Our solar system is just a tiny glimpse intoconstantly expanding universe<
Many of these new planets are very different fromthose that revolve around our Sun, and even the architecture of exoplanetary systems bears little resemblance to ours. As time passed, a tremendous amount of information was found in some of these distant worlds. What's even more remarkable is how quickly the field of exoplanetary research has grown in a relatively short period of time.
Exoplanets - what are they?
An exoplanet is a planet beyond oursSolar system. The exoplanet revolves around its star - an analogue of our Sun. Together with a star, one or more exoplanets make up a solar system like ours. The distance from the nearest planet to the host star can be more or less than that of Mercury, and distant planets can be located farther than Saturn and Pluto and be larger than Jupiter - one way or another, an exoplanet, one or more form a solar system with its star.
What are the “other” solar systems?
- A system with one or more planets.
- A system with two stars and one planet.
- A system with planets that may have the right conditions for the stability of water on their surface, necessary for a component of life as we know it.
How are exoplanets searched for?
In 2006, the first spacecraft was launchedthe mission dedicated to exoplanetary research is a mission called CoRoT. Within months of launch, CoRoT discovered its first planet, hot Jupiter, orbiting a star like the Sun. Over the next few years, CoRoT put exoplanetary exploration from space on a sustainable footing with the constant detection of unusual planets.
When the NASA mission launched in 2009«Кеплер», число известных планет начало расти. «Кеплер» — космическая обсерватория НАСА, орбитальный телескоп со сверхчувствительным фотометром, специально предназначенный для поиска экзопланет.
Methods for detecting exoplanets are becoming more accurate.
Doppler method (радиальных скоростей, лучевых скоростей). The first planets found in the orbit of sun-like stars were discovered using exactly this method. A single star, devoid of a planetary system, will have its center of gravity located in the center of the star. However, when a planet orbits a star, the star-planet system's center of gravity shifts away from the star's center, causing the star to "wiggle" back and forth from the observer's perspective, just like stars and stars. The planet rotates around their common center of mass. Subtle changes in the radial (line of sight) speed of a star can, in principle, be measured to reveal the presence of otherwise invisible planets.
Doppler method(radial velocities, radial velocities)
Transit methodallows telescopes to measure the aurora to confirm the presence of planets around the star, as each time a planet passes in front of a star,Cyclical changes in brightness indicate the transit of a planet between Earth and a star.
Transit method
Astrometryis a method that detects the motion of a star by accurately measuring its position in the sky.This method can also be used to identify planetsaround a star by measuring tiny changes in its position as it oscillates around the center of mass of the planetary system.
Astrometry
Discover withgravity microlensingoccurs when a star's gravitational field warps space-time, which bends lightA distant star is behind us.the effect is only visible if the two stars are aligned with the Earth.If a star that acts as a lens has a planet, the planet's field canhave a small but noticeable effect.
Gravitational microlensing
Direct exoplanet detection is based on high-resolution, high-contrast images using adaptive optics.
How many exoplanets are there in the Universe? What are they?
By the end of 2019, it was found and confirmedmore than 4,000 exoplanets. Some are as massive as Jupiter, but orbit much closer to their star than Mercury is to our Sun. Other exoplanets are rocky or icy, and many simply have no analogues in our solar system.
For the most part, exoplanets are composed of the samethe very elements that make up the planets in our solar system, albeit with different compositional balances that give each exoplanet its distinctive qualities. There are four primary classifications of exoplanets, including neptune-like worlds, worlds with planets like hot Jupiter, worlds with super-Earths, and worlds with planet-like Earths.
Super-earths
A super-earth is a planet with a mass of 1 to 10 Earth masses. The super-earth classification refers only to the mass of the planet, but says nothing about its surface conditions or suitability for life.
The earth on the left and the artist's impression of the super earth on the right. Credit: NASA / JPL-Caltech
The first super-Earths, two exoplanets with masses four times that of Earth, were discovered in orbit around the pulsar PSR B1257 12 in 1992.
