At the "Planetary Science Vision 2050 Workshop" held around March 1, Jim Green, NASA's Planetary Science Division Director, presented a study to deploy an artificial magnetic shield at the Mars Lagrangian point L1, that would shield the planet from the solar wind. Modeling and simulation results show that such a shield could prevent the stripping of the Mars atmosphere which has been occurring for billions of years, cause the atmosphere to build up, warm the planet due to greenhouse effects, and cause polar ice and CO2 caps to melt, within a relatively short time span.
Note that this is different from terraforming (described later), where the climate is changed by artificial means such as deploying gases or materials on Mars or by heating Mars’s surface or atmosphere.
The full video of the presentations is available at livestream.com/…. Green’s talk starts at 1:36:00.
The paper “A Future Mars Environment for Science and Exploration” is located at www.hou.usra.edu/…
The Martian Atmosphere
Mars is an arid and cold world with a very thin atmosphere although it has significant frozen and underground water and CO2 resources. The thin atmosphere prevents liquid water from residing permanently on its surface.
Mars, several billion years ago, may have had a denser atmosphere and a significant water ocean covering perhaps 30% of the northern hemisphere.
Methane has been detected in the Martian atmosphere with a concentration of about 30 ppb. It is estimated that Mars must produce 270 tonnes per year of methane.
Methane can exist in the Martian atmosphere for only a limited period before it is destroyed—estimates of its lifetime range from 0.6–4 years. Its presence despite this short lifetime indicates that an active source of the gas must be present. Volcanic activity, cometary impacts, and the presence of methanogenic microbial life forms are among possible sources. Methane could also be produced by non-biological processes.
The axis of Mars is tilted by 25.19 degrees relative to its
orbital plane, which is similar to the axial tilt of Earth.
As a result, Mars has seasons like Earth, although they are nearly twice as long because its year is 687 Earth days long.
Over billions of years, sand transported by wind has sculpted Martian landscapes.
Why is the Martian Atmosphere so thin?
The authors, and others before them, estimate that Mars lost its atmosphere after it lost its magnetosphere 3-4 billion years ago, possibly because of numerous asteroid strikes. Consequently, the solar wind interacted directly with the Martian ionosphere and stripped away atoms from the outer layer. The relatively low mass of Mars means that atoms and molecules require a lower velocity to escape from the gravitational pull of Mars. This would in turn have resulted in evaporation and loss of its surface liquid water over time.
Earth’s magnetosphere is generated by rotating currents in the molten outer core which act like a giant electromagnet. Charged particles in the solar wind are deflected around Earth’s magnetic field while a small fraction are directed in toward the poles. Mars lacks such a mechanism, although it probably had one in its distant past.
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of mostly electrons, protons and alpha particles.
The diagram below shows that Mars cannot retain water vapor, ammonia or methane in its atmosphere due to its low mass and the low escape velocity of the molecules.
Mars Global Surveyor, Mars Express and MAVEN have detected ionized atmospheric particles trailing off into space behind Mars; the MAVEN orbiter has determined that Mars has been losing a significant amount of atmosphere due to the effect of the solar wind.
The atmospheric loss is partially balanced by the outgassing of the Mars interior and crust that contributes to the existing atmosphere.
The Proposed Approach
The proposed approach consists of deploying an artificial magnetic dipole shield that would deflect the solar wind around Mars and reduce the amount of solar wind impinging directly on Mars. This would naturally allow the Mars atmosphere to build up within the span of a few years.
The magnetosphere would be located at Mars’s L1 Lagrangian point.
The Lagrangian point L1 is a point on the Sun-planet line where a small object can stay in stable orbit as the combined effects of gravity from the Sun, the planet and the object’s centrifugal force “cancel” each other out and create a “gravity-well”. The Deep Space Climate Observatory (DSCOVR), and the LISA Pathfinder (LPF) spacecraft are located at Earth’s L1 point. The James Webb Space Telescope, to be launched next year, will be located at Earth’s L2 point.
The image below shows one of the simulation results for a magnetic field strength of 50,000 nanoteslas at the L1 point, deflecting solar wind around Mars. The intensity of magnetic fields is often measured in gauss (G), but is generally reported in nanoteslas (nT), with 1 G = 100,000 nT. The Earth's field ranges between approximately 25,000 and 65,000 nT (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field of about 10,000,000 nanoteslas (100 G).
