The Strange Signals Beneath Antarctica That Physics Still Can’t Explain
There was a balloon floating about 35 kilometers above Antarctica listening for some of the most energetic particles in the universe.
That sentence is already weird enough before I tell you what happened next.
The experiment was called ANITA, short for the Antarctic Impulsive Transient Antenna. It carried an array of radio antennas beneath a massive NASA balloon and flew over Antarctica looking for extremely high-energy neutrinos.
Neutrinos are the same ridiculous little particles I recently became obsessed with because trillions pass through us every second without us noticing. Most barely interact with matter at all. At extremely high energies, though, things get more interesting. Scientists realized Antarctica offered an enormous natural detector. If an ultrahigh-energy neutrino interacted inside the ice, the resulting particle cascade could produce a brief radio pulse. ANITA's antennas floating high above the continent could potentially detect it.
Which is such a strange use for Antarctica, but I guess it’s just sitting there, so might as well.
Instead of building the entire detector, you basically use a continent. ANITA flew multiple times between 2006 and 2016 and detected plenty of signals scientists could understand…then it found a couple that made very little sense. They appeared to be associated with particle showers traveling upward from below the horizon at surprisingly steep angles.
That was a problem…a very interesting problem.
First, ANITA Didn't Hear Something Talking Beneath the Ice
This is worth clearing up because the story became much stranger online than the science itself. There’s no mysterious transmission being broadcast from deep under Antarctica, it’s not a radio station under the South Pole. The experiment detected short radio pulses that resembled the signatures produced by enormous particle showers. Cosmic rays regularly slam into Earth's atmosphere and create cascades containing billions of secondary particles, and those particle showers can generate radio emission that ANITA detects.
Normally, when ANITA sees one of these showers indirectly after its radio signal reflects off the Antarctic ice, the reflection changes the signal in a predictable way, but a small number of events looked different.
Two particularly famous events from ANITA's first and third flights appeared to have the characteristics of showers moving upward, with arrival directions roughly 27 and 35 degrees below the horizontal. Basically, the data looked as though something had traveled through a substantial chunk of Earth, emerged from the ice, and created a particle shower in the atmosphere.
So people looked at that and said, essentially, “well, that's awkward.”
Couldn't a Neutrino Just Pass Through Earth?
This confused me at first because I had just spent an entire article talking about how neutrinos can pass through Earth, and they can, but the problem is energy.
A relatively low-energy neutrino has an absurdly small chance of interacting with matter. As neutrino energy increases, however, its probability of interacting also increases. At the enormous energies involved in the ANITA events, Earth becomes much less transparent to neutrinos.
So while a lower-energy neutrino can cruise through an enormous amount of rock without caring very much, an ultrahigh-energy neutrino traveling through thousands of kilometers of Earth has a much greater chance of being absorbed along the way. That makes the steep angles of these particular signals difficult to explain using an ordinary Standard Model neutrino.
One possibility involves tau neutrinos. A tau neutrino can interact inside Earth and produce a tau lepton. If this happens close enough to Earth's surface, that tau particle can escape into the atmosphere and decay, creating an upward-moving particle shower. That's real physics and exactly the sort of phenomenon experiments like ANITA and its successor PUEO are interested in detecting, but the geometry is the problem.
Earth-skimming neutrinos arriving at relatively shallow angles have a much shorter path through the planet.
The strange ANITA events seemed to come from much steeper directions. The deeper through Earth you ask an ultrahigh-energy neutrino to travel, the harder the explanation becomes.
So What Did ANITA Actually Find?
That remains the fun part because scientists still don't know.
A 2025 study used data from the Pierre Auger Observatory in Argentina to search for the same kind of upward-going particle showers. Auger had years of exposure and should have had opportunities to see similar events if they were part of a common population.
It didn't. Researchers found one candidate compatible with their expected background, and the results strongly disfavored an entire population of upward-going showers at a rate that would easily explain ANITA's observations.
Stephanie Wissel, a physicist who worked on ANITA, has said that the origin of the anomalous events is still unclear and that the evidence increasingly suggests they probably weren't neutrinos. I actually think that makes the story more interesting. ANITA was designed in large part to hunt neutrinos then found something stranger than a bat living inside my shower.
Years of follow-up work have increasingly suggested, “whatever that was, it probably wasn't the thing we built this experiment to find.” That is such a science problem. Some people think that it could be something we just don’t understand about ice yet. This is considerably less dramatic than a parallel universe, but it's also one of the possibilities I find most interesting.
