Antarctica is residence to a few of the clearest skies on Earth, and that brutal readability makes it the proper place to snoop on the cosmos. Hovering excessive above the continent, a NASA balloon carries the Antarctic Impulsive Transient Antenna, or ANITA.
The ANITA experiment catches radio murmurs born when ultra-energetic cosmic rays hit the environment.
Most of these pops behave precisely as physicists anticipate: the alerts flip polarity after bouncing off the two-mile-thick ice sheet, a clear mirror picture that tells researchers the particle got here from above.
However ANITA has additionally logged a handful of pulses that refuse to flip.
The implication is unsettling as a result of the one strategy to produce such upward-going radio waves is for a particle to plow straight via the planet, survive greater than 3,000 miles of rock, and burst out of the ice on the far facet. No identified particle ought to handle that trick.
ANITA finds rule-breaking pulses
These anomalous pulses arrived at surprisingly steep angles, rising from about 30° under the horizon as a substitute of the mild slopes seen in run-of-the-mill cosmic-ray echoes.
The geometry alone flags them as outliers, but the workforce verified that the pulses had been actual and never an instrumental hiccup.
“The radio waves that we detected had been at actually steep angles, like 30 levels under the floor of the ice,” mentioned Stephanie Wissel, an affiliate professor of physics, astronomy and astrophysics who combs the ANITA knowledge for surprising patterns.
“It’s an attention-grabbing drawback as a result of we nonetheless don’t even have an evidence for what these anomalies are, however what we do know is that they’re most definitely not representing neutrinos.”
Serving to ANITA filter cosmic chatter
Separating real particle signatures from noise takes painstaking effort. Researchers replay 1000’s of hours of balloon knowledge via pc fashions that mimic the detector’s response to lightning, satellite tv for pc transmissions, and even the crackle of auroras.
By evaluating these simulations with actual occasions, they’ll cull something that lacks the hallmark form of a particle-induced bathe.
The ANITA collaboration additionally leans on cross-checks with floor networks reminiscent of IceCube and the Pierre Auger Observatory. If a pulse seems solely within the balloon logs and nowhere else, it goes below the microscope.
The handful of unusual upward occasions survived each filter the scientists might devise, reinforcing the sense that one thing unfamiliar is in play.
Ghostly nature of neutrinos
The plain culprits could be neutrinos, the universe’s most elusive messengers. These chargeless wisps hardly collide with matter, making them excellent probes of distant cataclysms, but fiendishly onerous to identify.
“You’ve got a billion neutrinos passing via your thumbnail at any second, however neutrinos don’t actually work together,” she mentioned.
“So, that is the double-edged sword drawback. If we detect them, it means they’ve traveled all this manner with out interacting with anything. We may very well be detecting a neutrino coming from the sting of the observable universe.”
Listening from 25 miles up
“We use radio detectors to attempt to construct actually, actually giant neutrino telescopes in order that we will go after a fairly low anticipated occasion price,” Wissel defined.
ANITA tackles that problem by floating roughly 25 miles above the snow, a perch that expands every antenna’s footprint to a whole bunch of sq. miles with out planting a single pole within the ice.
“We’ve these radio antennas on a balloon that flies 40 kilometers above the ice in Antarctica,” Wissel mentioned. “We level our antennas down on the ice and search for neutrinos that work together within the ice, producing radio emissions that we will then sense with our detectors.”
Why does any of this matter?
When the workforce traced the bizarre alerts backward, the flight paths pointed via Earth’s inside, defying the usual mannequin of particle physics.
Further searches in knowledge from the IceCube and Auger neutrino detectors turned up no counterpart occasions, trimming the roster of unusual explanations.
“My guess is that some attention-grabbing radio propagation impact happens close to ice and likewise close to the horizon that I don’t totally perceive, however we actually explored a number of of these, and we haven’t been capable of finding any of these but both,” Wissel mentioned.
Hoping that PUEO may help
The subsequent balloon within the sequence is the Payload for Ultrahigh Power Observations, or PUEO, set for its first Antarctic voyage in December 2025.
It should carry extra antennas and sooner electronics, bettering sensitivity by not less than an element of 5 over ANITA.
“So, proper now, it’s considered one of these long-standing mysteries, and I’m excited that once we fly PUEO, we’ll have higher sensitivity,” Wissel concluded.
“In precept, we must always choose up extra anomalies, and perhaps we’ll truly perceive what they’re. We additionally may detect neutrinos, which might in some methods be much more thrilling.”
What occurs subsequent?
Elsewhere, devices buried deep in ice, anchored to the seafloor, or orbiting aboard satellites are racking up their very own successes.
In February 2025 a detector beneath the Pacific seafloor logged essentially the most energetic neutrino ever noticed, underscoring how shortly the self-discipline is advancing.
Whether or not ANITA’s anomalies show to be unique particles or a quirk of radio propagation, upcoming missions promise contemporary clues. Till then, we are going to all have to attend and surprise.
The complete research was printed within the journal Bodily Evaluation Letters.
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