Within the next few years, no one knows exactly when, three NASA satellites, each weighing as much as an elephant, will go dark.
They are already drifting, slowly losing their height. They’ve been looking after the planet for more than two decades, much longer than anyone expected, helping us predict weather, manage wildfires, track oil spills and more. But age is catching up with them, and soon they will send their final message and begin their slow, final descent to Earth.
It’s a moment scientists dread.
Sign up for The Morning newsletter from The New York Times
When the three orbiters (Terra, Aqua, and Aura) are shut down, much of the data they collected will end with them, and new satellites won’t be able to fill all of that gap. Researchers will either have to rely on alternative sources that may not fully meet their needs or seek workarounds that will allow their recordings to continue.
The situation is even worse when considering some of the data these satellites collect: No other vehicle will be able to continue collecting this data. In a few years, the subtle features they reveal about our world will become much less clear.
“Losing this irreplaceable data is simply tragic,” said atmospheric chemist Susan Solomon of the Massachusetts Institute of Technology. “We seem to be terribly asleep at the wheel, just at the moment when the planet needs us most to focus on understanding how we are affected by it and how we are affecting it.”
The real area where we lose sight is the stratosphere, the most important home of the ozone layer.
Throughout the cold, thin air of the stratosphere, ozone molecules are constantly being created, destroyed, blown around, and drifted as they interact with other gases. Some of these gases are of natural origin; Others are there because of us.
An instrument on Aura — a microwave limb probe — gives us our best view of this seething chemical drama, said Ross J. Salawitch, an atmospheric scientist at the University of Maryland. “When the aura is gone, our vision will darken significantly,” he said.
Recently, data from microwave limb sounding has proven its value in unexpected ways, Salawitch said. This showed how devastating bushfires in Australia in late 2019 and early 2020 and an undersea volcanic eruption near Tonga in 2022 damaged ozone. It helped show how far ozone-depleting pollution has risen into the stratosphere in the East. Asia by the region’s summer monsoon.
Salawitch said the siren could also help solve a big mystery if it hadn’t gone offline so quickly. “The thickness of the ozone layer in populated areas in the Northern Hemisphere has remained virtually unchanged over the past decade,” he said. “He must be getting better. And it’s not like that.
Jack Kaye, deputy director of research for NASA’s Earth Sciences Division, acknowledged researchers’ concerns about the probe’s end. But he argued that other sources, including instruments on the International Space Station and new satellites on Earth, would still provide “a pretty good window into what the atmosphere is doing.”
Kaye said financial realities forced NASA to “make difficult decisions.” “Would it be wonderful if everything lasted forever? “Yes,” she said. But part of NASA’s mission is also to provide scientists with new tools to help them look at our world in new ways, she said. “It’s not the same, but you know, if things can’t be the same, do the best you can,” she said.
For scientists studying our changing planet, the difference between identical and nearly identical data can be stark. They may think they understand how something develops. But only by watching it constantly, unchangingly and over a long period of time can they be sure of what is going on.
Even a short break in the records can cause problems. Suppose an ice sheet collapses in Greenland. William B. Gail, former president of the American Meteorological Society, said that unless you measure sea level rise before, during and after, you can never be sure whether the collapse caused a sudden change. “You can guess that, but you don’t have a numerical record,” he said.
Last year, NASA turned to scientists for their thoughts on how the demise of Terra, Aqua, and Aura would affect their work. More than 180 responded to the call.
In letters obtained by the New York Times through a Freedom of Information Act request, the researchers expressed concern about a wide range of data from satellites. Information about particles in wildfire smoke, desert dust and volcanic plumes. Measuring the thickness of clouds. Fine-scale maps of the world’s forests, grasslands, wetlands and crops.
Even if there are alternative sources for this information, they may be less frequent, lower resolution, or limited to certain times of day, all factors that shape how useful the data is, the scientists wrote.
Liz Moyer takes a close-up approach to studying Earth’s atmosphere: by flying instruments on jets that fly much higher than most aircraft can go. “I got into this because it’s exciting and hard to get there,” said Moyer, who teaches at the University of Chicago. “It’s hard to make tools that will work there, it’s hard to make measurements, it’s hard to find planes to go there.”
“Everything will be even harder after Aura is gone,” he said.
Airplanes can directly sample the chemistry of the atmosphere, but to understand the big picture, scientists need to combine aircraft measurements with satellite readings, Moyer said. “Without satellites, we’re taking snapshots with no context,” he said.
Much of Moyer’s research focuses on thin, icy clouds that form 9 to 12 miles above the ground in one of the most mysterious layers of the atmosphere. These clouds help warm the planet, and scientists are still trying to figure out how human-caused climate change affects them.
“It looks like we’re going to stop observing this part of the atmosphere right at the time when this area is changing,” Moyer said.
The end of Terra and Aqua will affect the way we monitor another important driver of our climate: how much solar radiation the planet receives, absorbs, and reflects back into space. The balance, or indeed imbalance, between these quantities determines how much the Earth will warm or cool. To figure this out, scientists rely on NASA’s Clouds and Earth’s Radiant Energy System (CERES) instruments.
Four satellites are currently flying with CERES instruments: Terra, Aqua, as well as two new satellites nearing their end. However, only one spare part is being worked on. Life expectancy? Five years.
“We will go from four missions down to one mission in the next 10 years, and the rest will be past their peak,” said Norman G. Loeb, the NASA scientist who leads CERES. “To me, that’s really sobering.”
These days, with the rise of the private space industry and the proliferation of satellites around Earth, NASA and other agencies are exploring a different approach to spying on our planet. The future may lie in smaller, lighter devices that can be deployed into orbit more cheaply and nimbly than at the time of Terra, Aqua, and Aura.
The National Oceanic and Atmospheric Administration is developing such a fleet to monitor weather and climate. Loeb and others at NASA are working on a lightweight device to continue measurements of the Earth’s energy balance.
But for such technologies to be useful, Loeb said, they need to start flying before today’s orbiters go dark.
“You need a good, long period of overlap to understand the differences, to work out the distortions,” he said. “Otherwise, it would be really hard to trust these measurements if we didn’t have a chance to prove them against existing measurements.”
Scientists said it was partly to NASA’s credit that Terra, Aqua and Aura lasted this long. “Thanks to a mix of excellent engineering and a tremendous amount of luck, we’ve had these for 20 years,” said Waleed Abdalati, a former NASA chief scientist who now works at the University of Colorado Boulder.
“We’ve kind of become dependent on these satellites. “We are victims of our own success,” Abdalati said. “Eventually,” he added, “the luck runs out.”
c.2024 New York Times Corporation