Pollux: The Nearby Star With a Planet

Gemini Double Star System
Gemini is a constellation high in the winter sky, containing a number of interesting observing targets. (Image credit: Starry Night Software)

Pollux is a star that lies in the constellation Gemini. Along with Castor, Pollux is one of the two main guideposts for the asterism, which is sometimes nicknamed "the twins."

The star is a red giant that has finished fusing hydrogen in its core and is now fusing other lighter elements into heavier ones. The star has a temperature of 8,360 F (4,627 C).

Recently, astronomers discovered that the star has an extrasolar planet, or exoplanet. At the time of the discovery publication in 2006, scientists estimated it has a mass at least 2.3 times that of Jupiter, with an orbital period of almost 590 days.

Locating Pollux

The giant star lies close to Earth, about 35 light-years away, with a luminosity of about 32 times that of the sun, according to NASA. Its apparent magnitude is 1.14, making it the 17th brightest star in the night sky. Unusually, the star is the brightest in the constellation Gemini but is designated Beta Geminorum; Castor, which is a little fainter, is Alpha Geminorum.

The location of Pollux is:

  • Right ascension: 07 hours 45 minutes 18.9 seconds
  • Declination: +28 degrees 01 minute 34 seconds

Pollux's name

Pollux is a Greek name, but the legend behind the name comes from both Greek and Latin cultures. Pollux and Castor were twins who were supposed to assist sailors in trouble. Together, the twins were called the Dioscuri in Greek and the Gemini in Latin.

In the 1960s, NASA called its two-man-crew space program "Gemini." The missions were intended to test procedures and technologies for moon flights and focused on aspects such as long-duration flights, rendezvous and docking.

In 2010, the Italian Center for Aerospace Research (CIRA) had a prototype space plane that it called Pollux. The plane was planned to execute test maneuvers that year and to get to a top re-entry speed of Mach 1.2.

"We want to fly while re-entering, and we want to reduce the logical gap between aeronautics and space," said Gennaro Russo, CIRA's Space Programs lead and unmanned space vehicles program manager in 2010.

Discovery of extrasolar planet

In 2006, astronomers published a paper confirming the existence of a planet orbiting Pollux. According to NASA, two teams independently discovered the planet using the "Doppler method," or watching the gravitational wobbles in Pollux that the planet produced.

The planet (known as Beta Genorium b) is much larger than Earth — about 1.6 times the size of Jupiter — and also orbits slightly farther away from Pollux than Earth does from the sun. The planet is at 1.6 astronomical units from its star, or 1.6 times the equivalent Earth-sun distance.

Because planet-hunting was relatively new in 2006 — this was before the Kepler planet-hunting space telescope launched into orbit, for example — astronomers were quite excited by the find. "It suggests that planet-formation around stars much more massive than the sun may [be] common," read an Astronomy and Astrophysics paper concerning the discovery.

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace