Mars Pathfinder

Atmospheric data
All graphics NASA.
   

This animation shows three images taken on the morning of Sol 16. Between frames, you can see the clouds moving across the screen from the northeast. The clouds are thought to be about 10 miles high and moving in 15 mile per hour winds. 
 
Pink stratus clouds are coming from the northeast at about 15 miles per hour (6.7 meters/second) at an appoximate height of ten miles (16 kilometers) above the surface. The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken by the Imager for Mars Pathfinder (IMP) on Sol 16 about forty minutes before sunrise showing areas of 2the eastern Martian horizon. 
 
This is the first color image ever taken from the surface of Mars of an overcast sky. Featured are pink stratus clouds coming from the northeast at about 15 miles per hour (6.7 meters/second) at an appoximate height of ten miles (16 kilometers) above the surface. The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken about an hour and forty minutes before sunrise by the Imager for Mars Pathfinder (IMP) on Sol 16 at about ten degrees up from the eastern Martian horizon. 
 
This is the first image ever taken from the surface of Mars of an overcast sky. Featured are stratus clouds coming from the northeast at about 15 miles per hour (6.7 meters/second) at an approximate height of ten miles (16 kilometers) above the surface. The "you are here" notation marks where Earth was situated in the sky at the time the image was taken. Scientists had hoped to see Earth in this image, but the cloudy conditions prevented a clear viewing. Similar images will be taken in the future with the hope of capturing a view of Earth. From Mars, Earth would appear as a tiny blue dot as a star would appear to an earthbound observer. Pathfinder's imaging system will not be able to resolve Earth's moon. The clouds consist of water ice condensed on reddish dust particles suspended in the atmosphere. Clouds on Mars are sometimes localized and can sometimes cover entire regions, but have not yet been observed to cover the entire planet. The image was taken about an hour and forty minutes before sunrise by the Imager for Mars Pathfinder (IMP) on Sol 16 at about ten degrees up from the eastern Martian horizon. 
Every several days, Mars Pathfinder will image the sunrise and sunset on Mars. Future images will show a larger area -- we have a higher data rate than we expected when we planned this image, so we can get more information. Images taken at sunset, like this, and up to two hours later, will be used to investigate the distribution of dust within the Martian atmosphere. Already, we can see some dust layers in the images. By seeing how the twilight fades with time -- it lasts for over two hours -- we can determine that the dust extends high into the atmosphere. 

Our observations of the Sun using the IMP camera showed more dust in the martian atmosphere than was expected. In fact, the amount of dust ("optical depth" of 0.4, to scientists) was comparable to Viking observations during clear (non-dust-storm) times. The measurements were made by taking images of the Sun with different colors and with the Sun at different elevations in the sky. As the Sun goes lower in the sky the light passes through more and more dust, becoming fainter and fainter, and allowing the amount of dust to be measured. 

On Mars, the dust intercepts essentially the same amount of sunlight in different colors. The reddish color of the sky is because the blue light is absorbed by the dust, but the red light is scattered throughout the sky. By contrast, the molecules in the Earth's atmosphere intercept about as much of the blue sunlight as the Mars dust does, because blue light is scattered easily by Earth's atmosphere (and red light is not, giving the Earth its blue sky).  

In future days, scientists will monitor the amount of dust in the atmosphere, and they will try to measure absorption by water vapor with a similar technique. Using other observations of the sky, scientists will measure the size and shape of the dust particles and try to determine how high in the atmosphere the dust extends. On some days, IMP will perform a cloud search, looking for clouds passing over the landing site. The Hubble Space Telescope will also observe Mars on some of the same days, so large clouds--if they are present--may be seen simultaneously from the Earth and from Mars. 
 
On sol 25, as the Hubble Space Telescope was preparing to take images of mars including the Pathfinder landing site, IMP watched the sunrise. This sequence of images was taken through the blue filter, and shows the sky just before sunrise continuing until the Sun rises out of the field of view. These images were taken as part of an atmospheric imaging project that was coordinated with the Space Telescope observations. They are also useful for refining our knowledge of the orientation of the landing site -- the position and timing of the sunrise give us a very good direction reference. 
 
