We Live Inside a Colossal Croissant-Shaped Bubble, After All
Physicists have unveiled an advanced new model of the heliosphere — the vast volume of space surrounding the Sun reaching more than twice the distance of Pluto — and it shows a crescent-shaped magnetic force-field in the shape of a freshly-baked croissant, reports Forbes.
The Sun's heliosphere, sans croissants
The heliosphere is a vast region of space extending far beyond the planets that make up our solar system. In a word, the heliosphere is the realm of the universe under the Sun's dominion, where the solar wind — charged particles flung out into the cosmos by the Sun — extends beyond the planets' orbits.
Solar wind creates a bubble around the solar system that moves with it as the Sun glides through interstellar space. On the fringes of the heliosphere is where the solar wind breaks against the force of cosmic wind between stars. The heliosphere casts a magnetic force field around the planets of our solar system and deflects charged particles that would otherwise enter our solar system, and fries DNA.
Voyager 1's data from beyond the Sun
Until recently, the idea of a heliosphere in any shape but comet-like — a sphere, with a trailing tail behind — was controversial. For a long time, the heliosphere was thought to stretch "behind" the solar system, creating a comet-like shape.
The shape of the heliosphere has also been described as a beachball. But according to Professor of Astronomy and Researcher at Boston University's Center for Space Physics Merav Opher, and co-author James Drake of the University of Maryland, the heliosphere is in reality more of a helio-crescent.
Drake and Opher's original paper — published in 2015 — used data from NASA's Voyager 1 spacecraft, which broke through the boundary from between the heliosphere and interstellar space in May 2012. Out in the infinite reaches of interstellar space, the spacecraft monitored two gigantic jets of material shooting backward from the north and south poles of the Sun, which curve delicately around in two short tails at the rear.
This is why the heliosphere looks much more like a crescent moon than a comet.
Deflating the 'beach ball' model
Drake and Opher's research made controversial waves in the astronomical community. "It was very contentious," she said, according to Forbes. "I was getting bashed at every conference! But I stuck to my guns." To make things more stressful, another model was put forward by scientists working on NASA's Cassini mission, in 2017. According to NASA's study, the heliosphere is much more compact and rounded than was previously thought — similar to a beach ball.
Baking up the 'croissant model'
Later, Drake and Opher's new theory — with colleagues Gabor Toth of the University of Michigan and Avi Loeb of Harvard University — proposed in a new paper published in Nature Astronomy — showed that two jets extend downstream from the nose, instead of a single fade-away tail. Developed on NASA's Pleiades supercomputer and supported by NASA and the Breakthrough Prize Foundation, the researchers' new 3D model of the heliosphere reconciles the "beach ball" with the "croissant" model.
The reconciliation went down by distinguishing between the solar wind and incoming neutral particles, which float into the solar system at a temperature so hot that they have a disproportionately large effect on the shape of the heliosphere.
However, uncertainty remains because there's no one way to define the edge of the heliosphere.
It's difficult to say which changes more: our understanding of the universe, or the universe itself. When it comes to our study of the Sun, the vast reaches of space beyond, and the heliosphere (where they meet), we're nearing the end an era for intrepid spacecraft like Voyager 1. But we're not there yet.
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