7 Mysterious Earth & Space Sounds

Unexplained acoustic or radio frequency signals linked to space or the upper atmosphere that scientists still have not fully pinned down.
 
1. The Wow! signal (1977)
A strong, 72‑second narrowband radio signal at the hydrogen line (around 1420 MHz) detected by the Big Ear telescope in Ohio, famously annotated “Wow!” on the printout. No repeat has ever been reliably observed from the same sky region, and proposed explanations now include a powerful magnetar flare hitting a neutral hydrogen cloud, but this remains unproven and controversial.
 
2. Fast Radio Bursts (FRBs)
Millisecond‑long flashes of radio waves, often from well beyond the Milky Way, with huge, implied energies but still uncertain progenitors. Models range from magnetar flares and collapsing neutron stars to more exotic ideas; multiple sub‑classes (repeaters vs non‑repeaters, different frequency drifts) suggest more than one underlying mechanism.
 
3. Mysterious infrasound in the stratosphere
Solar‑powered balloons carrying infrasound microphones at about 20–22 km altitude have recorded low‑frequency rumbling signals a few times per hour whose sources cannot yet be identified. Known contributors (thunder, waves, human activity, rockets) do not explain the repeating, unexplained component, which may involve unknown atmospheric dynamics or distant surface sources.
 
4. The Upsweep (NOAA, Pacific Ocean)
A persistent, upsweeping low‑frequency sound discovered by NOAA hydrophones in the central Pacific in 1991, strongest in spring and autumn each year, origin undetermined. Hypotheses include undersea volcanic or hydrothermal activity, but no specific geological source has been definitively matched to the signal.
 
5. The “Whistle” / chorus emissions near Earth
Spacecraft and probes routinely record eerie, whistling audio when plasma‑wave data from Earth’s magnetosphere are shifted into the audible range. The general mechanism (electromagnetic plasma waves interacting with charged particles) is understood, but detailed source regions and wave‑particle processes behind some specific spectral chorus structures remain active research topics.
 
6. The Space Roar (ARCADE excess)
The ARCADE balloon experiment measuring faint radio emission found a uniform radio background about six times brighter than predicted from known galaxies and early‑universe sources. No consensus explanation exists; possibilities include numerous faint radio galaxies, exotic early‑universe processes, or unknown astrophysical populations, but all struggle to match the amplitude of the observed roar.
 
7. Other unexplained NOAA ocean sounds
From NOAA’s catalogue, several named underwater sounds remain not fully explained, despite being localized approximately in the ocean.
 
Bloop: A powerful, low‑frequency sound detected in 1997; now often associated with large icequakes, but without a confirmed, directly imaged source.
 
Train, Whistles, and a few others: Have plausible links to seafloor seismic or cryogenic activity, yet individual events and their precise mechanisms are still not firmly tied to specific physical sources.
 
These examples span true deep‑space radio transients, near‑Earth plasma wave audio, a puzzling radio background, and enigmatic infrasound and hydroacoustic signals at the interface between Earth, ocean, and space, each still missing a fully agreed upon physical explanation.
 
References
Turner, B. & LiveScience. (2023, May 17). Bizarre, Unexplained Rumblings in Earth’s Atmosphere Puzzle Scientists. Scientific American.
 
(2026, January 22). Wow! Signal. In Wikipedia, https://en.wikipedia.org/wiki/Wow!_signal
 
(2026, February 18). List of Unexplained Sounds. In Wikipedia, https://en.wikipedia.org/wiki/List_of_unexplained_sounds
 
(2025, January 6). The Wow! Signal: A Lingering Mystery or a Natural Phenomenon? SETI Institute. https://www.seti.org/news/the-wow-signal-a-lingering-mystery-or-a-natural-phenomenon/
 
(2015, May 8). On the Origins of Fast Radio Bursts and Perytons: A Statement. CAASTRO. http://caastro.org/project/on-the-origins-of-fast-radio-bursts-and-perytons-a-statement/