Out of the glare of the Sun

CuriosityIt’s been over a month since I last reported on the Mars Science Laboratory mission on Mars. It’s not that I’d forgotten about it or lost interest in writing MSL reports; the lull has been because during the month of April, we’ve been in a period of Solar conjunction, which places Earth and Mars on opposite sides of the Sun relative to one another.

During these periods, communications between Earth and vehicles operating on and around Mars are severely disrupted / curtailed due to interference from the Sun, so NASA effectively places all of their Mars missions on “autopilot” until full communications can be re-established with them from Earth. This happened early in May, and since then, mission scientists and engineers have been running the Curiosity rover through a series of checks to confirm it is still OK after its enforced silence and also completing a complete software update.

Just prior to the moratorium on Earth / Mars communications coming into effect, Curiosity had been engaged in analysing samples obtained from drilling into a rock dubbed “John Klein” (see: Getting the scoop on drilling, and: It probably doesn’t taste like chicken …). The analysis was performed by the rover’s on-board Chemistry and Minerology (CheMin) and Sample Analysis at Mars (SAM) instruments, and produced evidence of an ancient wet environment that provided favorable conditions for microbial life, including both the elemental ingredients for life and a chemical energy gradient such as some terrestrial microbes exploit as an energy source.

Sol 229 (March 29th, 2013) The first holes drill into rock by NASA’s Mars rover Curiosity, with drill tailings around the holes plus piles of powdered rock collected from the deeper hole and later discarded after other portions of the sample had been delivered to analytical instruments inside the rover. The two holes are each 1.6 cm (0.6 in) in diameter. The shallower hole was cut on Sol 180 (Feb. 6, 2013) as a preparatory test. The deeper hole was bored on Sol 182 (Feb 8, 2013) and cuttings from this hole gathered by the drill were delivered to Curiosity’s on-board Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) instruments.

A Reduced, but Still Dynamic Atmosphere

Mars has a very thin atmosphere, so thin that the highest atmospheric density on Mars is equal to the density of the atmosphere found 35 km (22 miles) above the Earth‘s surface. However, evidence for free-flowing water having once existed on Mars suggests that the atmosphere was once very much denser. The mystery has been what happened to that atmosphere? Several theories have been put forward over the years to explain the apparent loss in atmospheric density, one of them being that over the millennia, much of Mars’ atmosphere “bled off” into space due to a combination of factors. As a result of data returned from Curiosity in March, scientists found the strongest evidence to date for this being the case.

As well as being able to “taste” and analyse Martian soil samples, SAM can also “sniff” and analyse the Martian atmosphere. An opportunity to do just this was carried out in the last week of March, and the data was transmitted back to Earth alongside that of the analysis of the “John Klien” rock sample.

This atmospheric analysis, using a process that concentrates selected gases, provided the most precise measurements ever made of isotopes of argon in the Martian atmosphere. Isotopes are variants of the same element with different atomic weights. “We found arguably the clearest and most robust signature of atmospheric loss on Mars,” said Sushil Atreya, a SAM co-investigator at the University of Michigan, Ann Arbor.

SAM found that the Martian atmosphere has about four times as much of a lighter stable isotope (argon-36) compared to a heavier one (argon-38). This removes previous uncertainty about the ratio in the Martian atmosphere from 1976 measurements from NASA’s Viking project and from small volumes of argon extracted from Martian meteorites. The ratio is much lower than the solar system’s original ratio, as estimated from argon-isotope measurements of the sun and Jupiter. This points to a process at Mars that favoured preferential loss of the lighter isotope over the heavier one – the lighter gas “bled off” into space.

Curiosity also carries a “weather station”, the European-made Rover Environmental Monitoring Station (REMS), which allows the rover to monitor the Martian atmosphere as it is today. REMS carries out a wide range of atmospheric measurements which are helping to build up a comprehensive set of data on wind speed, temperature, etc., but have also provided the first systematic measurements of humidity on Mars. REMS is also able to measure the passage of Martian dust devils, even when they cannot be captured by the rover’s cameras, by a combination of pressure, temperature and wind oscillations and, in some cases, a decrease is ultraviolet radiation. At the same time the Dynamic Albedo of Neutrons (DAN) has been able to provide data on the possible interchange of water molecules between the atmosphere and the ground.