The authors state —
This may sound “fanciful” but new research is starting to emerge revealing that a miniature magnetosphere can be used to protect humans and spacecraft. In the future it is quite possible that an inflatable structure(s) can generate a magnetic dipole field at a level of perhaps 1 or 2 Tesla as an active shield against the solar wind.
It has been determined that an average change in the temperature of Mars of about 4oC will provide enough temperature to melt the CO2 veneer over the northern polar cap. The resulting enhancement in the atmosphere of this CO2, a greenhouse gas, will begin the process of melting the water that is trapped in the northern polar cap of Mars. It has been estimated that nearly 1/7th of the ancient ocean of Mars is trapped in the frozen polar cap. Mars may once again become a more Earth-like habitable environment.
This is not terraforming, as you may think about it, where we actually artificially change the climate. We let nature do it. And we do that based on the physics we know today.
Notes:
- The south polar ice cap, if melted, is estimated to cover the entire planetary surface to a depth of 11 meters; not all surfaces will be covered, given the diverse terrain of Mars.
- The magnetic shield will not block or deflect sunlight (photons).
- The authors do not specify the physical size of the equipment needed to generate the magnetic shield nor the cost or complexity.
- This study does not address issues of human colonization such as transportation, bio-domes, economics, seeding Mars with life forms, and Martian factories and farms.
Other Mars Terraforming Approaches
Terraforming of Mars is a process by which the surface and climate of Mars would be deliberately changed to make large areas of the environment hospitable to humans, thus making the colonization of Mars safer and sustainable.
Terraforming of Mars has been studied over the past several decades, ranging from ideas in science fiction to more scientific studies and proposals, most of which entail prohibitively high economic and natural resource costs and technology hurdles.
Most approaches rely on warming the planet, melting the frozen ice and CO2 and accelerating the build up of the atmosphere through greenhouse effects. Here is a partial list of such approaches —
- Importing ammonia, powerful greenhouse gas, possibly from other planets or minor planets.
- Importing hydrocarbons, such as methane, from other planets or minor planets such as Titan.
- Deploying powerful fluorine-bearing greenhouse gases, such as sulfur hexafluoride and chlorofluorocarbons, to be exported from Earth. One study estimates that approximately 39 million metric tons of CFCs would be required to be transported to Mars. Proposals to mine and to produce CFCs on Mars itself have also been made. www.pnas.org/...
- Use of orbital mirrors to heat up Mars and melt the polar caps. www.users.globalnet.co.uk/...
- Reducing the albedo of the Martian surface to increase sunlight absorption. This can be done by spreading dark dust from Mars's moons, Phobos and Deimos or by introducing dark extremophile microbial life forms such as lichens, algae and bacteria. This idea was proposed by Carl Sagan in www.sciencedirect.com/….
- Explode thermonuclear bombs in the atmosphere, to help melt the polar caps, as proposed by Elon Musk.
Note that without a magnetosphere, Mars would constantly lose its atmosphere due to Solar winds and would require continuous replenishment.
Also, terraforming would invariably be followed by seeding of Mars with organisms and plants, to help sustain human habitation on Mars.
The Ethics of Terraforming
There are also several questions about the ethics of terraforming. Altering Mars and other planets in order to make them more suitable to human needs raises the natural question of what would happen to any lifeforms already living there. Do we have the right to cause their extinction? Should we wait until we have conclusive evidence that Mars neither harbors life nor has the potential to evolve life?
At the end of the presentation, Dr. Green said “the solar system is ours, let’s take it. And that of course includes Mars. And for humans to be able to explore Mars, together with us doing science, we need a better environment”. This astonishing statement presumably raised a few eyebrows.
References
- Planetary Science Vision 2050 Workshop video - livestream.com/….
- A Future Mars Environment for Science and Exploration - www.hou.usra.edu/…
- Mars wiki — en.wikipedia.org/…
- NASA Mars page — www.nasa.gov/...
- Terraforming of Mars — en.wikipedia.org/…
- Human mission to Mars — en.wikipedia.org/…
- Planetary engineering on Mars (Albedo reduction) - Carl Sagan - www.sciencedirect.com/…
- Technological Requirements for Terraforming Mars (orbital mirrors) — www.users.globalnet.co.uk/…
- Keeping Mars warm with new supergreenhouse gases (CFCs) — www.pnas.org/…
- The ethics of terraforming Mars: a review — igem.org/…
- Is There Life on Mars? — www.dailykos.com/…