Seasonal dark streaks in Newton Crater on Mars (Source: HiRISE, MRO, LPL (U. Arizona), NASA)

Mars & Planetary Habitability at EPSC 2012

Wednesday at the European Planetary Science Congress saw the oral presentations of the Mars sessions, plus I caught a couple on planetary habitability.

Turns out Mars scientists edge out those on Mercury in the style stakes – one Italian researcher sported a truly impressive handlebar moustache – but the cool kids are all into habitability. Quelle surprise.

Curiosity Unfulfilled

A sample weather report from the REMS instrument on Curiosity Rover (Source: NASA/JPL-Caltech/CAB(CSIC-INTA))

I was surprised to find the Curiosity mission didn’t get a look-in in the research presented, though I shouldn’t have been: most of the lander’s activity has been systems-checking so far, so there’s little data as yet. There was a talk from Gomez, who worked on the Curiosity REMS instrument to record environmental conditions like temperature, pressure and humidity data, but it’s early days for that.  Instead, he concentrated on their lab experiments, which have been encouraging in that they showed bacteria can survive some extreme Mars-like conditions.

The Active Surface

Seasonal dark streaks in Newton Crater on Mars (Source: HiRISE, MRO, LPL (U. Arizona), NASA)

In the Mars talks, much of the work was on surface processes. Two of these concerned activity which is occurring at the present day: McEwen et al.’s work on seasonal dark slope streaks and Raack et al.’s study of seasonal activity in gullies near the south pole. McEwen et al. have found 20 sites at which the dark streaks come and go from season to season. Though they’re not definite about what causes them, they do seem to coincide with the region of Mars where there are chloride deposits, so it may be that they’re brines. As these have a lower melting point than pure water, they’re more likely to get melted out of the surface when the weather hots up in the spring and summer. I found it odd that they’d say they come and go seasonally when I have streaks in my own study area which last between years, so I’ll drop them an email and let you know here if I get an explanation back.

Raack et al.’s work on gullies in south polar pits was pretty convincing: these clearly do grow from year to year, with peak activity in mid-spring. They’re a little more shaky on their formation mechanism: there’s a correlation with the surface temperatures at which CO2 and H2O sublimate, so it’s likely both are involved in gully formation.

A slew of landforms

There were a whole suite of talks on surface landforms, from phyllosilicate (clay) knobs to desiccation cracks to fluvioglacial eskers. These were convincing to greater and lesser degrees, but what they did prove is that you can put together a clear and consistent argument of how a landform was formed by one process – and someone else can do the same to show it formed by a completely different process. It’s challenging when you can’t get down there and ground-truth your findings but to their credit, everyone was very open to fresh perspectives from their audience.

The cause of the recent flood lavas?

Young volcanic plains across the Elysium region of Mars (Source: Jaeger et al. (2010) Icarus: 205, 230-243)

Kurita et al. presented a convincing theory about why recent volcanism on Mars has flood-lava style rather than edifice-building. Put in simple terms, the Martian lithosphere is made of high-Fe basalt and at certain pressures and temperatures this metamorphoses into eclogite, a denser material. Through the gradual thickening of the lithosphere over time, the thickest parts have recently (in the last 500Ma) reached depths there these conditions occur. When it does, the bottom of the lithosphere becomes denser than the mantle and delaminates, falling off through the mantle. This causes a counteracting upwards mantle flow and decompression melting of the mantle forms the magma which forms these flood lava eruptions. This is a nice neat theory, though of course that doesn’t mean it’s actually happening. Their model’s supported partly by lab experiments which show the transformation occurs at the relevant depth, and partly by the geographical location of these lavas at the north-south crustal dichotomy, where thick lithosphere is juxtaposed to thinner lithosphere through which magma could more easily ascend. It may not be proof, but it’s certainly suggestive.

Our Quest for Life of Icy Moons

An artist's concept of JUICE and Ganymede. (Source: ESA)

Over in the Habitability session, Grasset et al. went into the potential for life on Europa and Ganymede. This was much as I’ve outlined here and here, but I was interested to hear their justification for neglecting Europa in favour of Ganymede in the JUICE mission. It seems to hinge on how much more uncertain we are that Ganymede CAN support life, along with the likelihood that there a load more Ganymede-like exoplanets out there, making it very important that we work that out. As I’ve said, with dense ice mantle hundreds of kilometres thick between the liquid water and silicate portion of Ganymede, we can’t be sure enough nutrients can get through to that sea to support life. JUICE is aimed at determining that once and for all and it will be studying the moon in detail in pursuit of that goal. At closest approach, they hope to have it orbiting Ganymede at 200km from the surface!

Meanwhile, they accept that Europa is very likely to be able to support life in its subsurface ocean, so the question there is just how much interaction there is between that ocean and the surface. As Grasset described how much work had gone into trying to get this information out of the two flybys the moon’s been allocated, you could practically see the scientists pulling their hair out in frustration: way too little time for something incredibly important. So I feel a little reassured that the Ganymede work has value, but I’m still frustrated that Europa is the loser in the equation.

Meanwhile, on Enceladus…

And while on the topic of icy moons, I also picked up on a nice piece of work from the Outer Planet Satellites poster session. Work by Beuthe at the Royal Observatory of Belgium shows that tidal stresses which cause faulting on the surface of these moons are greater where the lithosphere is thinner. On Enceladus, melting from beneath has made the lithosphere thinnest at the south pole, so that means tidal forces work together with the eruptions to form the great tiger stripe fractures in that region.