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.
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
Germany: https://www.amazon.de/dp/B07NMR9WM8
Australia: https://www.amazon.com.au/dp/B07NMR9WM8
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.
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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