"We reached a milestone in the search for other worlds in 2008 with the discovery of the HR 8799 planetary system," said Dr. Christian Marois, an astronomer with NRC. Dr. Marois is the first author of the new paper and designed the improved image-processing software that made the new discovery possible. "The images of this new inner planet are the culmination of ten years' worth of innovation, making steady progress to optimize every aspect of observation and analysis. Compared with what was previously possible, this allows us to detect planets located ever closer to their stars and ever further from our own solar system."
Discovery of this fourth giant planet strengthens the remarkable resemblance between the HR 8799 planetary system and our own — the HR 8799 system appears as a supersized version of our solar system. "Besides having four giant planets, both systems also contain two 'debris belts,' composed of small rocky or icy objects along with lots of tiny dust particles," said co-author Ben Zuckerman, a professor of physics and astronomy at UCLA. The mass of the HR 8799 planetary system is much more extreme than that of our own — the combined mass of the four giant planets may be twenty times higher, and the debris belt counterparts are also much larger than our own.
"The four massive planets pull on each other gravitationally," said co-author Quinn Konopacky, a post-doctoral researcher at LLNL. "We don't yet know if the system will last for billions of years, or fall apart in a few million more. As astronomers carefully follow the HR 8799 planets during the coming decades, the question of the stability of their orbits could become much clearer."
The origin of these four giant planets remains a puzzle — neither of the two main models of planet formation can account for all four objects. Dr. Bruce Macintosh of LLNL, a co-author, noted that there's no simple model that can form all four planets at their current location. It's going to be a challenge for our theoretical colleagues.
This is a 3-D representation of the HR 8799 planetary system and the solar system in the Milky Way. The orbits of Jupiter, Saturn, Uranus and Neptune are shown with the Sun located at the center. HR 8799 is located 90 degrees away from the Milky Way galactic center, below the solar system. All orbital diameters are greatly exaggerated here to be visible.
(Photo Credit: NRC-HIA and C. Marois. Background image courtesy of 2MASS/UMass/IPAC-Caltech/NASA/NSF)
Travis Barman, a Lowell Observatory exoplanet theorist and study co-author stated images like these bring the exoplanet field, which studies planets outside our solar system, into an era of exoplanet characterization. Astronomers can now directly examine the atmospheric properties of four giant exoplanets that are all the same young age and that formed from the same building materials.
Detailed study of the properties of HR 8799e will be challenging due to its relative faintness and proximity to its star. To overcome these limitations, a team led by Dr. Macintosh, including NRC and several US institutions, is building an advanced new instrument, called the Gemini Planet Imager for the Gemini Observatory. This new instrument will physically block the starlight and allow quick detection and detailed characterization of planets similar to HR 8799e. The Gemini Planet Imager is scheduled to arrive at the Gemini South telescope in Chile late in 2011. "We can expect a tidal wave of new discoveries with the new planet imager. HR 8799 is really just the beginning, the tip of the iceberg," said Dr. Marois.
This image of HR 8799e obtained at the Keck II telescope, refined using NRCs adaptive optics system, shows all four confirmed planets. Arrows illustrate possible planet orbital motions for the next ten years.
(Photo Credit: NRC-HIA, C. Marois & Keck Observatory)
An animation demonstrating plausible orbits of the HR 8799 planets through one complete period (~465 years) of HR 8799b, the outermost planet. For each orbit of HR 8799b, HR 8799c and HR 8799d will orbit twice, and HR 8799e will orbit four times.
(Photo Credit: LLNL & Q. M. Konopacky)