NSF Delays Cosmic Microwave Background Experiment

A major project to study leftover radiation from the early universe using ultra-sensitive telescopes at the South Pole and Chile will not progress to the design stage “in its current form,” the National Science Foundation announced last week.

NSF said its decision to put the Cosmic Microwave Background Stage Four (CMB-S4) project on hold, despite strong scientific support, was because of the urgent need to upgrade aging infrastructure at the South Pole and elsewhere in Antarctica.

The interim director of NSF’s Astronomical Sciences Division, Chris Smith, explained at a May 7 meeting that the agency decided it “must prioritize the recapitalization of critical infrastructure at the South Pole so that the groundbreaking research it enables can continue to thrive.” The COVID-19 pandemic delayed infrastructure upgrades across Antarctica by years, and NSF has since sharply throttled back approvals for new research projects there as it works to clear the backlog.

Smith emphasized that the decision not to move the project from the development to the design phase is specific to its current form, leaving the door open to pursuing an alternative approach. Smith added that NSF remains committed to CMB science and will continue to support current CMB activities at the South Pole and in Chile.

NSF’s decision was a surprise and a disappointment for the hundreds of scientists involved in the project, particularly junior researchers considering their future careers, said Kevin Huffenberger, co-spokesperson for the CMB-S4 science collaboration and a physics professor at Florida State University, who was informed of the decision the day before the public announcement.

“We absolutely want the project to continue,” Huffenberger said. “Our planning always included telescopes in Chile, and from our prior planning, we considered a Chile-only option as a viable but somewhat more challenging alternative. We need to do some substantial work to develop the idea under the new guidance from NSF.”

Huffenberger added that project leaders “hope that the South Pole becomes available again, because our analysis does show that it is the best place to do the early universe / primordial gravitational wave portion of our science.”

Jim Strait, CMB-S4 project director and physicist at Lawrence Berkeley National Laboratory, confirmed his team is working on developing a new plan for the project with Chile as the only site.

“In selecting the configuration of CMB-S4, we conducted an Analysis of Alternatives, which identified the South Pole as the preferred location to address the inflation science, but we also identified the Chile site as a potentially viable location if the South Pole were not available,” Strait said. “We will now focus our effort on developing plans in that direction.”

The cosmic microwave background, sometimes referred to as the afterglow of the Big Bang, was discovered in 1964 and continues to be of deep interest to scientists studying the origin of the universe and the formation of galaxies. The CMB-S4 project has been in development for more than a decade, involving over 500 scientists across dozens of states and countries. Using an array of telescopes at the South Pole and the Chilean Atacama desert, the project planned to employ over 500,000 cryogenically-cooled superconducting detectors to measure the CMB with unprecedented precision. The project was estimated to cost around $800 million, jointly funded by NSF and the Department of Energy, and aimed to begin full operation in the early 2030s.

Recent major planning exercises by U.S. astronomy and particle physics communities identified the project as a top priority. It was also marked as “absolutely central” and “ready to initiate construction” in the High Energy Physics Advisory Panel’s facilities prioritization report , published the same week NSF announced it would not advance the project at this time.

The panel received a briefing about Antarctic infrastructure issues on May 9 from Jean Cottam, acting director of NSF’s Office of Polar Programs. She highlighted multiple infrastructure issues at the South Pole, including how the pandemic delayed construction of new lodging facilities at the McMurdo base on the coast. Until this lodging is completed in 2026, the number of people NSF can send to the South Pole will be significantly limited.

Cottam also said there is an urgent need to lift buildings at the South Pole due to snow accumulation, which has begun to deform steel support beams. How to prioritize solving these infrastructure challenges will be covered in the forthcoming South Pole Master Plan, Cottam said.

Asked when NSF will resume approving new projects at the South Pole, Cottam said a clearer timeline for the infrastructure upgrades would be available by the end of the year, once the master plan is completed. A draft of the plan was published on May 16 and is now open for public comment.

NSF’s latest budget request to Congress anticipates that Antarctica infrastructure upgrades will continue through the end of the decade.

Note: This article has been updated to include a comment from the CMB-S4 project director and to note the release of the draft South Pole Master Plan.