HD 209458 b, nicknamed "Osiris" after the Egyptian god of the underworld, is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some 157 light-years from the Solar System. It is a giant planet with a mass about 0.69 times that of Jupiter and a radius about 1.32 times that of Jupiter. It is classified as a "hot Jupiter" because it orbits very close to its star, only about 7 million kilometers away. This causes the planet to have a surface temperature of over 1,800 degrees Celsius (3,200 degrees Fahrenheit), hot enough to melt most metals.
HD 209458 b was first discovered in 1999 by the transit method, which means that astronomers were able to detect it by observing the slight dimming of its star's light as the planet passed in front of it. This discovery was significant because it was the first time that astronomers had been able to directly detect an exoplanet orbiting a Sun-like star.
Since its discovery, HD 209458 b has been the subject of much study. Astronomers have been able to determine that it has an atmosphere that is composed mostly of hydrogen and helium, with traces of water vapor and carbon monoxide. They have also been able to measure the planet's magnetic field, which is about one-tenth as strong as Jupiter's.
However, one of the most interesting things about HD 209458 b is that it is losing its atmosphere at an alarming rate. The intense radiation from its star is causing the planet's atmosphere to evaporate, creating a tail of gas that stretches millions of kilometers into space. This makes HD 209458 b a valuable laboratory for studying the atmospheres of exoplanets and the processes that can affect them.
Here are some additional facts about HD 209458 b:
It was the first exoplanet found to have a detectable atmosphere.
It is the first exoplanet found to have an evaporating hydrogen atmosphere.
It is the first exoplanet found with carbon and oxygen.
It is nicknamed "Osiris" after the Egyptian god of the underworld.
HD 209458 b is a fascinating exoplanet that has taught us a lot about the diversity of planetary systems. It is a reminder that there are many strange and wonderful worlds out there waiting to be discovered.
