Journey to the Sun
Abstract: NASA heliophysics research studies a vast system stretching from the Sun to Earth to far beyond the edge of the planets. Studying this system – much of it driven by the Sun’s constant outpouring of solar wind -- not only helps us understand fundamental information about how the universe works, but also helps protect our technology and astronauts in space. NASA seeks knowledge of near-Earth space, because -- when extreme -- space weather can interfere with our communications, satellites and power grids. The study of the Sun and space can also teach us more about how stars contribute to the habitability of planets throughout the universe.
Mapping out this interconnected system requires a holistic study of the Sun’s influence on space, Earth and other planets. NASA has a fleet of spacecraft strategically placed throughout our heliosphere -- from Parker Solar Probe at the Sun observing the very start of the solar wind, to satellites around Earth, to the farthest human-made object, Voyager, which is sending back observations on interstellar space. Each mission is positioned at a critical, well-thought out vantage point to observe and understand the flow of energy and particles throughout the solar system -- all helping us untangle the effects of the star we live with.
A Case for a Mission to Earth-Sun L4
The goal of Heliophysics science is to improve understanding of the Heliophysics system. Scientific understanding of coupled processes at the Sun, the Heliosphere and the Magnetosphere/Ionosphere system is best demonstrated by successfully forecasting of the behavior of the entire system. Besides that, a forecasting capability may have important real-world applications. Placing a sentinel spacecraft at Earth-Sun (E/S) L1, ~1.5M km upstream of Earth, has demonstrated utility for forecasting magnetospheric space weather through in-situ measurements of solar wind structures up to one hour before they reach Earth. The usefulness of E/S L5, 60 degrees behind Earth in its orbit, has recently been argued as important in this context as well, specifically through providing a “side-view” of the Earth-Sun line that can be monitored by heliospheric imagers, potentially extending lead-time, and by “peeking” around the east limb of the Sun in order to have advance knowledge of any active regions before they reach the visible disk as viewed from Earth. A vantage point that not been paid sufficient attention to in the scientific literature is the E/S L4 location, 60 degrees ahead of Earth in its orbit. The considerable advantages of this location for Heliophysics science and associated space weather applications, including a rationale for a subset of the needed scientific payload elements, will be discussed.