Planetary Sciences AGU News

Here Comes the Sun

This August, we look at the relationship we have to our closest star for AGU’s Centennial.

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One year ago this month, NASA’s Parker Solar Probe launched from Cape Canaveral in Florida on a mission to the center of the solar system. Passing closer to the Sun than any mission before it, the spacecraft is now taking the first in situ measurements of the corona. Soon, we may have insight not only into the baffling coronal heating problem but also into the complex Earth-Sun relationship—the theme for this month as part of our yearlong AGU Centennial celebrations.

Humans have surely been studying our closest star for as long as we could look up at the sky, though the modern era of heliophysics hit its stride in the 1950s. During the 1957–1958 International Geophysical Year (IGY), physicist James Van Allen played a key role in turning interest to the particles coming from space and interacting with our planet. He’d already been launching instruments with his University of Iowa students to study cosmic rays and probe aurorae. At the end of the IGY, an instrument package designed by Van Allen launched aboard Explorer 1, which collected data confirming the existence of the radiation belts that now carry his name, composed of charged particles carried to Earth by solar wind. (AGU awarded Van Allen its prestigious William Bowie Medal in 1977, and he later served as president of the organization from 1982 to 1984.)

In our August cover story, a team of scientists show how far we’ve come in understanding the Earth-Sun relationship and what challenges remain. Their group studies the response of Earth’s climate to solar variability, which involves an intricate statistical analysis to extract its actual effects from natural variability and anthropogenic effects. They suggest that modern analysis should use a newer observation data framework that takes into account variations at specific wavelengths, but these observations must be made from space from multiple well-calibrated instruments, making it a challenge even in an age when we can send spacecraft to make observations within spitting distance of the Sun’s surface. Solar physicists around the world are collaborating to create these data sets, as the team reports, and the result will eventually be a deeper understanding of how the Sun’s variability can affect us over the long term here on Earth.

The thermosphere is particularly sensitive to this variability, and another team of scientists recently published results from a study of how infrared power from two solar cycles affected this outer layer of Earth’s atmosphere. Because this radiative energy can cause the thermosphere to change density, this relatively new field of study can provide helpful information for spacecraft, including the International Space Station, that orbit through it.

Eos reports on a particularly intriguing result, in which scientists offer evidence that planetary alignment in the solar system may be what regulates the Sun’s 11-year sunspot cycle. They were able to match up, with decent regularity, sunspot minima with the alignment of Venus, Earth, and Jupiter in their orbits. Using simulations, these researchers “showed that even a weak tidal tug of 1 meter per second every 11 years forced unstable magnetic twists to pulse with that same period,” and indeed, the simulation showed the solar dynamo’s polarity flipping every 22 years, just as it does on the Sun.

We hope the Sun continues to shine on these studies explaining the unique give and take between our planet and the star it formed around over 4 billion years ago.

—Heather Goss (@heathermg), Editor in Chief

Citation: Goss, H. (2019), Here comes the Sun, Eos, 100, https://doi.org/10.1029/2019EO130151. Published on 01 August 2019.
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