Planet hunters found a giant Jupiter carving a path around a young star

For the first time, astronomers show planets can create gaps in protoplanetary disks.

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The detection method pioneered by the team was first used to detect planets around the young star, HD 163296.


Hiding in the constellation Chamaeleon, around 603 light-years away, a well-known young star dubbed HD 97048 is surrounded by a huge disk of gas and dust, forming giant rings and gaps around the blazing hot orb. That "protoplanetary disk" is where new planets can form, as the debris builds up. However, it's been difficult for astronomers to find exoplanets within the disks of young star systems because the star at the center is bright and active, masking their presence.

Instead of looking directly for a planet, an international team of astronomers decided to look inside the gaps of the disk. In doing so, they discovered a new planet, about twice as massive as Jupiter, carving a path through the gas and dust of a young system around HD 97048.

"It is a bit like if you have a stream of water and you put a rock in the middle," said lead author Christophe Pinte, an astronomer at Monash University in Australia. "The rock will perturb the flow of the water and generate a wave."

In this case, the rock is just very, very, very, very big and the water is a mammoth stream of gas and dust.

The study, published in the journal Nature Astronomy on Monday, details the "kinematic detection" of the planet by studying the gas in the protoplanetary disk. Kinematic detection is just a fancy way to say the movement of objects. In this case, the team used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to intensely study the way gas moved in the disk. ALMA has been used in this way just once before -- by the same team -- to study another star, HD 163296. 

Last year, astronomers found multiple planets around HD 163296 by studying the motion of the carbon monoxide gas and noticing a weird kink in the system's disk.  

"It's a fascinating way of finding exoplanets," said Jonti Horner, a professor of astrophysics at the University of Southern Queensland who wasn't associated with the study. "[It] allows us to search for planets that the main exoplanet search techniques are very heavily biased against finding: planets that exist far from their host stars."  

HD 163296 is very similar to HD 97048, although its a little further away from Earth, Pinte said.

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Unlike previous work, this time the team detected the movement of the gas inside a gap in the disk. Pinte says previous observations of HD 97048 revealed it has two large rings with a gigantic gap in the middle, and that was where the team found their baby Jupiter.

"We found the planet in the gap between those two rings," Pinte said. "The new result is that this gas velocity deviation is detected inside a gap, so we have evidence that a planet is causing the gap."

It's the first time astronomers have been able to show the gaps in protoplanetary disks are likely being caused by big, young planets moving through the disk.

Computer simulations backed up what the team was seeing, but Pinte noted there are other theories about how the gaps in protoplanetary disks form that may still be true. Astronomers have posited that snow lines, where the temperature is so cold that molecules freeze, or magnetic fields emanating from the star might cause the unusual gaps. However, alternative explanations for this particular find can be excluded. "The wave generated by the planet has a very distinctive signature in the gas velocity," he said.

"This is similar (but at a much larger scale) to the gaps or 'divisions' that are carved by moons in the rings of Saturn."

So is this what happened in our own solar system during its formation? Horner thinks it's fairer to suggest this gives us a better indication of the "diversity of outcomes" we might see during planetary system formation. He suspects our solar system would have likely looked very different when it was going through its cosmic infant years.

"This is a more massive planet than any in the solar system, in a more massive disk, orbiting a more massive star than the sun," explained Horner. "Studying systems like this can help us to better understand all the processes that come together for planet formation, around all kinds of stars."

Pinte's team will continue to keep their eyes fixed on HD 97048, hoping to get an image of the planet. Both ALMA and the European Space Agency's Very Large Telescope will help to better characterize how gas flows through the disk -- and the baby planets that may be lurking there. For now, the method will only be able to detect planets about the size of Jupiter (or bigger), but in the future we may be able to find even smaller planets lurking in these young star systems.

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Updated Aug 12, 3:46 p.m. PT