THE QUEST TO FIND THE EDGE OF THE SOLAR SYSTEM

NASA's newly launched IMAP mission is set to tell us more about the boundary between our Solar System and interstellar space than ever before

- by JONATHAN O'CALLAGHAN

Earth exists in a bubble. Our atmosphere forms a protective barrier between everything on the planet's surface and the near-empty vastness of space. But it's not the only bubble Earth sits inside. Beyond our familiar atmospheric cocoon lies a much larger bubble, an invisible boundary carved by the Sun itself.

This bubble, known as the heliosphere, is enormous. It encompasses the entire Solar System, spanning such a vast distance that only two spacecraft have ever managed to leave it. Launched in 1977, NASA's Voyager 1 and 2 passed beyond the heliosphere into interstellar space – the region between stars – in 2012 and 2018 respectively. They're the first man-made objects to ever travel beyond the Sun's protective bubble, and are still transmitting data about the charged particles and plasma waves that can be found there.

But astronomers want to learn more about the heliosphere and what lies beyond it. What's its exact size and shape? How do solar particles emitted by the Sun interact with interstellar space once they pass through it? And how effective is it at protecting us from the high-energy cosmic rays coming in from outside?

"We're still putting together a lot of pieces about how the local interstellar medium really interacts with the heliosphere," says Dr Ralph McNutt, a physicist at Johns Hopkins University Applied Physics Laboratory (JHUAPL) in Maryland, in the US.

It's hoped a new $782 million (£580 million) NASA mission will help put more of those pieces together. The Interstellar Mapping and Acceleration Probe (IMAP) spacecraft was launched on 24 September 2025. And instead of spending decades travelling to the edge of the heliosphere, over the next few months it'll travel to a position about 1.5 million kilometres (one million miles) from Earth called Lagrange Point 1 (L1). Once there, unhindered by interference from Earth, IMAP can carry out its purpose: study the heliosphere, from afar.