The brightest of exoplanets has been identified by astronomers


The brightest of exoplanets has been identified by astronomers

EXOPLANET. The brightest exoplanet ever discovered has been spotted 260 light years from Earth. Burning planet undergoing titanium rains, heading for this distant world surrounded by clouds of metals!

Designed by ESA to study exoplanets and their stars, the Cheops Space Telescope has just revealed a particularly stunning distant world. LTT9779b, a giant planet with a dantesque climate where titanium rains occur, is also the brightest exoplanet ever discovered by astronomers. Known since 2020, this burning world surrounded by metal clouds was studied more closely by Cheops in 2023. The European telescope thus made it possible to conclude that this exoplanet acts like a mirror, the largest known in the Earth. Universe, and reflects the vast majority of the light emitted by its star.

Beyond its exceptional brilliance, the "hot Neptune" type exoplanet intrigues researchers for other reasons. Indeed, the star is so close to its star that its temperature is estimated at around 2,000°C, a heat which in theory does not allow the presence of a planet of this type. In short, this exoplanet should not exist!

Discovered in 2020 by NASA's TESS telescope, then studied again in July 2023 by ESA's Cheops space telescope, LTT9779b is a unique exoplanet. Lying 260 light-years from Earth, this planet is the brightest known. Two elements explain this extraordinary brilliance. On the one hand, LTT9779b is almost glued to its star - it goes around it in just 19 hours - on the other hand, the exoplanet is surrounded by clouds made of metal which reflect 80% of the star's light. For comparison, Venus, the brightest planet in the solar system, reflects 75% of the Sun's light.

The proximity between the planet and its star poses certain problems for astronomers. Indeed, in theory, it is impossible to find such a planet with an atmosphere so close to a star because of the heat there. According to the researchers, it is precisely the presence of metal clouds that protect the atmosphere. These reflect light and prevent the planet from heating up enough for its atmosphere to evaporate. The James Webb Space Telescope has also studied this mysterious planet and should confirm the researchers' hypotheses after analyzing the data obtained.

An exoplanet is a planet located outside the solar system. It moves in orbit around stars other than the Sun. Exoplanets present a great diversity: telluric planets, composed of rocks, gaseous planets, or even giants of ice, they are given nicknames like "super Earth", "hot Neptune" or even "hot Jupiter" according to their characteristics and of their similarities with the planets of our solar system.

The first exoplanet orbiting a star was discovered in 1995 and is named 51 Pegasi b. It is 50.9 light years from Earth in the constellation Pegasus. This planet orbits the star 51 Pegasi. A yellow dwarf slightly older than the Sun, this star is also a little more massive and larger than it.

51 Pegasi b is located so close to its star that it circles it in just 4 days. However, it is a gas giant, like Jupiter or Saturn for example. It is for this reason that it is called "Hot Jupiter".

In May 2023, a group of researchers discovered an exoplanet in a star system 90 light years from Earth. The star, named LP 791-18d, is the site of very intense volcanic activity which is reminiscent of that of Io, one of the main moons of the giant Jupiter.

This new exoplanet has the particularity of following an elliptical orbit, which means that it passes alternately very close then very far from its star as it goes around it. This phenomenon is due to the fact that the two other nearby planets exert on it forces of attraction which deform its orbit.

The consequence of this elliptical trajectory is that the exoplanet experiences what are called tidal forces caused by its motion and by the attraction of its star. In other words, as the planet moves in its orbit, it is subjected to different forces that deform it and cause it to heat up. This thermal energy is released in the form of intense volcanism that could sustain an atmosphere around the planet.

Our knowledge of exoplanets could be greatly improved in the near future thanks to the James Webb Space Telescope. Indeed, one of its main missions is to study the composition of exoplanets and in particular that of their atmosphere. James Webb's mission is to probe the atmospheres of distant planets using a particularly ingenious system. The telescope waits for the exoplanet to pass in front of the star around which it is rotating to analyze its light. When light from the star passes through the planet's atmosphere, it acts as a filter and blocks some of the light. The telescope can then deduce the composition of the atmosphere surrounding the planet and therefore the conditions prevailing on the surface of the latter. On the program, "hot Jupiters", gaseous planets evolving close to their star, but also telluric planets more similar to Earth.

