NASA Mission Will Measure the Mysterious Glow of Earth’s Plants

April 20, 2019

Packed alongside supplies and equipment bound for the International Space Station on an otherwise routine SpaceX resupply run, something rather special is headed to orbit next week: a refrigerator-sized instrument that’ll measure the glow of Earth’s plant life.

That instrument, dubbed Orbiting Carbon Observatory-3 (OCO-3 for short), will study how carbon dioxide levels in our atmosphere fluctuate across space and time—critical information at a time when humanity’s fossil fuel addiction has pushed levels of the greenhouse gas to their highest point in millions of years. But one of the instruments OCO-3 uses to help it measure carbon is going to have a side gig.

It’ll also be looking at “solar-induced fluorescence” or SIF, light that plants emit just beyond the range of human eyesight as they’re sucking CO2 out of the sky and using energy from sunlight to convert it into sugar via photosynthesis. (To get a better visual sense of fluorescence, check out this photographer’s amazing work.)

This faint glow gives scientists a way to see, from orbit, where plants are thriving and how they’re responding to a changing climate. While it isn’t a new capability for NASA per se, OCO-3 will, for the first time, be able to measure how plant photosynthesis varies over the course of a day across the tropical forests of South America, Africa, and southeast Asia, some of the most important carbon storehouses on the planet.

As the name suggests, OCO-3 is a sequel to OCO-2, a satellite mission that launched in 2014. During its four-and-a-half years of action, OCO-2 has provided a steadfast record of CO2 and yielded important insights into how plants drive Earth’s carbon cycle. For instance, data from the mission helped scientists discover that 2015-2016 El Niño, which drove temperatures higher and altered global rainfall patterns, caused the tropics to leak an extra 2.5 billion tons of carbon into the air, thanks in part to reduced photosynthesis in the Amazon basin.

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