signals from space

This is what it looks like following the discovery of the first planet outside the solar system
14/4/1995

After years of research and monitoring without results, the first signs indicating the existence of a planetary system similar to our solar system were discovered in space. Let's put it with the utmost caution: if planetary systems are a common and routine phenomenon in the galaxy, there is a greater chance of the existence of extraterrestrial life

By Bisham Azgad

Little green people don't live on stars. The reason for this is simple: the stars are too hot. A star is a body that burns and produces energy by itself through nuclear fusion, in the same process that occurs when a hydrogen bomb explodes. In other words, a star is a sun. Our sun, "Sol", is actually a star.

People or living things of any kind are unable to live on hot suns. They can only develop and exist on the surfaces of planets, which are small, dark and much colder bodies compared to stars. The Earth, for example, is a planet. And so are the planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. These nine planets move, mainly under the influence of "Sol's" gravity, in closed orbits around the Sun. They - along with their moons and a fairly large number of asteroids and comets - make up our solar system.

Studies carried out, among other things, using robotic spacecraft and satellites, and which were designed to look for signs of life outside the Earth - have so far turned up nothing. It seems that some of the planets in our solar system are too hot, or too cold, or lack conditions and materials that might allow life to develop.

Because of this, those who wish to look for other life should look for it on the faces of planets that are found in other solar systems, and not in our solar system. Such planets were first discovered not long ago. Until then it was necessary to deal with the possibility that our solar system is a unique phenomenon and perhaps even the only one in the universe. If our solar system was created in a rare or one-time process, because then it is clear that there is no longer any chance of discovering life outside the earth; There is no longer any point in research aimed at this goal, and all science fiction stories that try to imagine such a life, while skipping the hurdle of time, have lost all steam.

On the other hand, if it turns out that a solar system with planets is a common phenomenon, and if we assume that only around each of the hundred stars in our galaxy (the Milky Way galaxy), a planetary system was formed - because then there should be several hundred billion planets in our galaxy. Where are all these planets? Where did they go?

Well, they may not be gone, just very hard to find. A planet does not emit light, but, at most, reflects the light of the star (the sun) that falls on it. The enormous distance between the stars in the galaxy, which is about a billion light-years in diameter, makes it very difficult to discover bodies that shine with such a low intensity. The closest star to us, Alpha Centauri, is 3.8 light years away. A light year is a unit of distance that symbolizes the distance a light ray travels in one year; Since the speed of light in empty space is constant (about 300 thousand kilometers per second), it is possible to calculate and find that in one year light travels a distance of about ten million million kilometers. About a hundred thousand times the distance between the Earth and the Sun.

From such distances, it is very difficult to observe such small, dark and cold bodies as planets that move around other stars (suns) in the vastness of the galaxy. Success will be equivalent, more or less, to the success of a resident of Tel Aviv to observe and identify a one shekel coin lying on the pavement in London. The combination between this technological obstacle, and the centrality of the question - is there possible life outside the Earth - gave birth to a global race in an attempt to discover any planets, around any star, in our galaxy, outside our solar system.

Along with the race to discover planets, many studies are also being conducted with the purpose of discovering stars around which a solar system is gradually forming and growing. These studies may teach a lot about the processes that led to the formation of our solar system. They may also give an answer, even if only partially, to the question of how common or rare planetary systems are around other stars in the galaxy.

Researchers Karen and Steven Strom of the University of Massachusetts at Amherst, and Michael Merrill of Kit Peak Observatory in Tucson, Arizona, reported some success. They examined "young" stars with a relatively small mass (similar to the mass of "our" sun), and found that around many of them there are disks of tiny dust grains. The grains may stick to each other and form clumps, which will also stick to each other, until over time they form planets.

