Volume 18 Issue 23
Based on Kepler Space Telescope data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way, 11 billion of which may be orbiting stars like our own sun. These are the “Goldilocks Planets,” planets at just the right distance from its Sun to allow temperatures for liquid water. They would be not too hot and not too cold and could potentially allow life to evolve.
On Earth, it is not just the presence of liquid water that gives our planet Goldilocks status. Our orbit, the percentage of reflective surfaces, and the chemical composition of our atmosphere all contribute. The energy Earth receives from the Sun is in balance with the energy our planet loses to space.
In speaking of the “habitable” zone surrounding a star, the word is a bit misleading. Habitable for what? Life found on Earth? We don’t really know what a planet needs to harbor life. Worlds inhospitable to human life could be teeming with life we can’t even begin to understand. All we know is that for the kind of life that exists on Earth, liquid water is a necessity – at least intermittently. With current technology, we don’t have the capability to conclusively detect liquid water on the surface of any worlds outside our own solar system, so we use the temperature of the star and the distance of the planet’s orbit. Even though water can be liquid on the surface, various geophysical aspects, such as atmospheric pressure, radiation, and planet chemistry must be taken into account.
But distance isn’t everything. When it comes to the temperature on a planet’s surface, the atmosphere has an enormous effect. Too thick (think Venus), the planet is too hot. Too thin (think Mars), the thin atmosphere might cause the planet’s store of ice to sublime directly into water vapor, yet both of these planets are considered to be within the habitable zone of our sun.
So, are we going to eventually find swamps, marshes, bogs, fens, lagoons, vernal pools, and pocosins on Goldilocks planets? Wetlands are areas that must meet three important factors: hydric soils, wetland vegetation, and wetland hydrology. By that definition, we already have a good chance of finding two criteria, soils and hydrology. But life on another planet, well, that’s the big question.
Since wetlands tend to be on larger bodies of water because of their topography and used for water retention and filtration, we would be looking for more than just a trace of water or ice. Liquid water would have to be at least intermittently present for the chemical processes that are required to make most hydric soils. Natural ponds and wetlands most often occur as lowlands or depressions, so the surface of the Goldilocks planet must also be compatible with these landforms.
Would seasons be a requirement for soil/wetland production? Perhaps not if there was still a significant period of liquid water through a “Goldilocks” year. A “day” corresponds to one rotation of a planet. Could wetlands survive a constant sun-oriented model with no rotation at all, or a whirlwind of day and night caused by a fast rotation?
Life originated in our seas on Earth. Would it do the same on “Goldilocks” or would it be so different that life would develop directly on land? Would there be wetland plants just because we had water? Maybe water is not essential to our new “exo-plants”. Depending on the density of the atmosphere and specifics of the sun, radiation could be strong and constant. Would this affect the evolution of plant life, causing mutations, or premature death of the plants? Would trace elements not usually found on Earth affect growth or spread of plants? Would the chemical processes of life not work, or would they just be different?
When it comes to the organic component of soils, we need plants! The plants characteristic of ponds and wetlands include moisture-loving plants, some of which are totally submerged, partially submerged, float on the surface or favor the shoreline and commonly include algae, grasses, sedges, rushes, water lilies, and forbs. On Earth, plants can grow and prosper in a variety of mediums from water to cracks in rocks. It seems that if life were to evolve then plants should do well if our Earth is any type of example.
At some point, the Army Corps of Engineers might have to come up with a brand-new set of indicators for the new “Exoplanet Regional Supplement,” but at least for hydrology, (the study of water), the presence of water on a planet would naturally give us many of the same indicators like standing water, saturation, etc. Would we see moss trim lines or evidence of aquatic fauna though?
For soils, would there be redox features without free oxygen in the atmosphere? Where would we be without our F3 indicator! Since so many of our soil indicators are based on the presence of plant life in some form or another, A indicators might be problematic.
In all likelihood though, it seems as if indicators would be found on a Goldilocks planet. They may not be the same on earth, but they would do the job. Maybe a pristine exo-wetland might even help us develop new and better wetlands on Earth!
Now, if we can only keep Earth invasives like Phragmites and Reed Canary Grass out, we’d be golden.
Cosmos 72 – Dec-Jan 2017, “‘Goldilocks’ planets might not be so nice,” issue 72, by Kate Mack https://cosmosmagazine.com/issues/parallel-worlds-science-or-sci-fi
NASA, Chromospheric variations in main-sequence stars, Jan. 01, 1995
E. E. Mamajek; L. A. Hillenbrand (2008). “Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics”. Astrophysical Journal. 687 (2): 1264