Patterns and Colors of Planetary Habitability: What Does an Exo-World Look Like?


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What is an exo-planet, and why are they so interesting? Image courtesy of NASA

What is an exo-planet, and why are they so interesting? Image courtesy of NASA

Identification of habitable zones throughout the Milky Way have come at a crucial juncture for science. The Kepler project ran its course and delivered copious amounts of data to researchers; potentially resulting in a ‘golden age’ of discovery for the understanding of habitability and life’s origins. Spotting habitable planets in a galactic habitable zone is more than knowing where to look, however.

Planets and Chemical Equilibria

Molecular dynamics of the atmosphere distinguishes our planet from Mars. Molecules, reactions and the direction of chemical equilibria—or dis-equilibria-dictate the presence of life. Consider a molecule like oxygen; it is highly reactive and forms molecular species with many different elements. In the atmosphere, ultraviolet light, in part, is responsible for the formation of ozone. So, once molecular oxygen takes to its ‘triplet-to-singlet’ state, it may react readily with itself to form ozone; or the ozone may degrade in the presence of CFCs to form the ‘ozone hole.’

Mars’ atmosphere, on the other hand, does not have a perceptible dis-equilibria or a biochemical profile.

From the Earth, observations of Mars’ vacillating landscape fed the imaginations of Schiaparelli, Lowell, Goddard, von Braun, Carl Sagan, and an inquisitive public. Unfortunately, however, sol after sol, (a Martial solar day is a ‘sol’) the Martian land and atmosphere chemistry have not yielded detectable life. Instead, the remnants of a ‘watery past’ reveal themselves to the world’s scientists.

Detecting life’s signatures, however, is like examining snowflakes or weather patterns; no single flake nor pattern is identical. Planets like Mars haven’t changed for billions of years while the Earth thrives in diversity. To the human eye, Earth’s habitability, from the edges of the Solar System, is the familiar ‘pale blue dot.’ Water, oxygen, carbon dioxide, nitrogen, and hydrocarbons characterize our existence. How else would we know of ourselves? Intelligence separates the rusty colors of Mars from the crimson, algal blooms of the Earth’s oceans.

Exo-Planet in Constellation Pegasus

Currently, our telescopes do not distinguish the finer details of exo-super-Earths nor the larger Jupiter-like exo-planets in other regions of the Milky Way. However, we have detected atmospheres in some larger exo-planets.

One case is point is HD209458b, a planet located 150 light years from Earth in the constellation Pegasus. The star HD209458 is approximately the age, size and temperature of our Sun. But the exo-planet could not be more different from any planet in our Solar System. While characterized as a hot-Jupiter, its spectral dynamism seems indicative of dis-equilibrium, which means it’s not actually like Jupiter.

According to the Exo-planet Encyclopedia, H2O, H, Na, TiO, VO, Mg science has detected water, hydrogen, titanium oxide, vanadium oxide, and magnesium; astronomers believe the planet’s temperature is in excess of 1100 degrees Celsius, or 2012 degrees Fahrenheit.

One distinguishing feature of dis-equilibrium is the atmospheric escape of its components, but publications in late 2013 and early 2014 seem to paint a more understandable picture. The exo-planet’s spectral dynamism may characterize HD209458b as a “cross between a brown dwarf and a Jupiter-sized planet.” This in-between characterization may be key to the understanding of the origin and fate of hot Jupiter-sized exo-planets.

Spectral Variability of ‘Purple Bacteria’

The next case is one of understanding how the spectral variability of its ‘purple bacteria’ -bacteria that produce energy by the process of photosynthesis -may characterize an archean exo-Earth. Non-oxygenated photosynthetic organisms changed the chemical make-up of early-Earth—and the early-Earth could readily be characterized by its source.

The purple-bacteria would have made the reflectance spectrum of the early Earth characteristic of a “reddened-and-darkened dot.”

According to a team of researchers affiliated with NASA, SETI Institute, and the University of La Laguna, Spain, the reflectance spectrum of our little world would have appeared quite differently 3.8 billion years ago. Spectral simulations would have shown no oxygen or ozone present; hydrogen, carbon dioxide, hydrogen sulfide and perhaps methane would have dominated the atmosphere.

This darkened world did not possess a protective layer of ozone either; but scientists conjectured that the bacteria may have adapted through the bio-synthesis of pigmented layers of organic and inorganic absorber molecules (carotenoids and metallo-porphyrins).

The Search for an Exo-World

How likely are we to detect such an exo-world? Presently, the direct search for, and detection of, such an exo-world seems very far off into the future—but not impossible to find. The exo-planet survey of Kepler uncovered many more planetary systems than most scientists have imagined within the past year.

If the last year is any indication of future trends of discovery, the crystal ball paints a bright future for exo-planetary research.

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