This image was taken by the Imager for Mars Pathfinder (IMP) about one minute after sunset on Mars on Sol 21. The prominent hills dubbed "Twin Peaks" form a dark silhouette at the horizon, while the setting sun casts a pink glow over the darkening sky. The image was taken as part of a twilight study which indicates how the brightness of the sky fades with time after sunset. Scientists found that the sky stays bright for up to two hours after sunset, indicating that Martian dust extends very high into the atmosphere. 

 
This figure shows the variation with time of pressure (dots) measured by the Pathfinder MET instrument during landing period. The two diamonds indicate the times of bridal cutting and 1st impact. The overall trend in the data is of pressure increasing with time. This is almost certaily due to the lander rolling downhill by roughly 10 m. The spacing of the horizontal dotted lines indicates the pressure change expected from 10 m changes in altitude. Bounces may also be visible in the data. 
 
  The Mars Pathfinder ASI/MET experiment is measuring the atmospheric pressure at the Martian surface. The pressures measured during the first three Martian days (Sols) of the mission have average values near 6.75 millibars. Typical sea-level pressures on Earth are about 150 times larger (1013.25 millibars). The Pathfinder pressures are 10 to 20% smaller than those recorded 21 years ago during the same Martian season (middle northern hemisphere summer) by the Viking Lander 1. These differences may result from differences in the elevations of the Pathfinder and Viking 1 landing sites. Despite these differences, the Pathfinder and Viking 1 pressure measurements display a similar daily cycle, with minimum pressures near 4AM and 6PM, and maximum values near midnight and 10AM. These daily pressure variations are due primarily to the atmosphere's response to daytime heating and nighttime cooling. The much finer resolution of the Pathfinder measurements (one one-thousandth of a millibar) will aid in studies of small scale weather phenomena which have small pressure signatures. 
 
  Surface pressure, in units of millibars, measured by the Pathfinder lander on the martian surface. Oscillations in measured pressure during a day are caused by the warming/expansion of the atmosphere which follows the sun around the planet and the cooling/contraction which follows the night. Similar atmospheric processes occur on Earth. We interpret the observed variations to indicate the presence of suspended dust over a large portion of the planet and mixed upwards to several tens of kilometers in depth. We resumed complete diurnal coverage with our meteorology measurements at 7 AM on Sol 18, following the successful uplink of a flight software patch.

We believe we have seen the minimum annual daily-averaged pressure at the landing site, which apparently occurred on either sol 14, 15 or 16. Our lack of complete diurnal coverage makes this estimation a bit uncertain. We had predicted that the minimum would occur between sols 15-20 of the mission (I erred several days ago in saying we expected an additional 15 sols of decline before reaching the minimum). Our estimate was based upon Viking lander 1 measurements from 1976-1982 and upon results from numerical models. The data shown in this and the additional three ASI/MET plots span the time from landing ( ~3 AM on Sol 1) through our most recent data (2:12 PM PM on Sol 23)
 

Atmospheric Pressure "Movie"

Sol-to-Sol pressure variations on Mars: The movie is a sequence of 10 sols worth of pressure data collected by the MET pressure sensor. Note the sol-to-sol changes in the variation of pressure within each sol. The daily pressure cycle is primarily produced by the thermal tides in the Martian atmosphere. Note that on some sols, four distinct peaks and four minima can be seen, corresponding to four basic components of the thermal tide being present in the atmosphere. 
 
This figure shows the signature of a dust devil that passed over the Pathfinder lander on Sol 25. Since then we have seen several similar features. The black line shows surface pressure plotted over a period of approximately two minutes. The sharp minimum approximately 0.5% below the background pressure is very clear. The dashed curves show raw data from two hot wire wind sensor elements (Blue = Wind Sensor 4 = East Wind, Red = Wind Sensor 1 = West Wind). When the wind blows directly on an element it cools. It is clear from the figure that the East wind increases suddenly as the dust devil approaches the lander and the pressure begins to fall. As the dust devil passes over the lander, pressure begins to rise, the East wind dies away and the West wind increases suddenly. Finally as the dust devil moves away, pressure returns to normal and the West wind dies away. This is a textbook dust-devil signature. 
 
