Our group uses data from a wide range of observatories to search for planets around other stars, and to scan the skies for signs of life:. These signals are likely very weak, so we use large radio telescopes to gather signals.
Given that we do not know where the signals may come from, what frequency they might be at, or in what format FM, AM, pulsing, etc , we need to search many channels and many locations across the sky to gather large amounts of data, which requires a lot of computing power to process and analyze.
We also search for evidence of extraterrestrial engineering such as Dyson Spheres. Since about , our group has made all of our peer-reviewed publications available for free on arxiv. Researchers from universities all around the globe contribute and participate in SETI efforts.
Kepler is a telescope that searches for planets around other stars. Recent Kepler results suggest that there are billions of Earth-like planets in our Galaxy, which make for promising places to search for signs of life.
In , after years of study and designing, NASA Headquarters adopted the programs and provided funding. Observations started four years later, but within a year Congress terminated the funding. SETI is primarily a privately funded project. There is no specific government agency program devoted to SETI. One easy and very helpful way to contribute is downloading and installing the SETI home program on your personal computer. This helps analyze the enormous amount of SETI data simply by letting it run as your screen saver.
You can also make a tax-deductible donation to help fund our programs and support our students and researchers. How did SETI start? Why radio waves?
Why are we searching?? Has anything been found? Who is involved in the Berkeley team? The technique is only sensitive enough, however, to detect the perturbations of a massive planet around the nearest stars. The single star closest to the sun is Barnard's star, a rather dim red dwarf about six light-years away.
Although Alpha Centauri is closer, it is a member of a triple-star system. Observations made by Peter van de Kamp of the Sproul Observatory at Swarthmore College over a period of 40 years suggest that Barnard's star is accompanied by at least two dark companions, each with about the mass of Jupiter.
There is still some controversy over his conclusion, however, because the observations are very difficult to make. Perhaps even more interesting is the fact that of the dozen or so single stars nearest the sun nearly half appear to have dark companions with a mass between one and 10 times the mass of Jupiter. In addition many theoretical studies of the formation of planetary systems out of contracting clouds of interstellar gas and dust imply that the birth of planets frequently if not inevitably accompanies the birth of stars.
We know that the master molecules of living organisms on the earth are the proteins and the nucleic acids. The proteins are built up of amino acids and the nucleic acids are built up of nucleotides.
The earth's primordial atmosphere was, like the rest of the universe, rich in hydrogen and in hydrogen compounds. When molecular hydrogen H2 , methane CH4 , ammonia NH3 and water H20 are mixed together in the presence of virtually any intermittent source of energy capable of breaking chemical bonds, the result is a remarkably high yield of amino acids and the sugars and nitrogenous bases that are the chemical constituents of the nucleotides.
For example, from laboratory experiments we can determine the amount of amino acids produced per photon of ultraviolet radiation, and from our knowledge of stellar evolution we can calculate the amount of ultraviolet radiation emitted by the sun over the first billion years of the existence of the earth.
Those two rates enable us to compute the total amount of amino acids that were formed on the primitive earth.
Amino acids also break down spontaneously at a rate that is dependent on the ambient temperature. Hence we can calculate their steady-state abundance at the time of the origin of life.
If amino acids in that abundance were mixed into the oceans of today, the result would be a 1 percent solution of amino acids. That is approximately the concentration of amino acids in the better brands of canned chicken bouillon, a solution that is alleged to be capable of sustaining life.
The origin of life is not the same as the origin of its constituent building blocks, but laboratory studies on the linking of amino acids into molecules resembling proteins and on the linking of nucleotides into molecules resembling nucleic acids are progressing well.
Investigations of how short chains of nucleic acids replicate themselves in vitro have even provided clues to primitive genetic codes for translating nucleic acid information into protein information, systems that could have preceded the elaborate machinery of ribosomes and activating enzymes with which cells now manufacture protein. The laboratory experiments also yield a large amount of a brownish polymer that seems to consist mainly of long hydrocarbon chains.
The spectroscopic properties of the polymer are similar to those of the reddish clouds on Jupiter, Saturn and Titan, the largest satellite of Saturn. Since the atmospheres of these objects are rich in hydrogen and are similar to the atmosphere of the primitive earth, the coincidence is not surprising. It is nonetheless remarkable. Jupiter, Saturn and Titan may be vast planetary laboratories engaged in prebiological organic chemistry. Other evidence on the origin of life comes from the geological record of the earth.
Thin sections of sedimentary rocks between 2. These inclusions have been identified by Elso S. Barghoorn of Harvard University and J. Bacteria and blue-green algae are evolved organisms and must themselves be the beneficiaries of a long evolutionary history. There are no rocks on the earth or on the moon, however, that are more than four billion years old; before that time the surface of both bodies is believed to have melted in the final stages of their accretion..
Thus the time available for the origin of life seems to have been short: a few hundred million years at the most. Since life originated on the earth in a span much shorter than the present age of the earth, we have additional evidence that the origin of life has a high probability, at least on planets with an abundant supply of hydrogen-rich gases, liquid water and sources of energy.
