high northern latitudes. A strong emission was detected in the 226 GHz transition of HDO at the disk center (latitude=+24°) and around the north pole. The 203 GHz transition of H 2 18O was also unambiguously detected. The thermal profile was retrieved from the simultaneous observation of 12CO(2-1) at 230 GHz, 13CO(2-1) at 220 GHz and 12CO(1-0) at 115 GHz . Using both HDO and H 2 18O transitions, we derive a water vapor content of 52 (+34,−23) pr μm at the disk center and 85 (+30,−33) pr μm at the north pole. These high values are consistent with the seasonal water cycle found by the MAWD Viking data (Jakosky, Haberle, in: H.H. Kieffer, B.M. Jakosly, C.N. Synder, M.S. Mathews (Eds.), Mars, University of Arizona Press, 1992.) in the case of the northern region, but higher than the Viking estimates at low latitude. The water vapor profile was found to be saturated at a level of 9 (+5/−4) km at the disk center and 5 (+3,−2) km at the north pole. These saturation levels are consistent with MAWD Viking data (H.M. Hart, Seasonal changes in the abundance and vertical distribution of water vapor in the atmosphere of Mars, Ph.D. Thesis, University of Colorado, 1989) and with millimeter measurements performed by Clancy et al. (Icarus 122 (1996) 36); they confirm that water is confined to the lower troposphere near aphelion. The quality of our data did not allow us to derive a precise determination of the D/ H Martian ratio, which is found to be, within a factor of 2, equal to 6 times the terrestrial ratio, in agreement with previous measurements.

Mars: The cloud effect on the blue clearing in the Syrtis Major region

We conducted imaging observations of Mars in March 1997 and April 1999; these apparitions were around its northern summer oppositions. Mars showed highly developed clouds that formed the aphelion cloud belt. Comparing the diurnal variations of the apparent contrasts of Syrtis Major to the adjacent bright areas with those of the optical depths of the aphelion clouds over those regions, we conclude that the time when those regions are subject to the morning clouds is around 0900 Martian Local Time (MLT) and that the diurnal variation of the degree of blue clearing strongly depends on the difference between the optical depth of H2O ice clouds over Syrtis Major and that over the adjacent bright area. Moreover, our simple linear regression analyses of the degree of blue clearing to the optical depths of H2O ice clouds suggest that the key region in which the H2O ice cloud optical depth determines the degree of blue clearing is Syrtis Major.

Unacceptable Renewals

Unacceptable Renewals

June 8, 2004: Venus in Transit

A transit of Venus is a relatively rare astronomical event in which the silhouette of Venus is seen to move across the face of the Sun. The phenomenon typically lasts several hours, during which Venus is seen as a small dot against the half-degree angular diameter of the solar disc. The last transit of Venus occurred in 1882; the next will be 8 June 2004. Such transits were once of great importance in astronomy. By observing a transit simultaneously from well separated points on the Earth's surface, astronomers were able to measure, with some degree of accuracy, the crucially important separation of the Earth and the Sun. Knowing this enabled them to convert the relative spacings of the planets indicated by Kepler's laws into absolute interplanetary distances expressed in miles or kilometres. Eli Maor's book presents the general reader with a full account of Venusian transits that covers the history of their observation as well as their significance and the reasons for their rarity. The book is a light and enjoyable read that opens well with an imaginative description of observing the 2004 transit from the hills outside Jerusalem. Following an account of Kepler's prediction of a transit of Mercury in 1631 and its observation by Gassendi, the book moves on to describe the transit of Venus in 1639, giving particular emphasis to the prescient work of Jeremiah Horrocks, the extraordinary young English curate and astronomer who died just two years later at the age of 21. The story, however, really takes off with Edmond Halley's realization, in 1677, that transits of Venus might provide the key to determining distances within the solar system. The details of Halley's method are confined to an appendix, but the central chapters of the book detail the increasingly elaborate efforts that astronomers made to observe transits of Venus up to the time of the 1882 transit, when, due to the impact of new photographic methods, interest in transit observations was waning. By that time the distance to the Sun was known to be about 93 000 000 miles and observations of Mars or the asteroids seemed to offer a better prospect of improved accuracy than further observations of Venus. The story is rounded off by a chapter that describes spurious transit observations (such as that of Vulcan, a planet that was supposed to orbit closer to the Sun than Mercury) and a chapter concerning transits of the Earth seen from Mars, Jupiter and the other outer planets. Maor, who is also the author ofe: The Story of a Number, and various other books, writes clearly and well, but Venus in Transit is not uniformly interesting throughout. The early chapters are generally very good, as is the account of Captain James Cook and theEndeavour's voyage to observe the 1761 transit. But after that I felt my interest flagging somewhat, just as the astronomers of the time seemed to find their own interest diminishing. The closing chapters helped to re-engage my interest, but I did feel that the discussion of the 19th century transits was rather perfunctory and that it would have benefited from more space. Still, these are minor criticisms of a book that I am personally very glad to have read. Venus in Transit will obviously appeal most to those with an interest in astronomy, particularly in its historical aspects. But there is also much that physicists can enjoy in the book and I can easily imagine it as a useful though non-essential addition to many school and college libraries. Robert Lambourne

