Exoplanets may have carved dusty tracks around a young star

It seems that planetary formation happens earlier than thought.

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LMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)
LMA (ESO/NAOJ/NRAO); A. Isella; B. Saxton (NRAO/AUI/NSF)

Astronomers have spotted what they believe are two Saturn-sized planets carving "tracks" through a young star's protoplanetary disk. Although scientists have found plenty of exoplanets ranging from gas giants like Jupiter to rocky, Earth-like worlds, most orbit mature stars. However, the not-yet-fully-formed worlds imaged by the ALMA telescope array show that stars can possibly spawn planets at an earlier age than previously thought.

The ALMA (Atacama Large Millimeter/submillimeter Array) telescope has spotted plenty of young stars that still have protoplanetary disks, many with similar gaps that could mark the presence of planets (see the video below). "However, since we were only looking at dust in the disks with sufficient detail, we couldn't be sure what created these features," says lead author Andrea Isella.

This time, the team used ALMA to create a composite image showing both dust and carbon dioxide gas. The dust image revealed three gaps, one at 60 astronomical units (AUs) or about twice as far as Neptune is from our sun, and the others at 100 and 160 AUs.

The CO2 sensor didn't pick up the inner gap that the dust sensor saw, indicating it may have been formed by something other than a planet. However, it did see gaps about the size of Saturn in the same two outer locations, providing evidence that planets knocked both gas and dust out of the way. "Our new observations provide intriguing evidence that planets are indeed forming around this one young star," Isella says.

Scientists figure that the star, dubbed HD 163296, is about five million years old, making it one of the youngest seen with evidence of a planet. (Kepler recently spotted a Neptune-sized world around a star about the same age.) The discovery could shake up planetary formation theory, though Isella advises some caution. "We certainly believe that these structures could be the work of a nascent planet plowing through the dust, but we simply can't rule out other possible explanations."

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