Snowball and Greenhouse Atmospheres Around Other Stars

Earth’s climate has been shown by a wide range of climate models to be bistable, which means that it can exist in both a frozen state or a warm, ice-free state with the same amount of solar energy. Earth today resides in a warm state with small ice caps, but geologic evidence suggests that the Neoproterozoic Earth, about 500 Myr ago, may have been frozen all the way down to the equator.

Other terrestrial planets orbiting other stars should behave similarly, although the transition point between climate states may differ for stars that are brighter and dimmer than the sun. In a recent paper published in The Astrophysical Journal, titled “Constraints on climate and habitability for Earth-like exoplanets determined from a general circulation model,” my co-authors and I analyze three-dimensional climate simulations of planets orbiting a range of stars. We show that planets can exist around such stars as a frozen snowball, partial melt with an equatorial waterbelt, temperature conditions everywhere, and a hothouse with gradual water loss. Stars slightly cooler than the sun could maintain habitable conditions for longer periods of time, due to the slower rate of water loss.

Why do we live around a yellow star?

Red dwarf stars outnumber yellow dwarf stars like our sun by over a factor of ten. Observations of exoplanets have also shown that rocky, and potentially habitable, planets are just as common around red dwarfs as yellow dwarfs. But if these much smaller stars are more commonplace, then why do we find ourselves around a yellow star like the sun, instead of a red dwarf?

My co-authors and I attempt to address this question of selection bias in a recent paper titled “Why do we find ourselves around a yellow star instead of a red star?” and published in International Journal of Astrobiology. We take a statistical approach to thinking about the region around all stars where life is most likely to develop. The liquid water habitable zone provides the best observational constraint on where we would expect to find planets that could support conscious observers like us, and this study examines the probability of finding oneself on a planet in the habitable zone of a yellow dwarf star, compared to a red dwarf. The results show that even though red dwarfs are much more numerous, they have a narrower habitable zone than yellow dwarfs, so our existence around a star like the sun is actually to be expected.

This study also considers that red dwarf stars will be even more numerous in the distant future of the universe, due to their much longer lifetimes than other stars. If these red dwarf stars will eventually become the predominant place for conscious observers to develop, then why do we not instead find ourselves around a red dwarf star billions or trillions of years into the future? The statistics for this aspect of the problem suggest that our existence around a yellow dwarf star today, compared to a red dwarf star in the future, might be a slight statistical anomaly—perhaps on the order of finding oneself born ambidextrous or with perfect pitch. But this statistical unlikelihood might also suggest that life is wholly impossibly around red dwarf stars, or else any type of conscious observers that do develop around such stars will be drastically different from our type of conscious life.

Mysterytrain 2017 Schedule

The train is still rolling. A few of these dates have already passed, and I’ll be adding later dates in the summer as we book them.

January 28 – Jammin’ for Standing Rock (White Haven, PA)

February 26 – The Pajama Jam (White Haven, PA)

March 12 – It’s All About the Bass Benefit (Newark, DE)

April 7 – Willie’s Midnight Crazy Train (Lehighton, PA)

May 19-20 – Private Party (Chalfont, PA)

May 27 – Gypsy Wind Festival (Northumberland, PA)

June 10 – Pacem Music Festival (Wilmington, DE)

July 7-8 – Grateful Getdown II (Biglerville, PA)

July 13-15 – Zucchini Moon 6 (Lennoxville, PA)

August 6 – 12th Annual Bear’s Picnic (Millmont, PA)

Part of the slowdown in our schedule is because several of us are working hard at building the GreenSpace permaculture center, specializing in fresh microgreens with indoor vertical farming. Check us out at farmers’ markets across Pennsylvania and Maryland, or order a microgreen subscription online!

A Lottery Bond to Fund the Search for Aliens

Finding sources of funding to search for life in the universe can be tricky, with only a few individual wealthy investors and limited opportunities for government research support. New fundraising ideas are needed in order to sustain the search for extraterrestrial intelligence (SETI) over the coming decades.

In a recent paper titled “Funding the search for extraterrestrial intelligence with a lottery bond,” published in Space Policy, I propose the establishment of a “SETI Lottery Bond” to help defray the costs of operating observing facilities like the Allen Telescope Array. The SETI Lottery Bond would provide a fixed-rate of interest that continues in perpetuity, until the first confirmed discovery of extraterrestrial intelligent life, at which point a subset of shares will be awarded a prize from a lottery pool. Investors can also trade their shares, so that SETI Lottery Bond shares may be passed between generations, teaching the value of intergenerational savings while maintaining hope for the discovery of extraterrestrial life.

Lottery-based savings products can only be offered by financial institutions with the legal authorization to engage in banking and gaming activities. I propose that one or more financial institution could realize a profit through the establishment and management of a SETI Lottery Bond, while simultaneously promoting individual savings habits and assisting the search for extraterrestrial intelligent life.