Thursday, September 27, 2007

The Loss of Beagle 2

Credit: NASA/JPL/Malin Space Science Systems/Virtual Analytics Ltd.

Credit: NASA/JPL/University of Arizona

As yesterday's photo caption indicates, Beagle 2 was released from Mars Express on December 19, 2003. Beagle 2 coasted for five days after release, and is believed to have entered the Martian atmosphere on the morning of December 25th. As no signals were received after the separation, nothing is known as to what happened during the landing sequence.

After an initial deceleration in the Martian atmosphere from simple friction, parachutes were to have been deployed and, about 1 km above the surface, large gas bags would have inflated around the lander to protect it from the surface impact. Landing was expected to occur at about 02:54 UT on December 25th (9:54 p.m. EST, December 24th). After landing the bags would deflate and the top of the lander would open. The top would unfold to expose the four solar array disks. Within the body of the lander a UHF antenna would have been deployed. A panoramic image of the landing area was to have been taken using the stereo camera and a pop-up mirror. A signal was scheduled to be sent after landing (and possibly an image) to Mars Odyssey at about 5:30 UT and another the next (local) morning to confirm that Beagle 2 had survived the landing and the first night on Mars. No signal was received at this time nor at any time afterwards. Nothing further is known about the lander.

Attempts were made throughout late December 2003, January, and early February 2004 to contact Beagle 2 using Mars Express. Although regular calls were made, particular hope was placed for communications occurring on January 12th, when Beagle 2 was pre-programmed to expect Mars Express to fly overhead, and on February 2nd, when the probe was supposed to resort to the last communication back-up mode, autotransmit. Beagle 2 was declared lost on February 6, 2004. A board of inquiry was appointed to look into the reason for the failure, and they released their report on August 24, 2004. No concrete reason for the probe's failure was determined. Factors that were considered as plausible causes of the failure included:
  • Beagle 2 entered an atmosphere that was not predicted by scientists (e.g., the atmosphere may have been unusually thin) and could have burned up.
  • Beagle 2 may have "bounced off into space."
  • The probe's parachute or cushioning airbags failed to deploy or deployed at the wrong time.
  • Beagle 2's backshell tangled with the parachute, preventing it from opening properly.
  • Beagle 2 became wrapped up in its airbags or parachute on the surface and could not open.
  • Other possible reasons included electronic glitches, damage to the heat shield, a broken communications antenna, or a collision with an unforeseen object.

    On December 20, 2005, the British media reported that Professor Colin Pillinger, the Beagle 2 chief scientist, had discovered the location of the spacecraft. Per The Times of London:

    They suggest that the probe was lost because of cruel luck as it touched down in one of the worst possible places for a soft and successful landing. Rather than dropping to the surface on a flat plain, it appears to have first struck the downslope of a small crater about 18.5 m (60 ft) in diameter, before crashing into its opposite wall, bouncing several times around the rim and eventually coming to rest at the bottom. Even if the gas bags that were meant to cushion its impact were fully inflated, and there is some evidence that they were not, their design would not have allowed them to protect the probe properly under these unlikely circumstances.

    “It’s a bit like hitting the side of the pocket in snooker,” said Professor Colin Pillinger, of the Open University, who led the mission. “The plan was for it to bounce along a flat surface, but instead it seems to have hit the wall of the crater and that messed up the bounce sequence, damaging the lander. If this is all true we were very unlucky. A sideswipe like this was just what we didn’t want.”

    The first picture above shows a specially processed Mars Global Surveyor (MGS) image taken by the Mars Orbiter Camera (MOC) of the crater Dr. Pillinger believed Beagle 2 came down in.

    The Beagle scientists believe that out of the many thousands of craters and hundreds of square kilometers of Beagle 2’s landing ellipse, no other candidate site has come close to providing such compelling evidence of Beagle’s landing.

    Impact ejecta can be seen similar to the one produced by MER-A’s [Spirit] front shield in the Bonneville crater and a cluster of symmetrically arranged objects that match a successful gas bag segment separation, dropping the lander to the ground. (Source)

    However, on January 1, 2007, the HiRISE camera aboard Mars Reconnaissance Orbiter took a photo of Dr. Pillinger's crater (the second photo above). As can be seen in this high-resolution image, no sign of Beagle 2 can be observed. As of this time, the remains of Beagle 2 are still lost.
  • Wednesday, September 26, 2007

    Beagle 2

    Credit: ESA

    Back to our history...

    Launched with Mars Express was Beagle 2, a lander that was developed separately from Mars Express, which was a project of the European Space Agency (ESA). Beagle 2 was conceived by a group of British academics headed by Professor Colin Pillinger of the Open University, in collaboration with the University of Leicester. The spacecraft's purpose was to search for signs of Martian life, past or present, and its name reflected this goal, as Professor Pillinger explained:

    HMS Beagle was the ship that took Darwin on his voyage around the world in the 1830s and led to our knowledge about life on Earth making a real quantum leap. We hope Beagle 2 will do the same thing for life on Mars.

