This is an artist's impression of the gas-giant planet orbiting the yellow, Sun-like star HD 209458, 150 light-years from Earth. Astronomers used NASA's Hubble Space Telescope to look at this world and make the first direct detection of an atmosphere around an extrasolar planet. The planet was not directly seen by Hubble. Instead, the presence of sodium was detected in light filtered through the planet's atmosphere when it passed in front of its star as seen from Earth (an event called a transit). The planet was discovered in 1999 by its subtle gravitational pull on the star. The planet is 70 percent the mass of Jupiter, the largest planet in our solar system. Its orbit is tilted nearly edge-on to Earth, which allows repeated transit observations.
The planet is merely 4 million miles from the star. The distance between the pair is so close that the yellow star looms in the sky, with an angular diameter 23 times larger than the full Moon's diameter as seen from Earth, and glows 500 times brighter than our Sun. At this precarious distance the planet's atmosphere is heated to 2000 degrees Fahrenheit (1100 degrees Celsius). But the planet is big enough to hold onto its seething atmosphere.
Credits
Science: NASA, D. Charbonneau (Caltech & CfA), T. Brown (NCAR), R. Noyes (CfA) and R. Gilliland (STScI);Illustration: G. Bacon (STScI/AVL)
| About The Object | |
|---|---|
| Object Name | HD 20945, 209458b |
| Object Description | Host Star and Transiting Extrasolar Planet, a Jupiter-like Planet with Detected Atmosphere |
| R.A. Position | 22h 3m 10.8s |
| Dec. Position | 18° 53' 3.99" |
| Constellation | Pegasus |
| Distance | Distance from Earth: 46 parsecs (150 light-years). Planet's Distance Above Star's Surface: 4 million miles (6.4 million kilometers) with an orbital period of 3.5 days. |
| Dimensions | Planet's Estimated Mass: 0.7 times Jupiter's mass (220 times the Earth's mass); Maximum Temperature: 2,000 degrees Fahrenheit (1100 degrees Celsius) About the Data |
| About The Data | |
| Data Description | Principal Astronomers: D. Charbonneau (CalTech and Harvard-Smithsonian CfA), T. Brown (High Altitude Observatory /NCAR), R. Noyes (Harvard-Smithsonian CfA), and R. Gilliland (Space Telescope Science Institute) |
| Instrument | HST>STIS |
| Exposure Dates | April 25 and 28, 2000; May 5 and 12, 2000, Exposure Time: 7 hours |
| Filters | G750M (581.3 to 638.2 nm) |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
