Modern astronomers know about three and a half thousand exoplanets, which are located at a distance of four to twenty-eight thousand light-years from us. Some of them are very similar to Earth. To get to any of them in the foreseeable future will be difficult - unless humanity will make a huge technological leap. Nevertheless, the exoplanets are already of great interest today in terms of astrochemistry. This is our new material, written in partnership with Ural Federal University.
The main part of the substance of the Universe (baryonic substance) is hydrogen - about 75 percent. The second place is occupied by helium (about 23 percent). However, a wide variety of chemical elements and even complex molecular compounds, including organic ones, can be found in space. Astrochemistry studies the formation and interaction of chemical compounds in space. Representatives of this specialty are very interested in studying exoplanets because they can realize a variety of scenarios that will lead to the emergence of unusual compounds.
Rainbow in the service of astronomers
The main tool for obtaining information on the chemical composition of remote objects is spectroscopy. It takes advantage of the fact that atoms of chemical elements (or molecules of compounds) can radiate or absorb light only at certain frequencies corresponding to the transitions of the system between different energy levels. As a result, a spectrum of radiation (or absorption) is formed, from which a substance can be unequivocally defined. It is like fingerprints, only for atoms.
A good example of the decomposition of light into a spectrum is the rainbow. To us, transitions from one color to another seem smooth and continuous, and actually, some colors in a rainbow do not exist because certain lengths of waves are absorbed by hydrogen and helium containing in the Sun. By the way, helium was first discovered by observing the Sun's spectrum (that's why it is called "helium", from other Greek. ἥλιος - "the sun"), and in the laboratory, it was isolated only after 27 years. This was the first successful example of using spectroscopy to study stars.
In the simplest case of the hydrogen atom, the emission spectrum is a series of lines corresponding to transitions between levels with different values of the main quantum number n (this picture is well described by the Rydberg formula). The most famous and convenient for observation is the Balmer line Hα, which has a wavelength of 656 nanometers and lies in the visible spectrum. For example, on this line, astronomers observe distant galaxies and recognize molecular gas clouds, most of which consist of hydrogen. The following series of lines (Pashena, Brackett, Pfunda, etc.) lie entirely in the infrared range, and the Lyman series is located in the ultraviolet range. This makes it a little more difficult to observe.
At the same time, molecules of complex compounds have another way of emitting quanta of light, in a sense even simpler. It is related to the fact that the rotational energy of the molecule is quantized, which also allows them to emit in lines (also, they can emit a continuous spectrum). The energy of such quanta of light is not very large, so their frequency is already in the radio range. One of the simplest rotational spectra belongs to the carbon monoxide molecule CO, and astronomers also often recognize cold gas clouds when they cannot see hydrogen in them. Methods of radio astronomy have also made it possible to find methanol, ethanol, formaldehyde, hydrocyanic acid, antic acid and other elements in molecular clouds. For example, it was with the help of a radio telescope that scientists discovered alcohol in the tail of the comet Lovejoy.
A single experiment does not allow conclusions to be drawn about the observed phenomenon. The experiment should be repeated many times and independently. Each open exoplanet system is an independent experiment. And the more they are known, the more reliably the general laws of origin and evolution of planetary systems are traced. We need to collect statistics!