    A point at 10.6° North, 270° West in Isidis Planitia, a large flat sedimentary basin that overlies the boundary between the ancient highlands and the northern plains of Mars, was chosen as the landing site. The lander was expected to operate for about 180 days and an extended mission of up to one Martian year (687 Earth days) was thought possible. The Beagle 2 lander objectives were to characterize the landing site geology, mineralogy, geochemistry and oxidation state, the physical properties of the atmosphere and surface layers, collect data on Martian meteorology and climatology, and search for possible signatures of life.

    Promotion for Beagle 2 was somewhat unusual for your typical mission to Mars. In an effort to publicize the project and gain financial support, the designers sought and received the endorsement and participation of British artists. The mission's call-sign was composed by the band Blur, and the "test card" (Calibration Target Plate) intended for calibrating Beagle 2's cameras and spectrometers after landing was painted by Damien Hirst.

    Beagle 2's instruments included a robotic arm known as the Payload Adjustable Workbench (PAW), designed to be extended after landing. The PAW contained a pair of stereo cameras, a microscope (with a 6 micrometer resolution), a Mössbauer spectrometer, an X-ray spectrometer, a drill for collecting rock samples, and a spotlamp. In addition, a Rock Corer/Grinder could collect a core sample from inside any rocks within reach of the robot arm. Rock samples were to be passed by the PAW into a mass spectrometer and gas chromatograph in the body of the lander, called the Gas Analysis Package (GAP). This instrument was to measure the relative proportions of different isotopes of carbon. Since carbon is thought to be the basis of all life, these readings could have revealed whether the samples contained the remnants of living organisms.

    In addition, Beagle 2 was equipped with a small "mole" (Planetary Undersurface Tool, or PLUTO), to be deployed by the arm. PLUTO had a compressed spring mechanism designed to enable it to move across the surface at a rate of about 1 cm every 5 seconds, and to burrow into the ground and collect a subsurface sample in a cavity in its tip. The mole was attached to the lander by a power cable about three meters long, which could be used as a winch to bring the sample back to the lander.

    The above photo is of the back side of Beagle 2, slowly drifting away from Mars Express. This image, taken December 19, 2003, shows the lander when it was about 20 meters away from Mars Express, on its way to Mars.

    Saturday, September 22, 2007

    Science@NASA: Cave Skylights Spotted on Mars

    The following news article was just published (September 21st) by SCIENCE@NASA. I've made a few minor changes, primarily adding additional information from several related webpages to the report and the captions, plus inserting the various links.

    NASA's Mars Odyssey spacecraft has discovered entrances to seven possible caves on the slopes of a Martian volcano. The find is fueling interest in potential underground habitats and sparking searches for caverns elsewhere on the Red Planet.

    Very dark, nearly circular features ranging in diameter from about 328 to 820 feet puzzled researchers who found them in images taken by NASA's Mars Odyssey and Mars Global Surveyor orbiters. Using Mars Odyssey's infrared camera to check the daytime and nighttime temperatures of the circles, scientists concluded that they could be windows into underground spaces.

    Above: A montage image of the "Seven Sisters" -- seven dark openings into cavenrous spaces on the slopes of Arsia Mons, located at 9° South, 239° East. They range in diameter from about 100 meters (328 feet) to about 225 meters (738 feet). The candidate cave skylights have been nicknamed Dena (top left), Chloe (top middle), Wendy (top right), Annie (bottom left), Abby (bottom middle; left), Nikki (bottom middle; right) and Jeanne (bottom right). Solar illumination comes from the left in each frame. Credit: NASA/JPL-Caltech/ASU/USGS

    Evidence that the holes may be openings to cavernous spaces comes from the temperature differences detected from infrared images taken in the afternoon vs. the pre-dawn morning. From day to night, temperatures of the holes change only about one-third as much as the change in temperature of surrounding ground surface.

    "They are cooler than the surrounding surface in the day and warmer at night," said Glen Cushing of the U.S. Geological Survey's Astrogeology Team and of Northern Arizona University, Flagstaff, Arizona. "Their thermal behavior is not as steady as large caves on Earth that often maintain a fairly constant temperature, but it is consistent with these being deep holes in the ground."

    A report of this discovery by Cushing and his co-authors was published online recently by the journal Geophysical Research Letters.

    "Whether these are just deep vertical shafts or openings into spacious caverns, they are entries to the subsurface of Mars," said co-author Tim Titus of the U.S. Geological Survey in Flagstaff. "Somewhere on Mars, caves might provide a protected niche for past or current life, or shelter for humans in the future."

    The discovered holes, dubbed the "Seven Sisters," are at some of the highest altitudes on the planet, on a volcano named Arsia Mons near Mars' tallest mountain.

