Billion-dollar NASA mission will provide unprecedented view of ocean life.
PACE satellite will capture subtle differences between plankton critical to their carbon-absorbing capacity.
BY PAUL VOOSEN
It isn’t easy seeing green. The ocean’s mix of plankton, algae, and bacteria absorbs vast amounts of carbon dioxide while producing 50% of Earth’s oxygen. But for decades, Earth-observing satellites could not tease apart the many species making up the green goop. That hampered attempts to study how the floating plants influence climate—and how global warming is affecting this foundational component of the climate system.
The $964 million Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE) satellite is about to change that. After surviving pandemic delays and four cancellation attempts by former President Donald Trump’s administration, it is set to launch no earlier than 6 February from Cape Canaveral, Florida, aboard a Falcon 9 rocket. Once in orbit, it will probe the plants floating in the ocean as well as the hazes of fine particles above it, another major influence on climate. “We’re not going to be limited technologically anymore,” says Collin Roesler, an optical oceanographer at Bowdoin College. “We’re going to be limited by our ideas.”
The satellite’s primary instrument is NASA’s first “hyperspectral” imager to fly on a major geoscience mission. Rather than collecting reflected light in just a few discrete channels, like the red, green, and blue cones of a human eye, the instrument divides light into more than 200 channels, including many shades of green, which can distinguish different pigments used by phytoplankton depending on their species and habitat. “Right now, what we have on orbit is a box of crayons with only eight crayons,” says Jeremy Werdell, the mission’s principal investigator at NASA’s Goddard Space Flight Center. “With PACE, we are getting a box of crayons with 200 different colors.”
By studying the mix of phytoplankton species, PACE should help answer a key climate question, Roesler says. Large phytoplankton, which dominate in colder waters, are bulwarks of carbon storage. “These really big cells get eaten by big zooplankton and then they poop really big poop,” she says. The carbon in the waste is more likely to reach the ocean floor and stay safely sequestered. In the warmer waters at lower latitudes, smaller phytoplankton thrive—but the carbon in their waste tends to be gobbled up by microbes and ultimately emitted back into the atmosphere. Models have suggested these smaller plankton could expand toward the poles with global warming; PACE could see whether these fears are true.
PACE’s sharp color vision should also help it track human impacts on lakes, rivers, and coastlines, by separating natural species from bacteria or dissolved organic matter associated with sewage or fertilizer runoff. And it will explore the role that eddies, kilometers-wide swirls of turbulent water, play in driving the movements of plankton species and the nutrients they depend on.
The satellite will restore NASA’s ability to study another key factor in climate: the small aerosol particles and clouds that reflect some 90% of the Sun’s light into space. NASA is still reeling from the loss of the $424 million Glory satellite, which crashed soon after launch in 2011. It carried an advanced polarimeter designed to capture polarized light, in which the waves all vibrate in the same plane. Sunlight bouncing chaotically off the ground and clouds tends to lose any polarization. But because aerosol particles are discrete and compact, they reflect polarized light and pop out vividly.
Brian Cairns, PACE’s deputy project scientist at NASA’s Goddard Institute for Space Studies, who also led development of Glory’s doomed instrument, says the new satellite carries two “petite but powerful” polarimeters, which “get almost all of what you wanted in a much more compact package.”
By identifying the type, size, and abundance of particles, the two polarimeters should fill out the inventory of aerosols, including elusive ones such as sea spray over the ocean. The instruments should also show how aerosols influence the growth and life span of clouds, Cairns says, which can affect the rate of warming. Researchers are currently debating the extent to which cleaner shipping fuels have suppressed the formation of reflective clouds over the ocean, thereby adding to global warming.
James Hansen, the famed former NASA climate scientist who is now at Columbia University, welcomes the new attention to aerosols. Hansen recently published work suggesting that global warming is accelerating as pollution wanes. “As the world realizes the climate predicament that we face, they will rue not having a monitor of aerosol climate forcing.”
The polarimeters, built with off-the-shelf components, may only last a few years, but PACE’s main instrument could run for a decade or more. It’s been a long wait for Roesler, who has spent her career preparing for this intimate green view from space. “The achievement of PACE is that it brings the observing capabilities almost to what I can do in the lab. That’s really astounding.”
Source:
Billion-dollar NASA mission will provide unprecedented view of ocean life | Science | AAAS