This figure is a very simplified schematic drawing of the dust-devil that passed over the Sagan Memorial Station on Sol 25. It shows direction of motion and the graphs of a textbook dust-devil in terms of wind speed and surface pressure. 
  The Mars Pathfinder Atmospheric Structure/Meteorology Experiment measures wind speed and direction with a sensor mounted on the top of the 40-inch (1 meter) tall meteorology mast. Measurements made during the late evenings and early mornings of the second and third Sols after landing indicate prevailing winds from the south-south-east. The wind direction then changed in the early afternoon, such that the prevailing winds blew from the north to north-east. These results are similar to those obtained by the Viking Lander 1 at this season. Wind speeds have not yet been precisely determined, but early estimates show that the winds are quite light (a few miles per hour) during the day, and somewhat stronger (about 10 miles per hour, or 16 kilometers per hour) at night. 
 
  Wind direction at the Mars Pathfinder site is indicated as the direction from which the wind
is coming: i.e. a southerly wind is a wind from the south. During the initial sols of the mission, wind direction rotated in a clockwise manner with time: southerly at night, westerly in the morning, northerly during early afternoon, and from the east in the evening. Winds from the south at night are consistent with flow down the Ares Valley at whose northern end Pathfinder is located. The change in the daily wind variation seen to begin late on sol 7 occurs in conjunction with a decrease in the measured sol averaged surface pressure and modulation to its diurnal cycle. Subsequently, we have seen a return to winds rotating through a full 360 degrees during the course of a sol. 
 
  Wind speeds have still not been absolutely determined from the signals we are receiving from the wind sensor located at the top of the ASI/MET mast. However, our wind sensor signals are strong, and do provide some qualitative information about wind speed (i.e., largest signal as indictaed in this plot corresponds to the fastest winds,...). During the mission's initial 10 sols, winds were strong during early morning hours. The time around noon also was a preferred time for relatively strong winds. Weakest winds occur during late afternoon/early evening on most sols. This general pattern of early morning maximum winds has persisted, as far as we can determine from our incomplete diurnal coverage, through to Sol 23. We continue to work towards producing the wind speed data set, and will put the data on this web page as soon as it is available. 
  10, 20, and 40 inches, (0.25, 0.50, 1.0 meters) above the solar panel. Air temperatures measured during the first three days of the mission show an afternoon high near +14 degrees Fahrenheit (264 Kelvin). [The 270 degree Kelvin temperatures measured at noon on Sol 1 were obtained while the mast was still lying down just above a warm solar panel]. During the day, the air temperatures measured by the lowest of the 3 sensors are 9 to 10 degrees Fahrenheit (5 to 6 Kelvin) warmer than those measured by the top sensor because the atmosphere is heated by the sunlit surface below it. At night, the ground cools more quickly than the atmosphere, and the warmest air temperatures are measured by the uppermost temperature sensor. These temperature differences provide information about the exchange of heat between the surface and the atmosphere. The Viking landers could not determine this quantity directly because they measured the air temperature at only one height (64 inches or 1.6 meters). The air temperatures measured by Pathfinder are slightly warmer than those seen 21 years ago at the nearby Viking Lander 1 site at the same Martian season. This may result because the somewhat darker surface at the Pathfinder landing site absorbs more sunlight than the Viking 1 Landing site. 
 
  Martian air temperature, in Kelvin (200 Kelvin = -100 Fahrenheit; 260 Kelvin = +8 Fahrenheit), measured by the three thermocouples (electronic temperature measuring devices) located at different heights on the Mars Pathfinder ASI/MET mast. The top mast thermocouple is located one meter above the outer edge of one of Pathfinder's three solar panels. The top of the solar panel is 0.4 meters (16 inches) above the martian surface, which puts the top mast thermocouple 1.4 meters (55 inches) above the surface. The middle mast thermocouple is located 0.5 meters above the solar panel; the bottom thermocouple at 0.25 meters. Since air temperature generally decreases with increasing distance from the sun-warmed ground during daylight hours, the bottom mast thermocouple measures the warmest temperature at those times of day. During the night, the ground rapidly cools and air temperatures are coldest nearest the ground. Thus, at night, the top mast thermocouple measures the warmest temperature. 
 