    "These are at such extreme altitudes, they are poor candidates either for use as human habitation or for having microbial life," Cushing said. "Even if life has ever existed on Mars, it may not have migrated to this height."

    Above: Each of the three images in this set covers the same patch of Martian ground, centered on a possible cave skylight informally called "Annie," which has a diameter about double the length of a football field. The Thermal Emission Imaging System (THEMIS) camera on NASA's Mars Odyssey orbiter took all three, gathering information that the hole is cooler than surrounding surface in the afternoon and warmer than the surrounding surface at night. This is thermal behavior that would be expected from an opening into an underground space.

    The left image was taken in visible-wavelength light. The other two were taken in thermal infrared wavelengths, indicating the relative temperatures of features in the image. The center image is from mid-afternoon. The hole is warmer than the shadows of nearby pits to the north and south, while cooler than sunlit surfaces. The thermal image at right was taken in the pre-dawn morning, about 4 a.m. local time. At that hour, the hole is warmer than all nearby surfaces. Credit: NASA/JPL-Caltech/ASU/USGS

    "The key to finding these [skylights] was looking for temperature anomalies at night -- warm spots," said Phil Christensen of Arizona State University, Tempe, principal investigator for the Thermal Emission Imaging System on Mars Odyssey. That instrument produced both visible-light and infrared images researchers used for examining the possible caves.

    "No other instrument at Mars could give the thermal information crucial to this research," said the project scientist for Mars Odyssey, Jeffrey Plaut of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This is a great example of the exciting discoveries Odyssey continues to make."

    The new report proposes that the deep holes on Arsia Mons probably formed as underground stresses around the volcano caused spreading and faults that opened spaces beneath the surface. Some of the holes are in line with strings of bowl-shaped pits where surface material has apparently collapsed to fill the gap created by a linear fault.

    The observations have prompted researchers using Mars Odyssey and NASA's newer Mars Reconnaissance Orbiter to examine the Seven Sisters. The goal is to find other openings to underground spaces at lower elevations that are more accessible to future missions to Mars.

    Thursday, September 20, 2007

    News Update: 2001 Mars Odyssey in Safe Mode After Glitch

    Credit: NASA

    I just came across this news report, dated September 17th (Monday), about 2001 Mars Odyssey on Yahoo news. Unfortunately, there's no new information on Odyssey's status on the NASA/JPL webpage.

    PASADENA, Calif. - The Mars Odyssey orbiter was in safe mode Monday after a computer glitch prevented the 6-year-old spacecraft from relaying data from the twin rovers rolling across the Martian surface.

    Project leaders said the Mars Odyssey was not in danger. Engineers discovered the problem Friday after a software glitch caused the onboard computers to reboot. The spacecraft last went into safe mode was in December when it was hit by a cosmic ray.

    Mission manager Bob Mase of the Jet Propulsion Laboratory in Pasadena said he expected the Mars Odyssey to return to normal by the middle of the week.

    The rovers depend on the Mars Odyssey to send data to Earth and have been using their high-gain antenna to speak directly with Earth since the problem occurred.

    One of the rovers, Opportunity, began a detailed investigation of the inner slope of Victoria Crater last week after doing a toe-dip of the massive hole. The six-wheeled robot is about 20 feet below the rim heading toward a light-toned layer of rock that may hold clues about the ancient environment.

    The above diagram is an engineering schematic of 2001 Mars Odyssey in its mapping configuration.

    Mars Express

    Credit: ESA/DLR/FU Berlin (G. Neukum)

    The 2003 launch window was very ambitious and largely successful. The first spacecraft to launch was Mars Express and the Beagle 2 Lander. These two spacecraft were the first efforts by western Europe to reach Mars: Mars Express was the first planetary mission attempted by the European Space Agency, and Beagle 2 was developed by a consortium of British universities and businesses, the lead party being the University of Leicester.

    The Mars Express Orbiter had a number of mission goals, including:
  • to image the entire surface at high resolution (10 meters/pixel) and selected areas at super resolution (2 meters/pixel);
  • to produce a map of the mineral composition of the surface at a 100 meter resolution;
  • to map the composition of the atmosphere and determine its global circulation;
  • to determine the structure of the sub-surface to a depth of a few kilometres;
  • to determine the effect of the atmosphere on the surface; and
  • to determine the interaction of the atmosphere with the solar wind.

    The Beagle 2 Lander, on the other hand, was to:
  • determine the geology and the mineral and chemical composition of the landing site;
  • search for life signatures (exobiology); and
  • study the weather and climate.

    The spacecraft were launched on June 2, 2003 from the Baikonur Cosmodrome in Kazakhstan, using a Soyuz-Fregat rocket. Mars Express and the Fregat booster were initially put into a 200 km Earth parking orbit. The Fregat was fired again, 89 minutes after launch, to put the spacecraft into a Mars transfer orbit. Two days later, a trajectory correction maneuver was performed to aim Mars Express towards Mars and allow the Fregat booster to coast into interplanetary space.

