Our Solar System is in motion and cruises at about 200 kilometres per second relative to the center of the Milky Way.
During its long journey, it has passed through different parts of the galaxy.
Research shows that the Solar System passed through the Orion star-forming complex about 14 million years ago.
The Orion star-forming complex, also known as the Orion molecular cloud complex, is part of a larger structure called the Radcliffe Wave (RW).
The RW was discovered very recently, in 2020. It’s a large, coherent structure that also moves through the galaxy.
It’s a wave-like structure of gas and dust that holds many star-forming regions, including the well-known Orion complex and the Perseus and Taurus molecular clouds.
It’s almost 9000 light-years long and is within the Milky Way’s Orion arm.
The environment in the RW and the Orion complex is more dense, and when the Solar System passed through it, the greater density compressed the Sun’s heliosphere.
This allowed more interstellar dust to enter the Solar System and reach Earth. According to new research, this affected Earth’s climate and left its mark on geological records.
The research, “The Solar System’s passage through the Radcliffe wave during the middle Miocene,” was published in the journal Astronomy and Astrophysics. The lead author is Efrem Maconi, a doctoral student at the University of Vienna.
“We are inhabitants of the Milky Way.”
João Alves, professor of astrophysics, University of Vienna
“As our Solar System orbits the Milky Way, it encounters different Galactic environments with varying interstellar densities, including hot voids, supernova (SN) blast wavefronts, and cold gas clouds,” the authors write.
“The Sun’s passage through a dense region of the interstellar medium (ISM) may impact the Solar System in several ways.”
14 million years ago, Earth was in the Middle Miocene Epoch. Notable events took place in the Miocene. Afro-Arabia collided with Eurasia, mountains were actively building on multiple continents, and the Messinan Salinity Crisis struck the Mediterranean. Overall, the Miocene is known for the Middle Miocene Climatic Optimum (MMCO). During the MMCO, the climate was warm, and the tropics expanded.
However, the Miocene is also known for something else: the Middle Miocene Disruption (MMD). The MMD followed the MMCO and saw a wave of extinctions strike both terrestrial and aquatic life. It happened around 14.8 to 14.5 million years ago, which is in line with when the Solar System passed through the Radcliffe Wave and the Orion complex.
The authors of the new research say the Solar System’s passage through the RW and the Orion complex could be responsible for the MMD.
“Imagine it like a ship sailing through varying conditions at sea,” explains lead author Efrem Maconi in a press release. “Our Sun encountered a region of higher gas density as it passed through the Radcliffe Wave in the Orion constellation.”
The researchers used data from the ESA’s Gaia mission, along with spectroscopic observations, to accurately determine when the Solar System passed through the RW. By tracing the movement of 56 open clusters in the RW, the researchers traced the motion of the RW and compared it with the Solar System’s movement. Their work shows that the two intersected from 18.2 to 11.5 Myr ago. The closest approach occurred between 14.8 and 12.4 Myr ago.
This period of time coincides with the MMD. “Notably, this period coincides with the Middle Miocene climate transition on Earth, providing an interdisciplinary link with paleoclimatology,” the authors write. The correlation is striking, and the researchers say that the influx of interstellar dust shifted Earth’s climate.
“This discovery builds upon our previous work identifying the Radcliffe Wave,” says João Alves, professor of astrophysics at the University of Vienna and co-author of the study. Alves was the lead author of the 2020 paper presenting the discovery of the RW.
“Remarkably, we find that the past trajectories of the Solar System closely approached (dSun–cloud within 50 pc) certain selected clusters while they were in their cloud phase, hinting at a probable encounter between the Sun and the gaseous component of the Radcliffe wave,” the researchers write in their paper.
“We passed through the Orion region as well-known star clusters like NGC 1977, NGC 1980, and NGC 1981 were forming,” Alves said in the press release. “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 that reached Earth during its passage through the RW could have had several effects. The interstellar medium (ISM) contains radioisotopes like 60Fe from supernova explosions, which could have created anomalies in Earth’s geological record. “While current technology may not be sensitive enough to detect these traces, future detectors could make it possible,” Alves suggests.
More critically, the dust could’ve created global cooling.
A 2005 paper showed that Earth passes through a dense giant molecular cloud (GMC) approximately every 100 million years. “Here we show that dramatic climate change can be caused by interstellar dust
accumulating in Earth’s atmosphere during the Solar System’s immersion into a dense GMC,” those researchers wrote. They explained at the time that there was no evidence linking these passages with severe glaciations in Earth’s history.
This new research from Maconi et al. is shedding some light on the issue.
“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,” 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,” says Maconi. “Future research will explore the significance of this contribution.”
With more research to come in the future, there’s most likely more to the story. In any case, one conclusion seems clear: the Earth passed through a region of dense gas that fits in with the Middle Miocene Disruption.
Research like this, when shallowly read, becomes cannon fodder in the tiresome debate about global climate change. The authors are quick to nip that in the bud.
“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,” Macon said.
The researchers also point out some weaknesses in their results. “Our results are based on the tracebacks of the orbits of the Solar System and of the clusters associated with the Radcliffe wave. As noted throughout the text, this method requires some approximations due to inherent difficulties in modelling the past structure and evolution of the gas,” they clarify. They explain that their tracebacks should be thought of as a first approximation of their movements.
However, if they’re right, their work draws another fascinating link between our planet, its climate, and life’s struggle to persist with much larger-scale events beyond Earth.
“Notably, our estimated time interval for the Solar System’s potential location within a dense ISM region (about 14.8–12.4 Myr ago for a distance of 20–30 pc from the center of a gas cloud) overlaps with the Middle Miocene climate transition,” the researchers explain. “During this period, the expansion of the Antarctic ice sheet and global cooling marked Earth’s final transition to persistent large-scale continental glaciation in Antarctica.”
“We are inhabitants of the Milky Way,” said Alves. “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.” In the future, the team led by João Alves plans to study in more detail the Galactic environment encountered by the Sun while sailing through our Galaxy.
Written by Evan Gough/Universe Today.