The researchers used a camera aimed at receiving infrared radiation, and observed a region of the universe where stars are formed and born: the molecular cloud known as Lindes 1461. The cloud, located 1,500 light years from Earth in the Orion constellation, is the closest cloud of its kind to Earth. It contains so much dust that, in the range of visible light, the dust obscured the stars that formed in the cloud not long ago. Thus, the first real evidence of the existence of the young stars in the depths of the cloud, comes from infrared radiation emitted from the dust disk that surrounds them (the same disk that can be seen as an initial stage in the formation of a planetary system). The disc emits this radiation (among other things) as a result of the radiation of the stars being absorbed by the material contained in it. The "Hubble" space telescope, which was also aimed at this area, recently succeeded in photographing several dozen such dust disks; The first of which was photographed around the star in the Pictoris chamber. In other observations, similar dust discs in the Orion Nebula were photographed using the Hubble.

The great difficulty involved in trying to observe planets that move around distant stars, gave birth to indirect ways of research and discovery. Instead of insisting and trying to observe the scant light reflected from the face of a distant planet, researchers look for circumstantial evidence of its existence. Such circumstantial evidence can be the effect of the planet's (relatively weak) gravity on the star (the sun) that it orbits.

One way of measuring these effects is based on the Doppler phenomenon, which is manifested in the change of the wavelength of light, depending on the movement of the light source. For example, when the distance between a certain star and the Earth is shortened, the light emitted from that star will appear to the observer from here to have a shorter wavelength, that is, bluer. On the other hand, when the distance between the star, the source of light, and the Earth increases, the light emitted from it will appear to us to have a longer wavelength. That is, more red. In other words, when you see that the light of a certain star dims and goes, you can know that it is moving away or "running away" from us. And on the other hand, when you see that its light is getting bluer and bluer, it is clear that it is getting closer to us.

Planets moving around a star in the vastness of the galaxy may slightly affect the position of the star. Thus, the star may "oscillate" back and forth in relation to the earth, a phenomenon that will manifest itself in the darkening and the earth of suits of its light. Using this technique, the astronomer, Prof. Zvi Maza from Tel Aviv University's School of Physics and Astronomy, together with a group of researchers from the Smithsonian Institution at Harvard University, discovered a body that seemed too small to be a normal star, and too large to be considered a planet. This body, moving around the star, HD-114762 was actually a small and relatively cold star of the type known as a "brown dwarf". It is a star that is a sort of intermediate stage between a planet of the type called a "gas giant" (such as Jupiter and Saturn in our solar system), and a star. Its mass may be ten times that of the planet Jupiter.

Other detection techniques are based on the measurement and identification of differences in the position of various stars on the "surface of the sky". With this technique, astronomers measure and compare the distance of a certain star from other stars. When a certain periodic difference in these distances is detected, it is possible to calculate and find out if the movement may be caused by the presence of planets in the system. Much effort has been invested in this field in recent years. The American space agency, NASA, outlined a master plan that is divided into four phases, in the search for planets orbiting other stars in the galaxy. The first phase of the program, which is now underway, is manifested in budgetary support for the construction of an observatory on the summit of Mount Mona Kea in Hawaii, which rises 4,270 meters above sea level. Viewing from a high altitude considerably reduces the effect of the atmosphere on the light radiation coming from the stars. This effect is considered the main factor weighing down attempts to accurately measure the position of various stars, using observation systems installed on the surface of the Earth (the desire to be freed from this interference was actually the main motive for the construction of the Hubble Space Telescope).

An observatory has been operating at the top of Mona Kea for several years, and the observatory being built there now is its exact twin. A telescope with a diameter of ten meters will soon be installed in the observatory; The distance between the two telescopes will be 85 meters. The observations that will be made at the same time from these two telescopes will help to detect fluctuations and tiny changes in the position of different stars, fluctuations that may be caused by the influence of the gravity of the planets that surround them.

In the next step, a double system of space telescopes will be launched into space, designed to perform the same mission - without the disturbing influence of the Earth's atmosphere. In the third stage, a more powerful system will be launched, and in the fourth, ambitious stage, a double system of large telescopes will be installed and operated on the soil of the dark side of the moon. These lunar telescopes will be completely free from the influence of the Earth's atmosphere; Scientists who live according to the plan on the lunar base will be able to manipulate them relatively easily, and with much greater efficiency than can be achieved with a remotely operated space telescope. In fact, all these efforts and programs have not yet managed to lead to the discovery of a planet outside our solar system. At least theoretically, there was a fear that all the expenses and efforts were spent in vain - that this is a search that has no dawn and has no purpose. But recently, the first "eureka" call came from the study of Pennsylvania State University astronomer Alexander Volchan, who was working in collaboration with Dale Fraile of the US National Radio Telescope Observatory in Socorro. The two operated the world's largest radio telescope, whose receiving antenna diameter is 305 meters, located in Arecibo, Puerto Rico.

