Visit to the red neighbor
Pathfinder has been on Mars for over two months now and the excitement of the internet community (565,902,373 hits on the mirror sites worldwide in the first 34 days) has subsided. Even NASA only holds a press conference every two to three weeks. So the right time for a review of the events and the first results of the project. Even NASA has to save. Gone are the days when money was plentiful for space projects; small, efficient missions like the Mars Pathfinder are in demand. As one of the first projects of the so-called "Discovery" type, it should provide information on how scientific payloads can be brought to the surface of Mars within a short time and within a tight budget. And so July 4th, when the probe landed, was already one of the most important dates for NASA technicians.
In the period leading up to August 3, the so-called Prime Mission, the lander sent 1.2 gigabits of data and 9669 frames of the Martian surface to Earth. The photos have been assembled into mosaics and can be viewed on the Internet. But the robots on our planetary neighbor turned out to be more robust than scientists dared hope, and they're still providing information and images of rocks, sunsets and "action" photos they take of each other.
The Fourth of July Landing
The landing took place in several phases: The probe entered the atmosphere 130 km above the ground of Mars at a speed of around 7.3 km/s and was slowed down by friction to around 400 m/s. After almost three minutes, a parachute opened at an altitude of about 9 km, shortly afterwards the heat shield was dropped. Airbags deployed 1,000 feet (300 m) above the ground and rocket rockets fired at 300 feet (98 m). When the descent was stopped, the connection to the parachute was severed. The rest of the time the probe fell freely, wrapped in the airbags. She jumped 15 m like a rubber ball and came to rest after another 15 bounces. The places where Pathfinder hit are clearly visible on pictures. There rocks have been pushed or pushed into the ground, revealing darker material.
For the next few minutes, the Pathfinder was on its own with no radio contact to Earth. Within the first hour, the airbags were deflated, three protective flaps opened and erected the probe. This cleared the view for a camera that sent images from the landing site in the Area Vallis, the mouth of a huge dry valley, to Earth.
The position of the Pathfinder can be identified using a sequence of images from the DLR Institute for Planetary Exploration. Finally, starting from a photograph of all of Mars (197K) over a mosaic of Area Vallis (595K), the exact location of the landing site (150K) at 19.33N and 33.55W is shown.
Sojourner's Walks on Mars
The first photos from Mars revealed a problem for the technicians on the ground: The airbags had positioned themselves so unfavorably in front of the rover that the ramps could not be deployed safely. Only after the airbags had been successfully retracted in a second attempt was the way clear for Sojourner (engl. linger), the small robotic vehicle named after the American women's rights activist Sojourner Truth (actually Isabella Van Wagener, 1797 to 1883).
Using the extended right ramp, the rover exited the lander and became the first man-made vehicle to travel to another planet to study the nature of the soil and rocks.
His route (140K) led him to different boulders: the smaller Barnacle Bill, then to the much larger Yogi, to Scooby Doo, Lamb and Souffle, then around the landing unit, past the mini Matterhorn into the "rock garden " (Panorama showing the path from Sojourner and the names of the rocks, 1108K).
En route, Sojourner snapped photos of the lander, now officially named Sagan Memorial Station, with his front camera.
Geological investigations
Sojourner carried out the first measurements on the Martian soil directly at the landing site. They confirmed that Mars gets its red color from iron oxide. But the landscape in the Area Vallis has a lot to offer, as Jim Bell of Cornell University points out. There are also areas where the surface appears significantly brighter.
Five different colors can be distinguished on the photos: light red boulders, dark gray rock, soil whose hue lies between these two colors, dark red material and stones and crusts that appear pink to white.
The dark color of the rocks is consistent with iron-bearing minerals found in igneous rocks, while the light-colored tills are reminiscent of weathered material that has even higher iron content. The difference in the weathering condition is made even more visible by displaying it in false colors. Rocks and areas with little evidence of weathering appear blue, the most weathered soil and windblown material appear red, and the typical Martian soil appears green. Closer investigation has shown that it consists of a mixture of boulders and small dark gray particles, similar to the surrounding rocks.
Particularly deep red areas can be found on some stones, for example in some folds of ginger. Further analysis with better resolution will be necessary to decipher the formation of this iron-rich crust.
