Title: The Solar System’s passage through the Radcliffe wave during the middle Miocene
Authors: E. Maconi, J. Alves, C. Swiggum, S. Ratzenböck, J. Großschedl, P. Köhler, N. Miret-Roig, S. Meingast, R. Konietzka, C. Zucker, A. Goodman, M. Lombardi, G. Knorr, G. Lohmann, J. C. Forbes, A. Burkert, M. Opher
First Author’s Institution: University of Vienna, Department of Astrophysics, Türkenschanzstraße 17, 1180 Wien, Austria
Status: Published to ApJ, February 2025
The history of Earth is littered with examples of space phenomena influencing life on our planet. From its earliest days, such as with water being carried to Earth by comets, to the most famous example, the extinction of the dinosaurs by meteor strike. These events are excellent reminders that even though we think of space as vast and empty, on large scales it isn’t and we very much do interact with the larger galaxy.
Within the galaxy, there are numerous structures that our solar system can interact with, such as molecular clouds and spiral arms. One of these such structures is the subject of today’s paper: the Radcliffe wave.
The Radcliffe wave is a close-by, relatively compact, stream of gas that houses numerous star clusters and stellar nurseries. How it formed is still up in the air, but evidence points to it being potentially formed from a past merger. Interestingly, there’s a chance that our own Solar System might have passed through it just a few million years ago. And if that’s the case, there’s a chance that it might have left a distinct mark on Earth, specifically on its climate. This is because the dense gas within the wave could have compressed the Sun’s heliosphere through ram pressure to the point that large parts of the Solar System would be exposed to the interstellar medium (ISM). In addition, the entire Solar System would be enriched with significantly higher densities of dust, which would affect the amount of radiation that planets received from the Sun. In short, there’s a chance that passage through the Radcliffe wave could have caused a period of global cooling on Earth. But did it?
Looking Back in Time
To answer this question, the authors of today’s paper pulled data from a variety of astronomical and geological sources. They started by identifying open star clusters associated with the Radcliffe wave, drawn from ESA’s Gaia space telescope. This is important for two reasons: Firstly it allowed the authors to get relatively precise ages and masses for the existing stars within each cluster, which is important for understanding the potential properties of the cloud from which each cluster originally formed . And secondly, it allowed them to get very precise distances and velocities for the currently existing gas clouds closely located to each cluster. From this information, they were then able to integrate the orbits of the gas and clusters to determine where the Radcliffe wave was located in the past few million years. They then also integrated the orbit of the Sun to determine where, if any, crossings with the Radcliffe wave occurred.
Figure 1: Here, the authors compared the past locations of the gas and star clusters within the Radcliffe Wave to the past locations of the Sun. From this plot it’s clear that at different points in the Sun’s history (its path shown by the red bands) mainly between 10 and 20 Myrs ago, it was passing through sections of the Radcliffe Wave. Adapted from Figure 3 in the paper.
The (Glacially) Cool Results
Figure 2: Here we compare the global atmospheric concentrations of carbon dioxide and δ18O (AKA the ratio of oxygen isotopes), both of which are good tracers for global temperature against time. The vertical black lines indicate when the Earth might have been exposed to the ISM due to compression of the Sun’s heliosphere. As you can see, there is a measurable downturn starting as the Earth enters the cloud. Adapted from Figure 4 in the paper.
The authors found that there was a greater than 50% chance that in the past 10-20 million years, the Sun did in fact cross through parts of the Radcliffe Wave! Specifically, our solar system likely passed through the gas clouds of around six different open clusters at various points. But how does that timescale compare to Earth’s geologic history? Well, during the proposed crossing time, the Earth was actually going through a climate transition during the Middle Miocene, which resulted in large numbers of glaciers and overall global cooling. But when the amount of cooling in the Miocene was compared to the Pleistocene cooling, which occurred less than 3 million years ago, the authors found that the expected drop in solar radiation was not fully explainable by the Radcliffe wave. However, their measured contributions were also very notable, not zero! This means that even if the Radcliffe wave didn’t cause an ice age, there’s a chance it certainly contributed. And given that evolution during the Miocene was crucial for humanity, if that is the case, I’m very grateful Earth got to hang ten and ride the (Radcliffe) wave.
Astrobite edited by Veronika Dornan
Author
I’m a 4th year graduate student at the University of Utah. I’m a galactic archeologist, and my specific research focus involves using stellar populations within the Milky Way to study its chemical and dynamical history!
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