At first glance, the night sky appears still. But in reality, everything moves, our Solar System being no exception. As it drifts along the Milky Way, it encounters unseen forces—dense clouds of interstellar gas, remnants of ancient supernovae, and gravitational waves rippling through the galaxy. Now, scientists have uncovered evidence that between 18 and 11 million years ago, the Solar System plunged into the Milky Wave’s largest structure: the Radcliffe Wave.
Through the Radcliffe Wave
Astronomers reconstructed the Solar System’s movement relative to the Milky Way’s core and found it passed through the Radcliffe wave, a star-forming gas cloud that snakes through our galactic neighborhood. What’s more, this passage aligns with a major shift in Earth’s climate.
The Radcliffe Wave is a massive, undulating structure filled with dense clouds of gas and dust, stretching across several prominent star-forming regions, including Orion, Taurus, and Perseus. The Solar System’s closest approach to Radcliffe, researchers estimate, occurred around 14 million years ago.
This journey may have altered the light of distant stars reaching Earth. “If we are in a denser region of the interstellar medium, that would mean that the light coming from the stars to you would be dimmed,” Efrem Maconi, an astrophysicist at the University of Vienna and lead author of the new study, told New Scientist. “It’s like being in a foggy day.”
His team reconstructed the past motion of 56 young star clusters that trace the Radcliffe wave, using their trajectories to infer the movement of the structure itself. Their analysis based on data from ESA’s Gaia mission shows that the Sun not only passed through the wave—it did so at a time when Earth was undergoing a dramatic transformation.
Did Interstellar Dust Help Cool the Earth?
Fourteen million years ago, Earth was transitioning into a cooler era. The Antarctic ice sheets expanded, and the planet moved away from a previously warm, tropical period known as the Middle Miocene Climatic Optimum. Maconi and his colleagues suspect that the influx of interstellar dust from the Radcliffe Wave may have played a role in this shift.
“Imagine it like a ship sailing through varying conditions at sea,” Maconi said. As the solar system passed through this region, its denser environment may have compressed the Sun’s protective bubble—the heliosphere. With the Sun’s shield weakened, interstellar dust and cosmic radiation could have more easily reached Earth’s atmosphere. A subtle alteration in the planet’s radiation balance could have possibly contributed to global cooling.
There’s also a chance this dust left traces in Earth’s geological record. One potential clue is the presence of iron-60, a rare radioactive isotope that originates from supernovae. If scientists can detect a spike in iron-60 deposits from this time period, it could serve as a cosmic fingerprint of the Solar System’s passage through the wave. However, finding this evidence won’t be easy. “Looking back in time is hard—no matter if you’re doing it in space or Antarctica,” astronomer Teddy Kareta of Lowell Observatory, who was not involved in the study, told Live Science.
Not everyone is convinced that the Radcliffe Wave’s dust caused significant change to Earth’s climate. Ralph Schoenrich, an astrophysicist at University College London, remains skeptical. “A rule of thumb is that geology trumps any cosmic influence,” he told New Scientist. Major climate shifts, he argues, are more likely to stem from terrestrial changes—shifting continents, ocean currents, and atmospheric chemistry.
Despite this skepticism, the idea of interstellar encounters shaping Earth’s history is gaining traction. The Radcliffe Wave, discovered only in 2020, is still revealing its secrets. Researchers are now eager to explore how past movements of the solar system might align with other climatic and evolutionary events in Earth’s history.
“We are inhabitants of the Milky Way,” said João Alves, an astrophysicist at the University of Vienna and co-author of the study. “The European Space Agency’s Gaia Mission has given us the means to trace our recent route in the Milky Way’s interstellar sea, allowing astronomers to compare notes with geologists and paleoclimatologists. It’s very exciting.”
The findings appeared in Astronomy & Astrophysics.
