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Space travel: arrogance or vision?

Space travel: arrogance or vision?

Caroline Dorn

This week, Caroline Dorn, Ambizione Fellow at the University of Zurich, tells us her view on space travel and why we shouldn’t pack our bags just yet. 

Space exploration is experiencing a new boom, a come-back since the 60s & 70s! First discoveries of planets outside our solar system in the 90s have set the foundations of a new discipline that is exoplanet science – the field in which I am working in.

I enjoy that there is a lot of fascination from the public about the newly discovered distant worlds.

However, I observe a new fascination about space travel or space tourism among people that I find worrisome and dangerous.

Recent efforts of crewed missions to the Moon or Mars are driven by national or private egotism rather than the broadening of our understanding of other worlds. Here, I want to ask the question whether there is any value to our society in supporting space travel?

Often technological advances are put in front as a pro-argument. However, the billions of money could be directly invested in tailored research for societal benefits. It is not surprising that the vast amount of investments for space travel yields alongside innovations which find applications in other fields or our daily life. This is not unique to investments in space travel but simply a question of money and human power.

The perspective of mining other planets is often mentioned. Yet, it won’t solve the problem of limited resources that we have on Earth.  We need to find a way to deal with limited resources and how to handle our impact on the Earth’s ecosystem, which is the only one we know of. Mining other planets would only push the margin of available resources slightly further on the immense cost of energy, Earth’s natural resources, and human passion.

Yes, human passion. It takes a lot of enthusiasm to work in a specific niche such as space travel engineering or research. I think, such enthusiastic thinkers and pioneers are needed to create inclusive societies in balance with our ecosystem for present and future generations.

Travelling to other planets won’t save humankind. We are made for life on Earth. Even if humans would start living on other planets, evolution doesn’t stop. Humans wouldn’t be humans anymore. Humans are lifeforms from Earth.

In my view, the only justifiable argument for space travel is curiosity. Of course, it is fascinating to think that some people from Earth can leave the planet, travel through space and set their foot on a nearby planet that is Mars! What a fictional idea that may be possible to actually achieve!

To my disappointment, Switzerland’s only astronaut is promoting crewed space travel. For me, he is from an old generation for which the further-faster-higher principle seems still attractive. This thinking is anachronistic. Future missions must justify not only the societal and scientific benefits but also the sustainability of resource use, which is the big challenge of the 21st century.

We will stay on Earth. Enjoy this planet!

If you can think of any other argument in favour of space travel, think about it twice and if it still holds then post it in the comments below.

The Sassy Scientist – Pluto Panic

The Sassy Scientist – Pluto Panic

Every week, The Sassy Scientist answers a question on geodynamics, related topics, academic life, the universe or anything in between with a healthy dose of sarcasm. Do you have a question for The Sassy Scientist? Submit your question here or leave a comment below.

After a distraught period (of more than a decade!) since the news first came out that Pluto was not considered a true planet anymore, and due to a post and comment/discussion on this very blog, Goofy finally found the courage to ask:


Do you think Pluto is a planet or a dwarf planet?


Dear Goofy,

Somethin’s wrong here! Definitely. I think Pluto is stellar in his own right, and I don’t think that the way you look at Pluto should change simply because some ‘authority’ dictates that you should change your opinion. That being said; does it matter that Pluto has been demoted to a dwarf planet status? There are a lot of great dwarfs: I know about seven who took in a beautiful lady lost in the forest and a couple who found a dragon in their pile of gold inside a mountain. Let’s take the rough with the smooth and don’t think of Pluto anymore as the last of the planets in our solar system, but rather as one of the main, and certainly the best known, dwarf planets.

