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Planets in the habitable zone of low-mass, cool stars are expected to be in synchronous rotation, where one side of the planet always faces the host star (the substellar point) and the other side experiences perpetual night (the anti-stellar point). Previous studies using three-dimensional climate models have shown that slowly rotating plants orbiting these low-mass stars should develop thick water clouds form at substellar point, at the point at which the star is directly overhead, which should increase the reflectivity, and thus stabilize the planet against increased warming at the inner edge of the habitable zone.

However these studies did not use self-consistent orbital and rotational periods for synchronously rotating planets placed at different distances from the host star, which are a requirement from Kepler’s laws of motion. We address this issue in a new study led by Dr. Ravi Kopparapu, on which I am a co-author, titled “The inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models.” In this study, we use correct relations between orbital and rotational periods to show that the inner edge of the habitable zone around low mass, cool stars is not as close as the estimates from previous studies. We also discuss how the stellar composition, or ‘metallicity,’ can affect the orbital distance of the habitable zone.

Earth’s climate is vulnerable to potential climate catastrophes that could threaten the longevity of civilization. Continued increases in greenhouse gas forcing could lead to the collapse of major ice sheets, which would cause catastrophic sea level rise and could cause the oceanic thermohaline circulation to halt. Further warming could cause the heat stress index to exceed survival limits, inducing hyperthermia in humans and other mammals. Even more extreme warming could shift Earth into a runaway greenhouse regime that would lead to the loss of all oceans, and the end of all life.

Geoengineering refers to the large-scale use of technology to alter Earth’s global climate, and geoengineering has been suggested as a way to ameliorate contemporary climate change. Addressing these immediate climate challenges through a combined strategy of adaptation, mitigation, and (if needed) geoengineering is a critical issue facing us today. Whether or not we decide to engage in geoengineering today, we must still devise a long-term strategy to address our changing climate.

But in the longer-term, could we also use geoengineering techniques to increase the size of the polar ice caps? In a paper published in a special issue of the journal Futures, I raise the question, “Should we geoengineer larger ice caps?” By doing so, the global average temperature of Earth could be lowered from its current state to a new stable regime with much larger ice caps. Earth has experienced shifts in ice coverage in its past, and a prolonged program of geoengineering–say, lasting a thousand years or more–could allow us to permanently shift the energy balance of Earth. More ice at the poles increases the amount of sunlight reflected back to space, leading to cooler temperatures.

Of course, the unfortunate side effects of this idea would be mass migration of populations near the poles, shifts in global agricultural zones, and a required commitment of millenia in order to avoid undesired side-effects. Human civilization today probably lacks the fortitude to embark on such a long-term goal. Nevertheless, thinking about the long-term management of our planetary system helps us realize that we have already entered the epoch of the Anthropocene. Our civilization itself is fundamentally intertwined with our global climate, and we should allow humility, rather than hubris, guide decisions to control our environment.

Global catastrophes are events that could severely cripple or destroy the foundations of civilization. Potential global catastrophes include nuclear winter, large asteroid impacts, super-volcanic eruptions, and pandemics. Humans may not necessarily become extinct under such scenarios, but, without adequate advance preparation, rebuilding civilization following such a catastrophe could prove difficult.

In a paper published in a special issue of the journal Futures, my co-authors and I present several concepts of “Isolated refuges for surviving global catastrophes.” Although catastrophic events could destroy a significant portion of the human population, isolated refuges would provide a way to protect a small group of humans so that they survive long enough to rebuild civilization. We discuss several factors that are critical for ensuring the success of a refuge, including self-sufficiency, a continuous population, secrecy, and adequate monitoring of the outside world.

We also discuss the concept of surface-independence, suggesting that an underground, underwater, or space-based refuge might provide the greatest protection of its inhabitants from the effects of global catastrophes. Any of these refuges could significantly make the human species more resilient to catastrophic threats. Space-based refuges provide an exceptional degree of isolation from Earth, and the cost of such an extraterrestrial refuge might be best “piggybacked” onto existing scientific endeavors that seek to establish a permanent presence on the moon or elsewhere in space.

Land Use on Mars

National space agencies, including NASA, ESA, the Indian Space Agency, and the Chinese space program, all have Mars in sight. Current Mars exploration programs all have human spaceflight in mind for the near future, and eventual plans for exploration often turn to thoughts of permanent settlement or colonization. Several private corporations have also declared their intent to visit, or even colonize, Mars within the next several decades. Whether or not they succeed in their planned time frame, it seems evident that humans have their eyes on Mars.

The patterns of history show us plenty of examples of how land resources have benefited the few over the many, or how conflict over scarce land resources have led to violence and war in extreme cases. Even more fundamentally, the amount of land on a planet is finite, but it is only recently that the practice of homesteading became impossible on Earth. Mars holds the potential for settlers to once again lay claim to open areas of unclaimed land, but is this the best policy for using the resources of space?

In a book chapter published in the Springer edited volume Human Governance Beyond Earth: Implications for Freedom, I discuss my research and thoughts in an effort that will lead “Toward a Sustainable Land Use Policy for Mars.” I discuss the constrains of existing treaties governing the use of space resources, and I present a few possible alternatives for what a land use policy on Mars might look like.

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