ISO LWS Observations of Mars—Detection of Rotational Modulation in the Far Infrared

A series of far infrared (FIR) spectra of Mars between 43 and 196 μm was taken with the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). Analysis of these medium-resolution data reveals a rotational modulation of the disk-averaged FIR brightness temperature. The observed variability of ±1.5% in the LWS wavelength range compares favorably with the predictions of a thermophysical model of the martian surface. A surface emissivity of ∼0.90 gives good agreement between the measured and the modeled brightness temperatures and leads to an improved estimate of the LWS photometric calibration uncertainty.

Mid‐Infrared Interferometry on Spectral Lines. I. Instrumentation

The Infrared Spatial Interferometer at University of California, Berkeley has been outfitted with a filter-bank system to allow interferometric observations of mid-infrared spectral lines with very high spectral resolution (λ/Δλ ∼ 105). This paper describes the design, implementation, and performance of the matched 32 channel filter-bank modules, and new spectral-line observations of Mars and IRC +10216 are used to demonstrate their scientific capability. In addition, observing strategies are discussed for accurate calibration of fringe visibilities in spectral lines, despite strong atmospheric fluctuations encountered in the infrared.

The Ulysses Supplement to the Granat /WATCH Catalog of Cosmic Gamma‐Ray Bursts

We present third Interplanetary Network (IPN) localization data for 56 gamma-ray bursts in the Granat/WATCH catalog that occurred between 1990 November and 1994 September. These localizations are obtained by triangulation using various combinations of spacecraft and instruments in the IPN, which consisted of Ulysses, BATSE, Pioneer Venus Orbiter, Mars Observer, WATCH, and PHEBUS. The intersections of the triangulation annuli with the WATCH error circles produce error boxes with areas as small as 16 arcmin2, reducing the sizes of the error circles by factors of up to 800.

Variability of Mars' North Polar Water Ice Cap: I. Analysis of Mariner 9 and Viking Orbiter Imaging Data

Previous studies interpreted differences in ice coverage between Mariner 9 and Viking Orbiter observations of Mars' north residual polar cap as evidence of interannual variability of ice deposition on the cap. However, these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season. Our more comprehensive analysis of Mariner 9 and Viking Orbiter imaging data shows that the appearance of the residual cap does not show large-scale variance on an interannual basis. Rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year. Our results suggest that this brightening was due to the deposition of newly formed water ice on the surface. We find that newly formed ice deposits in the summer season have the same red-to-violet band image ratios as permanently bright deposits within the residual cap. We believe the newly formed ice accumulates in a continuous layer. To constrain the minimum amount of deposited ice, we used observed albedo data in conjunction with calculations using Mie theory for single scattering and a delta-Eddington approximation of radiative transfer for multiple scattering. The brightening could have been produced by a minimum of (1) a ∼35-μm-thick layer of 50-μm-sized ice particles with 10% dust or (2) a ∼14-μm-thick layer of 10-μm-sized ice particles with 50% dust.