Aw shucks. Pluto should have a special status. Beyond the possibility of planetary status, I’m with Laurent in that status should be imposed upon geological/geodynamical features. Why bother with all those heavenly bodies that are just swerving around? Focus on interesting features. Let’s bundle Pluto with Ceres, Titan, Europe and all those other moons, satellites, dwarf planets and create a new scale, taking one step beyond the “Geophysical Planet Definition” of Runyon et al. (2017): “Interesting Units”. So Earth, with all its tectonics and earthquakes and atmosphere scores 10 IUs. Venus, with active volcanism, tectonics and atmosphere scores 9 IUs. Mars, with signs of water presence, geology and relief, but no atmosphere, scores 8 IUs, whilst the gas giants score 7 IUs. Pluto, along with Titan and Ceres scores 5 IUs – our own, rather unimpressive, Moon only takes 3 IUs home. Not too shabby for Pluto I would say. To be fair, let’s award space rubble like Halley’s comet still 1 IU on account of possible, future space mining. For now, as a humble Earth scientist, I urge us to put our primary focus on the highly ranked space monsters, and leave the rest to the astrologers. Oops, astronomers. That’s right (in my mind all the same…).

Yours truly,

The Sassy Scientist

PS: This post was written after some distressing emails from miss. Goofy about her husbands depression due to Pluto’s demotion. I urged her to arrange some counseling.

References:
Runyon, K.D., Stern, S.A., Lauer, T.R., Grundy, W., Summers, M.E. and Singer, K.N. (2017), A Geophysical Planet Definition, Lunar and Planetary Science XLVIII, Abstract 1448

Geodynamics in Planetary Science

Geodynamics in Planetary Science

It is a question that humankind has been asking for thousands of years:

Are we alone in the Universe or are there other worlds like our own?

As of today, it is unknown whether or not inhabited planets exist outside of our own solar system. With the discovery of the extrasolar planet 51 Peg b in 1992, it was confirmed that our sun is not the only star that hosts planets and therefore the search for extraterrestrial life has expanded beyond our own solar system.
However, before we look for an inhabited exoplanet, we must understand what makes a planet habitable.
Of course, the best example of an inhabited (and hence habitable) planet is our Earth and therefore it is a reasonable approach to first look for Earth-like planets. So, the question we should ask is

What makes Earth habitable?

  • The planet should be in the so-called habitable zone: the zone where the planet contains liquid water on its surface. One usually calculates this zone assuming an Earth-like atmosphere.  [e.g. Lammer et al., 2009]
  • The planet also needs to have an atmosphere that protects it from radiation but also keeps the planet warm with greenhouse gases. [e.g. Seager, 2013]
  • The planet should be made of rock and should have a molten core. A convective outer core gives rise to a magnetic field that protects the planet from solar winds and cosmic rays. [e.g. Shahar et al., 2019]

Interestingly, we can couple all three points: greenhouse gases in the atmosphere can heat a planet that is too far away from its host star and therefore make it habitable. On the other hand, they can also heat a planet too much such that it becomes inhabitable.
The third point (a planet made of rock with a molten core) brings geodynamics into play: plate tectonics and volcanic outgassing contribute to burial and recycling of atmospheric gases [Seager, 2013].
In our solar system, Earth is the only inhabited planet, and it is also the only planet we know of that exhibits plate tectonics (including exoplanets).
For example, Venus, our neighbouring sister planet, is very similar to Earth in terms of size, mass and composition. Some studies even suggest that Venus might have been the first habitable planet of our solar system [Way et al., 2016].
But present-day Venus is an inhospitable planet with a very thick carbon dioxide atmosphere (90 times denser than that of Earth) and an extremely hot surface temperature (up to 750K) which is mainly because of runaway greenhouse gases. But why did Earth become habitable and Venus did not?
To explain their different evolutionary paths, plate tectonics might play a major role. Through plate tectonics, Earth can efficiently recycle carbon back into its surface (deep carbon cycle) and this may help to prevent a runaway Greenhouse effect.

The importance of plate tectonics on the habitability of a planet is still being studied, and it is not yet fully understood how efficient this recycling is.

Plate tectonics also influences the generation of a magnetic field. Plate tectonics efficiently cools the mantle by subducting cold slabs into the deep interior, which leads to high heat flow out of the core. Therefore, the style of mantle convection controls the convection in the outer core. This then generates the magnetic field of a planet. The magnetic field acts as a protective shield from the solar winds, which otherwise might erode the planet’s atmosphere. As discussed above, the atmosphere controls the climate mainly through greenhouse gases. The resulting climate influences the tectonic regime: cool climates are favourable for plate tectonics because they facilitate the formation of weak shear-zones in the lithosphere [Foley et al., 2016].
This coupling between the climate, mantle and the core is called the “whole planet coupling” [Foley et al., 2016] and as a whole, it might explain why Earth and Venus have evolved so differently.

