NASA’s new solar system bubble discovery: It’s croissant-shaped, not comet-shaped

Our solar system is surrounded by a giant invisible bubble called the heliosphere. This protective bubble is created by the solar wind, streams of charged particles flowing out from the Sun, and it shields us from dangerous cosmic rays that come from the galaxy. For decades, scientists believed the heliosphere looked like a comet, with a rounded nose at the front and a long trailing tail. But, according to research published in Nature Astronomy, it may actually look more like a deflated croissant. Understanding this strange, unexpected shape is vital, as it reveals how our solar system is protected from harmful cosmic radiation and what this means for space travel, planetary safety, and even the possibility of life beyond Earth.Our solar system does not drift nakedly through the galaxy. Instead, it is wrapped in an invisible, protective bubble, the heliosphere, created by the constant outflow of charged particles from the Sun, known as the solar wind.For decades, scientists believed this bubble resembled a comet: a rounded nose at the front, with a long, trailing tail streaming behind as our Sun ploughs through the Milky Way. However, according to NASA research, the true shape of this cosmic shield may be very different, more like a deflated croissant.This surprising insight not only reshapes our understanding of the heliosphere but also has profound implications for space travel, planetary protection, and the search for habitable worlds beyond our own.The heliosphere is the magnetic bubble created by the solar wind. It stretches far beyond Pluto, to more than ten billion miles from Earth, and forms the boundary between our solar system and interstellar space.Outside lies the interstellar medium, the thin soup of charged particles, radiation, and magnetic fields that fills the spaces between stars. Because the heliosphere deflects and absorbs much of this incoming material, it serves as the first line of defence for our planets against harmful cosmic radiationTraditionally, the heliosphere has been pictured as a comet: a smooth, rounded front (the “nose”) with a long tail extending away from the Sun. This made intuitive sense, since the solar system moves through the galaxy at about 828,000 km/h.But research led by Merav Opher, an astronomer at Boston University, has revealed an alternative structure. By rethinking how different particles of the solar wind behave, her team has modelled the heliosphere not as a streamlined comet, but as something more squat and bulbous, a deflated croissant.This model suggests two curved jets curl away from the central bubble, but there is no long trailing tail.The breakthrough came from separating the solar wind into two distinct components:Cooler solar wind particles streaming directly from the Sun.Hotter “pick-up ions”, formed when neutral atoms in interstellar space become ionised and are swept up by the solar wind.Unlike the cooler particles, these pick-up ions carry far more energy and heat, dominating the heliosphere’s thermodynamics. Because they escape quickly beyond the termination shock (the region where the solar wind slows as it meets interstellar material), the heliosphere does not maintain a long tail. Instead, it “deflates” into a croissant-like structure.As Opher explains: “Because the pick-up ions dominate the thermodynamics, everything is very spherical. But because they leave the system very quickly, the whole heliosphere deflates.”Measuring the shape of the heliosphere is no easy task. Its edge lies billions of miles away, and only two spacecraft, Voyager 1 and Voyager 2, have directly crossed into interstellar space, giving us just two reference points.Other missions help fill in the gaps:Together, these missions allow researchers to build sophisticated models, like Opher’s, to predict the heliosphere’s true structure.The heliosphere is more than a curiosity, it’s a shield.High-energy particles, known as galactic cosmic rays, are constantly launched into space by supernovae and other violent cosmic events. Left unchecked, they could cause devastating effects on technology and living organisms:By blocking about three-quarters of incoming galactic cosmic rays, the heliosphere plays a crucial role in shielding Earth and the rest of the solar system. Knowing its shape helps scientists understand how effective that protection really is.The shape of our heliosphere may also provide clues for identifying potentially habitable exoplanets. Other stars have their own “astrospheres”, which can vary widely: some are short and compressed, while others stretch into long tails.If a star’s astrosphere is too weak, planets within it may be bombarded by cosmic radiation, reducing their chances of hosting life. Understanding whether our heliosphere resembles a long comet, a croissant, or something else entirely helps astronomers assess which star systems might offer the safest havens for life.Also read | NASA space telescope view of Pegasus: Stars, dust and a distant galaxy