As the Moon orbits the Earth, the Earth orbits the Sun and the Sun orbits the center of the Milky Way, oscillating up and down relative to the galactic plane.
A new study has suggested that this movement of our star through the galaxies potentially takes us through regions of space that could affect our planet’s climate. According to the study, the Solar System may have been passing through an interstellar cloud so dense that it could disrupt the flow of the solar wind and potentially cool the planets.
The Solar System is somewhat shielded from the interstellar medium (ISM) by our heliosphere.
“The Sun sends out a constant stream of charged particles called the solar wind, which eventually travels past all the planets to about three times the distance to Pluto before being slowed down by the interstellar medium,” explains NASA. “This forms a giant bubble around the Sun and its planets, known as the heliosphere.”
The Solar System currently resides in a “Local Bubble” or “Local Interstellar Cloud” (LIC) 1,000 light-years across. This “bubble” is much less dense than typical interstellar space, with 0.001 particles per cubic centimeter compared to the typical 0.1 atoms per cubic centimeter. The solar system will leave this rarefied region of space in the next few thousand years and re-enter the interstellar medium.
By looking at the path of the Solar System and mapping the local ribbon of cold clouds, the team found that we likely traveled through denser regions in the past.
“There are cold compact clouds in the ISM that the Sun has been passing through for the past few million years, which could have drastically affected the heliosphere,” the team explains in their paper. “We are investigating a scenario where the Solar System passed through a cold cloud of gas several million years ago.”
Although research into the effects of passing through such regions has been sparser than the atoms in the local bubble, the team believes it may have caused our heliosphere to contract, which in turn affected our climate. Our heliosphere is protective, and as it contracts, some of the material in these denser regions could reach Earth.
“Large amounts of neutral hydrogen due to encounters with cold clouds with densities above 1000 cm-3 will change the chemistry of Earth’s atmosphere,” the team wrote. “Very few papers have examined the climatic effects of such encounters quantitatively in the context of encounters with dense giant molecular clouds. Some argue that such high densities would damage ozone in the middle atmosphere (50–100 km [31–62 miles]) and eventually cool the Earth.”
The team claims that geological evidence of increased amt 60Fe (iron 60) a 244Isotopes of Pu (plutonium 244) found in ice cores, oceans, Antarctic snow and lunar samples could be evidence that these particles reached Earth when we passed through the Cold Cloud Local Feature 2 million years ago.
These isotopes are spewed out by the merger of supernovae and neutron stars, which are then captured by interstellar dust. These isotopes in the geological record were previously explained as having been sent here by a nearby supernova, but the current team believes they could be better explained by particles trapped in the cloud, as a nearby supernova would collapse the heliosphere to within 1 AU (the distance between the Earth and the Sun) , while a more distant supernova would not be enough to save 60Fe on Earth.
“This paper is the first to show quantitatively that there was a collision between the Sun and something outside the solar system that would have affected Earth’s climate,” Boston University space physicist Merav Opher said in a statement, adding later, “but once Earth moved away from the cold cloud, the heliosphere engulfed all the planets, including Earth.”
According to the team, the contraction of the heliosphere could have taken hundreds of years to a million years, and it is likely that we will encounter another such cloud contracting through the heliosphere within the next million years.
While this is interesting, there is much more to discover.
“This work should be reevaluated using modern atmospheric modeling,” the team writes. “It has been suggested that climate change around this time may have influenced human evolution. The hypothesis is that the origin of our species Homo sapiens it was shaped by the need to adapt to climate change. As the heliosphere contracted, the Earth was exposed directly to the ISM.”
The article is published in Nature Astronomy.