Whole planet coupling“: The atmosphere controls the climate which influences the tectonic regime. Subducting slabs cool the mantle which leads to high heat flow out the core. Therefore, the mantle convection controls the type of convection in the outer core which can generate a magnetic field. The magnetic field protects the atmosphere from solar winds and cosmic rays.

To understand the habitability of exoplanets, we therefore need to investigate all the components of the whole planet coupling. Most interestingly for geodynamicists, it is the interior dynamics of a planet’s mantle that couples all these different components!

In the past years, astronomers have discovered many exoplanets, and we expect many more to join this list. For some of them, astronomers and astrophysicists can measure its size, mass, and sometimes even the atmospheric composition and/or surface temperature.
This is very different from studying the Earth, where we can gather a lot of information about the interior through, for example, seismology. Geophysicists, Astronomers, Astrophysicists and many other research disciplines have to collaborate such that they can understand an exoplanet’s whole planet coupling and potential habitability. For geodynamicists the challenge will be to infer the exoplanet’s interior dynamics from a limited amount of data only.

References:
Foley, B. J. and Driscoll, P. E.: Whole planet coupling between climate, mantle, and core: Implications for the evolution of rocky planets, Geochemistry, Geophysics, Geosystems, Vol. 17, 2016.
Lammer, H., et al.: What makes a planet habitable?, The Astronomy and Astrophysics Review, Vol. 17, 2009.
Seager, S.: Exoplanet Habitability. Science, Vol. 340, 2013.
Shahar, A., Driscoll, P., Weinberger, A. and Cody, G.: What makes a planet habitable?, Science, Vol. 364, 2019.
Way, M. J., et al.: Was Venus the first habitable world of our solar system?, Geophysical Research Letters, Vol. 43, 2016.

Oceans on Mars: the geodynamic record

Oceans on Mars: the geodynamic record

Apart from our own planet Earth, there are a lot of Peculiar Planets out there! In this series we take a look at a planetary body or system worthy of our geodynamic attention, and this week we are back to our own solar system, more precisely to our neighbour Mars. In this post, Robert Citron, PhD student at the University of California, Berkeley, writes about the links between oceans, shorelines, and volcanism on Mars. A David Bowie approved blog post!

Robert Citron

Whether Mars was warm enough in its early history to support large oceans remains controversial. Although today Mars is extremely cold and dry, several lines of geological evidence suggest early Mars was periodically warm and wet. Evidence for ancient liquid water includes river channels, deltas and alluvial fans, lakes, and even shorelines of an extensive ocean.

Such features are carved into Mars’ ancient crust, which contains a remarkable geologic record spanning from over 4 billion years ago to present. How and where fluvial erosion takes place is highly dependent on topography. However, Mars is a dynamic planet and the topography observed today does not necessarily represent the planetary surface billions of years ago. Geological markers that seem misaligned today, such as river flow directions and sea levels, may be more consistent with ancient topography. Geodynamic models of how the planet has changed shape over time can therefore be used to test and constrain evidence of water on early Mars.

Shorelines are one example where geodynamic models have helped interpret the geological record. Perhaps the most compelling evidence for ancient Martian oceans are the hypothetical palaeo-shorelines that border Mars’ northern lowland basin. However, the shorelines fail to follow an equipotential surface, or contours of constant elevation, which would be expected if they formed via a standing body of liquid water. One explanation is that the shorelines used to follow an equipotential surface, but subsequent changes to the planet’s shape warped them to their present-day elevations, which vary by up to several kilometers.

Two geodynamic processes that likely changed the global shape of Mars are surface loading and true polar wander. True polar wander occurs when a planet reorients relative to its spin axis, which reshapes the planet because it changes the location of the equatorial bulge produced by the planet’s rotation. Large scale true polar wander on Mars was examined by Perron et al. (2007), which found that it could have warped past shoreline profiles to their present-day topographic profiles.