Images taken with different filters of the lander's IMP camera, so-called multispectral spots, allow conclusions to be drawn about the composition of Martian rocks in comparison with known samples. In the case of Barnacle Bill, the reflection spectra showed clear agreement with volcanic material from Earth. The color coding in the images highlights individual pieces: green represents the sand behind the rock, red represents lighter areas that have been dusted by wind, and blue represents the actual dark rock.
Stripe Rock seemed particularly interesting because of its bright stripe. However, the spectrum suggests that the band is windblown soil from the area.
Sojourner is equipped with an alpha-proton X-ray spectrometer (APXS), which was developed in part at the Max Planck Institute for Chemistry in Mainz. With this device, which emits alpha particles, the abundances of most chemical elements can be determined with an accuracy of 0.1% to 0.01%. To do this, the spectrometer analyzes intensity and energy distribution
- of elastically scattered alpha particles,
- of protons released when alpha particles react with the nuclei of light elements, and
- of characteristic X-rays emitted when alpha particles knock electrons out of the inner shells of the atomic shell and electrons from higher shells fall into the resulting holes.
On July 7th, Barnacle Bill was examined with the APX spectrometer. The preliminary evaluation of the data surprised the scientists: the rock consists of one third each of quartz, feldspar and pyroxene - a composition known from terrestrial volcanic rocks, so-called andesites. Mars meteorites, on the other hand, are mostly bas alts. Andesites form during a phase of planetary evolution called differentiation. In the course of this, the celestial body changes from a homogeneous planet to a body with a layered structure through repeated melting and cooling of crustal material. The presence of andesites would mean that Mars was more thermally active in its past than previously thought.
In principle, Barnacle Bill could have been a sedimentary rock composed of a mixture of bas alt and granite. But a reflectance spectrum revealed a uniform structure, confirming the rock's volcanic origin. P> The much larger stone Yogi seemed at first glance to have a less dramatic past than Barnacle Bill. But the rock is covered by a layer of windblown material, which falsified the measurements. The data could be corrected on the assumption that the results were caused equally by the dust and the actual rock. Yogi's composition then resembles that of Barnacle Bill.
Scooby Doo is probably a sedimentary rock composed mainly of soil material.
The ground of Mars in front of Yogi was also analyzed. The surface material at this point appears very soft and is reminiscent of a kind of moat around the stone. In addition to the APX measurements, Sojourner also carried out mechanical tests with his bikes, in which he churned up the material. It has been shown that the Martian soil is covered with extremely small particles of less than 50 micrometers (millionths of a meter) in diameter, i.e. finer than talcum powder. The results help engineers plan future rover generations.
The relative abundances of some elements in various materials of terrestrial origin, the Martian meteorites studied so far and the samples analyzed directly on Mars can be easily compared using graphics. The amount of magnesium or aluminum related to the silicon content shows that both the meteorites and the soil samples taken during the Viking mission follow a clearly different trend line in the diagram than the earth rocks. The rocks (stars) and soils (yellow dots) studied by Sojourner fall somewhere between these two ranges.
The elements calcium and iron can be analyzed particularly well with the APX spectrometer. Samples from Mars have a higher relative concentration of iron than material from Earth.
Testing of the Martian soil on the Pathfinder mission (A-2, A-4, A-9, A-10) gave similar results to the Viking project. However, there are small differences: the samples from the Pathfinder landing site have a higher aluminum and magnesium content and contain less iron, chlorine and sulfur. Barnacle Bill (A-3), on the other hand, is closer to terrestrial rock due to its high silicon content.
The magnetic properties of Martian dust are tested with circular permanent magnets of different strengths embedded in magnesium blocks. Images taken after 6, 13 and 26 Martian days show that fine material is slowly accumulating on the two strongest magnets. A more detailed analysis of the dust with the APX spectrometer should later provide information about its origin.
In earlier floods, the extent of which could have filled the Mediterranean Sea, is, according to many scientists, indicated by the diversity of the rocks and sediments. Rounded stones, perhaps formed by the force of water, are found alongside rocks with sharp edges and corners, suggesting that they were formed by volcanic activity or a meteorite impact. There are also some bright spots on the surface of Mars that could possibly be former puddles from which the water has evaporated.
