\n<\/p>\n
Sometime in the next few years \u2014 no one knows exactly when \u2014 three NASA satellites, each one as heavy as an elephant, will go dark.<\/p>\n
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.<\/p>\n
It\u2019s a moment scientists are dreading.<\/p>\n
When the three orbiters \u2014 Terra, Aqua and Aura \u2014 are powered down, much of the data they\u2019ve been collecting will end with them, and newer satellites won\u2019t 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.<\/p>\n
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.<\/p>\n<\/div>\n<\/div>\n
\u201cLosing this irreplaceable data is simply tragic,\u201d said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology. \u201cJust 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.\u201d<\/p>\n
The main area we\u2019re losing eyes on is the stratosphere, the all-important home of the ozone layer.<\/p>\n<\/div>\n<\/div>\n
Across the stratosphere\u2019s 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.<\/p>\n
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.<\/p>\n
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\u2019s summer monsoon.<\/p>\n<\/div>\n<\/div>\n
If it weren\u2019t going offline so soon, the sounder might also help unravel a big mystery, Dr. Salawitch said. \u201cThe thickness of the ozone layer over populated regions in the Northern Hemisphere has hardly changed over the last decade,\u201d he said. \u201cIt should be recovering. And it\u2019s not.\u201d<\/p>\n
Jack Kaye, the associate director of research at NASA\u2019s Earth Science Division, acknowledged researchers\u2019 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 \u201ca pretty good window into what the atmosphere is doing.\u201d<\/p>\n<\/div>\n<\/div>\n
Financial realities force NASA to make \u201ctough decisions,\u201d Dr. Kaye said. \u201cWould it be great to have everything last forever? Yeah,\u201d he said. But part of NASA\u2019s mission is also to offer scientists new tools, ones that help them look at our world in new ways, he said. \u201cIt\u2019s not the same, but, you know, if not everything can be the same, you do the best that you can,\u201d he said.<\/p>\n<\/div>\n<\/div>\n
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\u2019s going on.<\/p>\n
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\u2019ll never be sure a sudden change was caused by the collapse, said William B. Gail, a former president of the American Meteorological Society. \u201cYou might surmise it, but you don\u2019t have a quantitative record,\u201d he said.<\/p>\n
Last year, NASA canvassed scientists for thoughts on how the end of Terra, Aqua and Aura would affect their work. More than 180 of them answered the call.<\/p>\n
In their letters, which The New York Times obtained through a Freedom of Information Act request, the researchers voiced worries 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. Fine-scale maps of the world\u2019s forests, grasslands, wetlands and crops.<\/p>\n
Even if there are alternate sources for this information, the scientists wrote, they might be less frequent, or lower resolution, or limited to certain times of day, all factors that shape how useful the data is.<\/p>\n<\/div>\n<\/div>\n
Liz Moyer takes an up-close approach to studying Earth\u2019s atmosphere: by flying instruments through it, on jets that travel much higher than most planes can go. \u201cI got into it because it\u2019s exciting and it\u2019s hard to get there,\u201d Dr. Moyer, who teaches at the University of Chicago, said. \u201cIt\u2019s hard to build instruments that work there, hard to make measurements, hard to get aircraft that go there.\u201d<\/p>\n
It will be even harder once Aura is gone, she said.<\/p>\n
Planes can sample the atmosphere\u2019s chemistry directly, but to understand the big picture, scientists still need to combine aircraft measurements with satellite readings, Dr. Moyer said. \u201cWithout the satellites, we\u2019re out there taking snapshots with no context,\u201d she said.<\/p>\n
Much of Dr. Moyer\u2019s research focuses on the thin, icy clouds that form nine to 12 miles above the ground, in one of the atmosphere\u2019s most mysterious layers. These clouds are helping to warm the planet, and scientists are still trying to figure out how human-induced climate change is influencing them.<\/p>\n
\u201cIt seems like we\u2019re going to just stop observing that part of the atmosphere, and exactly at a time when it\u2019s changing,\u201d Dr. Moyer said.<\/p>\n<\/div>\n<\/div>\n
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 bounces back to space. The balance between these amounts \u2014 or, really, the imbalance \u2014 determines how much Earth warms or cools. And to understand it, scientists rely on the instruments of NASA\u2019s Clouds and the Earth\u2019s Radiant Energy System, or CERES.<\/p>\n
Right now, four satellites are flying with CERES instruments: Terra, Aqua, plus two newer ones that are also nearing their end. Yet only one replacement is in the works. Its life expectancy? Five years.<\/p>\n
\u201cWithin the next 10 years, we\u2019re going to go from four missions down to one, and the one remaining will be past its prime,\u201d said Norman G. Loeb, the NASA scientist who leads CERES. \u201cTo me, that\u2019s really sobering.\u201d<\/p>\n
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 eyes 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 their day.<\/p>\n
The National Oceanic and Atmospheric Administration is developing such a fleet for monitoring weather and climate. Dr. Loeb and others at NASA are working on a lightweight instrument for continuing their measurements of Earth\u2019s energy balance.<\/p>\n<\/div>\n<\/div>\n
But for such technologies to be useful, Dr. Loeb said, they have to start flying before today\u2019s orbiters go dark. <\/span><\/p>\n \u201cYou need a good, long period of overlap to understand the differences, work out the kinks,\u201d he said. \u201cIf not, then it\u2019s going to be really difficult to have trust in these measurements, if we haven\u2019t had a chance to prove them against the current measurements.\u201d<\/p>\n In a way, it\u2019s a credit to NASA that Terra, Aqua and Aura have lasted as long as they have, scientists said. \u201cThrough a mix of excellent engineering and a tremendous amount of luck, we\u2019ve had these for 20 years now,\u201d said Waleed Abdalati, a former NASA chief scientist now at the University of Colorado Boulder.<\/p>\n \u201cWe kind of got hooked on these satellites. We\u2019re victims of our own success,\u201d Dr. Abdalati said. \u201cEventually,\u201d he added, \u201cluck runs out.\u201d<\/p>\n<\/div>\n<\/div>\n