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by Christian Marois

An Exoplanet Family Portrait What do planets around other stars look like? This question

Figure 1.

A K-band (2.2 microns) AO image of the HR 8799 planetary system made using Gemini/Altair/ NIRI and acquired on September 5, 2008 (North is up and East is left). The three planets are designated with red circles. The stellar flux has been subtracted using ADI (see text for details) and the central saturated region is masked out. Multiepoch observations have shown counterclockwise Keplerian orbital motion for all three planets.

is driving an exciting quest to take

pictures

of

exoplanets.

This is challenging work. Until recently, surveys using direct imaging have uncovered only a few candidate worlds–even after much intense effort. These possible

planets

have

been

found in systems that are unlike our own in many ways. In addition, there is usually only one candidate world orbiting its parent star, and often it lies at a very wide separation (or distance) of more than 100 astronomical units (AU). Our team used the Gemini Observatory to capture a spectacular image showing not one, not two, but three planets in orbit around the star HR 8799. They lie at distances similar to those of the outer planets of our solar system. This is the first image of a multi-planet system, and these exoplanets are also the first at separations similar to Uranus and Neptune (which orbit the Sun at 20 and 30 AU, respectively) to be discovered by any

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GeminiFocus

Issue 38 - June 2009  

GeminiFocus