“There’s a Dark Cycle in our Galaxy” –Our Solar System’s Path Through the Milky Way (Weekend Feature)



Astrophysical phenomena derived from the Earth’s winding path through the Galactic disc, and the consequent accumulation of dark matter in the planet’s interior, can result in dramatic changes in Earth’s geological and biological activity. “There’s a cycle in our galaxy; the solar system bobs up and down through the plane of the disk-shaped galaxy—we’re pulled towards the plane, we go through it, we overshoot, we go back,” said Michael Rampino, professor of biology at New York University.

“We are fortunate enough to live on a planet that is ideal for the development of complex life,” says Rampino. “But the history of the Earth is punctuated by large scale extinction events, some of which we struggle to explain. It may be that dark matter – the nature of which is still unclear but which makes up around a quarter of the universe – holds the answer. As well as being important on the largest scales, dark matter may have a direct influence on life on Earth.”


Rampino’s model of dark matter interactions with the Earth as it cycles through the Galaxy could have a broad impact on our understanding of the geological and biological development of Earth, as well as other planets within the Galaxy.

“If the normal stuff, which is just 20% of the matter in the universe by mass, is so complicated, then why should the rest of the 80%, which is dark, be simple?” observes Manoj Kaplinghat, a professor of physics and astronomy at UC Irvine. But, he adds, as it currently stands, the theory requires additional data to back it up.

According to Kaplinghat, this model is novel because it includes a dark disk possibly thick enough to be stable, yet thin enough to match the periodicity in the crater record. He also said this was the first model to account for the motion of the solar system through the spiral arms of our galaxy. The gravitational forces exerted by the spiral arms impede the solar system as it bobs through the plane of the galaxy—which could explain why the periods between comet impacts are not always exactly 35 million years.

Rampino concludes that Earth’s infrequent but predictable path around and through our Galaxy’s disc may have a direct and significant effect on geological and biological phenomena occurring on Earth. In a new paper in Monthly Notices of the Royal Astronomical Society, he concludes that movement through dark matter may perturb the orbits of comets and lead to additional heating in the Earth’s core, both of which could be connected with mass extinction events.

The Galactic disc is the region of the Milky Way Galaxy where our solar system resides. It is crowded with stars and clouds of gas and dust, and also a concentration of elusive dark matter–small subatomic particles that can be detected only by their gravitational effects.

Previous studies have shown that Earth rotates around the disc-shaped Galaxy once every 250 million years. But the Earth’s path around the Galaxy is wavy, with the Sun and planets weaving through the crowded disc approximately every 30 million years. Analyzing the pattern of the Earth’s passes through the Galactic disc, Rampino notes that these disc passages seem to correlate with times of comet impacts and mass extinctions of life. The famous comet strike 66 million ago that led to the extinction of the dinosaurs is just one example.

What causes this correlation between Earth’s passes through the Galactic disc, and the impacts and extinctions that seem to follow?

While traveling through the disc, the dark matter concentrated there disturbs the pathways of comets typically orbiting far from the Earth in the outer Solar System, Rampino observes. This means that comets that would normally travel at great distances from the Earth instead take unusual paths, causing some of them to collide with the planet.

But even more remarkably, with each dip through the disc, the dark matter can apparently accumulate within the Earth’s core. Eventually, the dark matter particles annihilate each other, producing considerable heat. The heat created by the annihilation of dark matter in Earth’s core could trigger events such as volcanic eruptions, mountain building, magnetic field reversals, and changes in sea level, which also show peaks every 30 million years.

In the future, he suggests, geologists might incorporate these astrophysical findings in order to better understand events that are now thought to result purely from causes inherent to the Earth. This model, Rampino adds, likewise provides new knowledge of the possible distribution and behaviour of dark matter within the Galaxy.

In March 2016, Tokuhiro Nimura, a researcher at the Japan Spaceguard Association, which was formed to monitor near-Earth objects that might strike the planet, and his coworkers suggested that the extinctions, global cooling and iridium layer might have been caused by the Solar System passing through a molecular cloud: one of the great clouds of gas and dust in space from which stars form. As dust accumulated in the atmosphere, it would have formed a haze that reflected sunlight and cooled the planet.

The Hubble image at the top of the page shows the night sky within the youthful milky way galaxy 10 billion years ago ablaze with a firestorm of star birth glowing pink clouds of hydrogen.

The Daily Galaxy via New York University and pbs.org and bbc.com

Image Credit: darkmatterspace



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