A misbehaving coronal mass ejection (CME) that ejected a hidden cloud of charged particles headed toward Earth has been tracked by a record 17 spacecraft spread across the solar system, revealing that the CME is surprisingly imbalanced. CMEs are “burps” from the sun: huge clouds of magnetized plasma belched from the sun’s warm outer atmosphere, the corona, by the energy resulting from a solar flare. The magnetized CME cloud then expands into the solar system, and the charged particles contained in the cloud are a major radiation hazard to astronauts, spacecraft, and even airplane passengers, but they also have a beautiful side, as they can trigger the beautiful lights of the aurora when they intercept Earth. CMEs occur on a regular basis, but one that emerged from the sun at 00:48 UT (7:48 p.m. ET) on December 15, 2024 turned out to be quite special. “We used observations from 17 spacecraft to track and characterize this CME,” Adrienn Luspay-Kuti of the Johns Hopkins University Applied Physics Laboratory, who led the research that brought together all the observations, told Space.com. “This was a record number of spacecraft to track and characterize a single CME, and it gave us an exceptionally detailed view of how the CME evolved.” The previous record had been 10 spacecraft, but they had mostly been on a rough line from the Sun to Earth and beyond, meaning their measurements were somewhat one-dimensional. This time, for the December 2024 CME, the spacecraft were spread far and wide, not only at different distances from the sun, but also substantially along the Earth-sun line. You may like They revealed that the CME had two asymmetrical lobes, one that moved faster than the other. One of those lobes, heading toward Earth and Mars, would have gone unnoticed, obscured by the larger but slower lobe that tangented away from the Sun, if not for the wide spread of the spacecraft. “Our observations showed a fast lobe propagating through the Earth-Mars sector and a much slower lobe further west, towards STEREO-A,” Luspay-Kuti said. STEREO-A is half of NASA’s two-spacecraft space weather monitoring system known as the Solar-Terrestrial Relations Observatory. The onset of the CME was seen by the joint NASA-ESA Solar and Heliospheric Observer (SOHO), which has been constantly monitoring the Sun for more than 30 years. However, he only saw the slower lobe that erupted at an angle to the Earth; The faster lobe heading toward our planet was not seen, obscured by the larger, slower lobe. A schematic of the CME shows its two lobes advancing through the solar system and encountering various spacecraft and satellites. (Image credit: Johns Hopkins Applied Physics Laboratory) The CME was next detected at a distance from the sun of 0.35 astronomical units (AU; 1 AU is the distance from Earth to the sun) on December 16 moving through space near Mercury and the European Space Agency’s BepiColombo mission (which eventually reaches orbit around the innermost planet in November 2026). The next detection, on December 17, was of the “hidden” component. arriving at Earth, where a multitude of spaceships picked him up. The CME was not strong enough to produce significant auroras. Interestingly, Europa’s Solar Orbiter mission, in an elongated orbit around the Sun and at the time 0.94 AU from the Sun and just 10 degrees from the Earth-Sun line, did not detect the CME. This non-detection was really vital as it helped limit the form of CME. What to read next Then, on December 18, the slower-moving lobe reached NASA’s STEREO-A spacecraft, which orbits the Sun at the same distance as Earth (1 AU), but substantially ahead of Earth in its orbit. The Earth-crossing lobe had an average speed of 522 miles (840 kilometers) per second, but the other lobe dragged its feet, moving at an average of 332 miles (534 km) per second away from the sun and past BepiColombo and STEREO-A. In fact, by the time it reached STEREO-A, it had slowed to approximately 248.5 miles (400 km) per second. Both lobes slowed as a result of friction with the regular solar wind that the CME was overcoming, and the range of speeds measured in the CME indicated to researchers that the solar flare was not traveling as a single, unified front. Beyond Earth NASA’s Europa Clipper mission, for which Luspay-Kuti is the principal investigator for the spacecraft’s Plasma Instrument for Magnetic Survey (PIMS) experiment, detected the fastest-moving lobe at 1.19 AU as the spacecraft cruised. to Mars in search of gravitational assistance to help him on his journey to Jupiter. On the red planet, the now-defunct MAVEN mission also detected the CME on December 19-20. Having not only so many spacecraft tracking the progress of a CME but also enough spacecraft outside the Earth-Sun line to measure the shape of the CME, at least in two dimensions, is an important step forward in understanding and forecasting the spread of CMEs. The CME as seen by the Solar Dynamics Observatory (top left), SOHO (top right), and STEREO-A (bottom left and right). The faster lobe, directed toward Earth, was obscured by the slower lobe, directed toward the south. (Image credit: Luspay-Kuti et al.) “This is important for future human exploration because a missed CME can mean losing valuable warning time,” Luspay-Kuti said. “Fast CMEs can generate shocks that accelerate high-energy particles, which can pose a radiation hazard to astronauts outside of Earth’s protective magnetic field. This is why observations from multiple vantage points, including spacecraft far from the Sun-Earth line and planetary missions operating during their cruise phase, will be increasingly important for space weather forecasting as human exploration moves further away from Earth.” The asymmetric double-lobe structure of this particular CME was certainly a surprise. The cause of the asymmetry is still unclear at present, although Luspay-Kuti told Space.com that researchers are investigating. The main question is: how often are CMEs asymmetric? “In the context of previous observations, this event is at the most extreme end of the variability of observed CMEs,” Luspay-Kuti said. “Are highly asymmetric CMEs quite common but we fail to recognize them because we don’t have enough observational coverage, or are they really rare?” The 17 spacecraft that detected or imaged the CME in some or all of its various stages (the arc shock and turbulent envelope ahead of the magnetic cloud, the CME itself, and the turbulent wake left by the solar wind after its passage) were as follows: SOHO (initial images), BepiColombo, NASA Solar Dynamics Observatory, STEREO-A, the four Magnetospheric Multiscale (MMS) mission spacecraft, the two the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the sun) mission, NASA’s Wind, ACE (Advanced Composition Explorer), GOES (Geostationary Operational Environmental Satellite), and DSCOVR (Deep Space Climate Observatory), Europa Clipper, MAVEN, and Solar Orbiter missions, the latter of which made measurements but did not detect the CME. In the future, these missions will be joined by the European Space Agency’s Vigil mission, which will observe space weather when it launches in 2031 for the L5 Sun-Earth Lagrange point, 60 degrees behind Earth in its orbit and thus provide additional off-axis monitoring. The findings were published August 19 in the journal Science Advances.
