Every year, Earth gets a bit bigger. Thousands of metric tons of space dust fall from the sky, while about 50 tons per year of meteorites crash land somewhere on the surface. Since the 1960s, space junk has also occasionally returned to Earth, falling from a hazy sphere of trash encircling the planet. Remnants of rockets, tools lost by space-walking astronauts, defunct satellites, and more fly through lower Earth orbit, reaching speeds of 18,000 miles per hour. When any item—whether space rock or space junk—enters the atmosphere, scientists try to track its path to estimate where it will land. Will the item in question plunk straight down, or will it fly along at an angle before skittering to a halt? In a news tudy to be presented at the General Assembly of the European Geosciences Union next week, Elizabeth Silber, a scientist at Sandia National Laboratories, will consider how infrasound sensors—instruments that detect sounds at lower frequencies than humans can hear—listen for bolides. Bolides are the bright flashes and booms from large meteoroids breaking apart high in the sky. These events release huge amounts of energy, creating shock waves that travel as infrasound signals across thousands of kilometers. But here's the challenge: bolides aren't like explosions that happen in one place. They are moving, generating sound along their path as they travel through the sky. This movement matters, especially for meteoroids and space debris that enter shallow angles. In those cases, different infrasound stations might pick up signals coming from different directions, making it harder to pinpoint the source.
Motivated by this problem, Silber used a network of infrasound sensors around the world maintained by the Comprehensive Test Ban Treaty Organization (CTBTO), an organization tasked with listening for illicit explosions. These instruments also record anything else that claps or booms, from thunder to supersonic aircraft. Using signals specifically from bolides, Silber isolated the purely geometric component for her analysis. She found that if a bolide enters Earth's atmosphere at a relatively steep angle— greater than 60°—analysis of the infrasound signal gets the trajectory right. But when it comes more horizontally, the uncertainty increases.
"Infrasound from a bolide is more like a sonic boom stretched across the sky than a single bang," Silber says. "You must account for the fact that the sound is being generated along the flight path."
And so, this study highlights a critical need: to consider the trajectory of an object when interpreting infrasound data. Infrasound instruments are indispensable for planetary defense, according to Silber, and the findings are relevant to Earth-bound space junk. If you don't know where something is going, then you have a hard time preparing for it. If you'd like to learn more, don't miss the full PICO presentation on Friday, 02 May at 11:28-11:30 CEST at PICO spot 5. If you're interested in scientific applications of data collected by the International Monitoring System managed by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), check out the full SM8.5 PICO session on Friday, 02 May, starting at 10:45 CEST. PICO sessions are given in hybrid format supported by a zoom meeting.
Dr. Silber will be attending virtually, and would be happy to answer questions via email Caption: This photograph taken by an International Space Station astronaut shows a bright meteor from the Perseid meteor shower in Earth's atmosphere. The brightest meteors are known as fireballs, or bolides. Credit: NASA Note to the media When reporting on this story, please mention the EGU General Assembly 2025, which is taking place from 27 April– 02 May 2025. This paper will be presented in full [Session SSP1.2] at EGU25 on Fri, 02 May, 10:45–12:30 (CEST) PICO spot 5. If reporting online, please include a link to the session: https://meetingorganizer.copernicus.org/EGU25/session/53597
