Planet formation isn't an easy thing to observe. In the case of our solar system, the planets formed billions of years ago. Meanwhile, we've only just recently achieved the capability of identifying the existence of exoplanets in other solar systems.

So what Rice University astronomers have witnessed happening around a distant star 400 light-years away is fairly remarkable: a system of rings that appear to represent the early formation of planets out of a protoplanetary disc, reports Phys.org.

The star in question, HD 163296, which is best viewed from the Southern Hemisphere, has three notable dark rings. It's the darker rings that likely represent the orbital paths of freshly formed planets; gaps in the disc where gases and dust have coalesced into a new world. Scientists can't yet see the planets themselves, but their formation offers the best explanation for the dark rings.

The outer two rings are almost certainly inhabited by gas giants, probably with masses similar to Saturn. The inner ring remains something of a mystery, however, because it still contains a lot of gas that a large planet should have swept up.

"The inner gap is mysterious," said Andrea Isella, leader on the team. "Whatever is creating the structure is removing the dust but there's still a lot of gas."

HD 163296 isn't the first star ever witnessed with a protoplanetary disc surrounding it, but it is the first such star with clearly visible gaps where scientists have been able to analyze the dust and gas content of the rings. That's essential for identifying whether there are planets forming there or not.

"Of the material that formed this disk, about 1 percent is dust particles and 99 percent is gas," Isella explained. "So if you only see the dust, you cannot tell if a ring was formed by a planet or another phenomenon. In order to distinguish and really tell if there are planets or not, you need to see what the gas is doing, and in this study, for the first time, we can see both the dust and the gas."

The discovery is of utmost importance, since it gives researchers an opportunity to witness planet formation in action. How exactly planets form out of their protoplanetary discs is still an issue debated by astronomers, and understanding planet formation is crucial to not only understanding the origin of our own solar system, but also in identifying how planets might form elsewhere too.

If we know how exoplanets have formed, we might be able to learn more about what they're composed of.

"If we know the chemistry of the material forming a planet, we can understand the chemistry of the planet," said Isella.