Portrait of a youthful planet

New images have confirmed that a tiny point of light first photographed near the star Beta Pictoris in 2003 is indeed an orbiting planet, one of only a handful of extrasolar planets ever imaged. At a youthful 12 million years of age, the planet, which weighs the equivalent of nine Jupiters, is the youngest ever directly recorded orbiting a star, providing firm evidence that massive planets can form in a hurry.

The planet also lies much closer to its parent star — slightly farther than Saturn’s distance from the sun — than any other extrasolar planet previously imaged. This will enable astronomers to track its complete orbit in less than 20 years, says Anne-Marie Lagrange of Université Joseph Fourier in Grenoble, France. She and her colleagues describe the new findings in an article posted online June 10 in Science.

“People have been predicting the existence of this massive planet for many years, and these images are finally what we have been waiting for,” says Christian Marois of the Herzberg Institute of Astrophysics in Victoria, Canada, who is not part of the team.

Additional observations will provide new information on the composition of the atmosphere of this Jupiter-like planet, which lies about 65 light-years from Earth, notes Lagrange. Observations of the planet, dubbed Beta Pictoris b, will also reveal new details about its interaction with a disk of gas and dust known to encircle the star and extend beyond the planet. This debris disk is believed to have arisen from the dust generated by collisions within a reservoir of comets or asteroids.

“This discovery will be a gold mine for scientists who study how planets form and
evolve in the presence of a disk of comets and asteroids,” comments astronomer Paul Kalas of the University of California, Berkeley, who was not involved in the new study.

Given the youth of Beta Pictoris, which is only about 12 million years old, the massive planet orbiting the star “in some ways is a snapshot of what our sun-Jupiter system looked like just after our own solar system was born,“ Kalas adds. “We have several competing theories of how the planets form, so a picture of a young planet is going to tell us which theoretical principles we should be adopting.”

The youngest confirmed planets previously photographed around stars were a trio of 60-million-year-old planets circling the star HR 8799.

Marois says the amount of dust and gas that endures in the disk beyond the planet suggests that “Beta Pictoris is in the process of forming a multiplanet system.”

The disk, studied by countless telescopes for nearly three decades, first clued researchers that the star might harbor the raw materials for making planets. In 2003, Lagrange and her collaborators at the time, using a special camera on the European Southern Observatory’s Very Large Telescope atop Cerro Paranal in Chile, spotted a faint point of light within the disk, but they could not tell whether the object was a planet or a spurious signal from a background star.

In images taken in the fall of 2009 with the instrument, the researchers discerned that the object moved in sync with the star, confirming the body was an orbiting planet. The orb has the right location and mass to account for a known warp in the disk, the team notes.

“The result looks convincing and impressive,” says Michael Liu of the University of Hawaii in Honolulu, who was not part of the study. “The possibility of measuring the orbit over the next few years will be a great way to understand better how this object formed.”