Our Solar System is apparently shaped like a “deflated croissant”. That might sound like an obscure reference to Ricky and Morty, but it’s actually the latest findings of a recent study using data gathered from NASA spacecraft.
The Solar System is surrounded by a bubble of space known as the heliosphere, dominated by charged particles and magnetic fields. Created by solar wind particles streaming out from the Sun, the heliosphere keeps all the Solar System’s planets (and Pluto) shielded from galactic cosmic rays and other energetic events from elsewhere in the galaxy. Outside this bubble lies the Wild West of interstellar space.
Measuring the shape and size of the heliosphere, however, is a pretty difficult task whilst you're stuck inside it. Fortunately, humanity has sent out two spacecraft beyond the heliosphere: Voyager 1 and Voyager 2. Using data from these spacecraft and other NASA missions, including Cassini and New Horizons, scientists have used computer models to predict the heliosphere’s characteristics.
Most scientists previously believed that the heliosphere was comet-shaped with a rounded leading edge and a long trailing tail (shown below). However, this new research suggests it’s actually shaped like a “deflated croissant,” according to a new statement from NASA.
The findings were published in the journal Nature Astronomy in March 2020.
The unusual shape predicted by the study is a result of the complex forces inside and outside of the heliosphere. In regards to this research, the makeup of the heliosphere can be divided into two categories: solar wind particles that are streamed out from the Sun and “pick-up ions,” particles that are ionized out in space and are picked up by the gusts of solar wind. Complex interactions between these different components eventually result in the heliosphere not being elongated and comet-like, as expected, but rather has a swirly crescent-like shape.
“You have one component that is very cold and one component that is much hotter, the pick-up ions,” lead author Merav Opher, NASA scientist and professor of astronomy at Boston University, said in a statement.
“If you have some cold fluid and hot fluid, and you put them in space, they won’t mix — they will evolve mostly separately. What we did was separate these two components of the solar wind and model the resulting 3D shape of the heliosphere. Because the pick-up ions dominate the thermodynamics, everything is very spherical. But because they leave the system very quickly beyond the termination shock, the whole heliosphere deflates.”
The heliosphere helps protect life on Earth from damaging radiation, so the more we know about it and its shape, the more it may help us in the search for life in other star systems. Do other worlds have similarly shaped heliospheres that are also protecting them?