Astronomers using the Very Large Telescope (VLT) have obtained the first direct spectrum of one of three Jupiter-like planets orbiting the young star HR 8799.

The three planets in the 130 light year distant system were discovered in 2008, and have masses between seven and ten times that of Jupiter. The planets orbit the central star, which has a mass 1.5 times that of the Sun, at distances between 20 and 70 times the Earth-Sun separation. The system also contains two belts of debris analogous to the Asteroid Belt and Kupier Belt of our own Solar System.

Now, for the first time, astronomers have obtained the first spectrum of an exoplanet orbiting an almost Sun-like star, providing information on the planet's formation and composition.

“The spectrum of a planet is like a fingerprint. It provides key information about the chemical elements in the planet’s atmosphere,” says Markus Janson, lead author of a new paper describing the results presented in the Astrophysical Journal. “With this information, we can better understand how the planet formed and, in the future, we might even be able to find tell-tale signs of the presence of life.” The planet chosen for the study was the middle planet of the system, ten times the mass of Jupiter and with a temperature of 800 degrees Celsius. “After more than five hours of exposure time, we were able to tease out the planet's spectrum from the host star's much brighter light,” says team member Carolina Bergfors.

The observation was made possible by the infrared instrument NACO on the VLT, and its adaptive optics system that counteracts image distortion normally caused by ground-based observing through the Earth's atmosphere. Since the star is several thousand times brighter than the planet, this is a remarkable technological achievement – it is like trying to see what a candle is made of by observing it from a distance of two kilometres when it’s next to a blindingly bright 300 Watt lamp. Until now, spectra were obtained by space-based observatories watching as an exoplanet passes directly behind its parent star, and comparing the light of the star before and after, a technique that relies on a favourable orientation of the planet to the star. In contrast, the ground-based observations are not limited by the orientation of the planet's orbit.

In the case of HR 8799c, the team found that the spectrum differed from existing theoretical models, suggesting that phenomena such as cloud structure or dust contained in the planet's atmosphere need to be treated in more detail in the models.

“The features observed in the spectrum are not compatible with current theoretical models,” says co-author Wolfgang Brandner. “We need to take into account a more detailed description of the atmospheric dust clouds, or accept that the atmosphere has a different chemical composition from that previously assumed.”

The astronomers will next try and obtain spectra for the two other planets in the system, in order to make comparisons between the planets, and shed light on the processes that formed the planetary system, which may be similar to how our own Solar System formed.

Our latest 132-page Astronomy Now special edition is an extravaganza of astronomy for the year ahead, with a complete 30-page guide to observing the planets, moon, meteor showers, two solar eclipses, and the deep sky in 2010.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This special publication features the photography of British astro-imager Nik Szymanek and covers a range of photographic methods from basic to advanced. Beautiful pictures of the night sky can be obtained with a simple camera and tripod before tackling more difficult projects, such as guided astrophotography through the telescope and CCD imaging.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Explore the Universe with these new versions of the award-winning Starry Night Software. Available now from the Astronomy Now Store.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Astronomy Now is pleased to announce the publication of Exploring Mars. The very best images of Mars taken by orbiting spacecraft and NASA's Spirit and Opportunity rovers fill up the 98 glossy pages of this special edition!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE