There was another discovery of methane on Mars recently
(late June 2019), a fairly strong signal of some 21 ppbv (parts per billion by
volume). This is one of the strongest
indications of methane on Mars yet, and was discovered by the Curiosity rover
on Mars in Gale Crater. It should be
noted that the very thin atmosphere of Mars is 95% carbon dioxide, and about 3%
nitrogen, so this methane is mostly mixed in with carbon dioxide, and thus
won’t oxidize. That said, it can be
taken out of the atmosphere by various other means.
One way to think of
this parts per billion measure is by imagining a cube 1 meter (1000 mm) by 1
meter by 1 meter, which is one cubic meter or one billion cubic millimeters. A
crystal of salt is about .3 mm, so it would take out 25 such crystals to fill a
cubic millimeter. Therefore, if you
mixed about 25 crystals of table salt from the grocery store into a cubic meter
of tap water, the salt would be at about 1ppbv in the water. Of course the methane on Mars was in a
gaseous state, at a very low gas pressure, so the comparison is just meant to
be suggestive of the proportions involved.
Here is a rundown of the various discoveries of methane on
Mars so far:
- 2019 – Curiosity (surface of Mars), about 21 ppbv. That was followed by a 1 ppbv finding a week later by Curiosity, indicating that the 21 ppbv event was likely a plume (a large short term release rather than a small steady release).
- 2016 – Current, 0 ppbv by Mars Trace Gas Orbiter (orbiting Mars). It is odd that this detector hasn’t found anything, it may be that methane is destroyed in the upper atmosphere.
- 2012-2016 – Curiosity, seasonal background measures, varying from .2 to .7, with a seasonal component.
- 2013 – Curiosity, 7 ppbv. Likely a plume.
- 2013 – Mars Express (orbiting Mars), 15 ppbv. Measured the day after the Curiosity reading (from orbit), providing an independent verification of the same event.
- 2004 – Mars Express, 0 to 30 ppbv.
- 1990s – Current, various Earth-based observations, 10 to 50 ppbv.
The fingerprint of CH4 (methane) is shown in the graph
below. The graph shows the actual
spectrum, compared with several synthetic spectra, that would be expected given
different levels of methane. The actual
readings correspond to the synthetic spectra of 13 and 18 ppbv, yielding an
intermediate reading of 15 ppbv.
As noted earlier, this was an independent finding, that
corresponds with the in situ finding by Curiosity the previous day. It is very unlikely that the two different
instruments on two different platforms, would just happened to give false
positives from the same general area at the same general time. This is important, as many of the earlier
methane observations had been doubted, for various reasons.
The researchers then went further, and attempted to pinpoint
the likely source of the methane emissions.
The keys to their search were the following:
- The source couldn’t be too far from Gale Crater (less than 800 km) as methane would be fairly quickly dispersed, and thus it would require an inordinately large release to be from a very distant source and still register at this level.
- It was probably a very time limited release, as readings a few days before and few days after the Mars Explorer 15 ppbv observation were back to being quite low. Similarly, the high reading in situ by Curiosity lasted for only a short period of time.
The researchers then divided up the area around Gale Crater
into a grid, and estimated the likelihood that the plume arose from different
areas of the grid, based on knowledge of methane seepage from Earth and weather
patterns on Mars. They simulated, via a
Monte Carlo computer program, methane releases at different locations and concentrations,
and tracked whether these simulated events would leave a concentration similar
to that seen, at Gale Crater. From those
simulations they concluded that the release probably came from the east or
southeast of the crater, within about 500 km.
Geological theory implies that the methane release would
have most likely originated from a fault zone.
There do seem to be such areas to the east of Gale Crater, known as the Medusae
Fossae Formation. It is thought that
permafrost and ice would exist underground there, which would trap subsurface
methane, occasionally releasing it during partial melting episodes.
So, now it seems like we have
pretty conclusive evidence of methane releases on Mars. Of course the big question is what is the
source of the methane?
·The most tantalizing possibility is life,
probably bacterial, since life produces a lot of the methane found in the Earth’s
atmosphere, everywhere from cows’ stomachs, to hot springs, to the depths of glacial
ice.
·The other major possibility is the geological
process known as serpentinization, whereby olivine is converted to serpentine
via reaction with water. This releases
hydrogen molecules, which can then combine with carbon from CO2, producing
methane CH4, with the help of certain catalysts. However, this generally requires quite warm
water (300 degees Kelvin or about 30 degrees Celsius), and that might be hard
to find on Mars, even deep underground.
Naturally, it is the possibility of
life that interests most people. That
issue might be settled by determining the relative abundances of carbon 12 to
carbon 13 in the methane. Life will
produce a greater proportion of carbon 12, or at least that has been the
finding on Earth.
Another type of evidence that should help
determine the life vs geological origin of Mars methane is whether it is seen
in association with propane or ethane, as opposed to sulphur dioxide. The former would imply life, the latter
geology. The instrumentation on the Mars
Trace Gas Orbiter was meant to help make this distinction, but so far it hasn’t
turned up anything, strangely enough.
So, the source of Mars methane ultimately remains a mystery.
Sources:
·
Mars rover detects ‘excitingly huge’ methane
spike, Nature June 2019.
·
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
·
Methane Mystery, ESA website
·
Trace Gas Orbiter, Wiki
Some Related Blogs
Humanity
Lights a Fire on Mars and the Implications for Life on Mars
Life on
Mars, Hawaiian style
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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). Here’s a novel that features a neutron star
(and a pretty girl, who is also an engineer, among other characters). The second book in the series features a
lunar near-catastrophe and some science about Lagrange points:
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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And 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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