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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."
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.
Media contacts:
Sam Tonkin
Royal Astronomical Society
Mob: +44 (0)7802 877 700
press@ras.ac.uk
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
press@ras.ac.uk
Megan Eaves
Royal Astronomical Society
press@ras.ac.uk
Science contacts:
Dr Katie Hesterly
SKA Observatory
katie.hesterly@skao.int
Professor Jane Greaves
Cardiff University
greavesj1@cardiff.ac.uk
Dr Anita Richards
Jodrell Bank Centre for Astrophysics at the University of Manchester
a.m.s.richards@manchester.ac.uk
Further information
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.
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Submitted by Sam Tonkin