The first super-Earth around a main starThe sequence was discovered by a team led by Eugenio Rivera in 2005. It orbits Gliese 876 and has been designated Gliese 876 d (two Jupiter-sized gas giants have previously been discovered in this system). The planet has an estimated mass of 7.5 Earth masses and a very short orbital period of only about 2 days. Due to Gliese 876 d's proximity to its red dwarf host star, Gliese 876 d may have a surface temperature of 430–650 Kelvin (156.85–376.85 °C) and may support liquid water.
It was the first red dwarf to havediscovered a planetary system. Probably, massive giant planets are generally atypical for such stars. Since then, dozens of super-earths have been discovered, with a mass of only 1.9 Earth masses.
In April 2007, scientists announced the discovery of two new super-Earths around Gliese 581, at the edge of the star's habitable zone where liquid water may be possible on the surface.
Gliese 581 with a mass of at least 5 massesThe Earth and the distance to its star up to 11 million km (0.073 astronomical units) is located on the "warm" border of the habitable zone. Subsequent studies have shown that Gliese 581 c probably suffered a massive greenhouse effect, the same as Venus.
Astronomers have suggested that super-earths could bemore geologically active than our planet, and experience more vigorous tectonics due to thinner plates that are under greater stress. Those looking for alien life are thrilled with super-lands due to the possibility that they can be rocky and possibly habitable, unlike gas giants.
Mini neptune
Mini Neptune (sometimes known as gasdwarf planet or transition planet) is an exoplanet, from 2 to 10 Earth masses with a density less than 1. Planets of this type are smaller than Uranus (14.5 Earth masses) and Neptune (17.1 Earth masses).
Mini-neptune is a gas dwarf with liquidthe ocean is surrounded by a thick atmosphere of hydrogen and helium and a small rocky core. Although a recent discovery has shown that the mini-neptune, which everyone thought was gas planets, could be super-Earths with a rocky core surrounded by supercritical water. Water takes on this state at very high pressures and temperatures.
Planets in size and mass between the Earth andNeptune do not exist in our solar system, but they seem to be common in other parts of the universe. They are a cross between the rocky planets of our solar system and its ice giants. As a result, astronomers were able to analyze the atmosphere of one of these "middle" distant worlds, which are known as the "mini-neptune" class. The results of the peer review were announced on July 2, 2019 and published in Nature Astronomy on July 1, 2019.
Mini neptune - planet Gliese 3470 b - revolvingaround its star - a red dwarf. The planet weighs approximately 12.6 Earth masses, making it much more massive than Earth, but less massive than Neptune in our solar system (17 Earth masses). If you put Gliese 3470 b in our solar system, it would fit perfectly between Earth and Neptune in terms of size. The planet is believed to have a large rocky core buried under a deep, crushing atmosphere of hydrogen and helium.
This artist illustration showstheoretical internal structure of exoplanet GJ 3470 b. This is unlike any other planet in the solar system. Weighing 12.6 Earth masses, the planet is more massive than Earth, but less massive than Neptune. Unlike Neptune, which is 3 billion miles from the Sun, GJ 3470 b may have formed very close to its red dwarf star as a dry rocky object. It then gravitationally pulled in hydrogen and helium gas from the circumstellar disk to create a thick atmosphere. The disk scattered many billions of years ago, and the planet stopped growing. The bottom figure shows a drive that the system looked like for a long time. Courtesy of NASA / ESA
However, scientists periodically ask the question: is Gliese 3470 b a mini-neptune in the form in which it is mentioned now, or is it a super-earth?
Another example of mini-Neptunes - Kepler-11f hasa mass of 2.3 Earth masses and a density of 0.69, the same as Saturn, which has a mass of 95 Earths. These class properties, this exoplanet is in the category of mini-Neptunes or gaseous dwarfs, which have a liquid ocean surrounded by a thick atmosphere of hydrogen and helium and a small rocky core.
