Geotalks Webinar Recording: "Why on Earth have they put a Geologist on Mars?"

Mars is home to the solar systems’ largest volcano, its deepest canyon, and it has thick sedimentary rock formations that are mind bogglingly old. Join Dr Neil Hodgson to look at the view you get from the shoulders of NASA as we explore the geology of the Red Planet in one of our Geotalks webinars. Webinar recording is included in this article.
This article appeared in June, 2021


Why on Earth have they put a Geologist on Mars?

Nothing about Mars is normal. It is home to the solar systems’ largest volcano, its deepest canyon, and it has thick sedimentary rock formations that are mind bogglingly old. It is arid, cold, dusty and mostly red with nothing to breathe and little to do that doesn’t involve looking at rocks. So why are we still so fascinated? Because we have put a Geologist on Mars to read from the first pages of the most important book of all – the book of life.

With the spectacular arrival in the Jezero Crater of NASA’s latest robotic ‘geologist’, the Perseverance ‘Percy’ Rover on February 18, 2021, science fiction is becoming science fact. The safe landing of this incredible device alone was a technological masterclass, and somewhat more subtle that HG Well’s solution to crossing the void between the worlds that went so terribly wrong in Woking 124 years ago.

Stream On-Demand

This webinar took place on the 10th June 2021. The below video is the recording from the full session. 

Getalks Webinar Summary

Join Neil Hodgson to look at the view you get from the shoulders of NASA as we explore the Red Planet. We will unravel some odd geologies and some that can seem so Earth like. Spanning the seasonal antics of CO2 snow, exploding underground water reservoirs, volcanoes that erupt for 4 billion years with no plate tectonics and perhaps the strangest part – the 3 billion years of quiet winds gently blowing dust speck by speck to exhume water lain channels and deltas. Already we have seen breath-taking images from our brave ‘geo-robot’ on Mars – explore with Neil what this might mean for the geological and climate processes that have shaped our neighbour and the potential for us to be or perhaps just to have been, not alone to witness the Universe.

Questions Asked During the Live Webinar

Neil has very kindly answered all questions that were typed into the Q&A enabled chat box during the webinar. If you asked a question during the live the event and it was not answered, you might find it here!

How does one define North on Mars?

Good question. All the planets circle around the sun almost on a plane. Most of the planets rotate with axes that are at 90o to that plane (actually they all tilt a little – the earth and mars are tilted 23-35o from being at 90o to the plane. The sun also rotates so its axis is also at 90o to the plane. We have defined North on earth – and this is the same north (up if you like from the plane) on every other planet and the sun.

Uranus is different – its rotation is on the side – as if it has been knocked over by a bolide collision. All the planets rotate anticlockwise if you are looking down on them from the north pole, except for Venus which rotates backwards as if it has been knocked completely over by a bolide collision (!).

Fewer craters on flank of Olympus Mons due to burial by lava flows?

Yes – the youngest layer on Olympus mons is ca 2million years. The oldest – 3.5 billion years. So, this is a good example of how the dating by density of impacts works. Old – lots of impacts, young – not so many impacts.

Outside of Olympus Mount (red square on the presentation) there are 3 small and well aligned volcanoes right?

Yes – they are in a line – its mad that it’s so linear – the three volcanoes sit at the top of an extended bulge and are called the Tharsis Montes. These volcanoes are old too, at ca 3 bn years and have built to between 8 and 14 km high. NB - The Valley you can see to the east of the line of volcanoes is Valles Marineris. It too is very linear and to go from the west to the east is as far as from Long Beach California to Miami Beach in Florida.

Could the smaller craters within Olympus Mons' main large caldera be smaller (younger) calderas instead?

Indeed, you are right – there are 6 “nested calderas” – they just look like craters! There’s a few bolide imprints close to the caldera rim but the shield is immense – 21 km high so maybe easier to catch meteorites.

How many seasons are there in Mars?

Four, just like earth (well two – a hot one and a cold one and two transitional – so again just like earth).

Radial distribution of some lineaments around the crater??

I expect so – the movement of magma from chamber to chamber prior to eruption can be felt as Mars quakes.

Why is the sand red in colour? Oxidation?

Yes, the Iron in the basalt is oxidized – just like on earth.

Spiders = star dunes type??

The spiders on the south of mars near the pole are the remnant fissures left after the eruption of CO2 – this model is called the Keiffer hypothesis. They are built from seasonal CO2 snow. The dust patterns left by the eruptions show that there are winds blowing there of course most of the time – though gentle. The next season the spiders move in the direction of the wind – the direction of the dust marks. Star dunes occur when there is multidirectional wind and low sand flux. I suspect it would need very specific conditions to form on the scale that we see on mars although I have seen star dune ca 1km diameter 100m high spaced out on a desert surface. The properties of CO2 ice from which they are made should be considered – and you do get odd textures like the brain terrane forming. But the dendritic arms of the spiders do look more like collapsed fractures than smooth arms of sandy star dunes – however it is a really good observation and suggestion.

What is the real source of this huge quantity of C02 in Mars?

Good question. Whatever was in the atmosphere 4 GA has a) sunk into the ground (free water) b) reacted with rocks to make hydrated minerals, or c) been blasted into space by cosmic rays. All of this happened probably after the magnetic field shield to Mars switched off. Even though the atmosphere is 95% CO2 the greenhouse effect is minor just now because the atmosphere is so thin. Back 4 ga – the atmosphere was thinner, it was a lot hotter, have high water vapour content and rain probably so water could flow on the surface and not freeze. O2 vs CO2 on mars 4 ga – I don’t know but earth atmosphere had low O2 content until the banded iron formation algae changed the earth’s atmosphere to where we are today. On Mars – it just maybe didn’t get to BIF level of life before the magnetic field shut down. So, there is a lot of CO2 because the N2 was blown away by the solar wind and O2 never got into the atmosphere. Perhaps.

