Icy giant planet found growing around nearby star

Scientists have found signs of a baby planet thought to be an icy giant - similar to Uranus and Neptune - growing around a nearby star, a discovery that may help better understand the origins of various types of planets.
Astronomers spotted the planet around TW Hydra, a nearby young star, using the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile.
Based on the distance from the central star and the distribution of tiny dust grains, the baby planet is thought to be an icy giant, similar to Uranus and Neptune.
A number of extrasolar planets have been found in the past two decades and now researchers agree that planets can have a wide variety of characteristics.

However, it is still unclear how this diversity emerges.
Researchers led by Takashi Tsukagoshi at Ibaraki University in Japan, observed the young star TW Hydrae.

This star, estimated to be 10 million years old, is one of the closest young stars to Earth.
Due to the proximity and the fact that the axis of rotation points in Earth's direction, giving us a face-on-view of the developing planetary system, TW Hydrae is one of the most favourable targets for studying planet formation.
Past observations have shown that TW Hydrae is surrounded by a disk made of tiny dust particles. This disk is the site of planet formation. Recent ALMA observations show multiple gaps in the disk.

Some theoretical studies suggest that the gaps are evidence of planet formation.
The team observed the disk around TW Hydrae with ALMA in two radio frequencies. Since the ratio of the radio intensities in different frequencies depends on the size of the dust grains, researchers can estimate the size of dust grains.
The ratio indicates that smaller, micrometre-sized, dust particles dominate and larger dust particles are absent in the prominent gap with a radius of 22 astronomical units (au).
Theoretical studies have predicted that a gap in the disk is created by a massive planet, and that gravitational interaction and friction between gas and dust particles push the larger dust out from the gap, while the smaller particles remain in the gap.

The current observation results match these theoretical predictions.
Researchers calculated the mass of the unseen planet based on the width and depth of the 22 au gap and found that the planet is probably a little more massive than the Neptune.
"Combined with the orbit size and the brightness of TW Hydrae, the planet would be an icy giant planet like Neptune," said Tsukagoshi.
Following this result, the team is planning further observations to better understand planet formation.