What’s at the edge of our solar system? That’s easy, right? Interstellar space! Sure, but the boundary between the two isn’t as clearcut as you might think.
A new paper published today in Nature Astronomy describes the magnetic bubble around the solar system as one that’s slanted, fluctuates in size and has a rippled surface.
The bubble is referred to as the heliosphere, with the actual boundary called the heliopause.
It’s what stops cosmic rays from striking Earth and mutating DNA, wiping out all life.
The new data comes from the Interstellar Boundary Explorer (IBEX), a NASA satellite in orbit of Earth that’s been studying the shape and nature of the heliosphere since it launched in 2008. It can map the entire sky every six months.
Since then the Voyager 1 and Voyager 2 probes have passed through the heliopause and exited the heliosphere and are now moving deeper into interstellar space.
While those two spacecraft—limited through they are given they launched in the late 1970s—have been able to take in-situ measurements, IBEX has a much larger perspective, albeit from much farther away.
What IBEX is studying is effectively the extent of the solar wind. Solar wind is charged particles from the Sun. Where they cease is where the Sun’s influence ceases. That’s the logical extent of the solar system.
What this data from IBEX reveals is that in late 2014 the solar wind dynamic pressure increased by roughly 50% over a period of 6 months, which allowed the satellite to resolve the heliosphere and heliopause in 3D and see that they were both rippled and oblique to the local interstellar medium.
It also detected that the heliosphere’s extent radically changed depending on where it measured.
In short, the bubble around the solar system is not uniform and symmetric, but has huge variation in its shape and extent. The differences can stretch to 16 astronomical units. That’s 16x the Sun-Earth distance, or just shy of the distance from the Sun to Uranus. The heliosphere is thought to stretch to about 100 au from the Sun (about twice as far as Pluto’s farthest point in its egg-shaped orbit), but as this research indicates, it’s hugely variable and depends on when and where you measure it.
This data from IBEX contrasts with data collected from the Voyager probes, indicating large differences in the heliosphere boundaries in the northern versus southern hemispheres. It appears that the extent of the heliosphere where Voyager 1 passed though it in 2012 increased in the years after, but not enough to catch it up.
However, the results do suggest that a spacecraft could exit the solar system only to be swallowed up by it again years later.
It’s possible that the size and shape of the bubble around us shifts according to the solar cycle. The Sun has an 11-year cycle, roughly speaking, during which the intensity of the solar wind waxes wanes. However, what’s also important is how the solar wind interacts with the magnetic fields in interstellar space.
Now close to the end of its mission, IBEX will be replaced in 2025 by NASA’s Interstellar Mapping and Acceleration Probe (IMAP), which will have better range, accuracy and resolution. As well as being able to map the entire sky more frequently it will orbit at the L1 point in space, a million miles away from Earth and its interfering magnetosphere, just as the James Webb Space Telescope (JWST) does.
Wishing you clear skies and wide eyes.