LPL in the News
Dramatic Change Spotted on Faraway Planet
Astronomers using the NASA/ESA Hubble Space Telescope have seen dramatic changes in the upper atmosphere of a faraway planet, giving a tantalizing glimpse of the changing climates and weather on planets outside our solar system.
HD 189733b has a blue sky, but that's where the similarities with Earth end. The planet is a huge gas giant similar to Jupiter, but it lies extremely close to its star, more than 10 times closer than Mercury orbits the sun on average.
Even though its star is slightly smaller and cooler than the sun, this makes the planet's climate exceptionally hot, at above 1,800 degrees Fahrenheit, and its upper atmosphere is battered by energetic extreme-ultraviolet and X-ray radiation, or XEUV radiation.
As such, this "Hot Jupiter" is an excellent candidate to study the effects of a star on a planetary atmosphere.
An international team including Gilda Ballester, an associate staff scientist at the University of Arizona's Lunar and Planetary Lab, used the Hubble Space Telescope to observe the atmosphere of exoplanet HD 189733b during two periods in early 2010 and late 2011, as it was silhouetted against its parent star.
While backlit in this way, the planet's atmosphere imprints its chemical signature on the starlight, allowing astronomers to decode what is happening on scales that are too tiny to image directly. The observations were carried out using Hubble's Space Telescope Imaging Spectrograph, an instrument that, much like a prism, splits light into its constituent colors.
The relative brightnesses of different wavelengths of light carry a lot of information including the fingerprint of the types, properties, abundances and even motion of gases it has passed through. In this case, the team was looking for hydrogen gas, the predominant component of HD 189733b's atmosphere being blown off the atmosphere.
"The star is very active," Ballester said. "We had some indication of changes in the planet before, but this is the first time anyone has definitely observed changes similar to space weather in another solar system."
Stellar wind describes streams of charged particles, mostly electrons and protons that a star hurls out into space. Interactions between the solar wind and the Earth's magnetic field light up the sky as the Aurora Borealis, and, in extreme cases, can affect the function of satellites and electrical grids.
"In the case of HD 189733b, the weather in the exoplanet's atmosphere is driven by variations in the strong stellar XEUV radiation and also likely in the wind streaming from its parent star," Ballester said.
The study is published (pdf) in the June 28 issue of the journal Astronomy and Astrophysics.