For a long time, science has been dominated by the view that planets are a very rare phenomenon in space. This view was imposed, for example, by the theory of the origin of the planets by the English astronomer Jeans. According to Jeans, the planets of the Solar System were formed from a jet of matter torn out of the Sun by a randomly passing nearby star. This jet was thinner at the beginning, thicker in the middle, and ended up thinning again, which explained why the closest and most distant solar planets are small in mass and size, and the central ones are gas giants. The convergence of stars is not only an accidental situation, but also extremely rare (at least in our regions of the Milky Way), and therefore the formation of planets, according to Jeans ‘ theory, also turned out to be an extremely rare event. Indeed, until 1992, there was no indication that any other stars had the same planetary families as our Sun. One can only wonder at the persistent optimism of SETI enthusiasts, who even under these circumstances continued to insist that extrasolar planets exist.
This changed when, in 1992, Alex Volchan discovered one or more planets near one of the pulsars. The pulsar changed its position slightly, apparently as a result of the gravitational influence of one or more invisible objects. The oscillation parameters allowed Volchan to determine the total mass of these objects, which turned out to be much less than the stellar masses, but within the mass limits of one very large planet or several smaller ones.
This discovery paved the way for a regular search for invisible planets by their gravitational influence on their stars, and after just three years, such a search was crowned with outstanding success. In 1995, Major and Queloz, working at the Geneva Observatory, discovered a planet near a sun-like star called “51st in the constellation of Pegasus”in the catalog. A few months later, Marcy and Butler opened their “planetary account” by finding a planet near the 70th star of the constellation Virgo (today, Marcy and Butler have more than 60 planets found). By November 2003, the full list of extrasolar planets discovered by astronomers had reached 119! By December 2007, about 250 of them had been opened! All of them are found near the nearest stars to us. Today, we can already say with confidence that planets are not a rare, but a very common phenomenon. They will certainly be detected near more distant stars, as soon as it becomes practically possible. But to do this, you need to overcome serious difficulties.
Direct observation of extrasolar planets is difficult. Planets glow only because of the reflected light of their star, and this radiation (for example, in the Solar System) is a billion times less than the radiation of the star itself. The light of the star simply obscures the glow of the planet. And the thermal (infrared) radiation of the planet is also weaker than what existing instruments can detect.
The most promising method is the so-called interferometric star quenching. If you observe the same star in two telescopes at once and then bring both images together, then in two different rays they will extinguish each other. Then the radiation of the planet, if there is one, will be clearly marked on a dark background. Of course, it is so simple only in popular science narratives, and so good-only in science fiction novels, but the first practical attempt to use this method was already made in November 2003 by the Hinz group at the Chilean Magellan telescope. Although the starlight was dimmed by only 95 percent in this attempt, astronomers were able to detect a dark circular “moat” in the gas — dust disk surrounding the star, which, according to current ideas, indicates the formation of a planet-a gas giant several times heavier than Jupiter-at about the same distance from the star as Saturn is from our Sun.
This success is good news for the European and American space agencies, which are planning to launch (in 2008 and 2013) two projects of interferometric search for planets: “Darwin”, otherwise called SIM (Space Interferometry Mission, or “Space Interferometric Probe”), and TRF (Terrestrial Planet Finder, or “Earth-like planet Finder”), each of which will be able to darken the light of the star a million (!) times. Darwin is a system of six orbiting telescopes, whose interferometric communication should make it possible to distinguish objects only a few times larger than the Earth near the nearest stars. The TRF’s four large mirrors will be placed at the corners of a square the size of a football field, allowing it to distinguish between Earth-like planets even at a distance of 50 light-years, and its spectrometer will analyze the atmosphere of these planets mainly for the presence of ozone, methane and oxygen.
But all this, of course, is a matter of the future. However, even today, the total data on the first extrasolar planets allow us to make some generalizations. And the first of them is the very fact of the discovery of so many planets. As Marcy and Butler write, giant planets are found in 5-10 percent of the surveyed stars of the type of the Sun (or close to this type), and we can think that the same ratio will continue in the future. This would mean that there could be hundreds of thousands or even millions of planets in our galaxy. This conclusion is also supported by new theoretical ideas about the mechanism of planet formation, put forward to explain the strange properties of those that have already been discovered. I must say that these properties were really quite unexpected.
All or almost all newly discovered planets or planetary families show a sharp difference from the planets of the Solar System and from it. Only in a few cases have planets been found orbiting in circular or almost circular orbits at a sufficient distance from their star, comparable to the distance of the planets of the Solar system from the Sun. Otherwise, these are either circular orbits that pass at an inexplicably close distance from the star and require an incredibly fast rotation of the planet around this star (and we are talking about gas giants like Jupiter!), or sharply eccentric orbits, the appearance of which contradicts all previous views on the process of planet formation.
According to these views, which replaced the now discarded Jeans theory, the solar planets formed from the same protostellar gas-dust disk from which the Sun formed, at the same time and in about the same time period. And indeed, our Earth and other solar planets are the same age as the Sun. The difference between large and small planets, between gas giants with a small solid core and solid, rocky planets like Earth and Mars is connected in this theory with the fact that large planets were formed in the central part of the cloud due to the gradual sticking of a huge mass of gas to the primary ice core, and small planets formed in the closest and most distant parts of it, poorer in matter, due to multiple collisions and mergers of ” planetary embryos “(“planetesimals”).