Mar 21, 2022 12:00 PM

Astronomers Tally the Growing Carbon Footprint of Space Science

Observatories require electricity and computing power to process data from deep space. Is there a way to make them run greener?

For generations, astronomers have spent lonely evenings at remote mountaintop observatories peering at stars and planets as they whirl overhead. Today’s astronomy, however, is being conducted on a more massive scale: Huge arrays of receivers continually feed signals into power-hungry supercomputers, and multibillion-dollar spacecraft take years to build and tons of rocket fuel to launch. Next-generation ground-based observatories will be enormous, such as the Extremely Large Telescope, which will eclipse the size of the Colosseum in Rome when it is completed in 2024.

Now some researchers are thinking about the carbon footprint of modern astronomy and realizing that they, like everyone else, might have to consider alternative ways of doing business in order to keep climate-warming emissions in check. That could include switching to solar power, which makes sense for observatories in Australia or Chile, where there are clear skies and lots of sunshine. Or it could mean finding other ways to conserve energy.

“We’re at the point where we need to do science on an industrial scale,” says Adriaan Schutte, program manager for the Square Kilometer Array, a linked system of two radio telescopes under construction in South Africa and Australia, which will jointly comprise several thousand individual receivers. “If you want to discover something, you're not going to do this just with your telescope in the backyard,” says Schutte. “We are using industrial-scale energy, and you need to plan ahead for your increased CO₂ emissions.”

Today in the journal Nature Astronomy, a group of European astronomers released an estimate of the global carbon footprint of all modern astronomy, including both ground- and space-based observatories. They calculate that the energy used to build and maintain the existing infrastructure is equal to 1.2 million metric tons of carbon dioxide per year, and an overall lifetime footprint of 20.3 million metric tons. That larger figure equates to the annual emissions of five coal-burning power plants, according to the Environmental Protection Agency's Greenhouse Gas Equivalencies Calculator.

For example, NASA’s new $9.8 billion James Webb Space Telescope, which launched in December and will return its first images to Earth this summer, will have a carbon footprint of 300,000 metric tons of CO₂, according to the new study. That’s equal to burning 1,655 railcars of coal, using the same EPA calculator. The Very Large Telescope, which is based in Paranal, Chile, has an estimated carbon footprint of 540,000 metric tons of CO₂ over its 21-year lifetime, the study reported.

Some might ask why astronomers would worry about the size of their carbon footprint when other industries are much worse. Annie Hughes, a coauthor on the paper and a staff astronomer at France’s Institut de Recherche de Astrophysique et Planétologie (IRAP), says that it’s important for scientists to lead by example. “Humankind is facing a climate emergency,” Hughes said during a press teleconference on March 17. “The scientific evidence is unequivocal that human activities are responsible for modifying the Earth's climate. And the scientific evidence is equally clear that we must profoundly change our activities in the next decade. So faced with such urgency, I and the authors of this paper believe that everyone needs to act now to reduce their personal and professional carbon emissions. This includes astronomers, like everybody else.”

Hughes said scientists need to set a moral example if the rest of society is going to follow, otherwise “it's like your dad telling you that you shouldn't smoke while he himself is smoking a cigarette. Why would you take his word seriously?”

To come up with the new carbon footprint figures, the authors used estimates from previous papers showing how much energy was consumed during construction (for terrestrial observatories) and launch (for orbiting ones), and projections of the energy cost of operating them over their expected lifetimes. The authors say their figures are good approximations, but not perfect. Some uncertainty arises because the results change depending on whether the previous estimates were derived using the mass of the object or the carbon cost of building it. For example, the Hubble Space Telescope, which has been orbiting for more than 31 years, has an estimated footprint of 555,000 metric tons of CO₂ by mass, or 1.1 million metric tons by carbon cost.

Jürgen Knödlseder, research director at IRAP and the paper’s lead author, said that astronomical observatories are growing in both size and energy demands. “There is this general trend that these infrastructures are becoming bigger and bigger,” Knödlseder said. “So you can just imagine that things won't get better.”

Not everyone agrees with that assessment. Schutte, who has helped design the Square Kilometer Array telescopes over the past seven years, says there are ways to make big observatories less power-hungry. “The best way to not emit CO₂ is to not use the power,” he says.

In addition to installing solar panels at the two desert locations in Australia and South Africa, Schutte says he and his team required electronic equipment to switch to sleep mode when it’s not actively running. They also required a more efficient computer circuit called a field programmable gate array for data processing, instead of a graphics processing unit. Schutte says that as a result of these efficiency adjustments, the amount of energy budgeted for the telescopes' final contract was three times lower than the initial estimate in 2014. “We are giving every subsystem a power limit,” Schutte says. “We are writing that into the contracts.”

The notion of making astronomy greener has been percolating for the past few years. This 2020 study by Australian space and computing researchers estimated the carbon footprint of flights their nation’s astronomers take to attend conferences and the energy used by supercomputers to crunch data from space. They calculated that Australia’s astronomical supercomputing burned 15,000 metric tons of carbon dioxide per year, or four times as much as astronomers’ air travel. Similarly, a 2021 study by researchers in the Netherlands calculated the carbon footprint of the nation’s six astronomical institutions at just under 4,900 metric tons per year.

The 2020 Astrophysics and Astronomy Decadal Survey, which was actually released in November 2021 thanks to pandemic delays, also touched on environmental issues when recommending priorities for the next 10 years of space science. The panelists noted that the work of the typical astrophysicist generates 20 to 35 tons of carbon annually, largely owing to travel and data consumption. They recommended that scientists make use of remote observing opportunities and remote or hybrid conferences, and consider reducing or mitigating carbon production when planning new facilities. They encouraged researchers to participate in public discussions about climate change, and to use introductory astronomy classes to make students aware of it. The report also highlighted failures to engage with local and indigenous people when constructing new observatories, particularly the proposed Thirty Meter Telescope at Mauna Kea, where native Hawaiians have fought to preserve a volcanic peak they hold sacred.

Some astronomers believe that a reckoning on energy use might be good for astronomy. Travis Rector, a professor of physics and astronomy at the University of Alaska, Anchorage, says that astronomers are finding ways to be more energy-efficient while exploring the nature of the universe. “We want to be part of the solution,” says Rector, who studies early star formation with data from an observatory in Chile and was not involved in the new study. “The goal right now is first to determine where the sources of our emissions are, and then look for ways to reduce those emissions. We're trying to use this as an opportunity to find ways that we can do our profession better and still advance our science.”