Finding planets that are outside our solar system, called exoplanets, has changed the way we see the cosmos and our place in it. These faraway planets are extremely hard to find because they are small, dim, and in the bright light of their much brighter parent stars. Most of the time, exoplanets are not seen directly by astronomers, but they take help from very subtle clues like minute changes in the light or position of a star to confirm the presence of a planet. This was made possible due to the innovations in space technology and the introduction of very powerful telescopes, thereby giving the scientists the ability to detect a large number of exoplanets and even study their motions, birth, and changes.Understanding the methods used by theEuropean Space Agencyto find these planets helps explain how astronomers search for Earth-like worlds and assess their potential to support life.
Methods used by astronomers to find planets in other solar systems
Most exoplanets discovered so far have been found using indirect methods. These techniques measure how a planet affects its parent star.Radial velocity methodThe radial velocity method is the major one. When a planet goes around a star, it is the planet that, by its gravity, makes the star move side by side. This movement changes the wavelength of the star’s light due to the Doppler effect. When the star is coming from the Earth, its light becomes blue, and when it goes away, it becomes red.By looking at these slight changes in the star’s spectrum, astronomers can figure out a planet’s weight and its track. But this method is mostly responsible for the discovery of large planets, as an Earth-like planet would make a move that is too small to be measured from the ground.Astrometry methodAstrometry is all about recording the exact location of a star in the sky and noticing tiny changes that could be caused by planets going around that star. The Earth’s atmosphere has made it very hard to do this from the ground, but space missions have made it possible to be more accurate.One of the main goals of the European Space Agency’s Gaia mission is to define star locations with super high precision, and it is predicted to find a huge number of big exoplanets, up to tens of thousands. However, the identification of planets with the size of our Earth is still very difficult.transit methodThe transit method is used to find planets when they move in front of their parent star; thus, a very small decrease of the star’s brightness can be observed. This method is very strong, as it can, first of all give the size of the planet, and with the addition of the radial velocity data, the density of the planet can be figured out.Big planets cover more of the star’s light and it is easier to see them from Earth. In order to be able to detect tiny Earth-like planets, space missions like CoRoT and other missions are needed. Nowadays, this method has been turned into one of the most fruitful ways to find new exoplanets.
Direct detection of exoplanets
Direct detection tries to get the light that comes from the planet itself, which is either the starlight the planet reflects or the heat the planet emits. However, this is very challenging because, comparatively, stars are way brighter than their planets.At visible wavelengths, a star like the Sun is billions of times brighter than Earth. In the infrared, the difference in brightness is smaller, thus allowing the detection of planets to be done more easily from space, where there is no interference from Earth’s atmosphere.
Advanced techniques for direct detection
Doppler IsolationThis method separates the planet’s light from the star’s light by analyzing their different Doppler shifts as both move in space. While promising, it requires very large telescopes and has not yet been widely used.PolarimetryLight reflected by a planet becomes polarized, unlike the unpolarized light from stars. Polarimeters can detect this difference, helping astronomers isolate the planet’s signal. New, highly sensitive instruments are being developed to make this method more practical.Nulling InterferometryNulling interferometry combines light from multiple telescopes in a way that cancels out the star’s light while leaving the planet visible. This powerful technique is being refined on Earth and may one day be used by space missions such as ESA’s proposed Darwin mission to study Earth-like planets.
The role of space telescopes
Space telescopes do not suffer from atmospheric distortion and are not affected by heat; thus, they are significant for detecting tiny and very distant exoplanets. The next missions want to obtain the first pictures and to study the atmospheres of planets to find traces of habitability.Some astronomers, however, consider the possibility of planets orbiting white dwarf stars. These stars are very faint; thus, it is quite easy to detect orbiting gas giants with big ground-based telescopes.The discovery of exoplanets is a highly complicated task which requires very accurate measurements, advanced technology, and observations from space. Indirect methods have been used mainly to make the first steps, but future direct imaging techniques will allow much more to be revealed about these distant worlds. In fact, these different ways are supporting each other in the study of the processes of planet formation and in the search for possible extraterrestrial life.
