Sometime in the next few years — no one knows exactly when — three NASA satellites, each as heavy as an elephant, will go dark.
They were drifting, losing altitude little by little. They’ve been observing 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 last transmissions and begin their final slow fall to Earth.
It’s the moment scientists are dreading.
When three orbiters – Terra, Aqua and Aura – are decommissioned, much of the data they were collecting will end up with them, and newer satellites won’t be able to handle the rest. Researchers will have to rely on alternative sources that may not meet their exact needs or find workarounds that allow their records to continue.
With some of the data these satellites collect, the situation is even worse: No other instrument will continue to collect that data. In a few short years, the good features they reveal about our world will become much fainter.
“The loss of this irreplaceable data is truly a tragedy,” said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology. “Just when the planet needs our greatest focus on understanding how we are affected by it and how we are influencing it, we seem to be disastrously sleeping on it. steering.”
The main area we’re keeping an eye on is the stratosphere, the most important home of the ozone layer.
In the cold, thin air of the stratosphere, ozone molecules are constantly being formed and destroyed, thrown and swept as they interact with other gases. Some of these gases are naturally occurring; others are there for us.
Ross J. Salawitch, an atmospheric scientist at the University of Maryland, says an instrument on Aura, the microwave sounder, gives us our best look yet at this seething chemical drama. Once the Aura disappears, our vision will blur significantly, he said.
Recently, data from the microwave limb sounder has proven its value in unexpected ways, Dr. Salawitch said. It shows the extent of damage to the ozone layer by horrifying forest fires in Australia in late 2019 and early 2020, and to Undersea volcanic eruption near Tonga by 2022. It helps show how much ozone-depleting pollution has entered the stratosphere over East Asia by the region’s summer monsoon.
If it hadn’t gone offline so soon, Dr. Salawitch said, the sound meter might well have helped unravel a major mystery. “The thickness of the ozone layer over populated areas of the Northern Hemisphere has barely changed over the past decade,” he said. “It’s probably recovering. And it’s not.”
Jack Kaye, deputy director for research at NASA’s Earth Science Division, acknowledged researchers’ concerns about the end of the sound generator. But he argues that other sources, including instruments on newer satellites, on the International Space Station and back on Earth, will still provide “a pretty good window into what the atmosphere is doing.” work”.
Financial realities force NASA to make “difficult decisions,” Dr. Kaye said. “Wouldn’t it be great if things lasted forever? Yes,” he said. But part of NASA’s mission is also to provide scientists with new tools, tools that help them see 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 you can,” he said.
For scientists studying our changing planet, the difference between the same data and almost the same data can be huge. They may think they understand how something is evolving. But only by monitoring it continuously, consistently, over a long period of time can they be confident about what is going on.
Even a brief interruption in the profile can create problems. Suppose an ice shelf collapses in Greenland. William B. Gail, former president of the American Meteorological Society, said unless you measure sea level rise before, during and after, you will never be sure that a sudden change is caused by caused by the collapse. “You can infer that, but you don’t have a quantitative record,” he said.
Last year, NASA solicited scientists’ opinions on how the end of Terra, Aqua, and Aura would affect their work. More than 180 of them answered the call.
In letters obtained by The New York Times through a Freedom of Information Act request, researchers expressed concerns about a variety of satellite data. Information about particles in wildfire smoke, desert dust and volcanic plumes. Measurements of the thickness of clouds. Fine-scale map of the world’s forests, grasslands, wetlands, and crops.
Even if there are alternative sources for this information, the scientists write, they may be less frequent, have lower resolution, or be limited to certain times of day, all determining factors. Determine the usefulness of the data.
Liz Moyer takes a close-up approach to studying Earth’s atmosphere: by flying instruments through it, in jets that travel much higher than most machines can fly. “I got into it because it was fun and it was hard to get there,” said Dr. Moyer, who teaches at the University of Chicago. “It’s hard to make instruments that work there, it’s hard to make measurements, it’s hard to get planes there.”
She said it will be even more difficult now that Aura is gone.
Dr Moyer said aircraft can sample the chemistry of the atmosphere directly, but to understand the whole picture, scientists still need to combine aircraft measurements with data from satellites. pure. “Without satellites, we would take snapshots without context,” she said.
Much of Dr. 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 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 that part of the atmosphere and at the exact moment it’s changing,” Dr. Moyer said.
The end of Terra and Aqua will affect how we monitor another important factor affecting our climate: the amount of solar radiation the planet receives, absorbs and reflects back space. The balance between these quantities – or indeed the imbalance – determines how much the Earth warms or cools. And to understand it, scientists rely on the instruments of NASA’s Cloud and Earth’s Radiant Energy System, or CERES.
Currently, four satellites are flying with CERES instruments: Terra, Aqua, with two newer satellites also coming to an end. However, only one replacement is being made. Its longevity? Five years.
“Over the next 10 years, we will be down from four missions to one, and the remaining mission will be past its prime,” said Norman G. Loeb, the NASA scientist who heads CERES. “For me, that was really sobering.”
Today, with the growth of the private space industry and the development of satellites around Earth, NASA and other agencies are exploring a different approach to monitoring our planet. The future may lie in smaller, lighter devices that can be delivered into orbit more cheaply and quickly than the Terra, Aqua and Aura of their time.
The National Oceanic and Atmospheric Administration is developing a fleet of such vessels to monitor weather and climate. Dr. Loeb and others at NASA are working on a lightweight device to further measure Earth’s energy balance.
But for such technologies to be useful, Dr. Loeb said, they must start flying before today’s orbiters go dark.
“You need a good, long overlap period to understand the differences and iron out the kinks,” he said. “Otherwise, it will be difficult to trust these measurements if we don’t have a chance to prove them based on current measurements.”
In some ways, it’s a credit to NASA that Terra, Aqua and Aura have survived this long, scientists say. “Thanks to a combination of engineering excellence and extreme luck, we’ve had these things for 20 years,” said Waleed Abdalati, a former NASA chief scientist now at the University of Colorado Boulder. now”.
“We’re kind of drawn to these satellites. We are victims of our own success,” says Dr. Abdalati. “Eventually,” he added, “the luck ran out.”
