Whirlwinds and Radiation

Thanks to our blooming power company, writing this report for yesterday's telecon proved to be a challenge in and of its itself. It was all air and radiation yesterday as the speakers talked about what the data from Curiosity's weather and radiation-measuring instruments so far show.

REM (NASA/JPL)

The Dynamic Albedo of Neutrons (DAN) and the Rover Environmental Monitoring Station (REM) instruments showed nothing out of the ordinary in terms of a discovery although 2 strange things amid the graphs stand out.

DAN sits on the side of the rover (NASA/JPL)

Measurements from REM show pressure patterns typical of a southern spring equinox turning into summer. As that happens we should see a gradual increase in average daily pressure. This happens because the southern polar cap, which contains carbon dioxide locked away as 'dry ice' plus water ice, will release its bulk of dry ice gas back into the atmosphere as gas (i.e. sublimation) as summer approaches (this process leaves behind an ice cap richer in water ice as that cannot melt nor vaporise under current Martian conditions). This has been noticed together with a daily rise and fall of pressure which is caused by daily heating of the atmosphere during the day (which lowers the pressure) and cooling at night (which raises the pressure). These daily planetary transitions of pressure is called a 'thermal tide' (see the diagram below).

Thermal tide (NASA/JPL)

Things get interesting when we get to the wind data which shows two things. The first, more dramatic, find is a period of time when the direction of wind started to change in a sudden manner. These changes corresponded to significant dips in pressure by about 1 to 2 pascals. This indicates a small, low pressure with high speed winds  system passed over the rover at the time i.e. a whirlwind or dust devil which are common on Mars as well as Earth. Curiosity didn't image these events maybe because they simply missed them (there were 2 events on sol 75 of the mission) or, more likely, they weren't carrying enough dust to make themselves visible. This would agree with orbital images which can spot any signs of a previous episode of dust-moving-whirlwinds. None have been seen in Gale crater so far. It should be noted that despite the image below, Mars' dust devils have not enough power to blow over or damage the rover in any way because of the comparatively thinner air density.

Dust devil on Earth (Jeff T. Alu, Commons)

Second, the speakers at the telecon mentioned about the wind patterns in the area. Winds were simpler to understand in previous missions because their areas of investigation were mostly flat areas of land. But here the topography is wild and that makes the wind much harder to understand. The team expected to get winds directed towards them from a north-south direction, directed so by the slopes of mount Sharp that lies just south of the rover. Instead REM is giving directions from the east-west direction, indicating that it might actually be the rim of the crater that is directing the wind. The wind direction is, however, expected to shift to a north-south direction when the rover starts driving up the slope of Sharp. As Claire Newman, the PI of the REM package put it, it would  be a big surprise if that didn't happen. Already their computer models are being put to the test which also allows us to test out forecasting methodologies used here here on Earth (a direct return of investment).

Wind directions that are postulated to occur during the day. At night they reverse direction.
Curiosity is detecting a mixture of the winds directions marked blue painting a confusing picture
of the areas meteorology (NASA/JPL/ESA/DLR/FU Berlin/MSSS)

Radiation measurement is another key mission goal for Curiosity. The goal is to build up a comprehensive database of the total radiation levels on the surface of Mars for at least a whole Martian year to support future manned missions. So far the data shows an expected peak in radiation levels during the day (corresponding with the low pressure characteristic of the day). This is because with low pressure means that the atmosphere above the rover is even thinner than usual which means that there is less gas available to offer protection from radiation from space (which includes solar radiation, galactic and cosmic radiation). This means that potential astronauts might not want to idle around during midday especially during solar flare events which produce a heavier dose of radiation than usual. On Earth we derive protection from the Earth's powerful magnetic field (Mars' field has all but disappeared) and a thicker atmosphere which is rich in the crucial ozone gas which blocks excess ultra-violet rays.

Curiously there seems to be some evidence of a general upward trend in the radiation being received by DAN and may signal the existence of a new cycle that the team have yet to elucidate.

Can you see the trend upwards? (NASA/JPL/SwRI)

 And there you have it. SAM has already ingested another sample of Martian regolith and... the power is finally back after 2 whole days! Now I can cool down under the fan!