Back to Antarctica with SPIDER

It’s December, so that means it’s balloon time in Antarctica. McMurdo Station — the National Science Foundation’s field station on the southern tip of Ross Island — is once again buzzing with activity. Scientific ballooning operations were put on hold during the height of COVID-19, but scientists are now almost ready to make their first post-pandemic launch from Antarctica to the cusp of space.

Johanna Nagy, an assistant professor of physics in Arts & Sciences at Washington University in St. Louis, arrived in Antarctica a few weeks ago to help her team prepare for their upcoming launch. Balloon-borne experiments like hers have helped scientists answer important questions about the universe, Earth’s atmosphere, the sun and the space environment.

The instrument Nagy plans to fly, called SPIDER and led by researchers at the University of Illinois at Urbana-Champaign, will allow her team to look for a pattern, or polarization, in the earliest light we can measure. This statistically unique fingerprint would be produced by interactions with gravitational waves that could be traced back to the beginning of the universe.

“By searching for a particular polarization pattern in the cosmic microwave background — one that flips in a mirror — SPIDER will tell us about the universe when it was much less than one second old,” Nagy said.

Weather conditions and ground readiness will determine the exact launch date, but Nagy hopes their instrument will be airborne by early January 2023. The upcoming flight is the second of two planned flights for SPIDER (the first took place in January 2015).

“During the last flight, we were measuring light at two different frequencies,” said Nagy, who has been involved with SPIDER for more than a decade. “We are adding a third for this upcoming flight to let us measure galactic foregrounds better while also increasing the sensitivity of our measurement at the original two frequencies. We have also rebuilt or refurbished many subsystems in ways that could improve the quality and quantity of data.”

Nagy, a faculty fellow of the McDonnell Center for the Space Sciences (MCSS), and her graduate student Jared May built many new items for SPIDER’s next flight in her laboratory at Washington University.

“We’ve built several different types of radiation filters for our new high-frequency receivers, the vacuum windows that let light into the cryostat and the polarization modulators that help us separate signals from our own instrument from those that are produced in the sky,” she said.

“Both Jared and I spent the summer at the Columbia Scientific Balloon Facility in Palestine, Texas, assembling and testing the instrument alongside members of the hardware team from other institutions,” Nagy said. “This allowed us to demonstrate to NASA that our instrument was ready for an Antarctic deployment. It was the first time since the start of the pandemic that the team and instrument had been able to come together.”

May appreciated the collaboration as well.

“Seeing so many passionate and like-minded people come together to collaborate on such a complex project has truly been inspiring,” May said.

“From laminating some of SPIDER’s half-wave plates to filling our cryostat with liquid helium, knowing that my contributions are helping construct an instrument capable of measuring the afterglow of the Big Bang is incredible,” he said.

The team has prepared for a three-week flight at an altitude of roughly 110,000 feet above Antarctica. At this height, SPIDER will be collecting measurements above 99.5% of Earth’s atmosphere.

“This cosmic microwave background, or CMB, polarization signature is a unique probe of physics at much higher energies than we can access with terrestrial experiments,” Nagy said. “However, a major challenge in this measurement is distinguishing the light from the early universe from a similar pattern produced much later in our own galaxy. From this flight in particular, I’m hoping to learn more about these galactic foregrounds and how more complex models of them will help reveal more of the CMB.”

Even Antarctica hasn’t been spared from the challenges of COVID, and scientists like Nagy have faced a number of changes during this ballooning campaign as they have learned how to keep themselves safe and healthy while traveling internationally and living in a densely populated station. Some of these challenges have even made national news.

“Of course, when I was here for SPIDER’s first launch, I never dreamed I’d be back in the aftermath of a pandemic,” Nagy said. “This is the first season since 2020 that the Antarctic balloon facility has been able to operate, so we are very excited to have this launch opportunity.”

Nagy’s research focuses on experimental cosmology, with the goal of improving our understanding of the contents and evolution of the universe. Beyond the SPIDER effort, Nagy also has a leading role on a NASA-funded next-generation balloon mission known as Taurus, designed to map the polarization of the microwave sky.

“The physics department and MCSS have been really supportive of our SPIDER group at Washington University,” she said. “It’s really fun to work in a department with so many astro ballooning projects and lots of Antarctic flight experience in particular.”

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Funding: SPIDER is supported by NASA, through a grant from the Science Mission Directorate. Support in Antarctica is provided by the U.S. Antarctic Program, part of the National Science Foundation’s Office of Polar Programs.