Pair of infant planets spotted orbiting young star

Scientists have found evidence of two newborn planets, each about the size of Saturn, orbiting a young star located 400 light-years from the Earth.
The planets, which are not yet fully formed, unveiled themselves by the dual imprint they left in both the dust and the gas portions of the protoplanetary disk surrounding the host star HD 163296.
HD 163296 is roughly five million years old and about twice the mass of the Sun. It is located about 400 light-years from Earth in the direction of the constellation Sagittarius.
Previous observations of other young star systems have helped to reshape our understanding of planet formation, researchers said.

For example, images of HL Tauri and TW Hydrae taken by the Atacama Large Millimetre/submillimetre Array (ALMA) showed striking gaps and prominent ring structures in the dusty disks of the stars.
These features may be the tantalising first signs that planets are being born.

These signs appeared around much younger stars than astronomers thought possible, suggesting that planet formation can begin soon after the formation of a protoplanetary disk.
"ALMA has shown us amazing images and never-before-seen views of the rings and gaps around young stars that could be the hallmarks of planet formation," said Andrea Isella, astronomer at Rice University in the US.

"However, since we were only looking at the dust in the disks with sufficient detail, we couldn't be sure what created these features," said Isella.
In studying HD 163296, the researchers used ALMA to trace, for the first time, the distribution of both the dust and the carbon monoxide (CO) gas components of the disk at roughly the same level of detail.
These observations unveiled three distinct gaps in HD 163296's dust-filled protoplanetary disk.
The first gap is located about 60 astronomical units from the central star, which is about twice the distance from our Sun to Neptune.
The other two gaps are 100 AU and 160 AU from the central star, well beyond the extent of our solar system's Kuiper Belt, the region of icy bodies beyond the orbit of Neptune.

Using ALMA's ability to detect faint millimetre-wavelength "glow" emitted by gas molecules, researchers discovered that there was also an appreciable dip in the amount of CO in the outer two dust gaps.
By seeing the same features in both the gas and the dust components of the disk, the astronomers believe they have found compelling evidence that there are two planets coalescing remarkably far from the central star.
The width and depth of the two CO gaps suggest that each potential planet is roughly the same mass as Saturn.
In the gap nearest to the star, the team found little to no difference in the concentration of CO gas compared to the surrounding dusty disk.

The study was published in the journal Physical Review Letters.