Scientists search the earth and sky for clues to our planet’s climate history. Powerful and sustained volcanic eruptions can change climate over long periods of time, and the Sun’s output can change Earth’s climate over millions of years.
But what about interstellar hydrogen clouds? Could these regions of gas and dust change Earth’s climate when the planet meets them?
Not all interstellar clouds are alike. Some are diffuse, some are very dense. New research in Natural Astronomy This suggests that our solar system may have passed through one of the dense clouds two or three million years ago.
The effect is to change the chemistry of Earth’s atmosphere, affecting cloud formation and climate.
Research is „Earth’s direct exposure to the cold dense interstellar medium 2–3 Myr ago.„The lead author is Merav Ober of Harvard University’s Radcliffe Institute for Advanced Study and the Department of Astronomy at Boston University.
„Our results open a new window into the relationship between the evolution of life on Earth and our cosmic surroundings.” – Avi Loeb, associate editor, Institute for Theory and Computation, Harvard University
The Sun moves through a large hole in the interstellar medium (ISM). local bubble. Inside the LP, the Sun’s solar output forms a cocoon Heliosphere. It protects the solar system from cosmic radiation.
Inside the LP, more than the Sun. It also contains other stars, and Local interstellar cloud (LIC). The Sun moves through the LIC and leaves it in a few thousand years. LIC is not very dense.
But in the last few million years, as the Sun has passed through the local bubble, it has encountered much denser clouds than the LIC. Researchers studied the impact these encounters had on the Sun’s ability to carve out a niche for the Solar System and what effect this had on Earth.
„Stars are moving, and now this paper shows not only that they are moving, but that they are undergoing drastic changes.” – Merav Opher, Professor of Astronomy, BU College of Arts and Sciences
„Here we show that in the ISM, which the Sun has passed through for the past two million years, there are cold, compact clouds that can strongly affect the heliosphere. We investigate a scenario where the Solar System passed through a cold gas cloud a few million years ago,” Ober and his colleagues write.
Most of the Sun travels through the thin ISM. The Sun continues to move through the thin ISM without any effect.
„These clouds are abundant around the Sun, but are too dense to cause the heliosphere to contract farther.
However, dense clouds in the ISM are dense enough to dramatically affect the protective heliosphere.
„The ISM near the Solar System consists of a few, sparse, dense, cold clouds known as the Local Ribbon of Cold Clouds,” they write.
One of the clouds in that ribbon is called the Local Leo Cold Cloud (LLCC). It is one of the largest clouds in Ripon, and astronomers have studied it extensively. They know its density and temperature. The researchers haven’t paid much attention to the other clouds in the ribbon, but they expect them to be similar.
The paper’s authors say there is a small chance, about 1.3%, that the Sun passed through the LLCC’s tail.
„We name that region Local Links of Cold Clouds (LxCCs). LxCCs represent almost half of the total mass of the LRCC and are larger than the well-studied LLCC,” they write.
In the past there have been questions about the nature of these clouds.
„Note that these clouds are anomalous and unexplained structures in the ISM, and their origin and physics are not well understood,” the authors write. Their work is based on the assumption that they have not changed significantly in the 2 million years since the alleged encounter.
„We assume here that these clouds have not undergone any significant change in the past 2~Myr, although future work may provide further insight into their evolution.”
The researchers used simulations to study the effect of dense cloud cover on the heliosphere. They say the cloud’s hydrogen density pushed the Sun back, causing the heliosphere to contract, smaller than Earth’s orbit around the Sun.
This brought both the Sun and the Moon into contact with the dense, cold ISM. „Such an event could have had a dramatic effect on Earth’s climate,” they explain.
This junction is supported by the presence of the radioisotope 60Fe in Earth. 60Fe is mainly produced in supernovae and has a half-life of 2.6 million years.
Previous research linked 60Fe to a supernova explosion, where it was embedded in dust grains and then delivered to Earth. It is also on the moon. 244Pu was also released in the supernova ejecta at the same time.
Although there are many uncertainties, the researchers say that the deposition of 60Fe on Earth is through a dense cloud along the hypothesized path of our solar system, which compresses the protective heliosphere and allows the isotopes to reach Earth.
„Our proposed scenario is consistent with geological evidence from the 60Fe and 244Pu isotopes that Earth was in direct contact with the ISM during that period,” they write.
But if a supernova gave off radioisotopes, it must have been very close, and other evidence rules out a supernova source.
„A close supernova explosion contradicts the recent model of local bubble formation,” the authors explain. „The absorption of 60Fe and 244Pu into dust particles is not necessary for this scenario, which they provide specifically for Earth, such as scenes from nearby supernova explosions.”
The question at the heart of this issue is how did this affect the Earth?
An in-depth study of the effects is beyond the scope of this research. The group commented on some possibilities, while cautioning that very little research has been done on the subject.
„Few works have quantitatively examined the climatic effects of such encounters in the context of encounters with dense giant molecular clouds. Some argue that such high densities will deplete ozone in the middle (50-100?km) of the atmosphere and ultimately cool the Earth,” they write.
It’s a leap, but some research suggests that this cooling may have contributed to the rise of our species.
„The origin of our species, Homo sapiens, is hypothesized to have evolved in response to climate change. With the contraction of the Solar System, Earth was directly exposed to the ISM,” they write.
In their conclusion, they remind us that the probability of this meeting taking place is low. but not null.
„Stars are moving, and now this paper shows not only that they are moving, but that they are undergoing drastic changes,” said Ober, a professor of astronomy in the BU College of Arts and Sciences and a member of the university’s Center for Space Physics.
„While the coincidence of the past motion of the Sun with these rare clouds is truly remarkable, the turbulent nature of the ISM and the small current angular size of these clouds mean that the past error ellipse is much larger than the clouds and nothing else. Information, the probability of their encounter is measured to be low, ” they write in their conclusion.
Future work digs deeper into this matter.
Even if this particular meeting didn’t happen, the research is still fascinating. There seem to be a number of confounding variables that led us, and it’s not a stretch to imagine that moving through thick clouds in the ISM played some role at some point.
„Our cosmic environment beyond the solar system rarely affects life on Earth,” said Avi Loeb, director of Harvard University’s Institute for Theory and Computation and co-author on the paper.
„It is exciting to discover that our passage through dense clouds a few million years ago may have exposed Earth to a very large flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic environment.
„We hope that our current work will inspire future work describing the climate consequences of the LRCC in the heliosphere and potential consequences for evolution on Earth,” the authors conclude.
This article was originally published Universe Today. Read on Original article.