55 Cancri Ae

There is a far away world.

Its name is Janssen. This world is very big. It is much larger than Earth.

It stays very close to its star. This makes the world very hot. It moves around its star very fast. One trip takes less than 18 hours. The air there might have lots of carbon. This is a very strange place to visit.

There is a far away world named Janssen.

It is an exoplanet. This means it is a planet outside our solar system. Janssen is a super-Earth. This means it is much larger than Earth. It has about eight times the mass of Earth.

It orbits its star very quickly. One full trip takes less than 18 hours. Because it is so close to its star, it is very hot. The day side can reach 3,000 Kelvin. This is hot enough to melt iron. Scientists think the planet might have a lava ocean. It might even have volcanoes that let out dust.

People have studied the air around the planet. Some thought it was made of rock vapor. New data from the James Webb Space Telescope changed that. Now, we think the air has much carbon dioxide or carbon monoxide. This helps us learn how these distant worlds work.

There is a far away world called Janssen.

Its official name is 55 Cancri Ae. It is an exoplanet, which means it orbits a star outside our own solar system. This planet is a super-Earth because it is much larger than our home. It has about eight times the mass of Earth. Its diameter is also about twice as wide as Earth. Scientists find this world very important to study. It was the first super-Earth ever found around a main sequence star.

Janssen works in a very fast way. It orbits its star, 55 Cancri A, extremely quickly. One full trip around the star takes less than 18 hours. This happens because the planet is very close to its star. Because it is so close, the planet is incredibly hot. The side facing the star can reach 3,000 Kelvin. This is hot enough to melt iron. The planet might even be tidally locked. This means one side always faces the star and stays hot. The other side always faces away and stays dark.

Astronomers found this world using a special method. A team led by Barbara E. McArthur discovered it in 2004. They used the Hobby–Eberly Telescope in Texas. They looked for changes in the star's radial velocity. This means they watched how the star moved slightly. They used the Doppler shift to see these changes. At first, they thought the orbit took 2.8 days. Later, they found the true orbit was much faster. It is actually only about 0.74 days long.

Learning about the planet's air has been a big job. Scientists have used many different tools to study it. The Spitzer Space Telescope once suggested a lava ocean exists. It also thought the atmosphere might be made of vaporized rock. However, the James Webb Space Telescope changed what we know. In 2024, it showed the atmosphere is likely full of carbon dioxide. It might also have carbon monoxide. Some people even think the planet could be made of carbon. This could mean much of it is actually diamond.

Janssen reminds us how different worlds can be. Our Earth has an atmosphere of nitrogen and oxygen. But Janssen might be a carbon planet instead. It might even have huge volcanoes that release dust. These volcanoes could change how the planet looks. The planet's name also has a special story. In 2015, the International Astronomical Union gave it the name Janssen. This honors Zacharias Janssen, who helped invent the telescope. Studying Janssen helps us understand the many types of planets in space.

55 Cancri Ae, also known by its proper name Janssen, is a fascinating exoplanet. An exoplanet is a world that orbits a star outside our own solar system. Janssen orbits a Sun-like star called 55 Cancri A. This planet is classified as a super-Earth. This term describes planets that are larger than Earth but smaller than gas giants like Neptune. Janssen is about eight times the mass of Earth. Its diameter is roughly twice as wide as our home planet.

Scientists study this world to learn about different types of planets.

The planet moves through space at an incredible speed. It is the innermost planet in its system. Janssen orbits its host star in less than 18 hours. This very fast orbit happens because the planet is extremely close to its star. The average orbital distance is only about 0.01544 AU. Because of this proximity, the planet is incredibly hot. The day side can reach temperatures exceeding 3,000 Kelvin. This heat is intense enough to melt iron.

Due to its age and closeness to the star, the planet is likely tidally locked. This means one side permanently faces the star while the other side always faces away.

Astronomers discovered Janssen using a method called radial velocity. A team led by Barbara E. McArthur found the planet using data from 2003 to 2004. They used the Hobby–Eberly Telescope at the McDonald Observatory in Texas. This method works by measuring the Doppler shift in the star's spectrum. This shift shows how the star moves slightly due to the planet's gravity. At first, scientists thought the orbit took 2.8 days. However, later observations in 2010 showed the true orbital period is much shorter. The actual period is about 0.7365 days.

Determining what Janssen is made of has been a long scientific challenge. In 2011, scientists confirmed the planet's transit. A transit occurs when a planet passes in front of its star from our perspective. This allowed researchers to calculate the planet's density. Early studies suggested the atmosphere might be rich in hydrogen and helium. Other studies suggested it might be a world covered in a thin layer of vaporized rock. Some researchers even thought it might be a water planet. These different ideas show how much we are still learning about distant worlds.

Recent discoveries have changed our understanding of the planet's atmosphere. In 2016, the Hubble Space Telescope detected hydrogen cyanide. In 2017, the Spitzer Space Telescope suggested a global lava ocean might exist. It also thought the atmosphere had a pressure of about 1.4 bar. However, the James Webb Space Telescope provided new data in 2024. These observations ruled out the idea of a thin atmosphere made of vaporized rock. Instead, the data suggests a substantial atmosphere. This atmosphere is likely rich in carbon dioxide or carbon monoxide.

There is a unique theory that Janssen might be a carbon planet. In our solar system, terrestrial planets are made of oxygen-rich material. On Janssen, roughly one-third of the mass could be carbon. Because of the extreme temperatures and pressures, much of this carbon might be in the form of diamond. The planet also shows signs of possible volcanic activity. This volcanism might release large clouds of dust. These clouds could block thermal emissions and cause temperature variations. The planet's magma ocean might even be outgassing to sustain its atmosphere.

The name Janssen has a special history. In 2014, the International Astronomical Union started a contest called NameExoWorlds. This allowed the public to nominate and vote on names for exoplanets. In December 2015, the name Janssen was announced as the winner. The name was submitted by the Royal Netherlands Association for Meteorology and Astronomy. It honors Zacharias Janssen, a spectacle maker associated with the invention of the telescope. Studying Janssen helps astronomers connect many different ideas about how planetary systems form and change over time.