Solar Wind Levels Down
The Ulysses spacecraft (the one I wrote about a few months back that’s nearing the end of its mission) has measured the lowest levels of solar wind output in 50 years (since the beginning of the Space Age). What’s going on with the Sun? And, does this have implications for Earth?
The solar wind plasma is a stream of charged particles ejected from the Sun’s upper atmosphere. It flows past and interacts with every planet in our solar system. The solar wind ebbs and flows as solar cycles come and go, and right now there’s minimal activity on the Sun. In fact, it has been in a state of low activity for much longer during this current solar cycle than astronomers expected.
So, how does this affect Earth? Let’s talk about the protective properties of the solar wind. Its far limit (that is, the edge of the expanding “bubble” blown out around the solar system by the solar wind) pushes against the interstellar medium. That limit is called the “heliopause.” It acts as sort of an umbrella to protect the rest of the solar system against winds from other stars and wards off a significant portion of cosmic rays (high-energy particles) from outside the galaxy.
Galactic cosmic rays are radiation carriers, and if the heliopause gets smaller and weaker (and since the solar wind is at an all-time low, there could be some diminishment of the protective barrier of the heliopause), more galactic cosmic rays could make their way to the inner solar system–and Earth. How this affects us depends on much gets through. But, it’s not a dire thing. The heliosphere isn’t collapsing. Far from it. But, these measurements of solar wind output from Ulysses are giving us a new look at solar activity. Is it normal for the Sun to be so quiet? To ramp down its solar wind? Good questions.