Since those conditions are common throughout the universe, life may also be common. Until we have discovered at least one example of extraterrestrial life, however, that conclusion cannot be considered secure. Such an investigation is one of the objectives of the Viking mission, which is scheduled to land a vehicle on the surface of Mars in the summer of , a vehicle that will conduct the first rigorous search for life on another planet.
The Viking lander carries three separate experiments on the metabolism of hypothetical Martian microorganisms, one experiment on the organic chemistry of the Martian surface material and a camera system that might just conceivably detect macroscopic organisms if they exist.
Intelligence and technology have developed on the earth about halfway through the stable period in the lifetime of the sun. There are obvious selective advantages to intelligence and technology, at least up to the present evolutionary stage when technology also brings the threats of ecological catastrophes, the exhaustion of natural resources and nuclear war.
Barring such disasters, the physical environment of the earth will remain stable for many more billions of years. It is possible that the number of individual steps required for the evolution of intelligence and technology is so large and improbable that not all inhabited planets evolve technical civilizations It is also possible-some would say likely-that civilizations tend to destroy themselves at about our level of technological development. On the other hand, if there are billion suitable planets in our galaxy, if the origin of life is highly probable, if there are billions of years of evolution available on each such planet and if even a small fraction of technical civilizations pass safely through the early stages of technological adolescence, the number of technological civilizations in the galaxy today might be very large.
It is obviously a highly uncertain exercise to attempt to estimate the number of such civilizations. The opinions of those who have considered the problem differ significantly. Our best guess is that there are a million civilizations in our galaxy at or beyond the earth's present level of technological development. If they are distributed randomly through space, the distance between us and the nearest civilization should be about light-years. Hence any information conveyed between the nearest civilization and our own will take a minimum of years for a one-way trip and years for a question and a response.
Electromagnetic radiation is the fastest and also by far the cheapest method of establishing such contact. In terms of the foreseeable technological developments on the earth, the cost per photon and the amount of absorption of radiation by interstellar gas and dust, radio waves seem to be the most efficient and economical method of interstellar communication. Interstellar space vehicles cannot be excluded a priori, but in all cases they would be a slower, more expensive and more difficult means of communication.
Since we have achieved the capability for interstellar radio communication only in the past few decades, there is virtually no chance that any civilization we come in contact with will be as backward as we are. There also seems to be no possibility of dialogue except between very long-lived and patient civilizations. In view of these circumstances, which should be common to and deducible by all the civilizations in our galaxy, it seems to us quite possible that one-way radio messages are being beamed at the earth at this moment by radio transmitters on planets in orbit around other stars.
To intercept such signals we must guess or deduce the frequency at which the signal is being sent, the width of the frequency band, the type of modulation and the star transmitting the message.
Although the correct guesses are not easy to make, they are not as hard as they might seem. Most of the astronomical radio spectrum is quite noisy. There are contributions from interstellar matter, from the three-degree-Kelvin background radiation left over from the early history of the universe, from noise that is fundamentally associated with the operation of any detector and from the absorption of radiation by the earth's atmosphere.
This last source of noise can be avoided by placing a radio telescope in space. The other sources we must live with and so must any other civilization.. There is, however, a pronounced minimum in the radio-noise spectrum. Lying at the minimum or near it are several natural frequencies that should be discernible by all scientifically advanced societies. They are the resonant frequencies emitted by the more abundant molecules and free radicals m interstellar space.
Perhaps the most obvious of these resonances is the frequency of 1, megahertz millions of cycles per second. That frequency is emitted when the spinning electron in an atom of hydrogen spontaneously flips over so that its direction of spin is opposite to that of the proton comprising the nucleus of the hydrogen atom.
The frequency of the spin-flip transition of hydrogen at 1, megahertz was first suggested as a channel for interstellar communication in by Philip Morrison and Giuseppe Cocconi.
Such a channel may be too noisy for communication precisely because hydrogen, the most abundant interstellar gas, absorbs and emits radiation at that frequency. The number of other plausible and available communication channels is not large, so that determining the right one should not be too difficult.
We cannot use a similar logic to guess the bandwidth that might be used in interstellar communication. The narrower the bandwidth is, the farther a signal can be transmitted before it becomes too weak for detection.. On the other hand, the narrower the bandwidth is, the less information the signal can carry. A compromise is therefore required between the desire to send a signal the maximum distance and the desire to communicate the maximum amount of information.
Perhaps simple signals with narrow bandwidths are sent to enhance the probability of the signals' being received. None have ever repeated. BETA operated until , when a storm damaged the antenna's drive gear. Around the same time, Horowitz's group, motivated by Charles Townes, who invented the laser, started tinkering with optical SETI searches.
Visible light has a higher frequency than radio waves, allowing more data to be encoded over any given period of time. Like radio waves, visible light also filters through our atmosphere, making it a logical portion of the spectrum for SETI searches. In , Horowitz and The Planetary Society constructed a 1. The search is still in operation, completing a full survey of the sky visible from Massachusetts every nights.
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