Its first target is WASP-96b, a gas giant located 1,150 light-years from Earth. When the first images from the space telescope were released in July 2022, NASA also released the results of the first analyzes of light passing through WASP-96b's atmosphere. The results are final, the latter contains water, traces of mist and clouds.

The closest planetary system to Earth is Alpha Centauri C. Its central star is Proxima Centauri and is 4.246 light-years from Earth, or 40,000 billion kilometers. Today, several planets are known to revolve around this star.

The first, Proxima b, was discovered in August 2016 and was the subject of a scientific press release from the European Southern Observatory as well as a publication in the journal Nature. A few years later, the planet Proxima c was detected, orbiting farther from the star Proxima Centauri than its neighbor Proxima b. Finally, in February 2022, Proxima d was discovered, bringing the number of planets orbiting Proxima Centauri to three.

The closest planet to Proxima Centauri would be the planet Proxima d, which would circle the star in 5 days. Proxima b would be located in the star's habitable zone, which means that it could harbor water in liquid form. Finally, Proxima c would be located much further from the star and would go around it in 5 years according to National Geographic magazine.

After Proxima Centauri b and Proxima Centauri c, a third planet was discovered orbiting around Proxima Centauri. It was a team of astronomers from the University of Porto, in Portugal, who spotted the planet thanks to the variations in the speed of its star due to the force of gravity of the planet.

Called Proxima Centauri d, this exoplanet has a mass about a quarter of Earth's and a size just over a quarter of Earth's. It takes about 5 days to go around its star, because it is extremely close to it. According to astronomers, a priori, this position excludes it from the habitable zone of this star. This means that it is placed too close to its star for conditions to be conducive to the emergence of life on its surface.

Kepler-452 b is an exoplanet located 1,400 light-years from Earth in the constellation Cygnus. Its particularity is to be relatively similar to our planet Earth. Indeed, its radius measures 1.6 times that of the Earth. Their sizes are almost identical. It takes 384 days to go around its star, a duration comparable to that of the revolution of the Earth around the Sun which is 365 days. This planet is therefore in the habitable zone of its star and receives approximately the same amount of energy from its star as the Earth receives from the Sun. All these elements make it a planet very similar to ours but located in another planetary system, explains the magazine Sciences et Avenir.

The star around which it revolves, Kepler-452, is a slightly brighter star and a little larger than the Sun, but has the same temperature as the latter. The planetary system that contains the star and the exoplanet, however, is 1.5 billion years older than our planetary system. Thus, it could give us an idea of ​​what the Earth could become in the future.

According to a NASA press release published in October 2020, there are 300 million potentially habitable planets in our galaxy. To arrive at this figure, the researchers evaluated the number of stars likely to be accompanied by a rocky planet where water could exist in a liquid state in a sustainable way. The work of the James Webb telescope could help us to clarify this question and identify candidate planets for this category.

Some exoplanets are true aquatic worlds. This is the case of TOI-1452 b, a planet located in the constellation of the Dragon discovered by a Canadian team in August 2022. The planet would be entirely covered by an ocean deeper than those we know on Earth. The James Webb Space Telescope could tell us a little more about this planet during its mission.

More recently, in December 2022, NASA announced that it had discovered, using the Spitzer and Hubble telescopes, that two planets orbiting the star Kepler-138 are also part of these aquatic worlds. Located in the constellation of Lyra, these planets, named Kepler-138c and Kepler-138d, are located much closer to their star than we are to the Sun. Their atmospheres would be particularly hot and humid and the oceans that cover them would be composed of water at high pressure.

In addition to these two planets, telescopes have revealed signs of the presence of a third planet, called Kepler-138e. The latter is very promising since it would be located in the star's habitable zone and could therefore accommodate liquid water. It would therefore be more likely than others to see life appear in its oceans.