Ashwin Vasavada, NASA Jet Propulsion Laboratory, Pasadena, Calif.; Deputy Project Scientist for Mars Science Laboratory
Manuel de la Torre Juarez, JPL; Investigation Scientist and Co-Investigator for Rover Environmental Monitoring Station (REMS) on Curiosity
Claire Newman, Ashima Research, Pasadena; Collaborator for REMS on Curiosity
Don Hassler, Southwest Research Institute, Boulder, Colo.; Principal Investigator for Radiation Assessment Detector (RAD) in Curiosity
Ashwin Vasavada talked us through the image of 5 scoops of soil that Curiosity lifted on Rocknest.
Curiosity used a mechanism on its robotic arm to dig up five scoopfuls of material that resulted in the the five bite-mark pits visible in this image taken bij de left Navcam of the rover. Each of the pits is about 5 centimeters (2 inches) wide.
The fifth scoopful at Rocknest — leaving the upper middle bite mark — was collected during sol 93 (Nov. 9, 2012). This image was taken later that same sol. A sample from that fifth scoop was analyzed over the next two sols by the SAM (Sample Analysis at Mars) suite of instruments inside the rover. A second sample from the same scoopful of material was delivered to SAM for analysis on Sol 96 (Nov. 12). No further scooping of soil samples is planned at Rocknest.
The first Rocknest scoop was collected during Sol 61 (Oct. 7). Fine sand and dust from that scoopful and two subsequent ones were used for scrubbing the inside surfaces of chambers in the sample-handling mechanism on the arm. Samples from scoops three, four and five were analyzed by the Chemistry and Mineralogy instrument (CheMin) inside the rover.
Manuel de la Torre Juarez talked about the regular signs of whirlwinds passing the rover in Gale Crater
Twenty-one times during the first 12 weeks on Mars, the rover’s Rover Environmental Monitoring Station (REMS) detected brief dips in air pressure that could be caused by a passing whirlwind. The blue line in this chart shows two examples, both shortly after 11 a.m. local Mars time, when the air pressure dipped on sol 75 (Oct. 25, 2012). In both cases, wind direction monitored by REMS changed within a few seconds of the dip in pressure, as indicated by the green line on the chart. That is additional evidence that the pressure dips were whirlwinds.
A Finnish, Spanish and American team is using REMS, which Spain provided for Curiosity, to watch for signs of dust devils — whirlwinds carrying dust.
In many regions of Mars, dust-devil tracks and shadows have been photographed from orbit, but those visual clues have not been seen at Gale Crater, where Curiosity is working. The evidence from REMS indicates that whirlwinds may be forming in Gale Crater. While Curiosity is watching for them with cameras on some days, researchers are also considering the possibility that these swirling, convective winds do not lift as much dust at Gale as in other parts of Mars.
In this chart, the air-pressure scale is in Pascals. The wind direction scale is an estimate in degrees relative to the front of the rover. On Sol 75, the rover was facing approximately westward, and 90 degrees on this graph indicates winds coming from the north.
Claire Newman elaborated on the mountain winds that are present at Gale Crater
This graphic shows the pattern of winds predicted to be swirling around and inside Gale Crater. Modeling the winds gives scientists a context for the data from the Rover Environmental Monitoring Station (REMS).
Curiosity’s current location is marked with an “X.” The rover’s setting within a broad depression between Mount Sharp to the southeast and the rim of Gale Crater to the northwest strongly affects wind measurements collected by REMS.
This snapshot shows midday conditions. In the daytime, winds rise out of the crater, shown by the red arrows, and up the mountain, shown by the yellow arrows. Blue arrows indicate winds that flow along the depression and seem, to Curiosity, to be coming up out of the depression since Curiosity is near the bottom. At its current location, Curiosity may be seeing a mixture of these winds, making it challenging to understand its weather readings.
The patterns reverse in the evening and overnight, when winds flow in the downhill direction.
The background image is an oblique view of Gale Crater, looking toward the southeast. It is an artist’s impression using two-fold vertical exaggeration to emphasize the area’s topography. The crater’s diameter is 154 kilometers (96 miles).
The image combines elevation data from the High Resolution Stereo Camera on the European Space Agency’s Mars Express orbiter, image data from the Context Camera on NASA’s Mars Reconnaissance Orbiter, and color information from Viking Orbiter imagery.