    After a mere six-month voyage (Mars and Earth were, at that time, closer to each other than they had been in the previous 60,000 years), the Beagle 2 lander was released on December 19, and the orbiter entered Mars orbit on December 25, 2003. Mars Express' orbit was later adjusted by four more main engine firings to the desired 259 km × 11,560 km near-polar (86 degree inclination) orbit with a period of 7.5 hours. During periapsis the top deck of the spacecraft is pointed down towards the Martian surface, and during apoapsis the high gain antenna is pointed toward the Earth for uplink and downlink communications. After 100 days the apoapsis was lowered to 10,107 km and the periapsis raised to 298 km to give an orbital period of 6.7 hours.

    The above photo was taken by the High Resolution Stereo Camera (HRSC) on board Mars Express, showing Crater Galle (aka the "Happy Face" Crater), an impact crater located on the eastern rim of the Argyre Planitia impact basin on Mars. Crater Galle is named after the German astronomer J.G. Galle (1812-1910), and was first pointed out in images taken during the Viking Orbiter 1 mission. The picture is a mosaic of overlapping images gathered during five separate orbits. The ground resolution ranges between 10-20 meters per pixel, depending on the location within the image strip. Crater Galle is located near 51° South, 329° East. North is up.

    The image shows Crater Galle containing a large stack of layered sediments forming an outcrop in the southern part of the crater. Several parallel gullies, possible evidence for liquid water on the Martian surface, originate at the inner crater walls of the southern rim. The crater's interior also shows a surface that is shaped by "aeolian" (wind-caused) activity as seen in numerous dunes and dark dust devil tracks that removed the bright dusty surface coating.
  • Tuesday, September 18, 2007


    Credit: NASA

    The third major instrument aboard 2001 Mars Odyssey was the Mars Radiation Environment Experiment (MARIE). Sponsored by NASA's Johnson Space Center, this instrument investigated the amount of radiation present both on the way to Mars and in Martian orbit. The goal of the project was to predict anticipated radiation doses that would be experienced by future astronauts, and in helping to determine possible effects of Martian radiation on human beings. While similar spectrometers like MARIE have flown on various space shuttles and the International Space Station (ISS), none had flown outside of the Earth's magnetosphere, which blocks much of the radiation from reaching the surface of our planet.

    MARIE, with a 68-degree field of view, collected data during Odyssey's cruise from Earth to Mars and while in orbit around Mars. On October 28, 2003, a large solar event bombarded the Odyssey spacecraft, crippling MARIE. The instrument has been unable to collect data since that time, and engineers believe the most likely cause is that a computer chip was damaged by a solar particle smashing into the MARIE computer board.

    The above graph shows the daily average dose rate of radiation from March 13, 2002 to September 30, 2003. MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the ISS. Levels at the Martian surface might be closer to the level at the ISS. Average in-orbit doses were about 22 millirads per day (220 microgray/day or 0.08 gray/year)). However, occasional solar proton events (SPEs) produced much higher doses. SPEs were observed by MARIE that were not observed by sensors near Earth, confirming that SPEs are directional. (Note: The above graphic comes from Wikipedia, although the data is originally from NASA. However, the MARIE instrument website at the Johnson Space Center is down at this time.)

    Monday, September 17, 2007

    The Gamma Ray Spectrometer Aboard 2001 Mars Odyssey

    Credit: NASA/JPL/University of Arizona

    Another instrument aboard the 2001 Mars Odyssey is a Gamma Ray Spectrometer (GRS). The GRS aboard the Odyssey is actually a set of three instruments. Two of these instruments, the Neutron Spectrometer and the Russian-made High Energy Neutron Detector, detect neutrons released from the surface of the planet. The third instrument (the Gamma Ray Spectrometer) detects gamma ray photons coming from the planet. The information collected by the GRS is used to determine the composition and location of various elements on Mars (such as hydrogen, iron, chlorine, and so on). This also includes the production of a global map of water deposits and other elements on Mars, an estimation of the depth of water deposits (up to one meter deep), and a continuing study of how seasons affect the polar ice caps. The GRS also contributes to the study of cosmic gamma ray bursts.

    The gamma ray detector is a large (1.2 kg) high-purity Germanium (Ge) crystal. The crystal is held at a voltage of approximately 3000 volts. Little or no current flows (less than one nanoAmp) unless a high-energy ionizing photon or charged particle strikes it. The electric charge from such a strike is amplified, measured and digitally converted into one of 16,384 (214) channels, or bins. After a specified number of seconds, a histogram is produced, which shows the distribution of events (number of strikes) as a function of energy (channel number).

    The GRS is mounted on the end of a long (6-meter) boom attached to the orbiter. The boom is necessary to reduce interference from gamma rays generated by the spacecraft. (All elements in space radiate gamma-rays by the same processes that generate them on the surface of Mars.)