Any Mars-quakes?

Yes, the Insight lander has a geophone and has detected 500 mars quakes – up to 3.6 on the Richter Scale.

Does heat become trapped in the CO2 atmosphere on Mars?

Yes – the greenhouse effect is important – so it’s not really cold on Mars. But the atmosphere is thin, and Mars is a long way from the sun so it’s still really cold on Mars.

Is it observed Any Mountains, hills, valley and river flow?

I don’t fully understand the question, but I think the answer is yes – the highlands of 3.5-4.5 Ga are full of evidence for water, and lowlands 3 ga- recent have few signs of water. All the running water disappeared 3 ga or so – except for the water underground below the cryosphere which occasionally exploded to the surface when heated by volcanic activity.

Regarding the 3 "NE" aligned features beside Olympus mount: are they small craters? If they are small craters, some impacts on Mars seems not be aleatory

They are a string of volcanoes – the Arisa Mons, Pavonis Mons and Ascreaus Mons Volcanoes.

What instrument would you add to the next mission to Mars?

Me. Or, less likely to moan about the food - a drone that had autonomy to systematically scan the surface of mars – and disappear into the lava tubes, looking for organic chemicals – i.e. fitted with a Luminescence/Raman spectroscope.

What are results of radiometric measurement? Gamma ray spectroscopy?

Not sure of the question – Curiosity has a mass spec designed to analyse rocks and mineral chemistry that they retro designed to perform some K-AR dating on a basalt in Gale crater – finding a ca 3.8 Ga age. So I am told by Nasa – I can’t find that written up yet…

What happens if there is organic contamination from rovers on mars?

Good question. They have tried their best to ensure that there is no contamination of course. Most things on earth would die on mars in minutes, if they hadn’t died on the 9-month journey with no air. But extremophiles being what they are – it just might happen which would be a disappointment. There are quite a few bits of junk (heat shields), landers and rockets on Mars – any of them could have brought something – let’s hope not.

What was the depth of the palaeo-lake that filled the Jezero crater? Was it deep enough to favour anoxic conditions? Shouldn't we expect organic matter at the deepest part of the crater as well if life emerged?

Good question – 100m deep, possibly anoxic – but was any of Mars oxic at that time? Yes – pro-delta basin floor mudstones would be target 1. Secondly, fringing the lake (so up behind the delta where sulphates and carbonates are suspected from satellite spectroscopy – target 2. Curiosity was sampling mudstones at the bottom of Gale crater when it discovered complex carbon compounds and sulphur. In Gale crater, 380m of section have been mapped so far. Was that crater 380m deep? Or did the crater slowly fill up over time?

The progrades that Percy photographed are 10-12 m high – but these I think are channel features – so fluvial dunes in the rivers feeding the lake telling us the water depths in the river channels of the delta – we’d need to measure the sequence from basin floor muds through the progrades up into the channels. The Delta is some 50m above the basin floor where Percy is now – so I’d say the maximum water depth was ca 50m. But maybe we’ll see something that changes that.

There are basaltic eruptions on the surface of the Mars. How about acidic, andsite volcanic rocks?

I love this question. Like earth most of the volcanic rocks are Basaltic– not evolved volcanics (I know our mountains have granites but ocean plates are 5/7 ths of the Earth). But on Mars – no plates. Andean type Granites and evolved magmas occur on earth where plates have collided and/or subducted. This doesn’t happen on Mars. The plate collision granites we see on earth are found where they have been uplifted and erosion has exposed them (and there was subduction etc – you know the story). This doesn’t happen on Mars. One more thing - the small size of Mars and low gravity means that the buoyant forces of magma are weaker on mars – so most magma probably cools in the crust – is never erupted because it can’t break through to the surface. There may be more complexity in the outgassing of volatiles early (earth too) but lack of re-injection of volatiles by subduction. However, on the other hand, in some of the big magma chambers below the big volcanoes, crystal fractionation will be evolving the lavas – so you do get evolved basalt lavas which get to the surface and give us lavas and tuffs. But we can’t map them without sampling them. And here’s the odd thing. Of the 61 meteorites that are identified as parts of Mars that have landed on earth (evidenced from oxygen isotopes etc) called Shergottites, they are often evolved basalts (as well as lerzolites etc) . So, your question – where are the evolved volcanics – well there are less than on earth but the coarse-grained ones are still stuck deep in the crust because there are no plate tectonics etc. and the fine grained evolved basalts are probably all over - more of them than we know but they will look like basalts until we analyse them with XRD (which Percy has).

About the Speaker: Dr Neil Hodgson

Neil is a ‘hands on, get your fingers dirty’ geologist who loves nothing better than being in the field at the forefront of exploration. Since studying volcanoes on ocean islands for a PhD, Neil has been hunting for oil and gas on planet Earth for over 30 years. Working globally in various exploration roles for operating oil companies such as BP, BG, and Premier Oil, he has been continually distracted by the weird geologies of Mars. After directing exploration for Matra Petroleum in Russia, Neil joined a Multi-Client (MC) Seismic company to put hydrocarbon stories into their legacy datasets and acquire new datasets. He is currently working globally as the VP Geoscience with Searcher, the largest private MC seismic company on this world, and is AAPG Europe president, whilst also keeping an eye on what NASA is doing on the red planet.

Cover image credit: NASA/JPL-Caltech/ASU/MSSS

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