Astronomers have discovered more than 3,700 confirmed exoplanets in the last few decades, but studying the origins of exoplanets is still difficult. Young solar systems are cloaked in swirling disks of gas as planets form, which obscures our detection methods. Now, two teams have independently discovered three different exoplanets forming in a star’s protoplanetary disk.
The most common way of detecting exoplanets is watching for brief drops in brightness as these objects pass in front of their host star. The Kepler Space Telescope spotted thousands of potential exoplanets using this “transit” method. However, young stars still have a dense disc of dust and gas around them, which slowly coalesces into planets. The interference from the disc makes it impossible to accurately detect planets via the transit method.
Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study a nearby star called HD 163296. This star is twice the size of the sun, but it’s only 4 million years old (the sun is more than 4 billion). Its planetary system is still forming, which is something astronomers would like to see. One team, led by University of Michigan scientist Richard Teague discovered a pair of Jupiter-sized exoplanets 7.4 billion miles (12 billion km) and 13 billion miles (21 million km) from the star. Meanwhile, Christopher Pinte from the Monash University in Australia discovered a third planet in a more distant orbit of 24 billion miles (39 billion km).
All three exoplanets reside within the protoplanetary disk, and that’s how the researchers managed to find them. The ALMA array scanned HD 163296 in the millimeter wavelength to track carbon monoxide gas pockets. The Doppler shift reveals how the gas moves throughout the disk. If there are no planets in its path, the gas should flow in a predictable way along with the rotation of the disk. Instead, there were three distinct disruptions in the carbon monoxide currents — like water breaking around a rock in a stream. You can see one of these “kinks” in the gas distribution above. The astronomers say those disruptions in the flow of gas are caused by gas giants forming in the protoplanetary disk.
This is good evidence of planetary formation, but there’s not much more we can learn right now. When the James Webb Space Telescope comes online, it will be able to peer through the veil of dust and gas using infrared sensors to take a closer look at objects like the potential exoplanets around HD 163296.
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