Hot Jupiters
Hot Jupiters are gas giant planets withwith a circulation period of less than 10 days. The short period means that hot Jupiters are very close to their host stars. They are typically less than 0.1 astronomical units away, which is one-tenth the distance from the Earth to the Sun. Hot Jupiters have dominated planetary discoveries for at least one decade because they are easiest to find using the radial velocity (Doppler) and transit methods.
Hot Jupiters are massive gas giant planets that orbit their suns a short distance from the Earth-Sun in our solar system. Credit: ESA
According to modern models of planetary formation,technically hot Jupiters shouldn't exist. A gas giant cannot form that close to its star because gravity, radiation, and intense stellar wind must keep the gas from sticking together.
However, they do exist; of the more than 4,000 confirmed exoplanets discovered to date, up to 337 may be hot Jupiters.
One possible solution is thathot jupiters form further, where building materials are sufficient, and then migrate to their current positions. The migration of hot Jupiters can be caused by various mechanisms. It is believed that the reason is the imbalance of currents in the protoplanetary disk. Some scientists believe that the orbits of hot Jupiter are excited to very high eccentricity (a numerical characteristic of the orbit of a celestial body, which characterizes the "compression" of the orbit).
However, new research presented atThe 233rd meeting of the American Astronomical Society in Seattle confirms an idea that contradicts previous ideas about planet formation but is gaining momentum in the field.
Giant planets that revolve aroundtheir stars may have formed in a place close to their suns in a few days, instead of forming in the distance and later migrating towards the star.
Work published October 5, 2018 in TheAstrophysical Journal Letters shows that such giant planets, called hot Jupiters, can form in a place close to their stars and stay there throughout their lives without evaporating.
Protoplanetary disks that form planetsaround young stars have a hole in the middle created by the star's magnetic field. New research has shown that the inner disc boundary can form gas giant planets without requiring them to form further and migrate. Credit: NASA / JPL-Caltech
In 2017, a Jupiter-like world was discovered.so hot that the planet is vaporized by its own star. With a daytime temperature of over 4,315.556°C (4,600 Kelvin), KELT-9b is a planet that is hotter than most stars. But its blue A-type star, called KELT-9, is even hotter—in fact, it is likely disintegrating the planet through evaporation.
This artist's concept shows the planetKELT-9b, orbiting its leading star, KELT-9. It is the hottest gas giant planet discovered so far. Credit: NASA / JPL-Caltech
In 2019, a new record was set amongorbits of hot Jupiters. The study suggests that a gas giant called NGTS-10b orbits its star so close that it completes a full revolution in 18.4 hours. The discovery makes this solar system an incredible laboratory for studying tidal interactions between a star and a dangerously close giant exoplanet.
Earth analogues
Before scientific search and study of extrasolar planetsthis possibility of the existence of planets like Earth has only been discussed in philosophy and science fiction. The principle of mediocrity suggests that planets like ours should be common in the universe, while the hypothesis of a unique Earth suggests that they are extremely rare. The thousands of exoplanetary star systems discovered so far are very different from our solar system, while confirming the hypothesis of a unique Earth.
Philosophers note that the size of the universe is suchthat there must be an almost identical planet somewhere. In the distant future, humans may use technology to artificially produce an Earth analogue by terraforming. The multiverse theory suggests that an Earth analog could exist in another universe, or even be a different version of Earth itself in a parallel universe.
Based on a study dated November 4, 2013,there are 40,000,000,000 Earth-sized planets orbiting their stars in habitable zones within the Milky Way. The nearest such planet could be 12 light years away. Astronomers have provided results based on data from the Kepler mission.
Scientific findings since the 1990s have profoundly influenced the field of astrobiology, planetary habitability models, and the search for extraterrestrial intelligence (SETI).
Where to look for life?
We only know one planet that haslife is Earth. And on our planet, water is the most important component of life as we know it. While astronomers are still not sure if there is life on other planets, they narrow down the search for potentially habitable worlds using several criteria.
