As our Solar System orbits the Milky Way, it encounters various environments, including dense regions of the interstellar medium. These encounters can expose parts of the Solar System to the interstellar medium, while also increasing the flow of interstellar dust into the Solar System and Earth’s atmosphere. The discovery of new Galactic structures, such as the 9,000-light-year-long Radcliffe wave, raises the question of whether the Sun has encountered any of them. According to new research, the Solar System’s trajectory intersected the Radcliffe wave in the Orion star-forming region between 15 and 12 million years ago (Miocene epoch). Notably, this period coincides with the Middle Miocene climate transition on Earth, providing an interdisciplinary link with paleoclimatology.

As the Solar System orbits the Milky Way, it encounters different Galactic environments with varying interstellar densities, including hot voids, supernova blast wave fronts, and cold gas clouds.

The Sun’s passage through a dense region of the interstellar medium may impact the Solar System in several ways.

For instance, the enhancement of the pressure compresses the heliosphere, exposing some parts of the Solar System to the cold and dense interstellar medium.

Additionally, the amount of interstellar dust loaded into Earth’s atmosphere would increase, potentially enhancing the delivery of radioisotopes, such as iron-60, via dust grains.

The Radcliffe wave is a narrow sinusoidal gas structure, which comprises many known star-forming cloud complexes, such as CMa, Orion, Taurus, Perseus, Cepheus, North America Nebula, and Cygnus.

This gas structure, with an estimated mass of 3 million solar masses, appears to coherently oscillate like a traveling wave and it is thought to be part of the Milky Way’s spiral structure.

“Imagine it like a ship sailing through varying conditions at sea,” said Dr. Efrem Maconi, a doctoral student at the University of Vienna.

“Our Sun encountered a region of higher gas density as it passed through the Radcliffe wave in the Orion constellation.”

Using data from ESA’s Gaia mission and spectroscopic observations, Dr. Maconi and his colleagues pinpointed the Solar System’s passage through the Radcliffe wave in the Orion region.

“This discovery builds upon our previous work identifying the Radcliffe wave,” said University of Vienna’s Professor João Alves.

“We passed through the Orion region as well-known star clusters like NGC 1977, NGC 1980, and NGC 1981 were forming.”

“This region is easily visible in the winter sky in the northern hemisphere and summer in the southern hemisphere.”

“Look for the Orion constellation and the Orion Nebula (Messier 42) — our Solar System came from that direction!”

“The increased dust from this Galactic encounter could have had several effects.”

“It may have penetrated the Earth’s atmosphere, potentially leaving traces of radioactive elements from supernovae in geological records.”

“While current technology may not be sensitive enough to detect these traces, future detectors could make it possible.”

The research indicates the Solar System’s passage through the Orion region occurred between approximately 18.2 and 11.5 million years ago, with the most likely time between 14.8 and 12.4 million years ago.

This timeframe aligns well with the Middle Miocene Climate Transition, a significant shift from a warm variable climate to a cooler climate, leading to the establishment of a continental-scale prototype Antarctic ice sheet configuration.

While the study raises the possibility of a link between the past traverse of the Solar System through its Galactic neighborhood and Earth’s climate via interstellar dust, the authors emphasize that a causal connection requires further investigation.

“While the underlying processes responsible for the Middle Miocene Climate Transition are not entirely identified, the available reconstructions suggest that a long-term decrease in the atmospheric greenhouse gas carbon dioxide concentration is the most likely explanation, although large uncertainties exist,” Dr. Maconi said.

“However, our study highlights that interstellar dust related to the crossing of the Radcliffe wave might have impacted Earth’s climate and potentially played a role during this climate transition.”

“To alter the Earth’s climate the amount of extraterrestrial dust on Earth would need to be much bigger than what the data so far suggest.”

“Future research will explore the significance of this contribution. It’s crucial to note that this past climate transition and current climate change are not comparable since the Middle Miocene Climate Transition unfolded over timescales of several hundred thousand years.”

“In contrast, the current global warming evolution is happening at an unprecedented rate over decades to centuries due to human activity.”

The study was published in the journal Astronomy & Astrophysics.

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E. Maconi et al. 2025. The Solar System’s passage through the Radcliffe wave during the middle Miocene. A&A 694, A167; doi: 10.1051/0004-6361/202452061