A radio telescope is a device that tracks and receives radio radiation emitted by various stars, and on the basis of it locates and measures, among other things, their exact place in space. Vulcan and Fraile followed a pulsar that they marked.PSR 1257+12 A pulsar is a special star; In fact, it is the remnant of a huge apricot that exploded and "lost itself to know" in the process of supernova. In this process, the sun simply throws off most of the material that makes it up: the material is scattered in space in all directions, and the light of the explosion illuminates large parts of the galaxy. The Sun's core remains in place, but it begins to collapse and contract in on itself, under its own gravitational forces.

When it is a sun whose mass is ten or more times the mass of our sun, this process ends in the formation of a black hole. When these are smaller and lighter suns, the process stops at the stage where only compressed neutrons remain in the core. That is why such a collapsing sun is called a "neutron star". At this stage, the star contains a mass at the rate of 1.4 of the mass of our Sun, while its radius does not exceed ten kilometers. Hence, the compression of the neutron star is so great that one teaspoon of the material that makes it up is equal to the mass of all the mountains of Jerusalem.

Neutron stars spin on their axis very quickly. Some of them complete one rotation around their axis for about one second (that is, their speed of rotation - at their equator - is about 60 km per second). Others spin even faster, completing each rotation around their axis in fractions of a second. Some of those fast spinners emit radio waves as they spin from a "broadcasting site" in front of them, and function in space as a sort of flashing flashlight mounted on ambulances or police cars. Those who perceive them from a distance, using a radio telescope, actually perceive a kind of flicker or signal that repeats itself at a fast rate and with great accuracy. That is why these neutron stars are called "pulsars".

The first pulsar was discovered by Jocelyn Bell and Anthony Heuish in 1967. While making various measurements with a radio telescope, Bell (who was then a research student for a PhD in astronomy, under the guidance of Prof. Heuish), noticed a "signal" coming from space - a kind of flickering constant at intervals of 1.33 seconds. At first glance it seemed that intelligent beings living on a planet somewhere in the galaxy were trying to inform the human race of their existence. Therefore, the origin of these transmitters was called the acronym LGM ("Little Green People"). But this exciting theory soon gave way to another theory, about rotating neutron stars.

Since then, about 550 pulsars have been discovered. Volchan and Fraile, who picked up and recorded the "signal" of the pulsar, PSR 1257+12 discovered a certain change - cyclical - in the rate of its "signal". A mathematical analysis of these changes showed that they are most likely caused by periodic changes in the distance between the pulsar and the Earth, caused by the gravitational influence of other bodies located near the pulsar. Further calculations showed that it is two bodies, two planets, the mass of one of which is 2.8 times greater than the mass of the Earth, while the mass of the other is 3.4 times greater than the mass of the Earth. The first planet orbits the pulsar in a time equal to 66 Earth days, while the second completes a circle around its star in a time equal to 98 Earth days. The orbit is close, about the same as the orbit of the planet Venus around our sun.

Later it turned out that there is actually another planet in the system, whose mass is more or less equal to the mass of the Earth's moon. This small and relatively light planet completes one revolution around the pulsar in a time equal to 25 Earth days. At this stage, a mathematical model was built at Cornell University in New York, which performed - using an extremely powerful and fast supercomputer - a simulation of the bodies found in the pulsar system, on the complex gravitational interactions that exist between them. When you run such a model, based on the known laws of physics, you can see how this or that solar system should work. Indeed, the model clearly showed that a system like the one described by Volchan and Fraile would operate and behave exactly as the results of the measurements made with the radio telescope indicated.

