LPSC 2017 Trip Report, 4/4

[To the previous chapter][To the beginning]

CLIMATE OPTIMUM ON MARS INITIATED BY ATMOSPHERIC COLLAPSE

Cold, dry and sterilized are three words that best describe Mars today. Yet we know that there were better times there. Warmer times with denser atmosphere and liquid water that left riverbeds clearly visible even today. How long ago was that? How long did that period last, what have started and stopped it? That’s where the certainty steps away to be replaced with various hypotheses.

One of them is proposed in this paper. At the first glance, it looks awkward. The concept behind it is akin to a fire being accidentally started by a firefighter machine arriving on a false call.

It states that warmer climate was a response to the very first atmosphere collapse on Mars. That collapse triggered release of large quantities of methane clathrates that have accumulated under martian soil earlier. Photolysis and oxidation products of that methane increased greenhouse warming to the point of climate change, enabling liquid water flows on the surface.

But did it all happen exactly like that? I guess nobody knows for sure yet.

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CAN MARS BE TERRAFORMED?

The short answer is No.

Of course, there are details. In theory, many approaches to that problem are imaginable. But at least the most straightforward of them isn’t likely to work. It suggests that if enough CO2 from the Martian polar cups is artificially evaporated, the greenhouse effect on Mars could be boosted to the point where the planet’s climate would become warm and self-sustaining.

However, after accounting for CO2 supply based on the most recent data, the authors concluded that there is not enough of that gas there for this project to work. And even complete evaporation of the Martian polar cups would warm the planet by ~10 C (~20 F) only. That would not be enough to shift the atmosphere into a self-sustaining warm mode.

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EFFICIENCY OF ATMOSPHERIC EROSION BY IMPACTS: ENERGY CONSIDERATIONS AND APPLICATIONS

Let’s start with Shuvalov parameters. They are formulas that relate efficiency of planetary atmosphere erosion by impacting asteroids to parameters of those asteroids, mainly mass and velocity:

That efficiency has a maximum. A meteorite (or an asteroid) that is too large or too fast is less efficient in “splashing out” an atmosphere than a smaller or a slower one:


[Efficiency of atmosphere erosion by an asteroid as a function of its Shuvalov parameter ξ. Image Credit: Shuvalov, V., 2009. Meteorit. Planet. Sci. 44, 1095-1105.]

By choosing asteroids of the maximum efficiency, one can calculate how many of them would be required to completely strip off the atmosphere of Venus. The answer is “a lot”. Unrealistically many. We are talking about (0.5-9)% of the mass of the Moon. The upper limit of that estimate exceeds Solar System asteroids’ mass combined. Using that figure, I can crudely estimate that the energy needed to deflect that enormous fleet of asteroids is no less than ~1027 Joules. That is a million times more than the current yearly energy “budget” of the whole human race.

Alas, the plan of terraforming Venus by removing its atmosphere with asteroid impacts remains a sci fi – at best.

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A GEOPHYSICAL PLANET DEFINITION

From the standpoint of geophysics, Pluto and all sufficiently large bodies like Titan, Ganymede or Europa are genuine planets irrespective of their orbits.

Their descriptions usually mention most features absent in small bodies but common in “real” planets, such as spherical equilibrium shape, differentiation, tectonic activity (current or past), atmosphere, certain resurfacing processes, formation and thermal history. In planetary science textbooks Pluto or Ganymede are more naturally presented in the same chapter with Mars or Venus rather than with small asteroids or comets. Language used when writing about Pluto is closer to that of Mars rather than of comets. Finally, the authors mention over 40 peer-reviewed publications referring to Titan and Europa as planets, “both pre- & post-IAU planet decision”.

And none of that depends on the body’s orbital parameters.

Therefore, the proposal is to stop messing around with “dwarf planets” and, without waiting for IAC approval (which is not needed anyways), just start calling all these bodies planets.

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Planetary Topography from Laser Altimetry

A great lecture on laser altimeters in service around other worlds. The video opens with honors and awards. If you are eager to see the technical part, jump to the 16th minute.

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NASA Headquarters Briefing

In this video, NASA reports on past progress, budget and plans. Q&A start at the 51st minute and is worth attention in its own.

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