(Sen) - More than 850 planets have now been found orbiting other stars in the galaxy and yet more wait to be confirmed. Virtually all of these have been discovered by indirect methods - usually either the wobble effect their gravitational pull has on their host star or the dip they cause in the star's light as they pass in front of it.
Despite the many dramatic pictures that accompany discovery announcements, these are usually the products of their creative artist's imaginations, helping bring the news stories alive for the general public.
Now, however, an international team of astronomers has successfully imaged a giant planet that was detected orbiting Kappa Andromedae, a star 2.5 times the mass of the Sun that lies 170 light-years away from us. It is visible to the naked eye in the constellation of Andromeda.
The scientists used Japan's giant Subaru Telescope on Mauna Kea in Hawaii to record the star. By using adaptive optics, a tool that counters the disturbing effects of our own atmosphere, and then removing the speckly glare of the star, the team were able to isolate the light of the planet itself.
The overwhelming brightness of the stars is usually the biggest obstacle to taking direct photos of their much fainter exoplanets. The team, from Japan, Germany, the USA and Canada, were working as part of the SEEDS Project which aims to explore hundreds of nearby stars in a bit to image either their larger planets or debris discs surrounding them and which may become planets in the future.
Near-infrared images of Kappa And b with and without the glare of the host star removed. Credit: NAOJ
The "super-Jupiter" gasball orbiting Kappa Andromedae was detected by using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) and the Infrared Camera and Spectrograph (IRCS) at the observatory. By observing it in January and July this year, the astronomers were able to confirm that the star and planet were related. Their results will be published in Astrophysical Journal Letters.
The planet, labelled Kappa And b, appears to be about 13 times the size of Jupiter and travelling in an orbit larger than that of Neptune in our own Solar System. The discovery team will continue to monitor Kappa Andromedae to learn more about the new planet's composition but also to see if they can find evidence for further planets in the same system.
Kappa Andromedae is a relatively young star, with an age of only 30 million years, compared to the Sun's nearly five billion years. The discovery team notes: "Young star systems are attractive targets for directly imaging planets because young planets retain significant heat from their formation, thus enhancing their brightness at infrared wavelengths."
Images from Hubble that revealed the motion of planet Fomalhaut b. Credit: NASA/ESA
Only a tiny handful of planets have been directly imaged - other notable examples include one orbiting Beta Pictoris and four orbiting HR8799 - but more are certain to be pictured as telescope instruments continue to improve.
One that was revealed by the Hubble space telescope orbiting the star Fomalhaut in 2008 was confirmed to exist earlier this year after suggestions that it might just be a clump within a disc of dusty debris orbiting the star. It is known as Fomalhaut b.
Also this year, the revolutionary high-altitude ALMA telescope array in Chile provided valuable new information about the nature of the dust disc around Fomalhaut and the planets that help shape it.