Amazing stuff! How does the temporal dynamics of the heliosphere (shrinking/expanding) influence climate on Earth while our solar system travels through the Milky Way?
Notice the researchers limit the frequency of such disturbances to "every couple of million years", while I would propose it may happen more often.
If I am not mistaken, we still know very little about the trajectory of our solar system traversing the interstellar space within the Milky Way galaxy. For example, the researchers investigated only the extreme event when the heliosphere shrank so much that the Earth was no longer protected by heliosphere anymore.
Notice Merav Opher (the author of the paper below) has extensively written about the influence of the heliosphere on paleoclimate on Earth for several years (see e.g. her webpage on this subject).
I have been arguing here on blog for some years that the climate (e.g. long warming and cooling periods) on Earth may significantly be influenced by our solar system traveling or its trajectory through the Milky Way galaxy.
"... In new research ... trace the trajectory of the heliosphere, the massive bubble created by our sun that envelops our solar system, as it moved through our galaxy and influenced Earth's climate along the way. ...
Our heliosphere orbits around the center of our galaxy, the Milky Way. Throughout the sun's 4.6-billion-year existence, our heliosphere has traversed various regions within our galaxy. In a paper ..., researchers ... used computer modeling to reverse-engineer the path of the heliosphere through our galaxy, revealing that the environments it passed through may have triggered changes on Earth. ...
ran simulations that showed the sun has encountered frigid expanses of gas and dust at least three times in the past few million years. In these instances, massive interstellar "cold clouds" pushed against the heliosphere to such an extent that it shrank to smaller than Earth's orbit, stranding our planet outside the sun's protective shield.
These exposures—approximately 2–3 million years, 6–7 million years and 13–14 million years ago—would have exposed Earth's atmosphere to different surroundings. The simulation results match geologic evidence: Elements prevalent in interstellar dust appear in deep-sea sediment core samples, Antarctic snow and lunar samples from these periods.
These heliosphere collapse events may also explain ancient climatic patterns on Earth. In the simulations, when Earth's atmosphere was exposed to a cold, dense galactic hydrogen cloud, water vapor content increased and upper-atmospheric dynamics shifted, ultimately altering conditions at the surface. In summary, our heliosphere's trips through colder regions in our galaxy may be a key factor in driving some of Earth's ancient climate changes, including possible ice ages. ..."
From the abstract:
"This article reviews today's open issues, frontiers of research, and advances in our understanding of the heliosphere throughout the Sun's last 10 million years. Today's heliosphere, the cocoon formed by the solar wind as it moves through the Galaxy, engulfs all the planets extending in the nose direction to ∼120 astronomical units (AU).
- ▪ The Sun moves at 19 pc/Myr and has traversed many different structures in the interstellar medium that affect the heliosphere, at times collapsing it to sub-astronomical-unit scales. These periods of collapse introduce climate and radiation changes in Earth's environment.
- ▪ The frequency of such encounters could be as often as every couple of million years, making it a major external disturbance to the development of life on Earth.
- ▪ Stepwise shifts in past global climate, seen in deep-sea sediment cores, indicate intervals of more rapid cooling at 13–14 Mya, 6–7 Mya, and 2–3 Mya, for which the driving mechanisms are subject to ongoing debate. Such cooling events might be triggered by heliosphere collapse."
Understanding the Heliospheric Shield: Laying the Groundwork to Predict Habitable Astrospheres (open access)
Fig. 1 Schematic of the heliosphere. Several elements that form the heliosphere are noted (see also the definitions in the margins throughout this article). The width of the sector region is expected to vary with the solar cycle.
Figure 3
(a) The heliosphere of today is immersed in a warm ISM ...
(b) The heliosphere of the past after the Sun encountered dense cold clouds ... that compressed the heliosphere to sub-astronomical-unit scales
Abbreviation: AU, astronomical unit; ISM, interstellar medium.
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