    The gamma sensor head contains the detector, a radiative cooler, a low temperature pre-amplifier, a thermal shield with door, and a bracket to mount the sensor head to the end of the boom. The cooler has a door that opens in flight, exposing a radiator, and allowing the sensor to cool to below 90° Kelvin for science data collection. The thermal shield and door are needed to periodically warm up the sensor head to 100° Celsius to anneal radiation damage to the crystal.

    The advantage of the high-purity Germanium sensor is that the lines identifying elements in the surface layer of Mars are very sharp. The count rate is very low, but long integration times permit most elements to be determined with a precision of about 10%. The GRS spectra are typically only 30 seconds in duration, but longer accumulation times are achieved by summing up spectra over a particular region of the planet.

    The spatial resolution of the instrument is about 300 km; a region this large receives about 6 hours of accumulation time near the equator at the end of the mission and much longer accumulation times near the poles (about a factor of 5 more). Elements that need longer accumulation times can be determined with degraded spatial resolution by summing up spectra over larger regions of the planet. For example, Oxygen, Silicon, Chlorine, Potassium, and Iron can be determined in a 300 km spot, but Nickel and Chromium can only be determined by summing up the data over very large regions; e.g., all of the highlands or all of the lowlands.

    The above map shows concentration estimates of equivalent-weight water found in the regions around the equator of Mars. The map is based upon gamma ray data collected for the element hydrogen. Regions of high hydrogen concentration are shown in red while regions of low hydrogen concentration are shown in violet and blue. The highest equatorial concentrations of hydrogen are found around and to the east of Apollineris (left and right center of map) and centered around Arabia Terra (center of map). This hydrogen may be in the form of hydrated minerals or buried ice deposits, but the former is more likely. The white sections at the top and bottom of the map represent regions of the planet with high hydrogen concentration due to large amounts of buried water ice. The locations of the five successful lander missions are marked: Viking 1 (V1), Viking 2 (V2), Pathfinder (PF), Spirit at Gusev (G), and Opportunity at Meridiani (M).

    Sunday, September 16, 2007

    THEMIS and Atmospheric Dust Levels

    Credit: NASA/JPL-Caltech/Arizona State University

    THEMIS's infrared camera is able to detect infrared energy at ten different wavelengths. Nine of these have wavelengths between 6 and 13 micrometers, an ideal region of the infrared spectrum to determine thermal energy patterns characteristic of silicate minerals. At a tenth wavelength, 14.88 micrometers, the atmosphere of Mars becomes opaque, so that THEMIS cannot see the surface of the planet.

    Using the 9 micrometer wavelength, THEMIS is able to show the atmosphere's opacity due to the level of dust in the atmosphere. This was very beneficial in the past few months as a major worldwide dust storm blew around Mars. The dust storm erupted during the last week of June 2007. Beginning in the equatorial region west of Meridiani Planum, it moved into the heavily cratered southern highlands. The storm took roughly a week to grow large enough to spread around the planet south of the equator. Dust also drifted into the northern hemisphere as well.

    The dust storm affected operations for all five spacecraft operating at Mars. For the orbiters, the storms obviously interfered with visible light observations of the surface. However, the dust storms were mission-threatening for the twin rovers, Spirit and Opportunity, both of which went into hibernation mode to wait out the dust storms. The problem was that the dust storms caused a steep decrease in the amount of electricity generated by the rovers' solar panels, threatening the rovers' survival. The solar panels on the rovers can normally generate up to 700 watt hours per day, of which any output below 150 watt hours forces the rovers to rely upon batteries to operate their heaters, which keeps the rovers operational. At the worst part of the dust storms, Spirit's electrical output fell as low as 261 watt hours, and 128 watt hours for Opportunity. However, by early August, the Martian skies began to clear enough so that Opportunity could fully recharge its batteries and Spirit could bring its batteries' energy levels to a nearly full charge. (Opportunity has since resumed its mission, beginning its exploration of the interior of Victoria crater; meanwhile, on September 5th, Spirit climbed onto its long-term destination called Home Plate, a plateau of layered bedrock bearing clues to an explosive mixture of lava and water.)

    In the above GIF animation, THEMIS's infrared maps of the atmosphere show the atmosphere's opacity between June 15th through July 19th of this year, covering a significant portion of the dust storms' creation and expansion. The scale bar's values run from nearly clear (0.05) to roughly a one-third reduction in sunlight (0.40). (Note: For some reason, only the first slide of the nine in the animation is showing up; please let me know in the comments if you are or are not able to see the entire animation.)

    Saturday, September 15, 2007

    Melea Planum by THEMIS

    Credit: NASA/JPL/Arizona State University

    A week and a half ago (before my end-of-term workload crashed down on me), we were discussing THEMIS's cababilities to observe Mars in both visible light and infrared radiation. The previous post discussed THEMIS's visible light camera; this post and the next will focus on its infrared camera.

