An international team of astronomers has spotted a pair of baby planets forming in a young star system located 400 light-years from Earth. Their discovery is reported in Physical Review Letters.

The star, known as HD 163296, has been observed using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, whose 66 radio dishes looks for the faint signal of gas and dust around stars. The team observed three gaps around HD 163296 and the outer two are consistent with Saturn-size planet forming.

“Dust and gas behave very differently around young stars. We know, for example, that there are certain chemical and physical processes that can produce ringed structures in the dust like the ones we have seen previously,” said lead author Andrea Isella, from Rice University, Houston, in a statement.

“We certainly believe these structures could be the work of a nascent planet plowing through the dust, but we simply can't rule out other possible explanations. Our new observations provide intriguing evidence that planets are indeed forming around this one young star.”

The team looked at the concentration of carbon monoxide in the system and noticed that a distinct lack of it in the outer gaps, which are located from the star at a distance of over 100 times the distance between Earth and the Sun. The astronomers have interpreted this difference as an indication of a planet coalescing.

^{Artist impression of HD 163296 and its planets. B. Saxton, NRAO/AUI/NSF}

HD 163296 is estimated to be 5 million years old and twice the mass of the Sun. This system is producing planets at a younger age than what was considered possible. These observations, alongside previous ones of HL Tauri and TW Hydrae, strongly suggest that planets can form very quickly after their star starts shining.

"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,” added Isella.

These young systems are not exactly what our Solar System looked like 5 billion years ago, but they are providing enough clues to expand and challenge our ideas about planetary formation.