Epsilon Eridani: a Magnetic Young Star

Epsilon Eridani Planet - Artist's Concept of Nearest Exoplanet to Our Solar System Around Epsilon Eridani
an artist's concept of Epsilon Eridani b, the first planet found at Epsilon Eridani and the nearest exoplanet to the Sun. NASA, ESA, and G. Bacon (STScI)

Ever hear of Epsilon Eridani? It's a nearby star and famous from a number of science fiction stories, shows, and movies. This star is also home to at least one planet, which has caught the eye of professional astronomers.

Putting Epsilon Eridani into Perspective

The Sun lives in a relatively quiet and fairly empty region of the Milky Way galaxy. Only a few stars are right nearby, with the closest ones being 4.1 light-years away.

Those are Alpha, Beta, and Proxima Centauri. A few others lie a bit farther away, among them Epsilon Eridani. It's the tenth closest star to our Sun and is one of the closest stars known to have a planet (called Epsilon Eridani b). There may be an unconfirmed second planet (Epsilon Eridani c). While this nearby neighbor is smaller, cooler and slightly less luminous than our own Sun, Epsilon Eridani is visible to the naked eye, and is the third closest star that is viewable without a telescope. It's also featured in a number of science fiction stories, shows, and movies. 

Finding Epsilon Eridani

This star is a southern-hemisphere object but is visible from parts of the northern hemisphere. To find it, look for the constellation Eridanus, which lies between the constellation Orion and nearby Cetus. Eridanus has long been described as a celestial "river" by stargazers. Epsilon is the seventh star in the river that extends from Orion's bright "foot" star Rigel.

 

Exploring this Nearby Star

Epsilon Eridani has been studied in great detail by both ground-based and orbiting telescopes. NASA's Hubble Space Telescope observed the star in collaboration with a set of ground-based observatories, in the search for any planets around the star. They found a Jupiter-sized world, and it's very close to Epsilon Eridani.

The idea of a planet around Epsilon Eridani is not a new one. Astronomers have studied this star's motions for decades. Tiny, periodic changes in its velocity as it moves through space indicated that something was orbiting the star. The planet gave mini-tugs to the star, which caused its motion to shift ever so slightly.

It now turns out that, in addition to the confirmed planet(s) that astronomers think are orbiting the star, there is a dust disk, likely created by collisions of planetesimals in the recent past. There are also two belts of rocky asteroids orbiting the star at distances of 3 and 20 astronomical units. (An astronomical unit is a distance between Earth and the Sun.) There are also debris fields around the star, leftovers indicating that planetary formation did indeed take place at Epsilon Eridani. 

A Magnetic Star

Epsilon Eridani is an interesting star in its own right, even without its planets. At less than a billion years old, it's very youthful. It's also a variable star, which means that its light varies on a regular cycle. In addition, it shows a lot of magnetic activity, more so than the Sun does. That higher rate of activity, along with its very fast rotation rate (11.2 days for one rotation on its axis, compared to 24.47 days for our Sun), helped astronomers determine that the star is likely only about 800 million years old.

  That's practially a newborn in star years, and explains why there's still a detectable debris field in the area. 

Could ET Live on Epsilon Eridani's Planets?

It's not likely there's life on this star's known world, although astronomers once speculated about such life signaling us from that area of the galaxy. Epsilon Eridani has also been suggested as a target for interstellar explorers whenever such missions are finally ready to leave Earth for the stars. In 1995, a microwave survey of the sky, called Project Phoenix, searched for signals from extraterrestrials that might inhabit various star systems. Epsilon Eridani was one of its targets, but no signals were found. 

Epsilon Eridani in Science Fiction

This star has been used in many science fiction stories, TV shows, and films. Something about its name seems to invite fabulous stories, and its relative closeness suggests that future explorers will make it a landing target.

 

Epsilon Eridani is central in the Dorsai! series, written by Gordon R. Dickson. Dr. Isaac Asimov featured it in his novel Foundation's Edge, and it is also part of the book Factoring Humanity by Robert J. Sawyer. All told, the star has shown up in more than two dozen books and stories and is part of the Babylon 5 and Star Trek universes, and in several movies. ​

Edited and expanded by Carolyn Collins Petersen.