Possible formation site of icy giant planet spotted
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. Especially, there is still debate about how the icy giant planets, such as Uranus and Neptune, form.
|Artist's impression of the dust disk and a forming planet around TW Hydrae |
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 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.
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. One of their plans is to observe the polarization of the radio waves. Recent theoretical studies have shown that the size of dust grains can be estimated more precisely with polarization observations. The other plan is to measure the amount of gas in the disk. Since gas is the major component of the disk, the researchers hope to attain a better estimation of the mass of the forming planet.
The findings are published in The Astrophysical Journal.
See also: The death of a planet nursery?
Source: National Institutes of Natural Sciences [October 14, 2016]