Since our concept of life is Earth, astronomerslooking for planets with characteristics similar to her. Such, for example, as liquid water. But a celestial object can only rotate so close (like Mercury) or so far (like Pluto) from its star that water first evaporates or freezes on its surface, than life can form there. The habitable zone is the range of distances with the right temperatures to keep the water on the planet liquid. Scientists hope that discoveries in habitable zones such as Earth-sized planets Kepler-186f will lead us to water - and one day to alien life.
The habitable zone is in the middle. Credit: NASA
If life can be found anywhere, then most likely it will be exoplanets in the habitable zone.
The future of exoplanet research: major missions and objectives
JWST (James Webb Space Telescope)
NASA / ESA / CSA Space Telescope MissionJames Webb's launch in 2021 will provide game-changing new possibilities for observing exoplanets and their atmospheres. With a suite of four instruments operating at infrared wavelengths, Webb will use several methods to study these extrasolar bodies.
Highly sensitive spectroscopic observations of transiting planets - with similar characteristics in terms of size and mass - will usher in an era of comparative planetary science for exoplanets.
Artist's impression of Webb. Credit: ESA, NASA, S. Beckwith (STScI) and HUDF Team, Northrop Grumman Aerospace Systems / STScI / ATG medialab
Webb will characterize exoplanet atmospheresby capturing absorption, reflection and emission spectra at infrared wavelengths for planets spanning the size range from super-earths to gas giants. It will take advantage of the fact that at these wavelengths, molecules in the atmospheres of exoplanets have a large number of spectral characteristics, providing observers with a rich set of diagnostic tools, many of which are not available from Earth.
Webb will also be able to directly rendersome young and massive exoplanets orbiting at greater distances from their parent star than most transit. Three of Webb's tools have high-contrast imaging capabilities (in two cases, this is done using a coronagraph) to minimize glare from the parent star and simplify the image of the planet. Observations with several infrared filters will provide a lot of information about these planets, their properties and their formation mechanisms.
PLATO
Mission ESA PLATO (PLAnetary Transits andOscillations of the Stars) should start in 2026. PLATO aims to detect and characterize a large number of new extrasolar planetary systems by searching for hundreds of thousands of bright stars for transiting planets. PLATO will have the unique ability to find and determine the properties of the terrestrial planets that revolve in the habitable zone around stars similar to our Sun.
By combining precise PLATO radius measurements fora large sample of planets with corresponding planetary masses determined from ground-based observations, scientists will be able to explore the diversity of existing planets. These observations will also allow scientists to determine the volumetric composition of a large number of minor planets, study how similar they are to Earth, and investigate their habitability.
Discovering planets revolving around bright starsPLATO will pioneer subsequent missions looking for signatures of life - these types of planets are the best candidates for subsequent spectroscopic measurements to measure the structure and composition of planetary atmospheres.
ARIEL
Space telescope in development,which is slated to launch in 2028 as part of the European Space Agency's fourth medium-class mission Cosmic Vision. It is planned that with the help of the telescope at least 1,000 exoplanets will be investigated using the transit method.
Since its launch in 2028, ARIEL willis designed for high-precision observations using simultaneous photometry in the visible region of the spectrum and spectroscopy in the near infrared region of waves. She will observe and study about 1,000 predominantly hot and hot transit gas giants, Neptunes and super-earths around a range of stellar types and planetary system architectures.
Forecasts
With this set of space telescopes thatLaunched over the next decade, we can look forward to the discovery of "Earth 2.0," while adding more bizarre and unexpected planets to the exoplanet collection. There are exciting times ahead.
Why study exoplanets?
“Are we alone in the Universe?" is one of the deepest questions humanity can ask. The discovery of the first exoplanet orbiting a star like our Sun was made in 1995, and today exoplanet research is one of the fastest growing fields in astronomy.
Exploring a diverse spectrum of exoplanets andplanetary systems that have been discovered to date - from small to large, from those that appear terrestrial to deeply bizarre - not only help us learn about how these particular systems formed and developed, but also provide important clues to understanding whether and where life can exist elsewhere in the universe.
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