This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: During a coronal mass ejection (CME), the sun hurls billions of tons of magnetized plasma into space. These eruptions are among the most powerful events in the solar system, and when they are aimed toward Earth, they can seriously threaten the satellites and power grids we depend on.
For now, it remains notoriously difficult to predict how these eruptions evolve over time—and, in turn, whether they might be heading toward us. Taking observations from an extensive network of spacecraft across the solar system, a team led by Adrienn Luspay-Kuti at Johns Hopkins University has revealed how a component of one recent CME headed straight toward Earth, completely hidden from Earth-based observations. Published in Science Advances, the work reveals just how easily a dangerous piece of a CME can go unnoticed.
CMEs form when the sun's magnetic field lines become tangled and suddenly snap, flinging immense bubbles of charged particles into space. If these bubbles interact with Earth's atmosphere and magnetic field, they can trigger geomagnetic storms: disturbances that scramble satellite signals, disrupt radio communications and expose astronauts to dangerous bursts of radiation. To forecast whether a CME is heading our way, astronomers generally search for them from Earth's own vantage point.
However, a CME isn't always a tidy, symmetric bubble, as these measurements often assume—potentially leaving dangerous gaps in the space weather forecast. In December 2024, NASA's Europa Clipper spacecraft detected just the kind of signal that would be missed by Earth-based forecasting techniques. During a routine instrument check on its voyage to Jupiter, the spacecraft detected that the surrounding solar wind was hotter and thinner than expected.
In their study, Luspay-Kuti's team traced this signal back to a CME that had erupted from the sun a few days earlier. But in a lucky coincidence, an unusually dense group of spacecraft was positioned around the inner solar system at the time. Using an unprecedented network of 17 spacecraft, including Clipper, the researchers could reconstruct the CME's true shape.
From Earth's perspective, the bulk of the CME appeared to be heading safely away from us. However, NASA's STEREO-A spacecraft, viewing the eruption side-on, spotted a separate, faster-moving piece heading straight toward Earth: an asymmetric component of the CME, invisible from our planet's line of sight. Had astronauts been traveling through that same stretch of space, they would have had no warning to shelter from the radiation risk.
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