NSF delays major cosmic microwave background experiment

This article is adapted from a 15 May post on FYI, which reports on federal science policy. Both FYI and Physics Today are published by the American Institute of Physics.

A planned $800 million project to study ancient cosmic radiation using ultrasensitive telescopes at the South Pole and in Chile will not progress to the design stage “in its current form,” NSF announced on 7 May. The agency said the strong scientific support for the Cosmic Microwave Background Stage 4 (CMB-S4) experiment is outweighed by the urgent need to upgrade aging infrastructure at the South Pole and elsewhere in Antarctica.

NSF “must prioritize the recapitalization of critical infrastructure at the South Pole so that the groundbreaking research it enables can continue to thrive,” said Chris Smith, the interim director of the agency’s astronomical sciences division, at a National Academies of Sciences, Engineering, and Medicine meeting . The COVID-19 pandemic delayed infrastructure upgrades across Antarctica by years, and NSF has since sharply cut back on approvals for new research projects there as it works to clear the backlog.

The decision to not 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 emphasized. And he said that NSF remains committed to CMB science and will continue to support current studies of the early universe at the South Pole and in Chile.

In development for more than a decade, the CMB-S4 project would install more than 500 000 cryogenically cooled superconducting detectors in telescopes at the South Pole and in the Chilean Atacama Desert to measure the CMB with unprecedented precision. Research goals include searching for evidence of primordial gravitational waves, an expected signature of cosmological inflation, in CMB polarization measurements. Jointly funded by NSF and the Department of Energy, the experiment was slated to begin observations in the early 2030s .

Recent major planning exercises by US astronomy and particle-physics communities have identified CMB-S4 as a top priority (see Physics Today, February 2024, page 18 ). It was marked as “absolutely central” and “ready to initiate construction” in the High Energy Physics Advisory Panel’s facilities prioritization report , which was published the same week NSF announced that it would not advance the project for now.

The NSF decision was a surprise and a disappointment for the hundreds of scientists involved in the project, particularly junior researchers considering their future careers, says Kevin Huffenberger. A spokesperson for the CMB-S4 Science Collaboration and a physics professor at Florida State University, Huffenberger was informed of the decision the day before the public announcement. “We absolutely want the project to continue,” he says.

Huffenberger and Jim Strait, the CMB-S4 project director and a physicist at Lawrence Berkeley National Laboratory, say that the team has considered a Chile-only option and is now working on developing a new plan that does not involve the South Pole. But Huffenberger adds 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.”

The High Energy Physics Advisory Panel received a briefing on 9 May from Jean Cottam, acting director of NSF’s Office of Polar Programs, about the problems plaguing Antarctic infrastructure. The issues include pandemic-caused delays in constructing new lodging facilities at McMurdo Station. Until the 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 because of the accumulation of snow, which has begun to deform steel support beams. How to prioritize solving those infrastructure challenges will be covered in the forthcoming South Pole Station Master Plan.

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 is now open for public comment.

NSF’s latest budget request to Congress anticipates that South Pole station upgrades will continue through the end of the decade .