    By making repeated observations on the same sites over a period of time, THEMIS is able to measure the ground temperatures and determine the depth (roughly) of ice below the surface, from shallow (less than one centimeter) to deep (up to 20 centimeters). The sensitivity of this method for estimating the depth is not good for depths greater than about 20 centimeters.

    In the above photo, THEMIS observed the above site (67° South, 36.5° East, near Melea Planum) in infrared wavelengths during night time, providing surface-temperature information. It did so once on December 27, 2005, during late summer in Mars' southern hemisphere, and again on January 22, 2006, the first day of autumn there. The colors on this map signify relative differences in how much the surface temperature changed between those two observations. Blue indicates the locations with the least change, while red indicates areas with the most change. This site, like most of high-latitude Mars, has water ice mixed with soil near the surface. The ice is probably in a rock-hard frozen layer beneath a few centimeters or inches of looser, dry soil.

    The dense, icy layer retains heat better than the looser soil above it, so where the icy layer is closer to the surface, the surface temperature changes more slowly than where the icy layer is buried deeper. On the map, areas of the surface that cooled more slowly between summer and autumn (interpreted as having the ice closer to the surface) are coded blue and green. Areas that cooled more quickly (interpreted as having more distance to the ice) are coded red and yellow.

    The depth to the top of the icy layer estimated from these observations suggests that in some areas, but not others, water is being exchanged by diffusion between atmospheric water vapor and subsurface water ice. Differences in what type of material lies above the ice appear to affect the depth to the ice. The area in this image with the greatest seasonal change in surface temperature corresponds to an area of sand dunes.

    The temperature-change data are overlaid on a mosaic of black-and-white, daytime images taken in infrared wavelengths by the same camera, providing information about shapes in the landscape. The 20-kilometer scale bar is 12.4 miles long.

    Sunday, September 9, 2007

    Meridiani Planum by THEMIS

    Credit: NASA/JPL/Arizona State University

    (This post and the next one or two will highlight the capabilities of THEMIS.)

    The THEMIS VIS (visible light) camera on board the 2001 Mars Odyssey is capable of capturing color images of the Martian surface using five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from using multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    The above false color image shows one portion of the surface in the Meridiani Planum region (1.6° North, 5.6° East). The overall image covers an area of 18.4 km by 65.7 km, at a resolution of 36 meters per pixel. The Opportunity rover landed west of this image. This image was collected during the northern spring season, and was released to the public on May 23, 2005.

    Tuesday, September 4, 2007


    Credit: NASA/JPL/Arizona State University

    The Thermal Emission Imaging System (THEMIS) is a camera on 2001 Mars Odyssey. THEMIS takes images of Mars in the visible and infrared parts of the electromagnetic spectrum in order to determine the thermal properties of the surface and to refine the distribution of minerals on the surface of Mars as determined by the Thermal Emission Spectrometer (TES), which is on board Mars Global Surveyor. Additionally, THEMIS helps scientists to understand how the mineralogy of Mars relates to its landforms, and it can be used to search for thermal hotspots in the Martian subsurface.

    THEMIS detects thermal infrared energy emitted by the Martian surface at 10 different wavelengths. Nine of these have wavelengths between 6 and 13 micrometers, an ideal region of the infrared spectrum to determine thermal energy patterns characteristic of silicate minerals. The tenth band is at 14.9 micrometers, and is used to monitor the Martian atmosphere.

    The absorption spectrum measured by THEMIS contains two kinds of information: temperature and emissivity. The temperature contribution to the measurement dominates the spectrum unless the data is corrected. In effect, a THEMIS infrared image taken during the day will look much like a shaded relief map, with slopes facing the sun being bright (hot) and shaded areas being dark (cold). In a THEMIS image taken at night however, thermophysical properties of the surface can be inferred, such as temperature differences due to the material's grain size.

    The effect of temperature can be removed from THEMIS infrared data by dividing the image by a black body curve. The resulting energy pattern is an emissivity spectrum characteristic of the specific minerals (or other things) found on the surface. The presence of minerals such as carbonates, silicates, hydroxides, sulfates, amorphous silica, oxides, and phosphates can be determined from THEMIS measurements.

    In particular, this multi-spectral method allows researchers to detect the presence of minerals that form in water and to understand those minerals in their geological context.

    The THEMIS infrared camera was designed to be used in conjunction with data from the Thermal Emission Spectrometer (TES), a similar instrument on Mars Global Surveyor. While THEMIS has a very high spatial resolution (100 m) with a low spectral resolution of only 10 bands between 6 and 15 micrometers, TES has a low spatial resolution (3x6 km), but with very high spectral resolution of 143 bands between 5 and 50 micrometers.

    THEMIS also has a visible imaging camera that acquires data in five spectral bands, takes images with a spatial resolution of 18 meters (59 feet). This resolution is intermediate between large-scale images from the Viking Orbiters (150 to 300 meters per pixel) and the high-resolution images from the Mars Orbiter Camera (MOC) onboard Mars Global Surveyor (1.5 to 3 meters per pixel).

