by Fragments of rock and ice, also known as meteoroids, are constantly being blasted from outer space. Most meteoroids are as small as grains of sand and small pebbles, and they burn up completely high in the atmosphere. You can see meteoroids larger than about a golf ball when they light up like meteors or shooting stars on a dark, clear night.
Although very small meteoroids are common, larger ones – bigger than a dishwasher – are not.
Meteoroids are difficult things for aerospace and geophysics researchers like us to study, because we usually can’t predict when and where they hit the atmosphere. But on very rare occasions, we can study artificial objects that enter the atmosphere like a meteoroid.
These objects come from space missions designed to transport extraterrestrial physical samples from outer space to Earth. Because of this similarity to meteoroids in entry, we often refer to these sample return capsules, or SRCs, as “artificial meteors.”
More than 80 researchers from more than a dozen institutions recently teamed up to study an “artificial meteor” – NASA’s OSIRIS-REx sample return capsule – as it re-entered Earth’s atmosphere.
These institutions included Sandia National Laboratories, NASA Jet Propulsion Laboratory, Los Alamos National Laboratory, Defense Threat Reduction Agency, TDA Research Inc., University of Hawaii, Air Force Research Laboratory, Blacknest Atomic Weapons Establishment, Boise State University, Idaho National Laboratory, Johns Hopkins University, Kochi University of Technology, Nevada National Security Site, Southern Methodist University, University of Memphis and Oklahoma State University.
This sample return gave our teams a unique opportunity to measure the sound waves and other phenomena produced by objects from space as they speed through the Earth’s atmosphere.
To capture signals, we installed many sensitive microphones and other instruments in key locations near the SRC’s flight path.
While space agencies and private companies launch objects into space all the time, the OSIRIS-REx SRC is one of a handful of objects to return to Earth from interplanetary space since the Apollo missions ended. Only these objects can reach the speed of natural meteoroids, making their re-entry valuable for studying the properties of natural objects.
Sampling an asteroid
NASA launched the Origin, Spectral Imaging, Resource Identification, Security, Regolith Explorer, or OSIRIS-REx, mission on September 8, 2016. It traveled to Bennu, a near-Earth asteroid, and collected a sample from its surface in October of 2020.
The sample returned to Earth in the early morning of September 24, 2023, in a sample return capsule. The SRC re-entered the Earth’s atmosphere over the Pacific Ocean at a speed of over 27,000 mph (43,500 kph) and landed in Utah a few minutes later.
SRCs produce a shock wave as they penetrate deep into the atmosphere, similar to the sonic boom generated by a supersonic jet that breaks the sound barrier. The shock wave then loses strength until only a low frequency sound remains, known as 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 are suspended in the air from balloons.
Viewing the SRC
Our team of scientists jumped on the SRC re-entry as an opportunity to learn more about meteors. One of the teams, led by Siddharth Krishnamoorthy at NASA’s Jet Propulsion Laboratory, used the SRC re-entry to test infrasound balloons that could later be used on the planet Venus.
Another team, led by one of us – Elizabeth Silber – and Danny Bowman at 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 observational campaigns.
Our crews strategically placed instruments in locations across a distance of 300 miles (482 km) from Eureka, Nevada, near the landing site in Utah. The instruments included high-tech custom sensors to smart phones on the ground around the SRC’s flight path and landing site. They monitored the low-frequency sound waves from the re-entry of the SRC.
In addition to the ground-based sensors, our researchers attached instruments to balloons that floated at twice the height of commercial airplanes during the SRC re-entry. The sensors attached to these balloons recorded the sound waves produced by the SRC shock wave. These sound waves carried information about the SRC, its movement and the environment it passed through.
The balloon teams had to time the balloons carefully to ensure they were in the right position when the SRC went over. Team members from NASA’s Jet Propulsion Laboratory, Oklahoma State University and Sandia National Laboratories launched several different types of balloons before dawn from Eureka, Nevada.
Researchers from OSU, Sandia and the University of Hawaii deployed ground-based infrasound sensors closer to the SRC landing site, along the Utah-Nevada border and at Wendover Airport. Although 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 on these teams are now analyzing the data to identify the points along the path where instruments recorded the SRC’s re-entry signals. Because the SRC’s flight path was about 300 miles (482 km), the researchers need to figure out the points of origin of the signals as they were detected by the various sensors.
This was the largest instrumented hypersonic reentry in history.
This research will help our teams to find out what patterns the low frequency sound waves traveled through the atmosphere and where the shock wave was at its peak intensity.
Although our teams are still analyzing the data, preliminary results show that our instruments picked up many signals that will help future research using low-frequency sound waves to study meteors.
And gaining insights into the intricacies of how low-frequency sound waves travel through the atmosphere can help researchers use infrasound to detect hazards on Earth, such as tornadoes and tornadoes.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Written by: Brian Elbing, Oklahoma State University and Elizabeth A. Silber, Sandia National Laboratories
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Brian Elbing of NASA has received funding related to this project for the balloon activities and his ground measurements were supported by the Gordon and Betty Moore Foundation.
Elizabeth A. Silber has received funding related to this project from the DTRA.