The discovery of the small Earth-like planets, precisely in the pulsar system, raises new hopes regarding the reality of millions of Earth-like planets throughout the galaxy. Volchan and Fraile reported their discovery at the same conference where a group of scientists from England announced that they were canceling their previous report of a similar discovery. The members of the team, from the University of Manchester (Andrew Lane, Matthew Bayles and Santam Shimar), reported about three years ago the detection of one planet moving around the marked pulsar, PSR 1829-10 located in the constellation Sagittarius, about 30,000 light years from Earth . In the end, it turned out that the measurements of the English scientists showed wrong results, which could have disappointed many researchers - had not Volchan and Fraile appeared with their discovery.

The chance of the existence of life on the surface of the new planets is zero: the pulsar, their sun, does not give them enough heat necessary to create life. The question that preoccupies many astronomers today is, what is the origin of these planets. They may have existed in this system even before the supernova that produced the pulsar erupted. But it is also possible that after the supernova explosion, a ring of material formed around it, from which the planets were formed. If this is indeed how things happened, the study of these planets may teach us a lot about the formation processes of planets and different solar systems.

One such possible insight was recently raised by Prof. Zvi Maza and Dr. Yitzhak Goldman, also from Tel Aviv University. Maza and Goldman noticed a certain structural similarity that exists between the planets of the pulsar system and the planets in our solar system. Thus, for example, the mass ratios and orbital periods between the three planets in the pulsar system are very similar to the mass ratios and orbital periods between the three innermost planets in our solar system: Mercury, Venus, and Earth.

More than that: various reports (which have not yet reached the publication of an orderly research report) show that in the pulsar system there is actually another planet, a fourth, which, in terms of its mass ratio and the time it orbited the pulsar, compared to the other planets in the system, is very similar to the fourth planet In our solar system - Mars. This phenomenon, whose purpose has not yet been fully understood, may seemingly indicate a structural similarity between two planetary systems, moving around distant and different stars in the galaxy. From this it may be possible to conclude that not only are planetary systems a common and routine phenomenon in the galaxy, but that their formation is an obligation of reality, and that it is carried out according to certain rules, whatever.

The broader meaning of the discovery, of course, concerns the possibility of the existence of extraterrestrial life, and our attempts to discover it. Prof. Maza says that if it were possible to identify the areas in space where planets are found, it would be possible to immeasurably optimize the operations of listening to space signals, recently carried out by the American space agency, NASA.

However, even if we could ever pick up signals originating from an alien culture, it seems we'll never be able to reach it. At least not in the way described in my science fiction books and movies. A "conventional" manned spaceship, which will be equipped for a journey several million light years long, will need all the energy that can be produced by the means found on Earth. And that's without taking into account the fact that traveling a million light years would take a lot longer than a million years, since even the fastest spacecraft we could ever build would be traveling at slower than the speed of light.

That leaves two alternatives for interstellar travel. One option is based on sending a tiny robotic spacecraft; Future miniaturization technologies may enable the construction of a robotic spacecraft of this type. Robots, as we know, do not suffer from a short lifespan, like humans. They are able to fly in space and function for millions of years, until they reach their desired region.

The second alternative is the so-called "ship of generations": a manned spaceship powered by nuclear fusion energy (which is not yet within our reach, but may be developed in the future). On board this ship will be placed men and women, who during the journey will give birth to children, and afterwards, their children will give birth to their own children, and so on. This program, a sort of spaceship Noah's ark, raises sharp moral and educational questions, which until now have only been discussed in science fiction books. Can children born in generation number 40 aboard the spacecraft be considered "citizens"? Do they owe loyalty and solidarity to the humans who remained on their original planet?

Can they see themselves as representatives of "Earth" on the alien planet they will reach at the end of their journey? And how do people who are, and their parents and their parents' parents have not seen - and will not see the "land" of their day, represent the human race?

All these may seem like hypothetical questions far beyond the horizon, but experience shows that the rate at which science fiction becomes science has been steadily accelerating in recent decades. It is possible that none of the readers of this article will be asked these questions in their lifetime. But it is equally possible that they will employ - in a completely practical way - those who will be born in the first decade of the 21st century.