Massive planets orbiting young star could reveal how 'hot Jupiters' and systems form

Images and models show distinct gaps in the system where more gas giants could be orbiting.

New research has imaged and described a solar system housing a young star that has four massive planets orbiting it, in the first discovery of its kind.

The young star at the heart of the system, CI Tau, is located 500 light years away from our system in a region of dense star-formation.

CI Tau is 2-million-years-old, a mere ‘toddler’ in astronomical circles. The disc of ice and dust that surrounds CI Tau — its ‘protoplanetary disc’ — houses the many other components of its stellar system.

Researchers used the Atacama Large Millimeter/Submillimeter Array (ALMA) telescope to study the planets around the CI Tau system’s hot Jupiter.

One of the planets in CI Tau’s system is the first ‘hot Jupiter’ to orbit such a young star, the study reports. Not only were ‘hot Jupiters’ one of the first kind of exoplanets to be discovered, they are particularly interesting to astronomers for how close they are to their parent star — too close to have formed where they are now.

The study found that the CI Tau system has some of the most extreme planetary distances known for any stellar system. While the closest (the hot Jupiter) is roughly as far as Mercury is from the Sun, the farthest planet orbiting CI Tau is roughly three as far as Neptune.

This, the researchers believe, could be crucial to understanding how the system was formed.

Artist's impression of the four gas giants orbiting the young star, CI Tau. Image courtesy: University of Cambridge

Artist's impression of the four gas giants orbiting the young star, CI Tau. Image courtesy: University of Cambridge

The two inner planets are roughly one and ten times the mass of Jupiter, respectively, and the outer planets roughly the size of Saturn, the study revealed.

"It is currently impossible to say whether the extreme planetary architecture seen in CI Tau is common in hot Jupiter systems,” Professor Cathie Clarke, the study's first author told the University press.

“The way that these sibling planets were detected — through their effect on the protoplanetary disc — would not work in older systems which no longer have a protoplanetary disc."

The researchers are also unclear if the outer planets have a hand in the inner planets being so close to the star.

"Saturn-mass planets are known to form by accumulating a solid core first and then pulling in a layer of gas on top… these processes are supposed to be very slow, at large distances from the star,” Clarke said.

“Most models will struggle to make planets of this mass at this distance."

The images captured by the researchers along with theoretical modelling showed three distinct gaps in the system where they believe additional gas giants could be orbiting.

The findings from the study were published in the The Astrophysical Journal Letters.

The researchers are now studying the system using ALMA at different wavelengths, to capture different features of the star, planets and disc.

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