Facts about HD 209458
- 07
Roughly 1.9 times Jupiter's radius, HD 209458 b represents an anomalously inflated hot Jupiter whose unusual size challenged theoretical models of gas giant cooling and contraction.
- 06
HD 209458 b's atmosphere contains carbon monoxide in addition to water vapor and methane, making it chemically distinct from any planetary atmosphere in our solar system.
- 05
Spectroscopic analysis of HD 209458 b's atmosphere revealed the presence of water vapor, methane, and carbon dioxide, making it the first exoplanet where multiple molecular species were detected beyond sodium.
- 04
At 47.5 light-years away, HD 209458 b was the first exoplanet to have its radius directly measured through transit photometry in 1999, revealing it to be larger than Jupiter despite being much closer to its star.
- 03
In 2003, observations with the Hubble Space Telescope revealed that HD 209458 b loses approximately 10,000 tons of hydrogen and helium per second due to stellar wind stripping.
- 02
The exoplanet orbits its star every 3.52 days at a distance of only 4.7 million miles, making HD 209458 b one of the hottest known worlds with a surface temperature exceeding 1,400 Kelvin.
- 01
Discovered in 1995, HD 209458 became the first exoplanet with an observed atmospheric composition when astronomers detected sodium in its gaseous envelope.