The Blue Planet

Artist's conception of HD 189733b.
Image Credit: NASA, ESA, M. Kornmesser

If you are in a good stargazing location near the 40th parallel north on a summer night, you may be able to see a faint constellation known as Vulpecula located within the triangle formed by the stars Deneb, Vega and Altair. If you have a telescope or a good set of binoculars, you might be able to see a binary star system that astronomers refer to as HD 189733.

One of the stars in this binary system, which is a mere 63 light-years or so from earth, has a planet designated as HD 189733b. This planet, which was discovered in 2005, is a gas giant that orbits close to it's sun. Planets of this type are sometimes called "hot Jupiters," and HD 189733b has been an object of study because it's the closest planet of this type that we know.

According to NASA & ESA, the sun-facing side of this planet is a furnace, with surface temperatures reaching nearly 2000°F and glass "rain" blowing sideways in up to 4,500-mph winds. It seems unlikely that life could exist under these conditions, yet this planet has provided information that's relevant to the question of whether life may exist on outside our solar system. HD 189733b was the first exoplanet on which water was detected (see NASA JLP article "Steaming Hot Planet" for details), and water is deemed essential for the survival of lifeforms as we know them. In addition to having significant amounts of water vapor, the atmosphere of HD 189733b has been found to contain oxygen, carbon dioxide and the organic compound methane (see NASA/ESA article "Hubble finds carbon dioxide on an extrasolar planet" . If these substances are common on planets outside our solar system, we may someday find them on planets similar to our earth in size and distance from their sun.

HD 189733b has recently been in the news because of it's color. What's special about the color of this planet is that we now know it. Planets are difficult to "see" in the usual sense, so scientists discovered the color in this case from careful measurements and logical inference. If you're interested in knowing more about how this was done, you can read the details in the new release "Hubble spots azure blue planet."