Are there any extraterrestrials

With the results of this study, astronomers searching for extraterrestrial life can now focus on stars and planetary systems that have a view of Earth and thus might already expect to hear from us. Of those stars, the authors further identified 75 that are close enough — within 30 parsecs — for radio waves from Earth to already have washed over them since humans started to produce them.

Those might be particularly good targets, Kaltenegger says, because aliens there could have both seen and heard us by now. But other stars assume new prominence.

Kaltenegger, L. Nature , — Article Google Scholar. Shostak, S. Union , — Heller, R. Astrobiology 16 , — PubMed Article Google Scholar. Download references. Article 27 OCT Nobody pretends the Drake Equation is the final word. Astronomers looking for alien signals have examined only a few thousand star systems so far. But as SETI Institute senior astronomer Seth Shostak has noted , the rate at which researchers are able to process the massive amounts of data that radio telescopes receive doubles approximately every 18 months to two years, meaning it grows by a factor of ten every six years or so.

The Milky Way has around billion 10 11 star systems that could conceivably host intelligent life under our current assumptions. An estimate of , 10 5 active civilizations in the galaxy would mean one per million star systems. At the exponential rate of growth in signal processing, researchers will have examined one million candidates by around , bringing the odds of a discovery into the probable.

See you in , aliens. 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. Perhaps information-rich signals with broad bandwidths are sent in order to achieve rapid and extensive communication.

The broad-bandwidth signals would be intended for those enlightened civilizations that have in vested major resources in large receiving systems. When we actually search for signals it is not necessary to guess the exact bandwidth, only to guess the minimum bandwidth. It is possible to communicate on many adjacent narrow bands al once.

Each such channel can be studies individually, and the data from several adjacent channels can be combined to yield the equivalent of a wider channel without any loss of information or sensitivity. The procedure is relatively easy with the aid of a computer; it is in fact routinely employed in studies of pulsars. In any event we should observe the maximum number of channels because of the possibility that the transmitting civilization is not broadcasting on one of the "natural" frequencies such as 1, megahertz.

We do not, of course, know now which star we should listen to. The most conservative approach is to turn our receivers to stars that are rather similar to the sun, beginning with the nearest. Two nearby stars, Epsilon Eridani and Tau Ceti, both about 12 light-years away, were the candidates for Project Ozma, the first search with a radio telescope for extraterrestrial intelligence, conducted by one of us Drake in Project Ozma, named after the ruler of Oz in L.

Frank Baum's children's stories, was "on the air" for four weeks at 1, megahertz. The results were negative. Since then there have been a number of other studies. In spite of some false alarms to the contrary, none has seen successful. The lack of success is lot unexpected. After all, there have been enough previous studies on this topic to fill a small horde of hard drives. Astronomer Carl Sagan figured that the Milky Way houses a million societies.

A more conservative claim is that the number is closer to 10, So why do these Brits disagree? This famous formula, which was introduced by astronomer Frank Drake in , is a string of seven parameters that, when multiplied together, estimate the number of technologically adept societies in the galaxy.

The parameters include the abundance of Earth-like planets, the fraction that spawn life, etc. They note that humans have been beaming signals into the ether for about a century.

Whatever we on Earth have done, the rest of the universe has imitated perfectly.