The Search for Extraterrestrial Archeology

By DailyGlaxy

The Search for Extraterrestrial Archeology --Probing Kepler Mission Data (Today's Most Popular)

Fifty years ago the physicists Freeman Dyson speculated that vast structures could ring or completely enclose their parent star. These Dyson Spheres, the work of a Kardashev Type II civilization — would be capable of drawing on the entire energy output of its star. Geoff Marcy, Professor of Astronomy at the University of California, Berkeley, who is famous for discovering more extrasolar planets than anyone else, 70 out of the first 100 to be discovered, received a grant last year from the UK’s Templeton Foundation to search for Dyson spheres.

Marcy studies thousands of Kepler systems for telltale evidence of such structures by examining changes in light levels around the parent star as well as possible laser traffic among extraterrestrial civilizations. "Fermi Bubbles," which might appear as a void in visible light in spiral galaxies, is the term used by Richard Carrigan,  a scientist emeritus at Fermilab,  in his work on the search for cosmic-scale artifacts like Dyson spheres or Kardashev civilizations using Infrared Astronomical Satellite (IRAS)  data .  A Fermi bubble would grow as the civilization creating it colonized space, according to Carrigan. 

As Carl Sagan observed, the time to colonize an individual system is small compared to the travel time between stars. A civilization, believes Carrigan, could engulf its galaxy on a time scale comparable to the rotation period of the galaxy, or every 225–250 million years, and perhaps shorter.

Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization.

This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. The constraints of the anthropic principle, for example, would have to be loosened if a different type of intelligence was discovered elsewhere.

A variety of interstellar archaeology signatures could include non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering.

The concept of a Fermi bubble due to interstellar migration grew out of the the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale, developed by Nikolai Kardashev, who divided civilizations into those harvesting all the energy of a planet, of a star, and of a galaxy. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are currently under way.

According to the Kardashev scale, radio SETI might be a type 0 civilization. A type I civilization would utilize the energy available from a planet. Signals from exosolar planetary atmospheres fall roughly in this category. A Dyson Sphere, a star cloaked in broken up planetary material, would be an example of type II. Another example would be some sort of engineering of the stellar burning process suggested by Martin Beech. A civilization using all of the energy of a galaxy would be type III.

James Annis,a member of Experimental Astrophysics Group at Fermilab, has suggested that elliptical galaxies, which exhibit little structure, might be a more likely place to look for Fermi bubbles than spiral galaxies. Annis examined existing distributions for spiral and elliptic galaxies and looked for sources below the normal trend lines where more than 75% of the visible light would have been absorbed. But no candidates were found in his sample of 137 galaxies. From this Annis inferred a very low probability of a Type III civilization appearing that would be found using this search methodology.

In 1960 Dyson suggested that an advanced civilization inhabiting a solar system might break up the planets into very small planetoids or pebbles to form a loose shell that would collect all the light coming from the star. The shell of planetoids would vastly increase the available "habitable" area and absorb all of the visible light. The stellar energy would be reradiated at a much lower temperature.