Updated Wednesday, 21-Jan-2004 10:19:37 EST
Life in the Universe
Life on Mars?
Viking I and II spacecraft visited Mars in 1976
- Took pictures, tested air and soil for evidence of life
- No evidence of life found
Search for Extraterrestrial Intelligence (SETI)
extraterrestrial intelligent species
Operational definition of intelligent is "capable of communicating via radio"
Probability of finding ETIS -- 2 schools of thought
- Found in Antarctica in 1984
- Chemical composition matches that of soil tests from Viking I and II
- Theoretical history
- 4.5 billion yrs ago -- crystallized from molten rock on Mars
- 4 billion yrs ago -- shocked by an impact, but remains on Mars
- 1.8-3.6 billion yrs ago -- carbonate minerals are deposited from warm or hot H2O running through rock
- 16 million yrs ago -- ejected into space by another impact on Mars
- 13,000 yrs ago -- lands in Antactica
- 1984 -- found in Antarctic ice
- Evidence in rock
- Carbonate minerals -- iron-rich and calcium rich iron-oxide
- Can form by non-biological processes, but each by different chemical conditions
- Terrestrial bacteria produce these types
- Organic molecule (polycyclic aromatic hydrocarbon)
- Form on Earth either by degradation of larger organic molecules associated with decay of larger organic molecules or by incomplete burning of organic fuels
- Can form in interstellar space, but process is different
- Does this require life? No.
- Could this be from Earth contamination? Yes.
- Fossils -- structures appear really similar to fossils of terrestrial bacteria
- Could these structures have been formed by non-biological processes? Yes.
- Cosmological principle -- makes the assumption of mediocrity. We live in an average "neighborhood" in the universe. There is nothing special about our location or time in history or conditions that make life possible. Therefore, one would expect to find similar conditions (and life) elsewhere in the universe.
- Anthropic principle -- assumes that we exist because of very special conditions in our "neighborhood." Therefore, what we observe in our part of space is not typical of the universe as a whole, and so we shouldn't expect to find life elsewhere.
Note that both of these principles implicitly assume that ETIS would have certain similarities to us. Removing that assumption complicates these arguments somewhat.
- Drake Equation (aka Greenbank Equation)
- Developed by Frank Drake (at the Greenbank Observatory) in the 1960's
- Tool for examining effects of various assumptions on the estimate of number of ETIS in our galaxy (but it can be applied to any part of the universe)
N = R×
[numbers in brackets below indicate permitted values to use in the equation]
N = number of ETIS in our galaxy
R = rate of star formation [number/year]
Our galaxy (Milky Way) is about 10 billion yrs old and contains about 100 billion stars, so R = 10 stars/yr is the standard assumption
P = fraction of stars with planets [0-1]
E = environmental factor = number of planets in a solar system that are ecologically suitable for life [0-?]
L = fraction of planets with suitable environment where life actually did develop [0-1]
I = fraction of inhabited planets where intelligent life-form evolves [0-1]
C = fraction of planets with intelligent life that has developed radio communications [0-1]
T = time [years] that a technically developed civilization survives
- Values used in the equation are somewhat subjective.
R = 10, P = 1, E = 5, L = 1, I = 0.1, C = 1, T = 5000 yrs
N = 25000 ETIS
R = 10, P = 1, E = 1, L = 0.1, I = 0.1, C = 0.2, T = 100 yrs
N = 2 ETIS
- The Great Silence
- Enrico Fermi (physicist) asked "So where are they?"
- Possible reasons for no evidence of ETIS (yet)
- Some factors in Drake equation may be much smaller than we believe
- Deadly probes scenario (the ultimate in paranoia). All other ETIS hiding from one xenophobic ETIS that is attempting to destroy them using deadly probes that wander throughout space.
- ETIS may have reached approximately same technical level as humans, so there hasn't been sufficient time for their radio signals to reach us.
- Searching for ETIS
- Radio waves are form of e/m radiation -- its intensity diminshes with the square of the distance that it travels
- Cosmic dust, gases absorb many radio wavelengths
- Earth's atmosphere absorbs some wavelengths
- Infinite number of wavelengths to examine for intelligent signals
- Choose a logical wavelength (one not readily absorbed by many materials)
- Present listening systems use the band 1400-1720 megahertz (this could be easily generated by ETIS and is not strongly absorbed by atmospheric gases).
- Congress provided funding to NASA for SETI until 1993
- Present efforts all privately funded
- SETI Institute (Frank Drake). You can participate through
seti@home -- use your own computer to help analyze data from the SETI project.
- Planetary Society
- META (million channel extraterrestrial assay) -- scans one million channels in the band
- BETA (billion channel version of META)
- 84 ft. dish antenna at Harvard Univ.
- connected to supercomputers that look for non-random patterns in the signals (most of the signals come from natural sources such as stars)
- 250 megabytes of data each second
- How might ETIS detect us?>
- Pioneer spacecraft carry a plaque showing two humans and a map of our solar system and its location in the Milky Way.
- Voyager spacecraft carry a plate showing where Earth is located in the Milky Way (click on image for a larger version)
- Under this cover plate was a phonograph recording titled "Sounds of Earth", which contains recordings of children sending greetings in over a hundred languages, as well as samples of music. (click on image for a larger version). The cover plate also contained instructions on how to operate the system to hear the sounds.
- In Nov. 1974, a message was beamed from the Arecibo radio telescope toward the M13 star cluster 24,000 light-years away (recall that one light-year is approximately 6 trillion miles). The message consisted of a series of 1's and 0's, which could be arranged in a two-dimensional pattern to form a picture showing a stick figure of a human, a DNA molecule, and some other information about the chemicals of life. The message was transmitted only once and was intended to serve as a exercise in how we might go about trying to contact ETIS.
- What will we do if we find ETIS?
Copyright © 1998, Robert G. Melton
Updated Wednesday, 21-Jan-2004 10:19:37 EST