Antarctic ice isn't a giant perfectly uniform block, it contains layers, changes in density, buried structures and complicated electromagnetic properties. Researchers have investigated whether unusual reflections or structures beneath the surface could make an ordinary downward-moving cosmic-ray signal appear strange.
Some proposed ice-reflection explanations have already been tested and disfavored, so there isn't currently a simple “we figured it out, the ice did it” answer either.
Maybe there’s an atmospheric effect we haven't modeled properly or something unusual about radio propagation in Antarctic ice and we're looking at an extremely rare cosmic-ray phenomenon. Right now, we don't know, and “we don't know” is a perfectly good scientific answer.
And Then the Internet Found a Parallel Universe
This is where the ANITA story got completely out of hand. At some point, headlines started claiming that NASA scientists had discovered evidence of a parallel universe where time runs backward. I won’t lie, I clicked that headline too, which is how I ended up looking into this and then writing this article in the first place.
Unfortunately for me and my sci-fi-loving-brain, that's not what happened.
Scientists have proposed some wild explanations for the ANITA events because that's something theoretical physicists do when interesting observations refuse to fit comfortably inside existing models. Researchers have published papers exploring new particles, supersymmetry, unusual dark matter scenarios and other beyond-the-Standard-Model possibilities. One 2018 paper specifically explored whether the ANITA events could be explained within a CPT-symmetric universe model involving a hypothetical dark matter particle.
That's quite different from ANITA detecting another universe, but I sort of like it anyway.
ANITA detected radio pulses, then theorists asked, “what kinds of physics could produce something like this?” That's how science is supposed to work. A theoretical paper saying this model could potentially explain these observations is not the same thing as an experiment demonstrating that the model is real.
It would be like finding an unusual footprint in my garden, writing a paper calculating whether an escaped kangaroo could have made it, and then announcing that Philadelphia has kangaroos. I mean…interesting hypothesis, but I still need the kangaroo to show people.
What About Dark Matter?
Dark matter inevitably enters this conversation because we already know something massive and invisible is affecting the universe gravitationally. Galaxies behave as though there is far more matter present than we can see and we don't yet know what that dark matter is made of.
That leaves physicists with an enormous playground of possible particles. Some researchers have investigated whether exotic dark matter particles or their decay products could generate events resembling the ANITA anomalies. Certain models can produce particles capable of crossing enormous amounts of matter before interacting.
That would be a spectacular answer, but would also require spectacular evidence, and right now we don't have it.
So ANITA belongs in my favorite category of science: something genuinely strange happened, we have several ideas, and none has earned the right to become the answer yet.
ANITA stopped flying years ago, but scientists didn't simply shrug at the unexplained events and move on. They built PUEO instead! PUEO stands for the Payload for Ultrahigh Energy Observations, and it's essentially ANITA's much more sensitive successor. Like ANITA, PUEO hangs beneath a giant NASA balloon and looks down across Antarctica for tiny radio signals associated with extremely energetic particles.
Its main instrument uses dozens of antennas and sophisticated real-time processing to combine faint radio signals, giving it much greater sensitivity than ANITA at key energies, and when I originally wrote about this, PUEO hadn't flown yet, but now it has.
PUEO launched from Antarctica in December 2025 and spent 23 days floating at roughly 120,000 feet above the continent before its flight ended on January 12, 2026. The instrument collected somewhere around 50 to 60 terabytes of data. Then scientists had to go retrieve the thing from Antarctica, because apparently building a floating radio observatory isn't enough work and you also have to go fetch your enormous science balloon afterward.
The payload and its data drives were successfully recovered. As of 2026, the team is still calibrating and analyzing the enormous dataset. NASA has said the process could take up to a year. So now there's an actual answer coming…we hope.
If PUEO detects events with the same strange characteristics as ANITA's anomalies, researchers suddenly have much more to work with. Replication matters enormously because a repeated event observed by a newer, more sensitive instrument would make it harder to explain the original events as something peculiar to ANITA. Scientists could examine the direction, energy, radio polarization, geometry and other details and compare them directly.
If PUEO sees nothing similar, that matters too. It wouldn't magically explain ANITA's events, but it would place tighter limits on how frequently whatever produced them can occur. This is what I mean when I say science isn't ruined by a null result, because sometimes finding nothing eliminates half the room.
Antarctica Is Such a Ridiculous Place to Do This
I also can't get over the setting because Antarctica is basically being used as part of an enormous physics experiment.
The Antarctic ice sheet is part of the detector. If an ultrahigh-energy neutrino interacts in the ice, it can create a particle cascade that produces a burst of radio emission through something called the Askaryan effect. PUEO watches an enormous volume of ice from high above and waits for one of those tiny signals.
