Sometime in the next few years—no one knows exactly when—three NASA satellites, each as heavy as an elephant, will go dark.
They are already drifting, losing height bit by bit. They’ve been watching the planet for over two decades, much longer than anyone expected, helping us predict the weather, manage wildfires, monitor oil spills, and more. But they are coming of age and soon they will send out their last transmissions and begin their slow, final fall to Earth.
It’s a moment scientists dread.
When the three orbiters — Terra, Aqua and Aura — are decommissioned, much of the data they’ve collected will be gone with them, and the newer satellites won’t be picking up all the slack. Researchers will either have to rely on alternative sources that may not meet their exact needs or seek solutions to allow their records to continue.
With some of the data collected by these satellites, the situation is even worse: No other means will continue to collect it. In a few years, the nice features they reveal about our world will become much more obscure.
“The loss of this irreplaceable data is just tragic,” said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology. “Just when the planet most needs us to focus on understanding how we are affected by it and how we affect it, we seem to be disastrously asleep at the wheel.”
The main area we lose sight of is the stratosphere, the all-important home of the ozone layer.
Throughout the cold, thin air of the stratosphere, ozone molecules are constantly being formed and destroyed, ejected and drifted, as they interact with other gases. Some of these gases are of natural origin. others are there because of us.
One instrument in Aura, the Edge Microwave Sounder, gives us our best look at this rainy chemical drama, said Ross J. Salawitch, an atmospheric scientist at the University of Maryland. Once the Aura is gone, our vision will fade significantly, he said.
Recently, data from the microwave sounder has proven its value in unexpected ways, Dr. Salawitch said. It showed how much ozone damage was caused by the devastating wildfires in Australia in late 2019 and early 2020 and by the undersea volcanic eruption near Tonga in 2022. It helped show how much ozone-depleting pollution reached the stratosphere in East Asia from the summer monsoon of the region.
If it didn’t go offline so soon, the sinker could also help solve a major mystery, Dr. Salawitch said. “The thickness of the ozone layer over populated areas in the Northern Hemisphere has hardly changed over the past decade,” he said. “He should recover. And it is not.”
Jack Kay, the associate director for research in NASA’s Earth Science Division, acknowledged researchers’ concerns about the probe’s end. But he argued that other sources, including instruments on newer satellites, on the International Space Station and back here on Earth, would still provide “a very good window into what the atmosphere is doing.”
Economic realities are forcing NASA to make “tough decisions,” Dr. Kaye said. “Wouldn’t it be great if everything lasted forever? Yes,” he said. But part of NASA’s mission is also to give scientists new tools, ones that help them see our world in new ways, he said. “It’s not the same, but, you know, if everything can’t be the same, you do the best you can,” he said.
For scientists studying our changing planet, the difference between the same data and nearly the same data can be huge. They may think they understand how something develops. But only by watching it continuously, in an unchanging way, over a long period of time, can they be sure of what is happening.
Even a small break in records can cause problems. Let’s say an ice shelf is collapsing in Greenland. If you didn’t measure sea-level rise before, during and after, you’d never be sure that a sudden change was caused by the collapse, said William B. Gail, former president of the American Meteorological Society. “You might assume that, 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 raised concerns about a wide range of data from the satellites. Information on particles in forest fire smoke, desert dust and volcanic plumes. Cloud thickness measurements. Fine-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 of lower resolution or limited to certain times of day, all factors that shape how useful the data is.
Liz Moyer takes an up-close approach to studying Earth’s atmosphere: 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 Dr. Moyer, who teaches at the University of Chicago. “It’s hard to make instruments that work there, hard to make measurements, hard to find aircraft that go there.”
It will be even more difficult when Aura is gone, he said.
Airplanes can measure atmospheric chemistry directly, but to understand the big picture, scientists still need to combine aircraft measurements with satellite measurements, Dr. Moyer said. “Without the satellites, we’re out there taking snapshots without a frame,” he said.
Much of the research by Dr. Moyer focuses on the thin, icy clouds that form nine to 12 miles above the ground, in one of the atmosphere’s most mysterious layers. These clouds are helping to warm the planet, and scientists are still trying to understand how human-caused climate change is affecting them.
“It looks like we’re going to stop observing this part of the atmosphere, and just at a time when it’s changing,” Dr Moyer said.
The end of Terra and Aqua will affect how we monitor another important factor in 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. And to figure it out, scientists are relying on NASA’s Cloud and Earth Energy Radiation System, or CERES, instruments.
Four satellites are currently flying with CERES instruments: Terra, Aqua, and two younger ones that are also nearing their end. However, only one replacement is in the works. His life expectancy? 5 years.
“Within the next 10 years, we’ll go from four missions to one, and the remaining ones will be past their prime,” said Norman G. Loeb, the NASA scientist who leads CERES. “For me, that’s really disappointing.”
These days, with the rise of the private space industry and the proliferation of satellites orbiting Earth, NASA and other agencies are exploring a different approach to keeping an eye on our planet. The future may lie 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. Dr. 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, Dr. Loeb said, they must begin flying before today’s orbits go dark.
“You need a good, long period of overlap to understand the differences, to work out the kinks,” he said. “If not, then it’s going to be very difficult to have confidence in those measurements if we haven’t had a chance to prove them against current measurements.”
In a way, it’s a credit to NASA that Terra, Aqua and Aura have lasted as long as they have, scientists said. “Through a combination of brilliant engineering and sheer luck, we’ve had these for 20 years,” said Waleed Abdalati, a former NASA chief scientist now at the University of Colorado Boulder.
“We’re stuck on these satellites. We are victims of our own success,” said Dr. Abdalati. “Finally,” he added, “luck runs out.”