When taken as a whole, the data gathered by REMS, DAN and even the rover’s laser-shooting ChemCam, provides ample evidence that while tenuous, the Martian atmosphere is still very dynamic – moreso than perhaps has been previously thought, despite the long history of observation of changing seasons and weather conditions (global dust storms, etc.), and data gathered by earlier missions.

Blowing in the Wind

While we have long known that Mars does have winds blowing across it – sometimes at speeds sufficient enough to generate dust storms which cover the entire surface of the planet, as mentions above), Curiosity was able to provide – if somewhat indirectly, and with the assistance of the Mars Reconnaissance Orbiter – a practical demonstration of the Martian wind in action.

During the so-called “seven minutes of terror”, when the MSL was making its descent through the Martian atmosphere, on its arrival at Mars in August 2012, the vehicle used a supersonic parachute to help slow it during a part of its descent. This parachute, together with a protective aeroshell, was detached from the vehicle some 2 km (1.25 miles) above the surface of Mars to allow the latter to make the final part of its descent using rocket motors. The parachute and aeroshell combination struck the ground several hundred metres away from Curiosity’s landing site, and since then has been images a number of times using the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s MRO.

In April 2013, NASA released selected images from HiRISE which show the parachute being blown about by the Martian wind, and which also shows changes in the impact marks created by the aeroshell attached to the parachute as the wind blows away the disturbed dust and exposed surface material.

This sequence of seven images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter shows wind-caused changes in the parachute of NASA’s Mars Science Laboratory spacecraft as the chute lay on the Martian ground during months after its use in safe landing of the Curiosity rover.

What Next for Curiosity?

Following the end of the communications moratorium with vehicles operating on / over Mars, MSL engineers re-established contact with Curiosity and spent a week check-out the vehicle’s status and uploading a new software set for the next phase of the mission. As regulars to these reports know, the rover suffered two computer glitches earlier in the year, one of which seriously impacted one of the two redundant computer systems on Curiosity – the so-called “A-side” computer. This system was fully recovered prior to the communications blackout, but Curiosity continues to operate on the “B-side” computer.

This has received a significant software update which, among other things, provides greater ability for the rover to navigate by itself. While the rover has had a degree of autonomous driving capability, it has primarily relied upon planners on Earth establishing daily routes for the rover to take, which it then essentially drives “blind” unless it encounters an issue. With the new software, Curiosity will be far more empowered to determine best routes to a given destination along its track and engage in greater autonomous hazard avoidance.

As the rover has switched to the “B-side” computer, it is also using a different set of navigation cameras – Navcams. While mounted in the same location as the Navcams it had been using, these cameras require further calibration tests.

Beyond these engineering activities, Curiosity has a new mission goal – a second drilling target has been selected in the “Yellowknife Bay” area, which is intended to obtain rock samples in order to confirm results from the first drilling, which indicated the chemistry of the first powdered sample from “John Klein” was much less oxidizing than that of a soil sample the rover scooped up before it began drilling.

This second drilling target, called “Cumberland,” lies some 2.75 metres (nine feet) west of “John Klein”, where the rover found evidence of an ancient environment favourable for microbial life. Both rocks are flat, with pale veins and a bumpy surface.

This patch of bedrock, called “Cumberland,” has been selected as the second target for drilling by NASA’s Mars rover Curiosity, with the favoured location for drilling lying in the lower right portion of the image.

“We know there is some cross-contamination from the previous sample each time,” said Dawn Sumner, a long-term planner for Curiosity’s science team at the University of California at Davis, when describing the reason for the additional drilling. “For the Cumberland sample, we expect to have most of that cross-contamination come from a similar rock, rather than from very different soil.”

Although “Cumberland” and “John Klein” are very similar, “Cumberland” appears to have more of the erosion-resistant granules that cause the surface bumps. The bumps are concretions, or clumps of minerals, which formed when water-soaked the rock long ago. Analysis of a sample containing more material from these concretions could provide information about the variability within the rock layer that includes both “John Klein” and “Cumberland”.

Related Links

All images courtesy NASA / JPL

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