For decades, the South Pole has been a wonderland for physicists. They have stared into its exquisitely clear sky to study the afterglow of the big bang—the cosmic microwave background (CMB)—and used the ice itself to spot nearly undetectable particles called neutrinos streaking from other galaxies. But plans for two big new projects at the pole could be delayed for years by less lofty infrastructure issues and a limited electrical supply.
In a 12 June “Dear Colleague” letter, the National Science Foundation (NSF) told researchers that, after the pandemic lockdown, it must attend to a backlog of maintenance at multiple Antarctic sites. At the South Pole, for the next several years the agency will only support experiments that have already been approved to go forward. “[P]roposers seeking support for new projects at South Pole Station should consult the cognizant program officer to discuss alternative locations,” the letter says.
That sentence has physicists wondering when NSF will go forward with two major projects that must be built at the pole. One would deploy new CMB telescopes there and the other would expand the gargantuan IceCube neutrino detector. The projects, known as CMB-S4 and IceCube-Gen2, aim to start building within 5 years. “Maybe in the next few weeks we’ll get a little more clarity what the Dear Colleague letter actually means,” says Mary Hall Reno, a theoretical physicist at the University of Iowa.
NSF’s warning comes at a delicate time, as by October an ad hoc Particle Physics Project Prioritization Panel (P5) must formulate a new 10-year plan for U.S. particle physics. “The problem is nobody knows” the true time frame for the projects, says Hitoshi Murayama, a theorist at the University of California, Berkeley, who chairs P5.
But physicists may be getting ahead of themselves, says James Ulvestad, acting director of NSF’s office of polar programs. Neither project has advanced beyond the R&D phase, he notes, much less gained approval for construction or funding from Congress. “Just getting through that process and then preparing for construction almost inevitably takes you nearer to the end of the decade anyway,” he says. He adds that as currently conceived, the projects would likely require more electrical power than the South Pole Station can provide.
CMB-S4 aims to be the definitive ground-based study of the big bang’s lingering radiation, which is rich in clues to the universe’s origin and structure. An $840 million collaboration between NSF and the Department of Energy, CMB-S4 would erect two 6-meter microwave telescopes in Chile and one 5-meter and nine 0.5-meter telescopes at the South Pole. Those at the pole would be essential for a key goal: detecting pinwheel-like swirls in the polarization of the CMB known as primordial B-modes. Those swirls would be a signal of distortions of space called gravitational waves rippling through the early universe, which in turn would be evidence that the newborn cosmos underwent an exponential growth spurt known as inflation.
The CMB-S4 team is ready to start prepping the site as soon as it gets the go-ahead, hopefully in 2028, says John Carlstrom, an astrophysicist and team member at the University of Chicago. There is some urgency, he notes, as that year Japan plans to launch a spacecraft called LightBIRD that also aims to detect the primordial B modes. “To be honest, late in the decade works,” Carlstrom says. “But if late in the decade becomes late in the next decade, we’re in trouble.”
IceCube-Gen2 would increase the size of the world’s biggest neutrino detector, which spots ultra–high energy neutrinos from space with strings of optical sensors embedded deep in the ice. The 5160 detectors watch for a flash of light—an optical shock wave—radiated by charged particles generated when a neutrino collides with an atomic nucleus. Last year, IceCube physicists reported 79 neutrinos coming from the heart of a nearby galaxy called NGC 1068, the first steady source of extragalactic neutrinos pinpointed.
The Gen2 project would deploy another 9600 optical sensors to increase the detector’s volume from 1 to 8 cubic kilometers, enabling it to detect more neutrino sources and ushering in an era of neutrino astronomy. Researchers hope to deploy the first new strings in 2028 and complete the task in 7 or 8 years. If the project slips several years, collaborators might look for other projects, Reno notes. “We’ve already had a 3-year delay with COVID,” she says. “With increased delays will you be losing the human resources you need to keep this sophisticated program going?”
But neither project can start before NSF fixes the infrastructure, Ulvestad says. The 7400-square-meter Amundsen-Scott South Pole Station and the support buildings for IceCube and the current CMB telescopes are all sinking into accumulating snow and need to be elevated. And the 48-year-old, snow-covered Quonset huts used to store fuel, supplies, and vehicles need reinforcing.
Congress has appropriated $60 million this year for such work, and NSF plans to spend similar amounts in the next 2 years. But the logistics of getting materials and people to the pole mean work there won’t begin until late 2026 and will likely take 2 or 3 years, Ulvestad says. That pushes construction for both science projects to 2028 or 2029 at the earliest.
It could come significantly later. Before either project can be presented to NSF’s governing National Science Board for approval, it must go through a design stage that typically lasts 3 to 6 years, says Linnea Avallone, NSF’s chief officer for research facilities. “Congress in particular has been very outspoken about wanting us to follow our processes,” she says. So, approval might not come until the end of the decade, with polar work to start a few years later.
Among the unresolved design issues is that of electrical power. CMB-S4 would require 170 kilowatts, 20% more than the current CMB telescopes. Eventually, IceCube-Gen2 would require 190 kilowatts, 2.5 times as much as IceCube. But power at the pole is limited, supplied by a diesel generator producing between 600 and 700 kilowatts.
In principle, NSF could install more generators and haul more fuel to the pole, says Albrecht Karle, a physicist and IceCube team member at the University of Wisconsin-Madison. Most fuel is towed overland 1600 kilometers from McMurdo Station on the coast by tractors in the so-called South Pole Traverse, which has run since 2006. “The traverse is generally scalable,” Karle says.
That’s not necessarily so, Ulvestad says. NSF runs three traverses per season, and for reasons of safety, increasing that number is unlikely, he says. Boosting the grid capacity at the South Pole would also require a separate project, not even proposed so far, that likely couldn’t be realized much before 2040, Ulvestad says.
Getting pushed late into the next decade is exactly what physicists hope to avoid. “It would be a shame to think after all these years, decades even, that we would get beat” to discovering primordial B modes, Carlstrom says. “It would feel like, ‘Really, we didn’t do it because we’re waiting for a building to be elevated?’”
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