Saturday 16 November 2019

Curiosity’s Discovery of Unexpected Oxygen Events on Mars and Implications for Life


Curiosity’s Discovery of Unexpected Oxygen Events on Mars and Implications for Life


There is new paper out, with some interesting news about the Martian atmosphere, based on data taken by the Curiosity probe (Seasonal Variations in atmospheric composition as measured in Gale Crater, Mars.  Trainer, et al.  Journal of Geophysical Research: Planets).  The title is descriptive of the work, but under-emphasises what I think most people find exciting, which is unexpected and unexplained variations in the proportion of oxygen in the Martian atmosphere found by Curiosity, over about a 4 year period.

Background on Martian Seasons and the Martian Atmosphere

To help understand what is going on, we need to first look at some other graphs in the paper and talk about the seasons on Mars.



The graph above (Figure 1 in the paper) shows how atmospheric pressure changed during the Martian years for which Curiosity took readings.  You can see that it had peaks and troughs.  The biggest troughs were in Northern Summer/Southern Winter, when the pressure falls to about 7 millibars.  There were other troughs in Northern Winter/Southern Summer.
In both cases, the minima are caused by carbon dioxide (CO2) freezing into the polar ice cap in one or the other hemisphere.  The Northern Summer/Southern Winter minimum is lower because the Southern Polar Ice Cap is much larger than the Northern Polar icecap, indicating that more CO2 is absorbed at this time.  Basically, the southern winter is colder than the northern winter, due to the eccentricity of Mars’ orbit having it farther than the sun at that time than during the northern winter (the seasons are mostly caused by the planet’s axial tilt, of course).  Conversely, the maximum pressure is during the spring/fall periods, when the least amount of CO2 is locked up in the two icecaps.


The fact that it is CO2 that is being absorbed at the poles is indicated by the graph above (Figure 5 in the paper), which shows the percentage of the Martian atmosphere that is accounted for by CO2 during the various times of the year, as well as the pressure.  It is evident that when the pressure is lowest, the CO2 percentage is also lowest, indicating that it is CO2 that is being absorbed and emitted seasonally, which reduces the atmospheric pressure.  That’s because the other gases in the atmosphere don’t freeze out at Martian temperatures (Nitrogen, Argon, Oxygen) and are mainly inert (Nitrogen, Argon), so they are conserved throughout the year (except for oxygen, apparently).  By the way, these measurements come from SAM (Sample Analysis at Mars), which is based on mass spectrometry.



Of course, as the amount of CO2 in the atmosphere changes, and the amount of the other gases remains the same, their percentages will vary, being highest when the amount of CO2 is lowest, and lowest when the amount of CO2 is highest.  You can see that by comparing the above graphs (Figure 5 and Figure 7).

The Unexpected Variation of Oxygen Levels in the Martian Atmosphere

For me, the most interesting result of the paper is in the graph below (Figure 10 in the paper), which shows the percentage of Oxygen to Argon found in the atmosphere at Gale Crater, over four Martian years.  As you can see, during the first part of the year (0 to 180 degrees, corresponding to Northern Spring-Summer and Southern Fall-Winter), the proportion of Oxygen as compared to Argon is increasing - after that it falls off again.  This pattern appears in multiple years, though not at exactly the same levels.




Argon is an inert gas, and it remains a gas at Martian temperatures, so there is a steady stock of argon in the Martian atmosphere which is neither created, destroyed or absorbed.  Oxygen is obviously not inert (though it is expected to have a mean atmospheric lifetime of about ten years on Mars), and it also remains a gas at Martian temperatures.  So, clearly the amount of oxygen in the Martian atmosphere (at least at Gale Crater) varies over the year, in a quasi-periodic way, since the ratio of oxygen to argon is changing.  That implies that there is a source and sink for the oxygen, which cycles oxygen into and out of the atmosphere in a way that varies with the seasons on Mars.

To quote the paper:

“The SAM measurements of O2 in Gale crater do not show the annual stability or seasonal patterns that would be predicted based on the known sources and sinks in the atmosphere. As mentioned in §3.2.2, based on known sources and sinks O2 should show the same seasonal patterns and annual repeatability as Ar.”

 The authors calculate that the “unexpected seasonal increase” of oxygen amounts to about 400 parts per million or 10 to the 14th power oxygen molecules per cubic centimeter.  They reject the possibility that the oxygen is coming from breakdown of H2O or CO2 in the atmosphere, as the processes involved would be too slow (CO2) and/or there just isn’t enough of the required material (H2O).  Similarly, there don’t seem to be good candidates for atmospheric destruction  or sequestration of the surplus oxygen during the low seasonal periods.

That leads to speculations about some sort of surface processes, whereby oxygen is stored and released from a reservoir.  Superoxides, hydrogen peroxide (H2O2), ozone (O3), and perchlorates are some suggestions.  Again, though, the time scales for these processes seem far too long to be candidates for seasonal variation.  Also, surface temperatures on Mars are too low for these processes and the other reaction products that would be expected have not been seen.  So, it is a mystery.

