Earth is constantly bombarded by fragments of rock and ice, known as meteoroids, from space. Most meteoroids are as small as grains of sand and small pebbles, and burn up completely high in the atmosphere. You can see meteoroids larger than about a golf ball as they glow like meteors or shooting stars on a dark, clear night.
While very small meteoroids are common, larger ones – bigger than a dishwasher – are not.
Meteoroids are difficult objects for space and geophysics researchers like us to study because we generally cannot predict when and where they will hit the atmosphere. But in very rare cases we can study artificial objects that enter the atmosphere, just as a meteoroid would.
These objects come from space missions designed to transport physical alien samples from space to Earth. Because of this similarity to entry meteoroids, we often call these sample return capsules, or SRCs, “artificial meteors.”
More than 80 researchers from more than a dozen institutions recently collaborated to study one such “artificial meteor” – NASA’s OSIRIS-REx sample return capsule – as it reentered Earth’s atmosphere.
These institutions include Sandia National Laboratories, NASA’s Jet Propulsion Laboratory, Los Alamos National Laboratory, the Defense Threat Reduction Agency, TDA Research Inc., the University of Hawaii, the Air Force Research Laboratory, the Atomic Weapons Establishment Blacknest, Boise State University, Idaho . National Laboratory, Johns Hopkins University, Kochi University of Technology, Nevada National Security Site, Southern Methodist University, the University of Memphis and Oklahoma State University.
This sample return provided our teams with a unique opportunity to measure the sound waves and other phenomena that objects from space produce as they speed through Earth’s atmosphere.
To capture signals, we have installed many sensitive microphones and other instruments at key locations close to the SRC’s flight path.
While space agencies and private companies are constantly launching objects into space, the OSIRIS-REx SRC is one of the few objects to return to Earth from interplanetary space since the end of the Apollo missions. Only these objects can reach the speed of natural meteoroids, making their return valuable for studying the properties of natural objects.
Sampling an asteroid
NASA launched the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer, or OSIRIS-REx, mission on September 8, 2016. The mission traveled to Bennu, a near-Earth asteroid, and collected a sample of its surface in October 2016. 2020.
The sample returned to Earth in a sample return capsule in the early morning of September 24, 2023. The SRC reentered Earth’s atmosphere over the Pacific Ocean at a speed of over 27,500 miles per hour, landing in Utah just a few minutes later.
SRCs produce a shock wave when they dive deep into the atmosphere, similar to the sonic boom generated by a supersonic fighter jet breaking the sound barrier. The shock wave then loses strength until only low-frequency sound remains, called infrasound.
Although humans cannot hear infrasound, sensitive scientific instruments can detect it even at great distances. Some of these instruments sit on the ground, while others hang from balloons in the air.
Observing the SRC
Our teams of scientists took the return of the SRC as an opportunity to learn more about meteors. One of the teams, led by Siddharth Krishnamoorthy of NASA’s Jet Propulsion Laboratory, used the SRC reentry to test infrasound-detecting balloons that could later be used on the planet Venus.
Another team, led by one of us – Elizabeth Silber – and Danny Bowman of Sandia National Labs, used the SRC to better understand how we can use sound to [gather information about meteoroids].
Researchers from many institutions across the country participated in these observation campaigns.
Our teams strategically placed instruments at locations spanning 300 miles (482 km), from Eureka, Nevada, to close to the landing site in Utah. The instruments ranged from high-tech custom sensors to smartphones on the ground around the SRC’s flight path and landing site. They tracked the low-frequency sound waves from the SRC’s return.
In addition to the ground-based sensors, our researchers attached instruments to balloons that floated at twice the height of commercial aircraft during the SRC’s return. The sensors attached to these balloons recorded the sound waves produced by the SRC’s shock wave. These sound waves carried information about the SRC, its movement and the environment it passed through.
The balloon teams had to carefully time the balloons to ensure they would be in the right position when the SRC passed. Team members from NASA’s Jet Propulsion Laboratory, Oklahoma State University and Sandia National Laboratories launched a few different types of balloons from Eureka, Nevada, before dawn.
Researchers from OSU, Sandia and the University of Hawaii also deployed ground infrasound sensors closer to the SRC’s landing site, along the Utah-Nevada border and at Wendover Airport. While the SRC was already slowing down and Wendover Airport was approximately three times further from the flight path than the Eureka deployment, we also detected a clear infrasound signal at this location.
Researchers from these teams are now analyzing the data to identify points along the trajectory where instruments recorded the SRC return signals. Because the SRC’s flight path spanned approximately 300 miles (482 km), researchers must determine the origin points of the signals as the various sensors detected them.
This was the most instrumented hypersonic reentry in history.
This research will help our teams figure out the patterns of low-frequency sound waves propagating through the atmosphere and where the shock wave had its peak intensity.
While our teams are still analyzing the data, preliminary results show that our instruments captured many signals that will help future research use low-frequency sound waves to study meteors.
And by understanding the complexity of how low-frequency sound waves travel through the atmosphere, researchers can use infrasound to detect hazards on Earth, such as tornadoes and avalanches.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Brian Elbing, Oklahoma State University and Elizabeth A. Silber, Sandia National Laboratories
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Brian Elbing received funding for this project from NASA for the balloon activities and the Gordon and Betty Moore Foundation supported his ground measurements.
Elizabeth A. Silber has received funding from DTRA for this project.