New observations from England’s e-MERLIN interferometer telescope array display cosmic pebbles that will one day grow into entire exoplanets, providing new data about early-stage planet formation.
The protoplanetary discs orbit a pair of young stars, DG Tauri and HL Tauri, located approximately 450 light years from Earth, offering two glimpses into how our local planets were formed, beginning 4.5 billion years ago with the formation of Jupiter. Astronomers presented the new observations at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham, England, held from July 7-11, 2025.
“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.”
E-MERLIN
Spread across 135 miles of the UK and joined by fiber-optic cables, the Jodrell Bank Observatory, under the University of Manchester, runs e-MERLIN. The array’s origins date back to the 1970s, with its predecessor being the MTRLI (Multi-Telescope Radio Linked Interferometer). Over several years of upgrades and additional telescope construction, the array eventually became e-MERLIN in the 1990s.
It holds a special place for astronomers interested in the universe’s beginnings, as it is currently the only radio telescope capable of the necessary resolution and sensitivity to study protoplanetary discs effectively. Since officially becoming e-MERLIN, the array has discovered nearly 2,000 planets and many early gas and dust discs over the last three decades. However, studies involving the middle stages of planet formation have remained challenging.
Professor Jane Greaves of Cardiff University leads the PEBBLeS project (Planet Earth Building-Blocks), a long-term e-MERLIN survey focused on observing rocky belts containing a multitude of stars for hints about planet formation, particularly around stars that will one day be similar to our own.
Protoplanetary Discs
“Decades ago, young stars were found to be surrounded by orbiting discs of gas and tiny grains like dust or sand,” explained Dr Anita Richards, of the Jodrell Bank Centre for Astrophysics at the University of Manchester, who has also been involved in the research.
The behavior of these discs over time presents a challenge for astronomical observation. In early stages, the individual grains required to form a planet may be spread over an area as large as its entire post-formation orbit, creating a large target for optical and infrared telescopes. However, when these tiny pieces start to form together into a single body, their surface area greatly diminishes, making them hard to see over vast distances, which makes e-MERLIN’s precision a necessity.
“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.
Imaging Planet Formation
E-Merlin is capable of extremely precise observations down to a 4-centimeter wavelength, ideal for peering at the small pebbles, measured in just centimeters themselves, emitting wavelengths close to their own size. The high-resolution images collected by e-MERLIN under the PEBBLeS project display small, centimeter-scale pebbles strewn in Neptune-like orbits around DG Tau and HL Tau, preparing to form the next generation of exoplanets.
While e-MERLIN remains alone in its quest today, South Africa’s Square Kilometre Array (SKA) is set to join the search early in the next decade. The upcoming array will boast a sensitivity and scale that exceed even those of e-MERLIN, allowing astronomers to view the early stages of planet formation on new levels of fidelity.
“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,” she said.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.