Mapping the Best Route for a Spacecraft Traveling Beyond the Sun’s Sphere of Influence

The heliosphere, our solar system’s personal shield, protects the planets from galactic cosmic rays. These extremely energetic particles, accelerated outwards from events like supernovas, would cause significant damage if not for the heliosphere’s absorption.

Currently, the scientific community is exploring mission concepts for an interstellar probe that travels beyond the sun’s sphere of influence to understand better the boundaries or contours of this protected space. A study led by the University of Michigan, published in Frontiers in Astronomy and Space Sciences, provides recommendations to maximize scientific measurements to understand our home in the heliosphere from the outside.

“Without such a mission, we are like goldfish trying to understand the fishbowl from the inside,” said Sarah A. Spitzer, a postdoctoral research fellow at U-M and first author of the study.

The study suggests that the best possible exit route is through the side of the heliosphere’s tail end. The interaction of the heliosphere with the local interstellar medium forms the shape of our heliosphere and influences the composition of the space environment within the solar system, including near Earth.

“A future interstellar probe mission will be our first opportunity to really see our heliosphere, our home, from the outside, and better to understand its place in the local interstellar medium,” said Spitzer.

The Voyager 1 and 2 spacecraft are the only missions to have potentially left the heliosphere. Now, 46 years after its 1977 launch, the spacecraft is well beyond its intended mission lifetimes and can no longer provide complete plasma measurements necessary for improving our understanding of the heliosphere’s boundaries.

A future interstellar probe mission aims to travel beyond the heliosphere to collect samples from the local interstellar medium. The research team analyzed the scientific merit for six possible interstellar probe trajectories ranging from noseward to tailward directions. The researchers concluded that a trajectory intersecting the heliospheric flank toward the tailward direction would provide the best perspective on the shape of the heliosphere and maximize scientific outputs.

In its 46-year journey, the Voyager spacecraft has traveled about 163 astronomical units (15.2 billion miles) away from Earth. Looking ahead, a future interstellar probe will be designed for a 50-year mission intended to travel around 400 astronomical units and may even last to around 1,000 astronomical units, providing an unprecedented view of our heliosphere and the interstellar medium beyond.