Next Claire talked about the pressure cycles on Mars
This graph shows the atmospheric pressure at the surface of Mars, as measured by the Rover Environmental Monitoring Station on Curiosity. The blue curve shows data from Sol 31 (Sept. 6, 2012) and the green curve shows data from Sol 93 (Nov. 7, 2012). Pressure is a measure of the amount of air in the whole column of atmosphere sitting above the rover.
The overall increase in pressure between Sol 31 and Sol 93 is the signature of the entire Martian atmosphere growing in mass as we move into springtime in the southern hemisphere. This happens because the south pole receives more and more sunlight, and carbon dioxide vaporizes off of the winter south polar cap. Each year the atmosphere grows and shrinks by about 30 percent due to this effect. The curves also show a strong daily variation in pressure of around 10 percent, with a peak near 7 a.m. on Mars and a minimum near 4 p.m. This daily cycle in pressure is caused by a “thermal tide,” a global-scale pressure wave in Mars’ atmosphere driven by sunlight heating the ground and air.
Thermal Tides at Mars
This diagram illustrates Mars’ “thermal tides,” a weather phenomenon responsible for large, daily variations in pressure at the Martian surface. Sunlight heats the surface and atmosphere on the day side of the planet, causing air to expand upwards. At higher levels in the atmosphere, this bulge of air then expands outward, to the sides, in order to equalize the pressure around it, as shown by the red arrows. Air flows out of the bulge, lowering the pressure of air felt at the surface below the bulge. The result is a deeper atmosphere, but one that is less dense and has a lower pressure at the surface, than that on the night side of the planet. As Mars rotates beneath the sun, this bulge moves across the planet each day, from east to west.
A fixed observer, such as Curiosity, measures a decrease in pressure during the day, followed by an increase in pressure at night. The precise timing of the increase and decrease are affected by the time it takes the atmosphere to respond to the sunlight, as well as a number of other factors including the shape of the planet’s surface and the amount of dust in the atmosphere.
Don Hassler explained the daily cycles of radiation and pressure at Gale Crater
The graphic on the right shows the daily variations in Martian radiation and atmospheric pressure as measured by Curiosity. As pressure increases, the total radiation dose decreases. When the atmosphere is thicker, it provides a better barrier with more effective shielding for radiation from outside of Mars. At each of the pressure maximums, the radiation level drops between 3 to 5 percent. The radiation level goes up at the end of the graph due to a longer-term trend that scientists are still studying.
The red line indicates the total dose rate of radiation from both charged particles and neutrons, as detected by the Radiation Assessment Detector (RAD. The blue dots represent atmospheric pressure in units of Pascal (divided by four) taken by Curiosity’s Environmental Monitoring Station (EMS). The atmospheric data were scaled to fit in the same plot as the radiation data.
The dosages and pressures are plotted over five sols, or Martian days, from the 21st sol of operations to the 26th. That corresponds to Aug. 26 to Sept. 1, 2012. Curiosity landed on Mars on Aug. 5, 2012. Radiation dose is given in arbitrary units to reflect the magnitude of the variations. Calibration of the absolute dose levels is ongoing.
Hassler continued with an explanation of the longer-term radiation variations at Gale Crater
The graphic to the left shows the variation of radiation dose measured by the Radiation Assessment Detector (RAD) on Curiosity over about 50 sols, (On Earth, Sol 10 was Aug. 15 and Sol 60 was Oct. 6, 2012.)
The dose rate of charged particles was measured using silicon detectors and is shown in black. The total dose rate (from both charged particles and neutral particles) was measured using a plastic scintillator and is shown in red.
The variations occur each day and also on longer timescales. The daily variations are driven by the thickness of the Mars atmosphere. The longer-term variations appear to be driven by the structure of the gas and plasma in the interplanetary space near Mars. This structure, called the heliosphere, is magnetically tied to the sun, and rotates together with the sun over a period of about 27 days. The density of this heliospheric structure, as seen at Mars, varies with a roughly 27-day period, and provides “shielding” from galactic cosmic rays outside the solar system, in much the same way that the Mars atmosphere provides shielding.
The graphic has a few gaps for software uploads and other mission priorities. Radiation dose is given in arbitrary units to reflect the magnitude of the variations. Calibration of the absolute dose levels is ongoing.