    The THEMIS visible camera's stated purpose is to determine the geological record of past liquid and volcanic environments on Mars. Additionally, this dataset can be used in conjunction with the infrared data to identify potential landing sites for future Mars missions.

    The above picture shows both a visible and a thermal infrared image taken by THEMIS on November 2, 2001. The images were taken as part of the ongoing calibration and testing of the camera system as the spacecraft orbited Mars on its 13th revolution of the planet.

    The visible wavelength image, shown on the right in black and white, was obtained using one of the instrument's five visible filters. The spacecraft was approximately 22,000 km (about 13,600 miles) above Mars looking down toward the south pole when this image was taken. The season is late spring in the Martian southern hemisphere.

    The thermal infrared image, center, shows the temperature of the surface in color. The circular feature seen in blue is the extremely cold Martian south polar carbon dioxide ice cap. The instrument has measured a temperature of minus 120° Celsius (minus 184° Fahrenheit) on the south polar ice cap. The polar cap is more than 900 km (540 miles) in diameter at this time.

    The visible image shows additional details along the edge of the ice cap, as well as atmospheric hazes near the cap. The view of the surface appears hazy due to dust that still remained in the Martian atmosphere from the massive dust storms that had occurred over the previous several months.

    The infrared image covers a length of over 6,500 km (3,900 miles) spanning the planet from limb to limb, with a resolution of approximately 5.5 km (3.4 miles) per pixel at the point directly beneath the spacecraft. The visible image has a resolution of approximately 1 km (0.6 miles) per pixel, and covers an area roughly the size of the states of Arizona and New Mexico combined.

    Monday, September 3, 2007

    2001 Mars Odyssey

    Credit: NASA/JPL/MSSS

    The only launch during the 2001 launch window was of NASA's 2001 Mars Odyssey (hereafter referred to as Odyssey). Odyssey was launched on April 7, 2001 aboard a Delta II rocket, and reached Mars on October 24, 2001. The spacecraft is still functional and is, among operating spacecraft, the current longest running mission at 2,141 days (as I write this).

    Odyssey was originally named Mars Surveyor 2001 Orbiter and was intended to have a companion spacecraft, Mars Surveyor 2001 Lander. The Lander's mission, however, was canceled in May 2000 following the failures of Mars Climate Orbiter and Mars Polar Lander in late 1999. Subsequently, the name 2001 Mars Odyssey was selected for the orbiter as a specific tribute to the vision of space exploration shown in the works of Arthur C. Clarke, including the novel and movie, 2001: A Space Odyssey.

    Odyssey's mission is to use spectrometers and imagers to hunt for evidence of past or present water and volcanic activity on Mars. To do this, Odyssey takes high spatial and spectral resolution images of Martian surface mineralogy and images of surface morphology using its Thermal Emission Imaging System (THEMIS). Odyssey also looks for shallow, subsurface hydrogen (as a sign of the presence of water) and is making a global map of elemental composition using a Gamma Ray Spectrometer (GRS). Another instrument, the Mars Radiation Environment Experiment (MARIE), was used to measure the radiation environment of Mars. That instrument was in use for about 18 months before failing. One other instrument aboard Odyssey is a High Energy Neutron Detector (HEND), provided by Russia.

    The initial mission was concluded in August 2004. NASA has approved an extended mission through September 2008 to allow observation of year-to-year differences in phenomena like polar ice, clouds and dust storms. Odyssey also acts as a relay for communications between the Mars Explorations Rovers and Earth. About 85 percent of images and other data from NASA's twin Mars rovers, Spirit and Opportunity, have reached Earth via communications relay by Odyssey, which receives transmissions from both rovers daily. The orbiter helped analyze potential landing sites for the rovers and is doing the same for Mars Phoenix, scheduled to land on Mars in 2008.

    Odyssey is also unique in that the mission has its own theme music, "Mythodea," by the Greek composer Vangelis.

    Above are two images of Odyssey: the first is an enlarged photograph of Odyssey taken by the Mars Orbiter Camera aboard NASA's Mars Global Surveyor; the second is an annotated computer drawing of Odyssey at the same angle as it appears in the actual image. At the time the photo was taken, the two spacecraft were about 90 km (56 miles) apart. The camera's successful imaging of Odyssey and of the European Space Agency's Mars Express in April 2005 produced the first pictures of any spacecraft orbiting Mars ever taken by another spacecraft orbiting Mars.

    Odyssey and Mars Global Surveyor are both in nearly circular, near-polar orbits. Odyssey is in an orbit slightly higher than that of Global Surveyor in order to avoid the possibility of a collision. However, the two spacecraft occasionally come as close together as 15 km (9 miles).

