Voyager 2 helps reveal ‘blunt bullet’ shape of interstellar space barrier

4 Nov 2019

Artist’s concept of the Voyager spacecraft in space. Image: NASA

There are now two human-made objects travelling in interstellar space after readings confirmed Voyager 2’s passage into the unknown.

Researchers have looked at the data returned by the Voyager 2 spacecraft to confirm that it has entered the interstellar medium (ISM), the region of space outside the bubble-shaped border produced by solar winds. In doing so, it joins Voyager 1 – the only object to reach this far out into the universe.

Less than a year ago, the spacecraft announced its exit from the heliosphere, where hot solar wind meets the cold, dense ISM, 18bn km from Earth. However, new research across five papers has been published documenting new scientific data on the mysterious region of space.

One of those studies, written by a team of researchers from the University of Iowa, confirmed the spacecraft’s passage into the ISM with a notable jump in plasma density by one of its instruments. This jump in plasma is evidence for the craft transitioning from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space.

Illustration showing the heliosphere and the Voyager spacecrafts' current location.

Illustration showing the heliosphere and the Voyager spacecrafts’ current location. Image: NASA JPL

‘Like looking at an elephant with a microscope’

“In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true,” said Don Gurnett, corresponding author on the study.

“We show with Voyager 2 – and previously with Voyager 1 – that there’s a distinct boundary out there. It’s just astonishing how fluids, including plasmas, form boundaries.”

Voyager 2’s breaking of the ISM bubble occurred at 119.7 astronomical units (AU), whereas Voyager 1 passed through at 122.6 AU. This, the team said, gives valuable insight into the heliosphere’s structure, implying it is symmetric, at least where the two spacecraft passed through.

“There’s almost a spherical front to this,” added Gurnett. “It’s like a blunt bullet.” The data also suggests the heliosphere has varied thickness, with Voyager 1 sailing 10 AU farther than its ‘sibling’, despite initial thoughts that Voyager 2 would break through the ISM first.

Bill Kurth, co-author of the study, said: “It’s kind of like looking at an elephant with a microscope”.

“Two people go up to an elephant with a microscope, and they come up with two different measurements,” he said. “You have no idea what’s going on in between. What the models do is try to take information that we have from those two points and what we’ve learned through the flight and put together a global model of the heliosphere that matches those observations.”

Colm Gorey was a senior journalist with Silicon Republic