Astronomers have found signs of a new planet growing around TW Hydrae, a young star that lies 176 light-years away from Earth. The discovery was made with the help of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the most expensive ground-based telescope currently in operation.

The distance and distribution of the dust grains from the star suggest that the budding exoplanet is an icy giant, just like the solar system's Neptune and Uranus.

Scientists have discovered several extrasolar planets over the past two decades but there are still questions that remain unanswered about these worlds. Scientists, for instance, are still uncertain how icy giant planets form.

Earlier observations revealed that TW Hydrae is surrounded by a disk of tiny dust particles and ALMA observations showed multiple gaps in this disk. The gaps were posited as evidence of a forming planet.

"TW Hydrae is quite special. It is the nearest known protoplanetary disc to Earth and it may closely resemble the solar system when it was only 10 million years old," said David Wilner, from the Harvard-Smithsonian Center for Astrophysics, who is part of the team that conducted an earlier study of the young star and its protoplanetary disk.

In a new study to be reported in the Astrophysical Journal Letters, Takashi Tsukagoshi, from the Ibaraki University in Japan, and colleagues observed the young star TW Hydrae. At about 10 million years old, the star is among the youngest stars that reside near the Earth, making it a favorable target for studying planet formation.

Using ALMA, Tsukagoshi and colleagues observed the disk around TW Hydrae to estimate the size of dust grains and found that the smaller dust particles dominate the bigger ones. The most prominent gap was likewise marked by the absence of larger dust particles.

Observations of smaller dust particles being selectively located in the gap match theoretical predictions that a gap in the disk is produced by a massive planet, and that friction and gravitational forces between the dust particles and gas push the bigger dust out, leaving the smaller particles in the gap.

Based on the depth and width of the gap, researchers said the new planet is likely a little more massive than Neptune.

The researchers plan to conduct more observations to shed more light on how planets form. Part of this plan is to observe the polarization of radio waves, which can more precisely estimate the size of the dust grains. They also plan to measure the amount of gas in the disk to have a better idea of the mass of the forming planet.