Signs of giant icy planet growing around nearby star

Tokyo: Astronomers have found signs of a giant icy planet growing around TW Hydrae, one of the closest young stars to Earth.

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 in our solar system. 

"Combined with the orbit size and the brightness of TW Hydrae, the planet would be an giant icy planet like Neptune," said lead researcher Takashi Tsukagoshi at Ibaraki University, Japan.

This result, to be published in the journal Astrophysical Journal Letters, is another step towards understanding the origins of various types of planets.

TW Hydrae is one of the most favourable targets for investigating 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 Atacama Large Millimeter/submillimeter Array (ALMA) observations revealed 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, micrometer-sized, dust particles dominate and larger dust particles are absent in the most prominent gap with a radius of 22 astronomical units.

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 believe that the planet is probably a little more massive than Neptune.