Astronomers made discovery about a planet located 63 light-years away. The planet, named HD 189733b, is the closest exoplanet to Earth that can be seen crossing the face of its star. Using the powerful Hubble Space Telescope, astronomers deduced the visible-light color of the distant world.
At a glance, the planet appears to be a “deep blue dot” — similar to Earth’s colour as seen from space. However, that’s where all resemblance ends. The atmosphere of this alien world is so hot that it reaches nearly 2,000 degrees Fahrenheit. What’s more, it likely rains glass – sideways – in howling winds at 4,500 miles (7,200 km) per hour!
So why is this faraway world such a vivid blue hue if it isn’t reflecting a tropical ocean? This fascinating colour comes from a hazy atmosphere and high clouds laced with silicate particles. These particles condense at a certain temperature to form very small drops of glass which scatter blue light more than red light.
In uncovering the chemical composition and cloud structure of this extraordinary “hot Jupiter” class planet, astronomers are gaining valuable insights into worlds beyond our own. Clouds play an important role in many planetary atmospheres, and detecting their presence and importance in hot Jupiters is crucial to our understanding of other worlds.
The research team utilized Hubble’s Space Telescope Imaging Spectrograph to measure changes in the color of light from this distant planet before, during, and after it passed behind its parent star. This technique was made possible because its orbit is tilted edge-on from our view on Earth; so it can routinely pass in front of and then behind the star.
The most observation of an exoplanet by the Hubble Space Telescope has provided remarkable evidence of the planet’s atmospheric composition. Although Hubble measured a small drop in light – about one part in 10,000 – when the planet HD 189733b went behind its parent star, an even more interesting finding was the slight change in the color of the light. The light was missing in the blue part of the spectrum, but not in the red or green, indicating that something in the atmosphere is absorbent to blue light.
This observation confirms earlier reports of blue light scattering on the planet. Those reports came from NASA’s Spitzer Space Telescope, which in 2007 produced one of the first-ever temperature maps of an exoplanet. That map showed that temperatures on the day and night sides of the planet differed by about 500 degrees Fahrenheit – a difference that should cause strong winds to blow from the day side to the night side.
The Hubble observation helps to reduce any interference from the planet’s own hot glow and instead provides a better view into what’s actually happening in its atmosphere. Although it’s difficult to determine what exactly causes a particular color in a planet’s atmosphere, lead researcher Frédéric Pont suggested that it could be due to unknown color-carrying molecules or absorbers in the atmosphere.This exciting discovery is just one more step towards understanding exoplanets and their atmospheres. While much is still unknown, researchers are now one step closer to unlocking some of their secrets.
