Treasure trove of planets hiding in dust

New research discovers 'super-Earths' forming around young stars

New research by a team of international astronomers, including a University of Leicester researcher, has found that ‘super-Earths’ and Neptune-sized planets could be forming around young stars in much greater numbers than previously thought.

The results, published in the Astrophysical Journal, will help scientists better understand how our own solar system came to exist 4.6 billion years ago.

Dr Giovanni Dipierro, Postdoctoral Research Associate at the University of Leicester’s Department of Physics and Astronomy, along with a team of international astronomers, measured the properties of rings and gaps observed using the Atacama Large Millimeter Array (ALMA). 

Considered as the world’s most powerful observatory for studying the universe at millimetre and submillimetre wavelengths, the ALMA is located on the Chajnantor Plateau in Chile’s Atacama Desert and made up of 45 radio antennas.

The team, which also includes Nathan Hendler and Ilaria Pascucci at the University of Arizona's Lunar and Planetary Laboratory (LPL), performed a survey of young stars in the Taurus star-forming region, a vast cloud of gas and dust located 450 light years from Earth.

Since detecting the individual planets directly is impossible because of the overwhelming brightness of the host star, the team made calculations to understand the kinds of planets that might be forming in the Taurus star-forming region.

By analysing the data, the team evaluated possible mechanisms that could cause the observed rings and gaps. When the researchers created images of 32 stars surrounded by protoplanetary disks, they found that 12 of them had rings and gaps. These rings and gaps are best explained as traces created by young planets in the making.

Dr Dipierro said: “Our results suggest that gaps and rings are common in protoplanetary discs, as a result of ubiquitous processes in the disc evolution.

“Although their origin is still debated, our analysis shows that these structures can be related to the presence of new-born planets, allowing us for the first time to connect the properties of young planets with the exoplanets statistics.”

Moreover, according to the findings, so-called super-Earths or Neptune-sized gas planets of up to 20 Earth masses should be the most common.

Previous research has suggested that the rings and gaps may be created by ice lines caused by changes in the chemistry of the dust particles across the disc.

However, the researchers performed analyses to test this hypothesis and could not find any correlation between ice lines and the patterns of gaps and rings they observed.  

Dr Dipierro said: "Analysing the morphologies of gaps and how they relate with the star and disc properties we rule out the idea of ice lines causing the rings and gaps. This strengthens the idea that new-born planets are the main cause for the origin of these structures.”

The paper’s lead author, Feng Long of Peking University, Beijing, China said: "This is fascinating because it is the first time that exoplanet statistics, which suggest that super-Earths and Neptunes are the most common type of planets, coincide with observations of protoplanetary disks.” 

Going forward, future research will use these data to predict how planetary systems are constructed.

Dr Richard Alexander, Reader in Theoretical Astrophysics, University of Leicester, said: “ALMA is providing us with exquisite new views of protoplanetary discs, and this new study essentially allows us to watch young solar systems as they are forming.

“In the coming years, we will combine this new data with precision models and computer simulations, in order to build up a comprehensive picture of how planetary systems are built."