Leonard J. Martin

Photoelectric observations of asteroids 3, 24, 60, 261, and 863

Abstract Observations of five asteroids, obtained from various observatories from 1978 to 1984, are presented. A Fourier analysis method was used to derive the composite lightcurves. This solution method yields a value for the rotation period, mean absolute magnitudes on each night of observation, and Fourier coefficients defining the shape of the composite lightcurve, to any degree specified. A major advantage of the method is that it yields formal error estimates for all the quantities computed. The Fourier coefficients derived can be used for studies of the shapes and pole orientations of asteroids and to define “rotation phase” in a more formal way, for connecting observations from one apparition to another. Periods, amplitudes, and phase relations are reported for four of the five asteroids. The presence of a substantial amplitude first harmonic in the lightcurves of 3 Juno, 24 Themis, and 60 Echo suggests that these asteroids may have significant surface albedo variegation. 60 Echo exhibits a difference of 0.2 magnitude in its mean absolute magnitude from different aspects, which suggests a somewhat polar-flattened figure. High-quality magnitude vs solar phase angle data were obtained for 24 Themis from 0°.3 to 21°. These data are perhaps the best available of a dark asteroid and provide a test for light-scattering theories.

An analysis of the history of dust activity on Mars

A new comprehensive list of possible and probable dust activity has been compiled from various published lists and additional data. All previously listed events have been reviewed and evaluated. For uniformity and clarity, each event is classified using a new system that includes a well-defined nomenclature. Maps showing the reported locations of individual major events, as well as a summary map of the smaller “local” events, have been compiled. Detailed commentaries describe the events and/or circumstances of their observation. The seasonal distribution of Martian dust events is diagrammed and discussed together with a seasonal and annual (Mars years) timeline that includes the frequency of photographic coverage. The new compilation shows that major dust storms have originated in many different regions across the planet, with some evidence of more activity in the southern hemisphere generally and in specific regions like Hellas. Regional dust storms have been observed in nearly all seasons, except for two relatively narrow periods which occur near times when the polar caps have reached their maximum/minimum extent. Regional dust storms tend to occur most frequently, and all planet-encircling dust storms have been observed during the southern spring and summer seasons, although there is significant interannual variability.

Interannual variability of planet‐encircling dust storms on Mars

Interannual variability of the atmosphere of Mars is dominated by the occurence, or absence, of planet-encircling dust storms. In this paper we use a recent review of Earth-based telescopic observations of Mars together with Viking orbiter and lander data to estimate the frequency of occurrence of planet-encircling dust storms over the past century and to test whether the period spanned by the Mariner 9 and Viking missions to Mars is representative of the decades prior to 1950. In doing so, we take into account the practical limitations imposed on Earth-based coverage of Mars by the orbital geometries of the two planets. Both spacecraft and Earth-based observations suggest that planet-encircling dust storms on Mars occur during a so-called “dust storm season” in southern spring and summer. Viking data demonstrate decidedly that planet-encircling dust storms could have occurred in the past on Mars without being detected from Earth during years in which Mars was far from Earth during the dust storm season and thus difficult to observe. However, the same historical record indicates that planet-encircling storms were absent during the dust storm seasons monitored during several favorable oppositions prior to 1956 and after 1986. Overall, the chance of a planet-encircling dust storm occurring in any arbitrary Mars year is estimated to be approximately one in three (18–55% at the 95% level of confidence), if such occurrence is random from year-to-year and yet restricted seasonally to southern spring and summer.

Clearing the Martian air: The troubled history of dust storms

Abstract This note is an attempt to resolve some misconceptions regarding the historical record of the Martian atmospheric phenomena referred to as “dust storms,” but often called yellow storms, yellow clouds, planetwide dust storms, global dust storms, great dust storms, etc. The known frequency of planet-encircling storms will be specifically addressed. Better knowledge of the sizes, frequencies, and locations of Martian dust storms is needed for atmospheric modeling and for future mission planning.

Global imaging of Mars by Hubble space telescope during the 1995 opposition

Hubble space telescope (HST) imaging of Mars near the 1995 opposition resulted in excellent synoptic-scale images of the planet during the spring season in the northern hemisphere. Because this season coincides with the aphelion position of Mars in its orbit, it is therefore the most difficult for ground based observation because of the relatively small angular size of Mars. This is the first sequence of images fully utilizing the capability of the new Planetary Camera to produce global synoptic images of the planet. The images reveal bright, discrete clouds associated with topographic features superimposed on a zonal band of condensate clouds between latitudes -10° and 30° ; the maximum violet optical depth of the cloud band is about 0.3. In a few instances, the appearance of clouds beyond the morning terminator can be used to infer cloud heights of roughly 8 km. A large, dark albedo feature in the Cerberus region, observed for many years by ground-based observers, has almost disappeared in the 1995 HST images. Other aspects of Mars, such as the north polar cap, appear much as they did during previous oppositions. Although cloudy regions were observed by spacecraft during this season, the HST images uniquely reveal the global extent of significant optical depth clouds.

