Tau Ceti (t Cet. T Ceti) is one of the closest sun-like stars to us, located in the constellation Ceti at a distance of almost 12 light years (114 × 1012 km). In December 2012, astronomers announced the discovery of five planets around this star at once, including potentially habitable ones.
Astronomical discovery
Among the more than 850 exoplanets (orbiting a star outside the solar system) discovered so far, these five have sparked an unexpected surge of interest outside of astronomical circles. The fact is that Tau Ceti is one of the first stars to come into the spotlight half a century ago, with timid attempts to hear signals from extraterrestrial intelligence.
The Tau Ceti system is part of our closest stellar environment, and the light of the Sun reaches it in just a dozen years. Tau Ceti itself is, like our star, a solitary yellow dwarf. This system ranks third in distance from the solar system, behind only Alpha Centauri (4.3 light years) and epsilon Eridani (10.5 light years), each having one planet. Thus, Tau Ceti is the closest multiplanetary system to us.
The return of interest to Tau Ceti occurred after a thorough analysis of jitters (jitter - "jump") in the speed of a star around the galactic center common to all the stars of the Milky Way. This first indication of the presence of an exoplanetary system and subsequent observations with calculations carried out by a large international team of astronomers confirmed the discovery.
The publication of 15 authors in the reputable journal Astronomy and Astrophysics was the result of many years of telescopic observations in Chile, Hawaii and Australia. This is how the new exoplanetary system HD 10700 appeared in the astronomical catalogs. All five planets of Tau Ceti are located rather compactly and rotate within the orbit of Mars, if compared with the scales of the Solar system. This yellow dwarf shines almost two times fainter than the Sun, but due to the proximity of orbits to the star, the first three planets are literally burned out by radiation streams. Naturally, in such conditions, protein life cannot exist on them.
Around Tau Ceti, tens of times more cometary and asteroid matter revolves than around the Sun. This was determined by the presence of a disk of cold dust around the star, most likely formed by collisions between small particles of cometary and asteroid matter.
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Birth of hopes
After disappointing results for the three inner planets, all astronomers' attention was focused on the fourth and fifth. The fourth planet is about four times more massive than Earth, with an annual turnover of 168 days, which is close to the Venusian year, which is 224.7 days. The fifth planet, Tau Ceti, revolves around its star in 640 days, which, in turn, is close to the Martian year - 687 days. There is a heated debate about the temperature conditions on these exoplanets, but many scientists are inclined to believe that these planets may well fall into the "belt of life", providing acceptable conditions for the existence of protein organisms. In addition, they are only several times more massive than the Earth, which serves as an additional argument in favor of the presence of atmospheres in them.
Project "Ozma"
The idea of interstellar communication using radio waves was born at the beginning of the last century and is well known to us from the novel by A. N. Tolstoy "Aelita". From time to time in different countries there are sensational reports about the reception of signals from other worlds. Previously, they were usually attributed to the inhabitants of Mars. Now, after several research expeditions of robots, the Martian surface does not seem so mysterious, and the search for radio sources has moved outside the solar system.
The first experimental apparatus for searching for "hydrogen" radio signals was developed under the guidance of the famous American radio astronomer Frank Drake. He named his project "Ozma" - after the queen of the fantastic land of Oz, inhabited by fantastic creatures, from the books of Frank Baum.
A giant radio telescope antenna with a diameter of 26 meters alternately tracked two stars similar to our Sun: Tau Ceti and Epsilon Eridani. The first searches for extraterrestrial intelligence caused a huge public outcry.
The tau star from the constellation Cetus can be seen in the sky with the naked eye. In addition, Tau Ceti became the first star to be found around a disk of dust, comets and asteroids, the size and shape of which is comparable to a similar disk found in the Sun.
However, the analogies seem to end there. And it is hardly worth counting on the fact that there is a planet similar to Earth near Tau Ceti. Astronomers' studies have shown that the number of comets and asteroids orbiting Tau Ceti is more than ten times the number of comets and asteroids in our solar system. So even if there are one or more planets, they must constantly be subjected to powerful impacts from large celestial bodies, like the asteroid, from which, as it is assumed, dinosaurs died out on Earth several tens of millions of years ago. Thus, if life once appeared on Tau Ceti, it could not go through the same long evolutionary path as on Earth.
The reasons why Tau Ceti has so many asteroids and comets are still unclear to scientists. It is possible that, on the contrary, this is a normal phenomenon, and our solar system is an exception. Maybe our Sun once passed in relative proximity to another star, and that one pulled most of the asteroids and comets to itself.
Interplanetary radio bridge
It is unlikely that in the near future mankind will be able to send an interstellar expedition to the HD 10700 system, so all hopes are connected with the possibility of establishing radio contact with the "Taukitians". For such a radio bridge, it is important to know in which range to transmit. Logically, we can assume that every advanced civilization knows that hydrogen is the most abundant element in the Universe. Under the influence of external causes, hydrogen atoms are often excited and emit vibrations at a strictly defined frequency. Terrestrial radio telescopes confidently receive the amount of radiation, which is called the hydrogen line on the frequency scale. The discovery of this line marked a new stage in the development of astronomy. A new means of understanding the Universe has appeared in the form of a kind of “natural standard of radiation frequency”. And a similar radio standard, in theory,must be well known to every technologically advanced civilization. This ingenious and simple idea gave a significant impetus to theoretical and experimental studies of the problem of contact.
Space dispatch
This message was sent in 1974 to star cluster M13 from the giant 305-meter radio telescope at Arecibo in Puerto Rico. The diagram represents information about humanity encoded using a sequence of zeros and ones: from left to right there are numbers from 1 to 10, data on atoms, including hydrogen and carbon, as well as on organic molecules and DNA, a description of man and the solar system, as well as the radio telescope itself … The addressee should receive this radio message in fifty millennia.
At the same time, many obstacles lie in the way of establishing communication with the same "Taukitians".
First, we still do not know everything about how radio signals propagate at ultra-long interstellar distances. Perhaps the message will be distorted in the interstellar space and, after multiple scattering, reflections and absorption, will become indistinguishable from the constant radio noise that the planets and stars fill the Universe with.
Secondly, the "Taukitians" may not rely on the frequency of hydrogen emission, but use some very unusual range, not audible by earthly radio astronomers.
Third, the Taukitian signals can have a very specific coding in the form of ultra-short pulses that occupy a wide frequency band. Terrestrial radio telescopes are usually associated with such signals with radio emission from stars and galaxies. Well and, generally speaking, an alien civilization, ahead of our technologies by several centuries or even millennia, may use some unknown communication channels. For example, by generating directed streams of high-energy elementary particles, which we perceive as cosmic showers or stellar wind.
Magazine: Secrets of the 20th century №8. Author: Oleg Faig