Epsilon Eridani b

Epsilon Eridani b, formally named AEgir, is an exoplanet about 10.5 light-years from Earth. It orbits the star Epsilon Eridani in the constellation of Eridanus, which means "the River" in Latin River. This fascinating world was discovered in the year 2000 and, as of 2025, it is the only confirmed planet in its whole planetary system.

What makes Epsilon Eridani b so special is that it looks a lot like our own planet Jupiter. It has a similar size and follows a path around its star that is very much like Jupiter’s path around our Sun. Scientists think that studying this planet can help us learn more about how gas giant planets form and change over time. Because it is so similar to Jupiter, Epsilon Eridani b gives us a unique chance to compare and understand the differences and similarities between planets in our solar system and those far away.

Name

The planet and its star were chosen by the International Astronomical Union to receive official names through a public contest. In December 2015, the winning names were announced: the planet is called AEgir, and the star is called Ran. These names come from old Norse mythology. A young person named James Ott, who was 14 years old at the time, suggested these names and won the contest. There is also a moon of Saturn named Aegir, which shares the same name but with different capitalization.

Characteristics

Epsilon Eridani b orbits its star, Epsilon Eridani, at a distance of 3.53 AU, taking about 7.33 years to complete one orbit. Its orbit is nearly circular, much like Jupiter's orbit in our Solar System.

The planet has a mass very close to that of Jupiter, measuring 1.00 Jupiter masses. This makes it a close match to Jupiter in both size and orbit.

History of observations

Scientists first thought they saw a planet around the star Epsilon Eridani in 1988, but they needed more information to be sure. The planet was officially discovered in 2000 by a team led by Artie Hatzes. They found it to be about the same size as Jupiter, our solar system's largest planet.

Over the years, scientists have kept watching Epsilon Eridani b to learn more about it. Sometimes they thought its orbit was very stretched out, and other times they thought it was almost circular. In 2019, new observations helped solve some puzzles about the planet's orbit. Even with new telescopes like the James Webb Space Telescope, scientists are still working to get clear pictures of this distant world.