[5] Because it is located at a distance of 157 light-years (48 parsecs) from the Sun as measured via parallax, it is not visible to the unaided eye.

[1] The spectrum of HD 209458 presents as a late F- or early G-type main-sequence star with a stellar classification of F9 V[3] or G0 V,[4] respectively.

[6][11] In 1999, two teams working independently (one team consisted of astronomers at the Geneva Observatory, the Center for Astrophysics | Harvard & Smithsonian, and the Wise Observatory; the second group was the California and Carnegie Planet Search team) discovered an extrasolar planet orbiting the star by using the radial velocity planet search method.

This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected.

Travis Barman at Lowell Observatory in Flagstaff, Arizona analyzed the emission spectrum of this planet in 2007, and believes that its atmosphere contains water vapor,[14] although previous research in 2007[15] suggests that the atmosphere is composed mostly of silicate clouds.