Gas disk around young planet raises questions on planet formation theory

In a recent study, astronomers have found a young star -- 49 Ceti -- using the instrument Atacama Large Millimeter/submillimeter Array (ALMA).

The star, 40 million years old, was seen surrounded by an astonishing mass of gas, which contradicts the conventional theories of planet formation that predict the gas disappeared by that age.

A large amount of gas around the star then led to a reconsideration of the current theories of planet formation.

"We found atomic carbon gas in the debris disk around 49 Ceti by using more than 100 hours of observations on the ASTE telescope. The carbon gas around 49 Ceti turned out to be 10 times more abundant than our previous estimation," said astronomer Aya Higuchi from the National Astronomical Observatory of Japan (NAOJ).

Carbon atoms are more widely distributed than carbon monoxide, the second most abundant molecules around young stars, hydrogen molecules being the most abundant.

The amount of carbon atoms is so large that the team even detected faint radio waves from a rarer form of carbon, 13C.

This is the first detection of the 13C emission at 492 GHz in any astronomical object, which is usually hidden behind the emission of normal 12C.

"The amount of 13C is only one per cent of 12C. Therefore, the detection of 13C in the debris disk was totally unexpected. It is clear evidence that 49 Ceti has a surprisingly large amount of gas," said Higuchi.

Researchers suggested two possibilities for the presence of gas, one being that it is remnant gas that might have survived the dissipation process during the final phase of the planet formation.

The amount of gas present around 49 Ceti could, however, be compared to those around younger stars in the active planet formation phase.

The other possibility is that the gas was produced by the collisions of small bodies like comets. But the number of collisions needed to explain a large amount of gas around 49 Ceti is too large to be accommodated in current theories.

The current results of ALMA prompt a reconsideration of the planet formation models.