A powerful instrument from the ISS will hunt minerals in dusty lands

What blows through the Sahara does not stay in the Sahara. The vast African desert regularly spits clouds of dust that fly towards Europe, turning the snow-capped mountains orange. They travel across the Atlantic Ocean, fertilizing the Amazon rainforest with phosphorus. The stuff can even reach the United States.

But for all their bluster, dust emissions from the Sahara – and grime from any other desert region – are not well accounted for in climate models. While satellites can track plumes as they move through the atmosphere, scientists don’t have enough data to show definitively how the dust could be cooling or warming the planet, speeding or slowing climate change. human origin.

“Our datasets are based on 5,000 soil samples, and that’s not enough coverage,” says Natalie Mahowald, Earth System Scientist at Cornell University. “Nobody wants to go out in the middle of the desert to find out what the soils are.” Mahowald has therefore collaborated with NASA on the Earth Surface Mineral Dust Source Investigation, or EMIT, mission which will launch to the International Space Station next month. Their instrument will use a powerful technique known as spectroscopy, which astronomers have used for decades to determine the composition of distant objects, but turn it to earth to analyze our own lands. This will finally give scientists a holistic picture of where dust comes from, what it is made of, and how these particles might influence the climate. “Remote sensing makes much more sense,” says Mahowald.

The molecules of any material absorb and then emit electromagnetic radiation in unique ways. So astronomers can use a spectrometer to analyze light coming from a distant planet, isolating individual elements like hydrogen or carbon based on their distinct signatures. This planet may be billions and billions of miles away, but its atmospheric composition is betrayed by the light bouncing off it. It’s a bit like being able to take someone’s fingerprint, even if you’re never able to touch it.

The EMIT spectrometer, which will be attached below the ISS, will image the Earth in bands 50 miles wide, looking for the unique signatures of specific minerals. Iron oxide, for example, will look different to the spectrometer than clay, even though to the human eye the surface of one desert region may look like another. “We need to measure mineral fingerprints in arid land regions,” says Robert O. Green, EMIT principal investigator and researcher at NASA’s Jet Propulsion Laboratory. “We will have enough mineral maps within a year to start providing new initialization information for climate models.”

Integrating these new data with existing models will allow climatologists to better understand the role of dust in the temperature of our planet. Traditionally, researchers have represented dust as a sort of simplified medium, a yellow haze. “But if you look at floors, they can be all different colors: black, red, white, a very reflective color,” says Mahowald, who is EMIT’s deputy principal investigator. “Anything darker will absorb more radiation and warm us up, and anything lighter will reflect the radiation and cool down.”

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