by Sometime in the next few years – no one knows exactly when – NASA’s three satellites, each as heavy as an elephant, will pass by dark.
Already they are drifting, losing altitude bit by bit. They have been looking down on the planet for over twenty years, far longer than expected, helping us predict the weather, manage wildfires, monitor oil spills and much more. But age is catching up with them, and soon they will send their final transmission and begin their slow, final fall to Earth.
It is a moment that scientists are afraid of.
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When the three orbiters – Terra, Aqua and Aura – are powered down, much of the data they’ve been collecting will cease, and newer satellites won’t pick up all the slack. Researchers will need to rely on alternative sources that may not meet their exact needs or look for work problems in order to continue their records.
With some of the data collected by these satellites, the situation is even worse: No other instruments will still be collecting. In a few years, the beautiful aspects they reveal about our world will be much more obscure.
“To lose this irreplaceable data is simply tragic,” said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology. “Just when the planet is most focused on understanding how it affects us, and how it affects us, we seem to be disastrously asleep at the wheel.”
The stratosphere, the vital home of the ozone layer, is the main area where we are wasting our time.
Throughout the thin, cold air of the stratosphere, ozone molecules are constantly being formed and destroyed, thrown and swept away, as they interact with other gases. Some of these gases have a natural origin; other people exist because of us.
An instrument on Aura, the microwave probe, gives us the best view yet of this exciting chemical drama, said Ross J. Salawitch, an atmospheric scientist at the University of Maryland. When Aura is gone, our vision will be greatly diminished, he said.
Recently, data from the microwave arm sounder is proving its value in unexpected ways, Salawitch said. It showed the extent of damage to the ozone caused by the devastating wildfires in Australia in late 2019 and early 2020, and by the volcanic eruption under the sea near Tonga in 2022. It helped show how much pollution depletes ozone. which was entering the stratosphere over the East. Asia at the region’s summer monsoon.
If it wasn’t going offline so soon, the sounder could also help to solve a big mystery, Salawitch said. “The thickness of the ozone layer has barely changed over populated regions in the Northern Hemisphere over the past decade,” he said. “He should be recovering. And no.”
Jack Kaye, the associate director of research at NASA’s Earth Science Division, acknowledged the researchers’ concerns about the end of the sounder. But he argued that other sources, including instruments on newer satellites, on the International Space Station and here on Earth, would provide “a really good window into what’s going on in the atmosphere”.
Financial realities force NASA to “make tough decisions,” Kaye said. “Would it be great for everything to last forever? Yes,” he said. But part of NASA’s mission is also to offer scientists new tools, ones that will help them look at our world in new ways, he said. “It’s not the same, but, you know, if everything’s not the same, you try your best,” he said.
For scientists who study our changing planet, the difference between the same and nearly identical data can be huge. They may think they understand how something is developing. But it is by continuously monitoring it, in an unchanging way, over a long period of time, that they can be confident about what is going on.
Even a short break in the records can cause problems. Say an ice shelf collapses in Greenland. If you haven’t measured sea-level rise before, during and after it, you’ll never be sure that the fall caused a sudden change, said William B. Gail, past president of the American Meteorological Society. “You might think so, but you don’t have a quantitative record,” he said.
Last year, NASA asked scientists for thoughts on how the end of Terra, Aqua and Aura would affect their work. More than 180 of them answered the call.
In their 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 the satellites. Information about the particles in wildfire smoke, desert dust and volcanic plumes…. Measurements of the thickness of clouds. Small scale maps of the world’s forests, grasslands, wetlands and crops.
Even if there are alternative sources for this information, the scientists wrote, they may be less frequent, or with lower resolution, or limited to certain times of the day, all factors that shape how useful it is. the details.
Liz Moyer takes an intimate approach to studying the Earth’s atmosphere: by flying instruments through it, on jets that travel much higher than most airplanes can go. “I got into it because it’s exciting and it’s hard to get there,” said Moyer, who teaches at the University of Chicago. “It’s hard to build tools that work there, hard to make measurements, hard to get aircraft that go there.”
It will be even harder when Aura is gone, she said.
Airplanes can directly sample the chemistry of the atmosphere, but to understand the big picture, scientists still need to combine aircraft measurements with satellite readings, Moyer said. “Without the satellites, we’re out there taking pictures without context,” she said.
Much of Moyer’s research focuses on the thin, icy clouds that lie 9-12 miles above the ground, in one of the most mysterious layers of the atmosphere. These clouds are helping to warm the planet, and scientists are still trying to figure out how they are affected by human-caused climate change.
“It looks like we’re going to stop observing that part of the atmosphere, and right at a time when it’s changing,” Moyer said.
The end of Terra and Aqua will affect how we monitor another important driver of our climate: how much solar radiation the planet receives, absorbs and bounces back into space. The balance between these amounts – or, really, the imbalance – determines how much the Earth warms or cools. To understand it, scientists rely on NASA’s Clouds and Earth’s Radiant Energy System, or CERES, instruments.
Currently, there are four satellites flying with CERES instruments: Terra, Aqua, as well as two newer satellites that are also nearing their end. But only one replacement is in the works. His life expectancy? Five years.
“Within the next 10 years, we’ll go from four missions to one, and the one that’s left will be beyond its primary mission,” said Norman G. Loeb, the NASA scientist in charge of CERES. “To me, that’s really shocking.”
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 keeping an eye on our planet. Perhaps the future will be with smaller, lighter instruments, ones that could be put into orbit more cheaply and nimbly than Terra, Aqua and Aura were back in the day.
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 instrument to continue their measurements of Earth’s energy balance.
But for such technologies to be useful, Loeb said, they must start flying before today’s orbiters go dark.
“You need a good long period of overlap to understand the differences, to work out the connections,” he said. “If not, it will be very difficult to trust these measurements, unless we have an opportunity to prove them against existing measurements.”
In a way, it’s to NASA’s credit that Terra, Aqua and Aura lasted as long as they did, scientists said. “Through a combination of excellent engineering and sheer luck, we’ve had these for 20 years now,” said Waleed Abdalati, a former NASA chief scientist who is now at the University of Colorado Boulder.
“We went into these satellites. We are victims of our own success,” said Abdalati. “Ultimately,” he said, “the luck is on.”
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