The use of laser altimetry in the orbit and attitude determination of Mars Global Surveyor

Altimetry from the Mars Observer Laser Altimeter (MOLA), an instrument on board the Mars Global Surveyor (MGS) spacecraft, has been analyzed for the period of the MGS Science Phasing Orbit‐1 (SPO‐1) mission phase. Altimeter ranges have been used to improve significantly the orbit and attitude knowledge of the spacecraft by the use of crossover constraint equations derived from short passes of the MOLA data. These constraint equations differ from traditional crossover constraints and exploit the small footprint associated with laser altimetry. The rationale for using this technique with laser altimetry over sloping terrain is laid out and evidence of the resulting benefit is presented.

Aerobot measurements successfully obtained during Solo Spirit Balloon Mission

Robotic balloons, also known as aerobots, have become candidates for collecting atmospheric data and detailed surface observations of Venus, Mars, and Titan. A mission to Venus over a decade ago used two of them. Their inclusion last year in attempts by a balloonist to circumnavigate the Earth aptly demonstrated their utility for remote sensing and in situ observations of planetary atmospheres.To simulate aspects of an aerobot mission, a small payload to measure local atmospheric conditions and balloon position and velocity was included on Solo Spirit “Round the World” flights during January and August of last year. These missions, flown in Roziere balloons, were attempts by Steve Fossett to become the first person to circumnavigate the globe in a balloon without stopping. Neither attempt was successful, but the aerobot came through with flying colors.

Gravitational waves from coalescing binaries and Doppler experiments

Doppler tracking of interplanetary spacecraft provides the only method presently available for broad-band searches of low frequency gravitational waves. The instruments have a peak sensitivity around the reciprocal of the round-trip light-time T of the radio link connecting the Earth to the space-probe and therefore are particularly suitable to search for coalescing binaries containing massive black holes in galactic nuclei. A number of Doppler experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI spacecraft will perform three 40 days data acquisition runs with expected sensitivity about twenty times better than that achieved so far. Central aims of this paper are: (i) to explore, as a function of the relevant instrumental and astrophysical parameters, the Doppler output produced by in-spiral signals -- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii) to identify the most important parameter regions where to concentrate intense and dedicated data analysis; (iii) to analyze the all-sky and all-frequency sensitivity of the CASSINI's experiments, with particular emphasis on possible astrophysical targets, such as our Galactic Centre and the Virgo Cluster.

North Polar Dust Storms in Early Spring on Mars

Observations of Mars during 1996–1997 by the Hubble Space Telescope covered the entire spring season in the northern hemisphere of Mars, which was favorably positioned for viewing the north polar region. This paper reports observations of dust activity during this period. Local dust activity occurred near the edge of the subliming north polar cap during early spring; this included local dust clouds, similar to those seen by Viking near the edge of the south polar cap, and unusual, arc-shaped dust features that seem to represent a new type of dust phenomenon. These dust arcs may explain the Rima Tenuis rift, which has been occasionally seen by groundbased observers of Mars. Analysis of numerical simulations from a Mars general circulation model for the early northern spring season have provided insights into the plausible meteorological background at high latitudes in the vicinity of the retreating north polar cap. These Hubble observations extend the geographic and seasonal ranges during which local dust activity seems to be common on Mars. The combination of image analysis and model calculations support the hypothesis that these dust storms are the result of winds associated with fronts moving across the seasonal cap that lift dust exposed on the cap during CO2sublimation.

