November 14, 2008 In two separate scientific show-stoppers, unprecedented direct images of planets outside of our own solar system have been captured by NASA's Hubble space telescope and terrestrial observatories in Hawaii. Over the past two decades astronomers have detected around 300 exoplanets and are rapidly finding more, but these have mostly been observed by methods such as monitoring the gravitational effects of a planet on its parent star rather than seen as a direct optical image. We now have the first visible-light snapshot of a planet circling another star from the Hubble, and the first-ever direct images of an exoplanetary system from the massive 8-meter Gemini North telescope on Mauna Kea.
The Hubble image is of the planet Fomalhaut b, a body more than three times the mass of Jupiter orbiting a bright southern star (Fomalhaut) which can be seen with the naked eye. The image has been taken using a coronagraph to block-out the bright light from the star, which is why the center of the image is black. Fomalhaut b, which lies 10.7 billion miles from the star, is highlighted on the right. It may not look like as cool as the artists impression, but its a very significant little dot.
The dusty ring that can be seen encircling the star is what lead scientists to point the Hubble at Fomalhaut in the first place. The existence of this debris belt has been known about for some time and in 2005 Hubble astronomer Paul Kalas proposed that its elliptical shape and sharp inner-edge was the result of the a planet orbiting the star. He was right.
The image also shows the path of the planets orbit using data from observations made 21 months apart. The next step is to look for evidence of water vapor clouds in the planet's atmosphere using infrared light, a task which the James Webb Space Telescope will be designed to accomplish when launched in 2013.
The near-Infrared image image produced by astronomers using the Gemini and Keck observatories is the first ever taken of a multi-planet system planets around a normal star outside of our solar system according to the research teams leader Dr. Christian Marois of the National Research Council of Canada’s Herzberg Institute of Astrophysics.
The host star (HR 8799) is about 1.5 times the mass of the Sun and is further away than Fomalhaut at about 130 light years away from Earth (though still faintly visible to the naked eye). The planets observed are also more massive than Fomalhaut b at about seven and ten times the mass of Jupiter, orbit HR 8799 at distances of 3.6 billion miles and 6.3 billion miles respectively and are young enough, at about sixty million years old, to retain glowing from heat from their formation. The planetary family is completed by a third planet not visible in the image that orbits closer to the star.