Explorations of Solar Activity and the Heliophysical Environment to Interplanetary Space Weather

Abstract:

As human activity expands into the solar system, the need for accurate space weather and space climate forecasting is expanding, too. Space probes are now orbiting or en route for flybys of Mercury, Venus, Earth and the Moon, Mars, Vesta, Ceres, Saturn, and Pluto. Agencies around the world are preparing to send robotic spacecraft into interplanetary space. Each of these missions (plus others on the drawing board) has a unique need to know when a solar storm will pass through its corner of space or how the subsequent solar cycle will behave. Ultimately, astronauts will follow, traveling beyond Earth orbit, and their need for interplanetary space weather and climate forecasting will be even more compelling.

Until recently, forecasters could scarcely predict space weather in the limited vicinity of Earth. Interplanetary forecasting was even more challenging. This began to change in 2006 with the launch of the twin STEREO probes followed almost four years later by the Solar Dynamics Observatory. These three spacecraft along with SOHO now surround the sun, monitoring active regions, flares, and coronal mass ejections around the full circumference of the star. No matter which way a solar storm travels, the STEREO-SOHO-SDO fleet can track it. Observations from future missions like Solar Probe Plus, Solar Orbiter and Aditya-L1 will greatly enhance our understanding of the inner hemisphere from a solar system perspective. Missions like SDO and Kepler are giving us a better view of sun-like stars and their inner workings to understand their cyclic behavior, while missions like MAVEN and JUNO are investigating interaction of solar radiation and solar wind with Mar’s upper atmosphere and Jupiter’s intense auroras, a branch of heliophysics called “comparative heliophysics”.

Finally, scientific research could be the greatest beneficiary of comparative heliophysics/interplanetary space weather. What happens to asteroids, comets, planetary rings, and planets themselves when they are hit by solar storms? Finding out often requires looking at precisely the right moment. As the scope of space weather forecasting expands to other planets, it also interacts with climate research. Climate refers to changes in planetary atmospheres and surfaces that unfold much more slowly than individual storms. There is no question that solar activity is pertinent to climate time scales. The radiative output of the Sun, the size and polarity of the Sun’s magnetic field, the number of sunspots, and the shielding power of the Heliosphere against cosmic rays all change over decades, centuries, and millennia.

To capitalize on the science that will naturally emerge from the growth and modernization of the observational assets, researchers from many different fields will have to work together. Interplanetary space weather and climate forecasting is essentially interdisciplinary. Progress requires expertise in plasma physics, solar physics, weather forecasting, planetary atmospheres, and more. In the past, NASA has assembled such teams under the umbrella of virtual institutes, where widely dispersed researchers confer from a distance using the Internet and other forms of tele-collaboration. Interplanetary space weather might call for a similar approach. One thing is sure: The Sun is not waiting and the stakes are as big as the solar system itself.