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Planet In The Making? Rings Around Young Distant Star Hint At Planetary Formation In Progress

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Rice University astronomers expressed that planet formation is taking place at a distant star after spotting dark rings around the star and mapping them for gases.

It was further reinforced by the fact that the rings around HD 163296 were bereft of dust. The target star, away by nearly 400 light-years from Earth, has a large disk of dust and gas, as evidenced in the Atacama Large Millimeter and Submillimeter Array (ALMA) telescope images.

The team believes that the upcoming planets might be gas giants similar to Saturn and they are clearing the outer rings of any trace of dust.

Astronomers spotted gases in three dark rings surrounding the star and believe the rings are the spaces where planets take birth from dust.

The key observations were made by Rice astronomer Andrea Isella suggesting the possibility of two planets being in the formative stage and having the size of Saturn. The inner ring still carries more carbon monoxide than the other two and no planet exists there, he said.

"The inner gap is mysterious," Isella said.

"Whatever is creating the structure is removing the dust but there's still a lot of gas," he added.

ALMA Telescope Images And Observations

ALMA observations over the protoplanetary disk around the star HD 163296 based on the disk's image in the 1.3 mm continuum emission revealed three dark rings indicating depleted gaps at 60, 100 and 160 A.U. from the star.

They revealed variations in the slope of the radial intensity profile in the positions of dark rings. After evaluating the observations, it was found that the density of carbon monoxide was less inside the middle and outer dust gaps.

However, the inner ring had an abundance of gas rather than showing any depletion. Rice researchers also said dust and gas densities and gas-to-dust ratio variation across the disk are up by a factor of 5 within the inner dust gap compared to adjacent regions of the disk.

Other Possibilities

As the largest radio telescope in the world, Chile's ALMA is ahead in studying protoplanetary systems and the results are more convincing. According to Isella, the material in the disk has 1 percent dust particles and 99 percent gas.

However, the team head also sees space for other phenomena.

Other options governing the formation of dark rings were indicated by the Rice astronomer. One interpretation is a lack of turbulence among non-ionized gas molecules in a magneto-rotational instability "dead zone" with gas and dust condensing into a ring at the edge of the dark zone. That may not lead to a planet making.

It is also possible that rings can emerge at the carbon monoxide frost line if the gas is too cold to condense.

Certainly, new ALMA results are driving up more research into the possible planet-forming activity.

The study is published in Physical Review Letters.

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