Telescopic Observations of Mars, 1996–1997: Results of the Marswatch Program

During the 1996–1997 apparition of Mars, Marswatch and the International Mars Patrol (IMP) of the Mars Section of the Association of Lunar and Planetary Observers (ALPO) received 2750 observations from 70 observers in 14 countries. Approximately 40% of these observations are CCD images, many of which were obtained through filters covering a spectral range from 330 to 820 nm. In addition, a large number of high quality visual observations were performed through standard color filters, permitting more accurate assessments of surface and atmospheric phenomena. The apparition coverage extended through 249° (11° to 260°) of areocentric longitude (Ls), permitting monitoring of the northern hemisphere spring/summer/autumn meterological activity, north polar cap (NPC) behavior, and albedo feature alterations.There were few significant changes in albedo feature morphology during the 1996–1997 apparition. The north polar cap rift, the Rima Tenuis, which had been observed and imaged during each aphelic apparition since 1980, was not observed, perhaps due to a slowing in the NPC regression after 80°Ls. The incidence of discrete clouds, orographic and localized, was higher than that predicted on the basis of the ALPO/IMP's martian meteorology study that spanned 14 previous apparitions from 1964 to 1993. Discrete clouds were more numerous than in 1993 or 1995, peaking in late northern spring, 30°Lsearlier than predicted. The Syrtis Blue Cloud was extensively observed and imaged between 66° and 115°Ls. The rate of occurrence of limb clouds was significantly lower than predicted for a given subseason. Their peak incidence occurred after aphelion, but their frequency decreased rapidly after 105°Ls, nearly two martian seasons earlier than observed during previous apparitions. Limb hazes, bright in blue and ultraviolet light, were more numerous and conspicuous throughout the northern summer, as predicted from the meteorology study. Arctic clouds increased in number around aphelion and were often large and bright during early northern summer. A variable north polar hood was observed after 160°Ls. We find clear evidence for the existence of extensive equatorial cloud bands, which became numerous between 50° and 120°Ls, peaking in early northern summer (105°Ls), and often merging into bright limb clouds. These bands were more frequent and prominent in 1996–1997 than during the 1993 or 1995 apparitions and were extensively imaged in blue and ultraviolet light by both groundbased observers and by the HST.

Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight

The Mars Observer spacecraft was launched on September 26, 1992 with a planned arrival at Mars after an 11-month cruise. Among the scientific instruments carried on the spacecraft was a Gamma-Ray Spectrometer (GRS) experiment to measure the composition of Mars. The GRS used a passively cooled high-purity germanium detector for measurements in the 0.2–10 MeV region. The sensor was a closed-end co-axial detector, 5.5 cm diameter by 5.5 cm long, and had an efficiency along its axis of 28% at 1332 keV relative to a standard NaI(Tl) detector. The sensor was surrounded by a thin (0.5 cm) plastic charged-particle shield. This was the first planetary mission to use a cooled Ge detector. It was expected that the long duration in space of three years would cause an increase in the energy resolution of the detector due to radiation damage and could affect the expected science return of the GRS. Shortly before arrival, on August 21, 1993, contact was lost with the spacecraft following the pressurization of the propellent tank for the orbital-insertion rocket motor. During much of the cruise to Mars, the GRS was actively collecting background data. The instrument provided over 1200 h of data collection during periods of both quiescent sun and solar flares. From the charged particle interactions in the shield, the total number of cosmic ray hits on the detector could be determined. The average cosmic ray flux at the MO GRS was about 2.5 cm −2 s −1. The estimated fluence of charged particles during cruise was about 10 8 particles cm −2 with 31% of these occurring during a single solar proton event of approximately 10 days duration. During cruise, the detector energy resolution determined from a background gamma-ray at 1312 keV degraded from 2.4 keV full-width at half-maximum shortly after launch to 6.4 keV 11 months later. This result agrees well with measurements from ground-based accelerator irradiations (at 1.5 GeV) on a similar size detector.