There are some similarities between the seasonal oxygen variations and seasonal methane variations, but the correlations are not all that tight.  As they state: “with respect to O2 and CH4 on Mars, the observations to date are inconclusive as to whether there is a definitive correlation between the them.”
They also look at some other possible environmental correlations.  It does appear that there may be an inverse correlation between dust opacity and oxygen release.  Similarly for UV absorption and oxygen variations.

The paper sums it up thusly:

“Thus the observed O2 variability remains a mystery until further measurements, models, or experiments are able to identify likely mechanisms through which the O2 can vary on short timescales. It is hoped that hypotheses that may be testable with further in situ measurements by Curiosity arise while the mission is still operating in Gale Crater.”

Speculations on the Implications for Life

These are just some educated speculations:

  • Curiosity has also found unexpected releases of methane (plumes), which could be a product of living things (e.g. bacteria in the soil).
  • The Viking Labelled Release Experiment had results that could be explained by metabolic processes of living things (e.g. bacteria in the soil).
  • There appears to have been a combustion event during one of the other Curiosity experiments, while examining an ancient mudstone, so there appears to be some complicated organic chemistry compounds in the soil (kerogen like).
  • Now we have seen unexpected oxygen variation, which could be the product of life (e.g. photosynthesis on Earth releases oxygen).

It is interesting that a lot of findings are accumulating that we would be inclined to attribute to living things on the Earth.  The question becomes, at what point would the accumulated evidence on Mars tip the scales to favour the explanation for these findings as being the products of living things.  Just how much extraordinary evidence is needed to support an extraordinary hypothesis?  ?  I don’t claim to know, but it does make you wonder.

Sources:

·       Nasa probes oxygen mystery on Mars https://www.bbc.com/news/science-environment-50419917
·       (Seasonal Variations in atmospheric composition as measured in Gale Crater, Mars.  Trainer, et al.  Journal of Geophysical Research: Planets). 
·       Independent confirmation of a methane spike on Mars and a source region east of Gale Crater, Nature Geoscience, Marco Giuranna, et al.  April 2019
·       Life on Mars?  American Scientist, March-April 2006

Some Related Blogs

Humanity Lights a Fire on Mars and the Implications for Life on Mars
Life on Mars, Hawaiian style

Curiosity’s New Discovery of Methane on Mars and Implications for Life



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If you want to see an area that is remarkably evocative of the landscape of Mars, here on Earth, try Newfoundland’s Table Lands, as described in the book below (along with plenty of other interesting features of Newfoundland):

A Drive Across Newfoundland


Newfoundland, Canada’s most easterly province, is a region that is both fascinating in its unique culture and amazing in its vistas of stark beauty. The weather is often wild, with coastal regions known for steep cliffs and crashing waves (though tranquil beaches exist too). The inland areas are primarily Precambrian shield, dominated by forests, rivers, rock formations, and abundant wildlife. The province also features some of the Earth’s most remarkable geology, notably The Tablelands, where the mantle rocks of the Earth’s interior have been exposed at the surface, permitting one to explore an almost alien landscape, an opportunity available on only a few scattered regions of the planet.

The city of St. John’s is one of Canada’s most unique urban areas, with a population that maintains many old traditions and cultural aspects of the British Isles. That’s true of the rest of the province, as well, where the people are friendly and inclined to chat amiably with visitors. Plus, they talk with amusing accents and party hard, so what’s not to like?

This account focusses on a two-week road trip in October 2007, from St. John’s in the southeast, to L’Anse aux Meadows in the far northwest, the only known Viking settlement in North America. It also features a day hike visit to The Tablelands, a remarkable and majestic geological feature. Even those who don’t normally consider themselves very interested in geology will find themselves awe-struck by these other-worldly landscapes.



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And now that you have read about some real cutting-edge science, you should think about reading some Science Fiction (because all work and no play can make you a dull person, or so they say). 

The Witches' Stones, Book 1 - Rescue from the Planet of the Amartos

Young Earth woman and spaceship mechanic, Sarah Mackenzie, has unwittingly triggered a vast source of energy, the Witches' Stones, via her psychic abilities, of which she was unaware. She becomes the focal point of a desperate contest between the authoritarian galactic power, known as The Organization, and the democratic Earth-based galactic power, known as The Terran Confederation. The Organization wants to capture her, and utilize her powers to create a super-weapon; the Terra Confederation wants to prevent that at all costs. The mysterious psychic aliens, the Witches of Kordea also become involved, as they see her as a possible threat, or a possible ally, for the safety of their own world.

A small but fast scout-ship, with its pilot and an agent of the Terra Confederation, Coryn Leigh, are sent to rescue her from a distant planet at the very edge of the galaxy, near space claimed by The Organization.  Battles, physical and mental, whirl around the young woman, as the agent and pilot strive at all costs to keep her from the clutches of the Organization.



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