Astronomical Data Mars Pathfinder's quest also includes studying the moon Deimos. The smaller of the two moons of Mars is hard to see from Earth and difficult to see even with the Hubble Space Telescope because of its close proximity to the planet. A first image with the Pathfinder camera shows him in low resolution. In addition, the data for her journey to Earth has been compressed, making Deimos appear larger than he actually is. Later observations should provide information about its composition.
Always a topic of conversation: the weather
Thin, cold air surrounds the Mars Pathfinder. The recording of the ambient temperatures shows night values around -70 °C and daytime temperatures around -20 °C (temperature in °C=temperature in Kelvin + 273°C). Measurements were taken with three thermocouples attached to a mast of the landing unit at a height of 140cm, 90cm and 65cm above the ground of Mars.
The air pressure is 6.75 mbar, 10 to 20% lower than recorded by Viking 1 21 years ago. The reason for the difference is that the Mars Pathfinder is about 100 m higher than the Viking probe. Fluctuations in the day-night cycle can also be observed in air pressure. The atmosphere heats up and expands due to solar radiation, and cools and contracts at night. The fluctuations are interpreted as an indication of the existence of finely divided dust particles in the air. This dust appears to reach several kilometers in altitude over much of the planet. It absorbs the blue light and scatters the red, giving the Martian sky its characteristic reddish color. The concentration of the dust can be determined on the basis of sun images taken with the camera on the landing unit. The lower the sun is above the horizon, the fainter it is to see. It can already be said that there is more dust in the atmosphere than previously thought.
In the first days of the Mars mission, the wind came from the south at night, from the west in the morning and turned north during the day until it finally blew from the east in the evening. Late on the seventh day, this oscillation changed at the same time as a slight change in barometric pressure. Measurements carried out later, however, could not confirm a connection. So far, only approximate statements can be made about the wind strength. The strongest winds are at night (16-32 km/h), in the early morning and around noon, while late afternoon and early evening are relatively calm periods.
Temperature readings taken at four-second intervals revealed large fluctuations of 15°C to 20°C, sometimes occurring within minutes or seconds. They are probably caused by turbulent flows between the warmer layers near the ground and the overlying colder areas. On the 25th day of the mission, the landing unit registered a small wind pane, recognizable by the brief drop in pressure (black curve) and the change in wind strength from east (blue curve) and west (red curve).
Before sunrise, the morning sky shows streaky clouds believed to be composed of water ice condensed on dust particles during the night. During the day the water evaporates and the clouds disappear.
The Lander's Sharp Eye
Scientists on Earth are determining where Sojourner will go based on images captured by the Imager for Mars Pathfinder (IMP) stereo camera. The Max Planck Institute for Aeronomy in Lindau and the Technical University of Braunschweig were involved in its development. The camera is mounted on a mast and is about 1.8 m above the ground. Two mirrors 15 cm apart direct the light onto a subdivided sensor area that allows a resolution of 248 rows and 256 columns for each individual image. By using filters, a computer can create a color photo from three black-and-white photographs. Since the field of view is only 14.4° horizontally and 14.0° vertically, the images for the Internet are usually composed of individual images. This is how the wonderful panoramic images of the surroundings of the Sagan Memorial Station, the landing site of the Mars Pathfinder, are created.
… And because it's always good to look at things from different angles, Sue Kientz has written The Story of a Little Rock on Mars.
Reading Tips:
The return to Mars: successful! in Stars and Space 10/97, pages 848-855
Pathfinder on Mars - scientific results of a media-effective mission in Spektrum der Wissenschaft 9/97, page 16-21
The climate history of Mars in Spectrum of Science 1/97, page 50-59
Meteorite ALH84001 – Witness to Archaic Life Form on Mars in Spectrum of Science 9/96, Page 112
Organic Material from Mars in Spectrum of Science 9/89, Page 14
How Mars Lost Its Atmosphere in Spectrum of Science 6/89, Page 34
Meteorites of volcanic origin in Spectrum of Science 8/80, page 78
The Heidelberger Verlag Spektrum der Wissenschaft is the operator of this portal. Its online and print magazines, including "Spektrum der Wissenschaft", "Gehirn&Geist" and "Spektrum – Die Woche", report on current research findings.
