Free Astronomy Magazine January-February 2020

34 JANUARY-FEBRUARY 2020 SPACE CHRONICLES T his animation shows the com- puter simulation of how the gas flows in the disk as a result of three planets in formation. [ALMA (ESO/NAOJ/NRAO), J. Bae; NRAO/AUI/NSF, S. Dagnello] magnetic field could also cause dis- turbances in the gas. “Right now, only direct observation of the plan- ets could rule out the other options. But, the patterns of these gas flows are unique, and very likely, only planets can cause them,” said coau- thor Jaehan Bae of the Carnegie In- stitution for Science, who tested this theory with a computer simulation of the disk. The location of the three predicted planets in this study corre- spond to the results from last year. Their positions probably are at 87, 140, and 237 AU (An astronomical unit – AU – is the average distance from the Earth to the Sun). The clos- est planet to HD 163296 is calculated to be half the mass of Jupiter, the middle planet is Jupiter-mass, and the farthest planet is twice as mas- sive as Jupiter. Gas flows from the surface towards the midplane of the protoplanetary disk have been predicted since the late nineties. But this is the first time that astronomers observed them. Besides being useful to detect infant planets, these flows can also shape our understanding of how gas giant planets obtain their atmospheres. “Planets form in the middle layer of the disk, the so-called midplane. This is a cold place, shielded from radia- tion from the star,” Teague ex- plained. “We think that the gaps caused by planets bring in warmer gas from the more chemically active outer layers of the disk and that this gas will form the atmosphere of the planet.” Teague and his team did not expect that they would be able to see this phenomenon. “The disk around HD 163296 is the brightest and biggest disk we can see with ALMA,” said Teague. “But it was a big surprise to see these gas flows so clearly. The disks appear to be much more dy- namic than we thought.” “This gives us a much more com- plete picture of planet formation than we ever dreamed,” said coau- thor Ted Bergin of the University of Michigan. “By characterizing these flows, we can determine how plan- ets like Jupiter are born and charac- terize their chemical composition at birth. We might be able to use this to trace the birth location of these planets, as they can move during formation.” !