thoughts on exoplanets

An undiscovered Earth-like exoplanet.

An undiscovered Earth-like exoplanet.

Based on current discoveries, I predict the following trends in exoplanetary systems.

Location / likelihood of Earth-like planets:

For systems with stars similar to the sun (K, G, F):

in systems with with rocky planets: Earth mass planets tend to form or migrate into orbits much 10-20x closer than the estimated habitable zone.  Gas/ice giants exist in the habitable zone instead.

{more common} in systems without rocky planets: Gas/ice giant planets migrate into close orbits over the life of the system, causing rocky planets either collide with the gas/ice giant, or through gravitational interacts be ejected from the system or forced into the star.

For systems with stars dissimilar to the sun (M):

Earth mass planets commonly exist in the habitable zone.  However, because stellar metallicity is very low, even Earth or “super-Earth” mass planets are not likely to be rocky, but rather gas/ice/liquid.

Too cold and too small?

Too cold and too small?

Some expected attributes of Earth-like planets existing the habitable zone of different stellar types:

[first, we assume for this exercise that other planet specific factors, such as magnetic field strength, cloud cover, the existence of an ozone layer, etc are similar to earth.]

F-> since the spectrum of stellar radiation is skewed toward the ultraviolet, planets in the habitable zone will have brighter daylight be colder surface temperatures when compared to the Earth.  Levels of ultraviolet radiation will be much higher than on Earth.

G-> these planets will [obviously] be Earth-like in temperature and daylight radiation levels.

K-> since the spectrum of stellar radiation is skewed towards the infrared, planets in the habitable zone will have dimmer daylight but tend to be warmer than earth.  Ultraviolet radiation levels will be lower.

M-> since the spectrum of stellar radiation skews heavily into the infrared, planets in the habitable zone will have appreciably dimmer daylight, but tend to be warmer than the Earth.  Planets in the habitable zone will be tidally locked, rendering a significant majority of the planet’s surface uninhabitable for Earth-like life.  Tidal forces may also increase volcanism, increasing the concentration of volcanic greenhouse gasses; pushing the temperature even higher.  Areas of the planet temperate enough for Earth-like life [typically the “twilight” bands between the permanently dark and light faces of the planet] are too dim for any photosynthesis to occur.

Ultimately, I don’t think any of the current exoplanet discoveries are viable candidates for Earth-like life.  Further, there are likely very few Earth-like exoplanets in existence, if any, as it appears the trends outlined here are the norm.  In other words, we’re not going to be finding the potential for life anytime soon; and if we do, it won’t be close.  

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