Exeter astronomers reveal turbulent ‘teenage years’ of alien planetary systems

Astronomers at the University of Exeter are leading an international effort to uncover what happens to planetary systems long after planets are born but before they settle into maturity – a crucial stage scientists describe as their “teenage years”.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers have produced the most detailed images yet of debris discs: vast belts of dust and gas that surround stars from around 10 million years to more than a billion years after their formation.

These debris discs are thought to be the distant equivalents of the Kuiper Belt in our own Solar System – the region beyond Neptune that holds icy remnants of planet formation. 

By studying them, astronomers can trace how planetary systems evolve over billions of years and identify signs of unseen planets shaping their surroundings through gravity.

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The work forms part of the ALMA survey to Resolve exoKuiper belt Substructures (ARKS), led by Dr Sebastian Marino, Associate Professor of Astrophysics at the University of Exeter. 

The programme brings together 60 scientists worldwide and has resulted in a series of papers published in the journal Astronomy & Astrophysics.

“These debris discs give us a unique window into the outer regions of planetary systems,” said Dr Marino, who is based in Exeter’s Department of Physics and Astronomy. 

“They show us what happens after planets have formed, when orbits are still shifting, collisions are common, and systems are anything but calm.”

The ARKS survey has analysed a diverse sample of 24 debris discs – also known as exoKuiper belts – using a combination of new observations and archival ALMA data. 

Around 300 hours of telescope time were used between October 2022 and July 2024, with ALMA configured specifically to capture faint, high-resolution detail that has previously been out of reach.

The resulting images reveal remarkable variety. Some discs consist of multiple narrow rings separated by gaps, while others spread into wide, smooth belts. 

Many display sharp edges, halos of dust, or striking asymmetries such as bright arcs and clumps.

About one-third of the systems studied show clear substructures, which researchers believe may be caused by the gravitational influence of planets, lingering features from earlier planet-forming stages, or interactions between dust and gas.

“These systems are the cosmic equivalent of adolescence,” Dr Marino said. 

“They’re more mature than newborn, planet-forming discs, but they haven’t yet settled into adulthood. What we’re seeing is a dynamic and sometimes violent phase of planetary history.”

The survey also examined the physical properties of the discs in unprecedented detail. 

In its first ten papers, the ARKS team studied the radial and vertical structure of dust belts, the density and motion of molecular gas, the relationship between dust seen in radio and optical light, and the causes of lopsided or eccentric features.

Several systems retain gas much longer than astronomers expected, which could influence how planets grow or push dust into extended halos. 

In other cases, asymmetries may point to hidden planets disturbing the disc as they migrate through the system.

Two particularly unusual systems stand out. HD 121617 shows a pronounced arc of dust along with unexpected gas motions, while HD 131835 contains two belts that switch brightness depending on whether they are observed in millimetre wavelengths or scattered light.

Dr Meredith Hughes, Associate Professor of Astronomy at Wesleyan University and co-lead of the study, said the work fills a long-standing gap in planetary science.

“We’ve often seen the ‘baby pictures’ of planets forming, but the teenage years have been a missing link,” she said. 

“These observations help us interpret everything from the structure of the Kuiper Belt to the craters on the Moon.”

By comparing debris discs around stars of different ages and types, the Exeter-led team hopes to determine whether the chaotic early history of our own Solar System was typical or unusual.

“These discs record a time when planetary orbits were being scrambled and huge impacts were shaping young worlds,” added Dr Luca Matrà of Trinity College Dublin, a co-lead on the project.

The ARKS programme is jointly led by the University of Exeter, Trinity College Dublin and Wesleyan University. 

A gallery of ALMA images, including observations tracing carbon monoxide gas, is available via the ARKS project website.