 
This figure shows RSS acceleration from the three Pathfinder science accelerometers plotted as a function of time during the Pathfinder spacecraft landing. Specific features are airbag deployment (1194 seconds), RAD motor firing (1198 seconds), the cutting of the bridal (1200 seconds), the first bounce (1204 seconds), and the second bounce (1210 seconds). 15 bounces are clearly shown before the high rate (32 Hz) data sampling period ends. Pathfinder is thought to have bounced and rolled for another 1 minute before coming to rest. The height of the peak shows how hard the lander bounced, and the time between peaks shows how high the bounce was (For example 6 seconds = 16.7 m, 5 seconds = 11.6 m, 4 seconds = 7.4 m, 3 seconds = 4.2 m, and 2 seconds = 1.9 m). 
 
  Atmospheric temperatures from the Mars Pathfinder Atmospheric Structure Instrument: This figure presents a preliminary evaluation of the atmospheric temperature structure encountered by Mars Pathfinder during its descent through the Martian atmosphere on July 4, 1997. The deceleration of the probe during its entry is directly related to atmospheric density. Pressures and temperatures can be derived from the density using well-established physical principles. The Atmospheric Structure Instrument measured the probe's deceleration using high precision accelerometers. The temperature profile measured by the Viking 1 lander during its descent to the surface of Mars on July 20, 1976 is shown for comparison. A key debate in the Martian atmospheric sciences community has been over whether Martian climate has changed significantly since the era of the Viking missions. The issue has been whether the lower and middle atmosphere of Mars (altitudes less than 50 km) are "cold" relative to Viking or whether they are "warm" as at the time of Viking. The temperature profile in this figure shows the upper atmosphere of Mars to be quite cold relative to Viking. In fact at about 80 km altitude, the temperature is the lowest ever measured on Mars-- a brisk -275 degrees Fahrenheit. The cold temperatures in this region are not surprising since Mars Pathfinder entered the atmosphere at 3 AM Mars Local Time when the upper atmosphere cools due to the lack of solar heating. Below 60 km altitude, the temperatures measured by Pathfinder are quite close to those measured by Viking. Therefore, the measurements by Mars Pathfinder, which represent one slice through the atmosphere at one location and time, show that the atmosphere is "warm" as it was at the time of Viking. 
 
  Temperature profile from Pathfinder Atmospheric Structure Instrument: This figure presents an evaluation of the atmospheric temperature structure encountered by Mars Pathfinder during its descent through the Martian atmosphere on July 4, 1997. The temperature profile measured by the Viking 1 lander during its descent to the surface of Mars on July 20, 1976 is shown for comparison. During the entry phase, a temperature below the condensation point for CO2 was registered at an altitude of 80 km above the martian surface. 
 
  This figure shows the entry vehicle deceleration in g's along its flight path during the entry phase of the mission. As the probe enters at 7.5 km/second, the deceleration forces produced by the atmosphere range from less than 10 micro g at time 0 (160 km) to about 20 g at 100 seconds (25 km). The deceleration pulse produced by parachute deployment is clearly seen at 185 seconds (10 km). Deceleration is plotted in logarithmic coordinates to reveal accelerations in the range 0.00001 to 20 g. These measurements allow the atmospheric density, pressure and temperature profiles to be calculated. 
 
  Atmospheric densities from the Mars Pathfinder Atmospheric Structure Instrument: This figure presents a preliminary evaluation of the atmospheric density structure encountered by Mars Pathfinder during its descent through the Martian atmosphere on July 4, 1997. The deceleration of the probe during its entry is directly related to atmospheric density. The Atmospheric Structure Instrument measured the probe's deceleration using accelerometers and these measurements were used in the derivation of this density profile. The density profile measured by the Viking 1 lander during its descent to the surface of Mars on July 20, 1976 is shown for comparison. Atmospheric densities above 60 km altitude at the time of the Mars Pathfinder entry are much lower (up to about a factor of 5) than at the time of the Viking 1 entry. These observations of upper atmospheric densities will be important in planning the aerobraking maneuver to put the Mars Global Surveyor spacecraft in its intended orbit starting in September 1997. The densities at lower altitudes also appear to be somewhat lower than those at the time of Viking. Further analysis of these observations will allow the determination of the variation of temperature with altitude. These results provide valuable detailed information on the Martian climate and by comparison with Viking results can provide information on the variation with time of the Martian atmosphere. 
 
Visit the Project Mars Pathfinder web page at NASA:

The missions are managed by the Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington, DC.