1995 observations of Martian dust storms using the Hubble Space Telescope

A synoptic monitoring program of Mars using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope has resulted in the observation of discrete dust activity for two dates following the 1995 opposition. Data obtained on April 8 (Ls=82°) and August 21, 1995 (Ls=145°) reveal the presence of local dust storms in the northern polar region. In addition, the August images show activity over the Hellas basin. We present a multispectral analysis of the data from which we derive lower bounds to the atmospheric dust loading. Our technique directly models the absolute photometry, and consequently also provides estimates of the cloud opacity and the ozone columns for the regions analyzed.

The major Martian dust storms of 1971 and 1973

Abstract The two largest Martian dust storms on photographic record occurred during the past two apparitions. The general characteristics of these events are compared using the hourly photography from the International Planetary Patrol. Dust storms are believed to be seasonal events on Mars, and therefore both storms had been predicted, but both turned out to be larger than expected, since they were each more extensive than the famous 1956 storm. The 1971 storm was much larger than the 1973 storm in both intensity and duration, although the 1973 storm had a more rapid initial expansion. Both storms began in the southern hemisphere but the 1973 storm began later (during summer, nearly three months beyond perihelion). The 1971 storm lasted approximately twice as long as the 1973 storm. Maps of the first nine days of both storms are presented to facilitate a comparison of their initial outbreaks and growth. Graphs of changes in contrast of albedo features during the 1973 storm are based on microdensitometer tracings of Planetary Patrol photographs. The frequency and regularity of storms of this size are uncertain because of the lack of comprehensive photographic observation during past apparitions. Identification and evaluation of such events in the future requires the continuation of well-coordinated worldwide observing efforts.

The major Martian yellow storm of 1971

Abstract Extensive Earth-based photography produced by the International Planetary Patrol has been used to map the positions of brightened areas (clouds) during the 1971 storm on Mars. The mapping was done on an hourly basis from two days prior to the onset of the storm through its twenty-second day. Summaries of these maps are presented to illustrate the changes that take place during the course of a Martian day, as well as the changes from one day to the next. It is shown that the storm goes through a daily cycle of regeneration, although each day it advances farther than it did the day before. The possible influence of Martian topography on the progress of the storm is examined. Comparisons between red- and blue-filter photographs of the storm are presented cartographically and are discussed. Areas most affected by the storm during this period are summarized in Fig. 8.

1973 dust storm on Mars: Maps from hourly photographs

Abstract The hourly progress of the 1973 major Martian storm has been mapped using photographic images from the International Planetary Patrol. The outlines of brightened areas were definable for about 3 weeks, which is about the same amount of time that could be mapped in this manner during the 1971 major storm. Two series of 20 daily maps show the semihourly positions of the storm brightenings in red light and blue light. The maps indicate that the 1973 storm had many similarities to the 1971 storm, as well as a number of significant characteristics of its own. The differences in color and location of several initial clouds that developed during the 1973 storm are compared using Patrol photographs taken through red, green, blue, and ultraviolet filters. The positions of the 1973 initial clouds are shown on a map together with the initial clouds that developed into the well-known storms of 1956 and 1971. The 1973 storm developed more of the characteristics of the 1971 storm after 8 to 10 days. Separate maps of every 2 hours showing the progression of the storms on their 11th days portray the extent of the similarities. The 1973 storm was mapped through its 22nd day (November 3), by which time it had begun to decay: the brightened areas had diminished in size and contrast. A summary map shows which areas on Mars were most affected by the brightenings seen during this storm. The map is more comprehensive than could be produced from the 1956 and 1971 photographs, although the areas which were active throughout these three major storms were very similar. Not only was the general latitudinal belt the same, but also the irregularities or indentations in the belt occured at nearly the same places.

The international planetary patrol program

Abstract An international photographic planatary patrol network consisting of the Mauna Kea Observatory in Hawaii, the Mount Stromlo Observatory in eastern Australia, the Republic Observatory in South Africa, the Cerro Tololo Inter-American Observatory in northern Chile, the Magdalena Peak Station of the New Mexico State University, and the Lowell Observatory has been in operation since April 1969. During 1969 this network produced over 11,000 fourteen-exposure filmstrips of Mars and Jupiter photographed through blue, green, and red filters. All of this material has been copied and catalogued by the staff of the Planetary Research Center at the Lowell Observatory. The complete facilities of the Planetary Research Center, as well as copies of the 1969 catalogue and observations, are available to qualified investigators.