Think about the scales involved here for a second, a literal microscopic particle and a continent-sized target with a giant balloon floating near the edge of space, dozens of antennas, and tens of terabytes of data. All because somewhere in that data there might be a radio pulse lasting a tiny fraction of a second that tells us something about a particle that traveled here from some violent place in the universe.
Physics gets wonderfully excessive sometimes.
The fun headline is: MYSTERIOUS PARTICLE SHOOTS THROUGH EARTH AND BREAKS PHYSICS.
The actual process afterward is years of simulations, detector calibration, statistical analysis, comparison with other experiments, arguments over radio propagation and researchers trying very hard to prove themselves wrong. Anyone can look at an unexplained signal and decide it confirms the thing they already wanted to believe, but science makes you keep asking increasingly annoying questions.
Could the equipment have produced it? What about the ice maybe have reflected it strangely? An ordinary cosmic ray can’t mimic it? Should IceCube have seen something?
As of 2026, I still can't tell you what this was. The famous ANITA events remain unexplained, and newer analyses have made a straightforward ultrahigh-energy neutrino interpretation increasingly difficult. The Pierre Auger results specifically found that a population of upward-going showers at the rate suggested by the ANITA events would conflict strongly with what Auger observed.
PUEO has now completed its first Antarctic flight, and its data is being analyzed. I hope the eventual explanation will involve some weird feature of Antarctic ice or we'll discover an extremely rare cosmic-ray effect. Scientists could very well find a mistake nobody noticed before and ruin the whole mystery of the thing.
I genuinely don't know which answer I want. There’s something equally satisfying about watching scientists chase an anomaly for years and eventually figure out that one tiny, overlooked physical effect made the whole thing make sense.
Either way, somewhere in tens of terabytes of PUEO data may be another clue, and I love that we're currently living in the part of the story where nobody knows the ending yet.
If you’re interested in listening to things from far away, this bird listening device captures sounds for you!
Reads You Might Enjoy:
Quantum Time Control: How Scientists Are Learning to Rewind Reality
When the Future Rewrites the Past: The Quantum Eraser Paradox
The Sun Isn’t Yellow: A Mind-Bending Dive into Light, Space, and the Lies Our Atmosphere Tells
The Great Attractor: The Mysterious Force Dragging Our Galaxy Toward the Unknown
Are Black Holes Actually Tunnels? The Mind-Bending Theory That’s Changing Space Science
The Light That Shouldn’t Exist: Discovering Stars in the Darkest Corners
Through the Shadow of a Giant: What We Learned from Uranus Passing a Star
The Impossible Signal: Mysterious Radio Pulses Beneath Antarctica
The River Doesn’t Forget: How Cocaine Ended Up in Every Shrimp Tested
Sources:
Abdul Halim, A., et al. “Search for the Anomalous Events Detected by ANITA Using the Pierre Auger Observatory.” Physical Review Letters, 2025, American Physical Society, https://link.aps.org/doi/10.1103/PhysRevLett.134.121003.
Shoemaker, Ian M., et al. “Reflections on the Anomalous ANITA Events: The Antarctic Subsurface as a Possible Explanation.” Annals of Glaciology, vol. 61, 2020, Cambridge University Press, https://www.cambridge.org/core/journals/annals-of-glaciology/article/reflections-on-the-anomalous-anita-events-the-antarctic-subsurface-as-a-possible-explanation/33C7346D70528285E88B5B909DF87ADB.
Naumova, Marina. “Strange Radio Pulses Detected Coming from Ice in Antarctica.” Penn State News, 13 June 2025, https://www.psu.edu/news/research/story/strange-radio-pulses-detected-coming-ice-antarctica.
“Scientists Propose a ‘Mirror Universe’ Where Time Moves Backwards.” ScienceAlert, 25 Jan. 2016, https://www.sciencealert.com/scientists-propose-a-mirror-universe-where-time-moves-backwards.
Wall, Martin. “‘A Mirror Universe That Moves Backward in Time? Scientists Say It Could Be Real!’” NASA Space News, 4 Nov. 2024, https://nasaspacenews.com/2024/11/a-mirror-universe-that-moves-backward-in-time-scientists-say-it-could-be-real.
“Big Bang May Have Created a Mirror Universe Where Time Runs Backwards.” NOVA, PBS, https://www.pbs.org/wgbh/nova/article/big-bang-may-created-mirror-universe-time-runs-backwards.
Gardner, Martin. The Ambidextrous Universe: Mirror Asymmetry and Time-Reversed Worlds. Penguin Books, 1969.
