Scientists have traditionally posited that the heliosphere, the huge bubble of charged particles that the sun blows around itself, has a rounded leading edge, where the solar system barrels through space, with a long tail streaming behind it.

Just two spacecraft, NASA's Voyager 1 and Voyager 2 probes, have directly sampled the boundary, and two data points are far from sufficient to outline the heliosphere's contours. .

For example, they've studied measurements of galactic cosmic rays, super-energetic charged particles that zoom into our neighborhood from very far away.

Researchers have also carefully tracked "energetic neutral atoms" that bounced sunward after interacting with the interstellar medium, the vast cosmic sea that lies beyond the heliosphere.

The recent study takes a new look at such data and also includes measurements of "pick-up ions" made by NASA's New Horizons Pluto probe, which is currently more than 4.3 billion miles (6.9 billion km) from Earth. .

Pick-up ions are carried along by the solar wind, the stream of charged particles flowing continuously from the sun.

(This flow is blocked by the interstellar medium to form the boundary of the heliosphere.) Pick-up ions are much hotter than the particles that make up most of the solar wind, which contributes to the heliosphere's weird shape, study team members found.

"What we did was separate these two components of the solar wind and model the resulting 3D shape of the heliosphere.".

The termination shock is the heliosphere boundary region, where solar wind particles begin pressing into the interstellar medium and slow to less than the speed of sound.