The sun does much more than provide Earth with light and warmth.
Two new studies suggest that events in the sun’s distant past—from traveling through cold clouds in the Milky Way to producing enormous solar eruptions—may have played an important role in shaping Earth’s climate.
In one study, scientists supported by NASA examined how our entire solar system has moved through different regions of the Milky Way.
The solar system is surrounded by a huge protective bubble called the heliosphere, which is created by charged particles constantly flowing from the sun.
Normally, this bubble helps shield Earth from material traveling through interstellar space.
But the sun and its planets are also moving around the center of the Milky Way, passing through very different galactic environments along the way.
Researchers at NASA’s SHIELD center used computer models to reconstruct this journey. Their simulations suggest that the solar system encountered extremely cold, dense clouds of gas and dust at least three times during the past several million years.
These encounters may have occurred around 2–3 million, 6–7 million and 13–14 million years ago.
The pressure from the clouds could have compressed the heliosphere until it became smaller than Earth’s orbit.
That would have temporarily left Earth outside the sun’s protective bubble and directly exposed to the surrounding interstellar environment.
Intriguingly, scientists have found elements associated with interstellar dust in deep-sea sediments, Antarctic snow and lunar samples dating from these periods.
The simulations also suggest that exposure to dense clouds of hydrogen could have changed Earth’s atmosphere, increasing water vapor and altering activity in the upper atmosphere.
These effects may eventually have influenced temperatures at Earth’s surface and could help explain some ancient periods of climate change, including possible ice ages.
A second study explores a much earlier mystery known as the “Faint Young Sun paradox.”
Around 3 billion years ago, the young sun was only about 70% as bright as it is today. Earth should therefore have been largely frozen. Yet geological evidence shows that liquid water existed on the planet.
NASA scientist Vladimir Airapetian and colleagues think the young sun’s violent behavior may provide part of the answer. Observations of other young sun-like stars show that they can produce frequent “superflares”—enormous eruptions that send high-energy particles into space.
To investigate what such eruptions might have done to early Earth, researchers recreated its ancient atmosphere in a laboratory chamber. They then bombarded the gases with protons to mimic particles from solar superflares.
The experiment produced nitrous oxide, a greenhouse gas far more powerful at trapping heat than carbon dioxide. Computer simulations showed that even if only a small fraction survived the young sun’s intense ultraviolet radiation, it could have helped keep equatorial temperatures around 5°C—warm enough for liquid water.
Those cool but above-freezing conditions may even have helped chemical reactions important to the emergence of life.
Together, the studies reveal Earth’s climate history as part of a much bigger story. Our planet has always been connected to an active sun traveling through a changing galaxy—and that cosmic journey may have helped make Earth the world it is today.
Source: KSR.
