REMS and the global dust storm on Mars

Since the end of May, a global dust storm on Mars has affected the entire planet, including Gale crater where NASA’s Curiosity rover is located. Onboard is the Rover Environmental Monitoring Station (REMS), developed at the spanish Centro de Astrobiología (CISC-INTA), which continues to send data on the environmental conditions of the planet during the storm.

Dust is one of the most important factors in the atmosphere of Mars. It greatly affects the climate, the circulation, and the variability of the Martian atmosphere and therefore, the operations of the spacecraft missions exploring its surface. The dust suspended in the atmosphere of Mars is so fine that we might compare it to smoke on Earth.

Regional dust storms happen every year on the Red Planet just after southern spring equinox, when Mars is closer to the Sun and the incident solar radiation in the southern hemisphere reaches its highest levels. The regional storms end when the incident solar radiation declines after southern autumn equinox. We don’t understand the mechanism that causes some regional storms to end up becoming a global dust storm (GDS) like the one that currently affects Mars, but it turns out to be a cyclical phenomenon that occurs every 6 to 10 Earth years (3 to 5 Mars years).

One of the affected places is Gale crater, where NASA’s Curiosity rover is located. Gale is an impact crater 154 km in diameter. In its center is Aeolis Mons (“Mount Sharp”), rising more than 5 km above the lowest part of the crater. The crater structure isolates the interior of Gale from its surroundings and can dampen external atmospheric phenomena that approach Gale.

One of the ten instruments onboard Curiosity is REMS, which was developed at the Centro de Astrobiología. REMS is composed of a series of sensors that measure relative humidity, air and soil temperature, wind direction and speed, atmospheric pressure, and ultraviolet radiation.

In the 1970s, the Viking spacecraft gave us information about global dust storms. Now, thanks to REMS, we will be able to obtain onsite information about the current global storm.

In the first days of the phenomenon, the atmosphere became more and more opaque every Sol (Martian day) and “REMS detected that the pressure began to oscillate in a way that was unusual," says Javier Gómez Elvira, principal investigator of REMS. With the passage of time, REMS has also registered an abnormal thermal oscillation. "In just five days, maximum temperatures on Mars dropped 30ºC and minimum temperatures rose 10ºC," says Daniel Viúdez Moreiras, REMS team researcher. "The thermal difference between day and night went from 75ºC to a difference of 35ºC. There has also been a dramatic change in solar radiation reaching the surface during the storm, with a drop in irradiance levels in the ultraviolet bands greater than 90%”, he adds.

These changes in temperature are the result of the variation in solar radiation that reaches the surface of the planet compared with a normal day. Atmospheric dust has an important radiative impact: both the insolation and the infrared downward flux are affected by the dust content. Generally, dust has opposite effects in the visible and in the infrared. An increase in the amount of atmospheric dust reduces the maximum temperatures each day (reduces the incoming solar flux), but increases the minimum temperatures at night (retains the infrared energy emitted from the ground).

Regional dust storms also occur on Earth but, unlike Mars, they never trigger a global storm. The reason is that our planet has a much thicker atmosphere and larger gravity that prevent this evolution. This year's Martian regional storm, which began on May 30 and triggered the current GDS, is comparable in size to the 1977 storm, but it is smaller than its immediate predecessor, the 2007 storm. It is also smaller than storms in 1971 and 2001 that completely enveloped the planet, exposing only the highest peaks of the volcanoes in the Tharsis region.

To predict the evolution of such phenomena, researchers compare temperature changes in the middle layers of the Martian atmosphere with those of previous storms. Everything points to the conclusion that "based on the surface temperature data obtained with REMS, environmental conditions seem to be gradually returning to normal levels, although the current conditions will persist for a few more weeks," says Jorge Pla-García, CAB researcher who develops atmospheric Martian models with REMS data. What makes this dust storm truly unique is that it will be the first to be studied directly from the Martian soil with high-resolution instrumentation.

The increasing opacity of the atmosphere, which has come to mask the Sun, has not been a problem for Curiosity. Its activity continues during the storm without any apparent problems because it does not use solar energy. On the other hand, the same is not true for the other rover active on the Martian surface, Opportunity. It uses solar panels to recharge its batteries, so it is currently in a 'hibernation' phase, saving energy and waiting for conditions to improve before it can get back on track. At least that's what scientists expect as they cross their fingers, hoping that this is not the end for the most traveler and veteran Martian rover.



Figure: Selfie of the Curiosity rover during Sol 2082 (June 15). The dust storm has reduced sunlight and visibility at the location of the rover in the Gale crater. © NASA / JPL-Caltech / MSSS

 

Fuente: UCC-CAB

 

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