Another possibility is that Martian shoreline markers were deflected by flexure associated with surface loads. The emplacement or removal of material on a planet’s surface can cause flexure and displacement of nearby crust. This is observed on Earth, where melting of glaciers has unburdened underlying crust, allowing for rebound and displacement of past shoreline markers. Similar processes could be at work on Mars, but on a global scale.

Mars topography: The massive Tharsis volcanic province (red) is situated on the boundary between the southern highlands (orange) and northern lowlands (blue). The lowlands may have been covered by one or more ancient oceans, and are bordered by palaeo-shorelines. Two of the most prominent shorelines are the older Arabia shoreline (dashed line) and younger Deuteronilus shoreline (solid line). Image constructed by R. Citron using MOLA data. Shoreline data from Ivanov et al. (2017) and Perron et al. (2007).

The largest load on Mars is the Tharsis rise, a volcanic province that dominates the topography and gravity of the planet. Tharsis was built by volcanic activity over hundreds of millions to billions of years. Its emplacement changed Mars’ shape on a global scale; in addition to the Tharsis rise, there is a circum-Tharsis depression and an antipodal bulge.

In recent work (Citron et al. 2018), we found that the present-day variations in shoreline elevations can be explained by flexure from Tharsis and its associated loading. Of the two most prominent Mars shorelines, the older (~ 4 billion years old) Arabia shoreline corresponds to pre-Tharsis topography, deformed by almost all of the flexure associated with Tharsis. The younger (~ 3.6 billion years old) Deuteronilus shoreline corresponds to late-Tharsis topography, requiring only ~17% of Tharsis loading to explain its variations in elevation. This suggests that the Arabia shoreline formed before or during the early stages of Tharsis, and the Deuteronilus shoreline formed during the late stages of Tharsis growth. The match between the present-day shoreline markers and ancient equipotential surfaces supports the hypothesis that the markers do indicate shorelines formed by an ancient ocean.

The timing of ancient Martian oceans is consistent with recent work by Bouley et al. (2016), which found that the Mars valley networks (ancient river channels) also better fit Mars’ pre-Tharsis topography. In the topography of Mars prior to Tharsis, the flow direction of the channels are more consistent with the topographic gradient, and the channels occur at latitudes and elevations where climate models predict water ice (resulting in ice melt) to form.

The timing of the shorelines and valley networks relative to Tharsis volcanism suggests a close link between the stability of water on Mars and volcanic activity. Atmospheric models predict a cold and icy early Mars, however it is possible that oceans may be more sustainable during periods of heightened volcanism. Tharsis activity has also been associated with outflow channels indicative of catastrophic flooding that may have inundated the northern plains with water. Further examination of the link between Tharsis volcanism and oceans could increase our understanding of early Mars habitability.

Further reading:

Bouley, S., Baratoux, D., Matsuyama, I., Forget, F., Séjourné, A., Turbet, M., & Costard, F. (2016). Late Tharsis formation and implications for early Mars. Nature531(7594), 344.

Citron, R. I., Manga, M., & Hemingway, D. J. (2018). Timing of oceans on Mars from shoreline deformation. Nature555(7698), 643.

Ivanov, M. A., Erkeling, G., Hiesinger, H., Bernhardt, H., & Reiss, D. (2017). Topography of the Deuteronilus contact on Mars: Evidence for an ancient water/mud ocean and long-wavelength topographic readjustments. Planetary and Space Science144, 49-70.

Matsuyama, I., & Manga, M. (2010). Mars without the equilibrium rotational figure, Tharsis, and the remnant rotational figure. Journal of Geophysical Research: Planets115(E12).

Perron, J. T., Mitrovica, J. X., Manga, M., Matsuyama, I., & Richards, M. A. (2007). Evidence for an ancient martian ocean in the topography of deformed shorelines. Nature447(7146), 840.

Ramirez, R. M., & Craddock, R. A. (2018). The geological and climatological case for a warmer and wetter early Mars. Nature Geoscience11(4), 230.