    Sunday, September 2, 2007

    Mars Polar Lander/Deep Space 2

    Credit: NASA

    The third and final launch of the 1998-99 launch window was the Mars Polar Lander (MPL), which was part of the Mars Surveyor '98 program. MPL also carried the Deep Space 2 surface-penetrator mission to Mars, two microprobes that, like the Russian Mars '96 penetrators, were supposed to bury themselves underneath the Martian surface upon impact and take measurements.

    MPL was to touch down on the southern polar layered terrain between 73°S and 76°S, in a region called Planum Australe, less than 1000 km from the south pole and near the edge of the carbon dioxide ice cap in Mars' late southern spring. The terrain appears to be composed of alternating layers of clean and dust-laden ice, and may represent a long-term record of the climate, as well as an important volatile reservoir. The mission had as its primary science objectives to:
  • Record local meteorological conditions near the martian south pole, including temperature, pressure, humidity, wind, surface frost, ground ice evolution, ice fogs, haze, and suspended dust
  • Analyze samples of the polar deposits for volatiles, particularly water and carbon dioxide
  • Dig trenches and image the interior to look for seasonal layers, and analyze soil samples for water, ice, hydrates, and other aqueously deposited minerals
  • Image the regional and immediate landing site surroundings for evidence of climate changes and seasonal cycles, and
  • Obtain multi-spectral images of local regolith to determine soil types and composition.

    These goals were to be accomplished using a number of scientific instruments, including a Mars Volatiles and Climate Surveyor (MVACS) instrument package that was comprised of a robotic arm and attached camera, a mast-mounted surface stereo imager, a meteorology package and a gas analyzer. Also, a Mars Descent Imager (MARDI) was planned to capture regional views from parachute deployment at about 8 km altitude down to the landing. The Russian Space Agency provided a laser ranger (LIDAR) package for the lander, which would be used to measure dust and haze in the Martian atmosphere. A miniature microphone would also be on board to record sounds on Mars. And, as mentioned above, attached to the Lander was the Deep Space 2 microprobes, named Scott and Amundsen, which were to be deployed to fall and penetrate beneath the martian surface when the spacecraft reached Mars.

    MPL and the Deep Space 2 probes were launched on a Delta 7425 rocket on January 3, 1999. After an 11-month hyperbolic transfer cruise, MPL reached Mars on December 3, 1999. A final 30 minute tracking session began at 12:45 UT (7:45 a.m. EST), and was used to determine if a final thruster correction was necessary. Final contact to retrieve data on the status of the propulsion system was made from 19:45 UT to 20:00 UT. At 20:04, 6 minutes before atmospheric entry, an 80 second thruster firing was to turn the craft to its entry orientation. The cruise stage was to be jettisoned at about 20:05 UT, and about 18 seconds later the microprobes were to be dropped from the cruise stage into the Martian atmosphere (also targeted at the southern polar layered terrain). The Lander was to make a direct entry into Mars' atmosphere at about 20:10 UT (3:10 p.m. EST). Due to a lack of communications, it is not known whether all these steps following final contact were executed, nor whether any of the descent plan took place as designed. The last telemetry from MPL was sent just prior to atmospheric entry on December 3, 1999. No further signals have been received from the Lander. The cause of this loss of communications is unknown.

    According to the investigation that followed, the most likely cause of the failure of the mission was a software error that mistakenly identified the vibration caused by the deployment of the Lander's legs as being caused by the vehicle touching down on the Martian surface, resulting in the vehicle's descent engines being cut off while it was still 40 meters above the surface, rather than on touchdown as planned. Another possible reason for failure was inadequate preheating of the catalysis beds for the pulsing rocket thrusters: hydrazine fuel decomposes on the beds to make hot gases that throttle out the rocket nozzles; cold catalysis beds caused misfiring and instability in crash review tests.

    Attempts were made in late 1999 and early 2000 to search for the remains of the MPL using images from the Mars Global Surveyor. These attempts were unsuccessful, but re-examination of the images in 2005 led to a tentative identification described in the July 2005 issue of Sky and Telescope magazine. However, higher resolution photos taken later in 2005 revealed that this identification was incorrect, and that MPL remains lost. NASA is hoping that the higher resolution cameras of the Mars Reconnaissance Orbiter, currently in Martian orbit, will finally locate the lander's remains.

    As for the fate of the two Deep Space 2 microprobes, the probes apparently reached Mars without incident; however, communications was never established after landing. The cause of the microprobes' failure is unknown. The crash review board suggests several possible causes for failure.
  • The probe radio equipment had a low chance of surviving the impact
  • The probes may have hit ground too rocky for survival
  • The batteries on the probes, which had been charged before launch almost a year earlier and not checked since then, might not have retained sufficient power.

    The recently launched Phoenix Lander carries some instruments derived from those on MPL.

    The above image shows the landing site for the Deep Space 2 microprobes, as taken by the Viking 2 Orbiter. The image is approximately 140 km across, and is located at 73° South, 210° West.