Sometime in the next few years — no one knows exactly when — three NASA satellites, each one as heavy as an elephant, will go dark.
Already they are drifting, losing height bit by bit. They have been gazing down at the planet for over two decades, far longer than anyone expected, helping us forecast the weather, manage wildfires, monitor oil spills and more. But age is catching up to them, and soon they will send their last transmissions and begin their slow, final fall to Earth.
It’s a moment scientists are dreading.
When the three orbiters — Terra, Aqua and Aura — are powered down, much of the data they’ve been collecting will end with them, and newer satellites won’t pick up all of the slack. Researchers will either have to rely on alternate sources that might not meet their exact needs or seek workarounds to allow their records to continue.
With some of the data these satellites gather, the situation is even worse: No other instruments will keep collecting it. In a few short years, the fine features they reveal about our world will become much fuzzier.
“Losing this irreplaceable data is simply tragic,” said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology. “Just when the planet most needs for us to focus on understanding how we are affected by it, and how we are affecting it, we seem to be disastrously asleep at the wheel.”
The main area we’re losing eyes on is the stratosphere, the all-important home of the ozone layer.
Across the stratosphere’s cold, thin air, ozone molecules are constantly being formed and destroyed, tossed and swept, as they interact with other gases. Some of these gases have natural origins; others are there because of us.
An instrument on Aura, the microwave limb sounder, gives us our best line of sight into this seething chemical drama, said Ross J. Salawitch, an atmospheric scientist at the University of Maryland. Once Aura is gone, our vision will dim considerably, he said.
Recently, data from the microwave limb sounder has been proving its worth in unexpected ways, Dr. Salawitch said. It showed how much damage was done to ozone 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 was getting lofted into the stratosphere over East Asia by the region’s summer monsoon.
If it weren’t going offline so soon, the sounder might also help unravel a big mystery, Dr. Salawitch said. “The thickness of the ozone layer over populated regions in the Northern Hemisphere has hardly changed over the last decade,” he said. “It should be recovering. And it’s not.”
Jack Kaye, the associate director of research at NASA’s Earth Science Division, acknowledged 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 back here on Earth, would still provide “a pretty good window into what the atmosphere is doing.”
Financial realities force NASA to make “tough decisions,” Dr. Kaye said. “Would it be great to have everything last forever? Yeah,” he said. But part of NASA’s mission is also to offer scientists new tools, ones that help them look at our world in new ways, he said. “It’s not the same, but, you know, if not everything can be the same, you do the best that you can,” he said.
To scientists who study our changing planet, the difference between the same data and almost the same data can be vast. They might think they understand how something is evolving. But only by monitoring it continuously, in an unchanging way, over a long stretch of time, can they be confident about what’s going on.
Even a short break in the records can create problems. Say an ice shelf collapses in Greenland. Unless you were measuring sea-level rise before, during and after, you’ll never be sure a sudden change…
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