A fascinating glimpse into how a solar system like our own is born has been revealed with the detection of planet-forming 'pebbles' around two young stars.
These seeds to make new worlds are thought to gradually clump together over time, in much the same way Jupiter was first created 4.5 billion years ago, followed by Saturn, Uranus, Neptune, Mercury, Venus, Earth and Mars.
The planet-forming discs, known as protoplanetary discs, were spotted out to at least Neptune-like orbits around the young stars DG Tau and HL Tau, both around 450 light-years from Earth.
The new observations, revealed at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham, are helping to fill in a missing piece of the planet formation puzzle.
"These observations show that discs like DG Tau and HL Tau already contain large reservoirs of planet-forming pebbles out to at least Neptune-like orbits," said researcher Dr Katie Hesterly, of the SKA Observatory.
"This is potentially enough to build planetary systems larger than our own solar system."
The latest research is part of the PEBBLeS project (Planet Earth Building-Blocks – a Legacy eMERLIN Survey), led by Professor Jane Greaves, of Cardiff University.
By imaging the rocky belts of many stars, the team are looking for clues to how often planets form, and where, around stars that will evolve into future suns like our own.
The survey uses e‑MERLIN, an interferometer array of seven radio telescopes spanning 217 km (135 miles) across the UK and connected by a superfast optical fibre network to its headquarters at Jodrell Bank Observatory in Cheshire.
It is currently the only radio telescope able to study protoplanetary discs – the cosmic nurseries where planets are formed – at the required resolution and sensitivity for this science.
"Through these observations, we’re now able to investigate where solid material gathers in these discs, providing insight into one of the earliest stages of planet formation," said Professor Greaves.
Since the 1990s, astronomers have found both disks of gas and dust, and nearly 2,000 fully-formed planets, but the intermediate stages of formation are harder to detect.
"Decades ago, young stars were found to be surrounded by orbiting discs of gas and tiny grains like dust or sand," said Dr Anita Richards, of the Jodrell Bank Centre for Astrophysics at the University of Manchester, who has also been involved in the research.
"Enough grains to make Jupiter could be spread over roughly the same area as the entire orbit of Jupiter, making this easy to detect with optical and infra-red telescopes, or the ALMA submillimeter radio interferometer.
"But as the grains clump together to make planets, the surface area of a given mass gets smaller and harder to see."
For that reason, because centimetre-sized pebbles emit best at wavelengths similar to their size, the UK interferometer e-MERLIN is ideal to look for these because it can observe at around 4 cm wavelength.
In one new e‑MERLIN image of DG Tau’s disc, it reveals that centimetre-sized pebbles have already formed out to Neptune-like orbits, while a similar collection of planetary seeds has also been detected encircling HL Tau.
These discoveries offer an early glimpse of what the Square Kilometre Array (SKA) telescopes in South Africa and Australia will uncover in the coming decade with its improved sensitivity and scale, paving the way to study protoplanetary discs across the galaxy in unprecedented detail.
"e-MERLIN is showing what’s possible, and the SKA telescopes will take it further," said Dr Hesterly.
"When science verification with the SKA-Mid telescope begins in 2031, we’ll be ready to study hundreds of planetary systems to help understand how planets are formed."
ENDS
Media contacts
Sam Tonkin
Royal Astronomical Society
Mob: +44 (0)7802 877 700
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
Megan Eaves
Royal Astronomical Society
Science contacts
Dr Katie Hesterly
SKA Observatory
Professor Jane Greaves
Cardiff University
Dr Anita Richards
Jodrell Bank Centre for Astrophysics at the University of Manchester
a.m.s.richards@manchester.ac.uk
Images & captions
Caption: An e-MERLIN map showing the tilted disc structure around the young star DG Tauri where pebble-sized clumps are beginning to form. Its long axis is southeast to northwest (lower left to upper right). Emission from an outflow of material from the central star is also seen in the northeast and southwest directions.
Credit: Hesterly, Drabek-Maunder, Greaves, Richards, et al.
Caption: The HL Tau disc captured by e-MERLIN is shown overlaid on an ALMA image, revealing both the compact emission from the central region of the disc and the larger scale dust rings.
Credit: Greaves, Hesterly, Richards, and et al./ALMA partnership et al.
Caption: An artist's impression of dust and tiny grains in a protoplanetary disc surrounding a young star.
Credit: NASA/JPL-Caltech
Caption: e‑MERLIN is an interferometer array of seven radio telescopes spanning 217 km (135 miles) across the UK, connected by a superfast optical fibre network to its headquarters at Jodrell Bank. Observatory in Cheshire.
Credit: e‑MERLIN
Further information
The talk 'PEBBLeS in Protoplanetary Discs' will take place at NAM at 09:00 BST on Monday 7 July 2025 in room TLC033. Find out more at: https://conference.astro.dur.ac.uk/event/7/contributions/867/
PEBBLES is an ultra-deep continuum survey of the circumstellar disks that are predicted to be the most conducive to planet formation. Imaging the thermal emission from pebble-sized dust grains shows where and when planet-core growth is proceeding, helping to identify actual accreting proto-planets. The survey sample comprises a mass-limited cut from all known northern disks with long-millimetre wavelength dust emission, above a threshold of 2.5 times the minimum-mass Solar-nebula, at the theoretical boundary for forming the Sun's planets.
The survey results will show how planet growth proceeds - where, when, and with what outcomes - for comparison to inferred histories of the Sun and extrasolar planetary systems. The scientific legacy will also include measuring quantities vital to theoretical progress - particle sizes, disk surface densities and radial distributions, for the first time on few-AU scales - and providing a database of proto-planet targets for future followup with EVLA, ALMA and SKA.
Notes for editors
The NAM 2025 conference is principally sponsored by the Royal Astronomical Society and Durham University.
About the Royal Astronomical Society
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.
The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.
Keep up with the RAS on Instagram, Bluesky, LinkedIn, Facebook and YouTube.
Download the RAS Supermassive podcast
About the Science and Technology Facilities Council
The Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI), is the UK’s largest public funder of research into astronomy and astrophysics, particle and nuclear physics, and space science. We operate five national laboratories across the UK which, supported by a network of additional research facilities, increase our understanding of the world around us and develop innovative technologies in response to pressing scientific and societal issues. We also facilitate UK involvement in a number of international research activities including the ELT, CERN, the James Webb Space Telescope and the Square Kilometre Array Observatory.
About Durham University
Durham University is a globally outstanding centre of teaching and research based in historic Durham City in the UK.
We are a collegiate university committed to inspiring our people to do outstanding things at Durham and in the world.
We conduct research that improves lives globally and we are ranked as a world top 100 university with an international reputation in research and education (QS World University Rankings 2026).
We are a member of the Russell Group of leading research-intensive UK universities and we are consistently ranked as a top five university in national league tables (Times and Sunday Times Good University Guide and The Complete University Guide).
For more information about Durham University visit: www.durham.ac.uk/about/