Astronomers studying the famous Ring Nebula have uncovered an unexpected and puzzling feature: a massive cloud of iron atoms arranged in a bar-like structure stretching nearly six trillion kilometres across the nebula.
The discovery has raised new questions about the nebula's history and the dramatic events that unfold when stars near the end of their lives.
The Ring Nebula, also known as Messier 57, lies about 2,600 light-years from Earth in the constellation Lyra. First identified in 1779 by French astronomer Charles Messier, it is one of the most familiar objects in the night sky for both professional and amateur astronomers. Despite centuries of observation, the nebula continues to reveal surprises.
Researchers detected the iron structure using a new instrument called WEAVE (WHT Enhanced Area Velocity Explorer) on the William Herschel Telescope in La Palma, part of Spain's Canary Islands. The observations revealed that the iron atoms form a distinct bar across the face of the nebula, a feature unlike anything previously seen in this well-studied object.
According to the research team, the total amount of iron in the bar could be comparable to the mass of Earth's molten iron core. One possible explanation, they said, is that the iron represents the remains of a rocky planet that was vaporised when the nebula's parent star expelled its outer layers. However, the scientists stressed that this idea remains speculative and that other explanations may yet emerge.
"If the origin is planetary, a planet like Earth would contain enough iron to form the bar," said lead author Roger Wesson of Cardiff University and University College London, as quoted by Reuters. "But how that material would end up in such a clearly defined bar shape has no good explanation at present."
The Ring Nebula formed around 4,000 years ago, a relatively short time in cosmic terms, when a star about twice the mass of the Sun exhausted its nuclear fuel. The star expanded into a red giant before shedding its outer layers, leaving behind a dense white dwarf roughly the size of Earth. The glowing shell of gas and dust expelled during this process is what astronomers observe today.
While the nebula appears ring-shaped from Earth, astronomers believe it is actually more like a cylindrical structure viewed end-on. It consists mainly of hydrogen and helium, with small amounts of heavier elements. What makes the newly discovered iron bar particularly intriguing is that no other detected chemical element seems to follow the same distribution.
"This is weird, frankly," said study co-author Janet Drew of University College London. "Its importance lies in the fact that we do not yet have a ready explanation for it. The iron might come from a vaporised planet, but there could also be another process at work that we have not identified."
Planetary nebulas like the Ring Nebula are relatively common, with about 3,000 known in the Milky Way. Studying them helps astronomers understand how stars recycle material into space, enriching the galaxy with elements that later form new stars and planets. The findings may also offer a distant glimpse of the fate awaiting the inner planets of our own solar system, including Earth, when the Sun undergoes a similar transformation billions of years from now.
Researchers say further observations will be needed to unravel the mystery of the iron bar. "We look forward to getting more data to follow up on this discovery," Wesson told Reuters, adding, "and to work out where this iron has come from."
