Astronomers Observe Possible Formation of Uranus-Like Planet

An international team of astronomers has detected signs of possible site of an icy planet similar to Uranus and Neptune around a young star about 176 light-years away in the constellation Hydra.

In an effort to learn more about the planet formation site, the researchers observed the young star named TW Hydrae, which is about 10 million years old, using the Atacama Large Millimeter/submillimeter Array (ALMA). TW Hydrae is considered to be one of the most targets for investigating planet formation. Due to the proximity and location of axis rotation points, which point roughly in the direction of Earth, the researchers were able to have a face-on-view of the developing planetary system.

TW Hydrae is surrounded by disk made of tiny particles. Previous observations of the young star showed that the disks have multiple gaps, suggesting the existence of unseen planets.

The researchers observed the disk around the TW Hydrae using ALMA in two radio frequencies. The ratio of radio intensifies in different frequencies depending on the size of dust grains, making it possible for the researchers to estimate the size of the dust grains. The researchers discovered that smaller, micrometer-sized dust particles are prevalent in the most prominent gap with a radius of 22 astronomical units while larger dust particles are relatively absent in the gap.

Their observations, explained in a paper published in The Astrophysical Research Journal, matched previous theoretical studies on the presence of small dust and absence of larger dust particles in the gaps. According to these studies, the gap in the disk is made by a large planet. The gravitational interaction between gas and dust particles pushes the larger dust particles out of the gap while the smaller dust particles remain.

Based on these theoretical predictions, the researchers calculated the mass of the unseen planet lying in the disk gap of TW Hydrae to be little more massive than the planet Neptune.

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