The Journey of a Carbon Atom: From Space, NASA’s PACE Mission Detects Carbon in the Sky, Land, and Sea

Whether in plants or animals, greenhouse gases or smoke, carbon atoms exist in various compounds as they move through a multitude of pathways within Earth’s system. That’s why NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission – scheduled to launch in January 2024 – was designed to peer down at Earth from space to see those many forms of carbon in a way no other satellite has done before by measuring colors not yet seen from the vantage point of space.

“PACE is standing on the shoulders of some giants, but previous and current satellites are limited in how many colors of the rainbow they can actually see,” said Jeremy Werdell, project scientist for the PACE mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Although one of the primary goals of the mission is to measure the colors on the ocean surface, in the 420 miles (676.5 kilometers) between PACE in orbit and sea level are parts of the complex carbon web that the satellite will also be able to monitor.

The connection between major wildfires and the subsequent explosion of phytoplankton production is an example of the events NASA’s upcoming Plankton, Aerosols, Clouds, and ocean Ecosystem (PACE) mission will help investigate. PACE’s suite of instruments will allow scientists to get a clearer picture of carbon as it links land use and fires, atmospheric aerosols and marine communities. Credit: NASA’s Goddard Space Flight Center


From PACE’s location in space, one of the nearest forms of carbon to detect could be the wispy plumes of smoke and ash rising into the atmosphere from fires. Carbon is a key building block of much life on Earth, including plant life. When burned, the vegetation’s carbon-based molecules transform into other compounds, some of which end up as ash in these plumes.

The instruments on PACE will be able to monitor these smoky clouds, as well as other atmospheric aerosol particles, measuring their characteristics including the relative amount of smoke in different places. Combinations of these measurements made by PACE’s two companion polarimeter instruments, SPEXone and the Hyper-Angular Rainbow Polarimeter-2 (HARP2), and the detailed color measurements of the smoke made by the Ocean Color Instrument (OCI) will also help scientists identify what was burnt.

“Each instrument brings something different,” said Andy Sayer, PACE’s project science lead for atmospheres at NASA Goddard. “Putting them all together though, you’re getting the most information.” Sayer is also a senior research scientist for the University of Maryland Baltimore County.

These measurements help scientists understand more about the balance between the incoming energy from the Sun, the outgoing energy from Earth, and where it may be absorbed in between by things in the atmosphere like these smoke plumes. Even at a local level, PACE can provide information about how smoke affects air quality, impacting communities that may be near fires.


Peering through the smoke particles and other aerosols, PACE can also tell us about the health of terrestrial plants and trees. Even after a devastating wildfire, fresh green plant life begins to grow and thrive. With more spectral bands and colors to see from the upcoming satellite, scientists will be able to understand what kinds of plants are recovering from fires over the years.

“In a time where we’re experiencing unprecedented climate change, we need to be able to understand how global vegetation responds to its environment,” said Fred Huemmrich, research associate professor at the University of Maryland, Baltimore County, and a member of the PACE science and applications team.

PACE will be able to monitor the different shades of colors in vegetation, and plant color can be an indicator of health. Just as house plants begin to fade to yellow if they haven’t been watered enough, plant life around the globe changes color as it experiences stress. Healthy plants take up carbon in the form of carbon dioxide as part of photosynthesis, while unhealthy plants that can’t complete photosynthesis leave the carbon dioxide roaming around the atmosphere. Given that carbon dioxide is a greenhouse gas, these measurements also play a significant role in understanding climate change in greater detail.

By measuring a full spectrum of color, PACE will view tiny changes in pigment to detect how plants are responding to stressors, helping scientists learn whether they are utilizing the surrounding carbon or not. Previously, these colors were primarily viewed in field studies of specific areas. Stressors like droughts were inferred using weather data, but covering large expanses was difficult.

“For the first time, we’ll really be able to look at changes in the health of plants over the globe,” Huemmrich said. “It will dramatically improve our understanding of how ecosystems function and how they respond to stress.”


From plants on land to organisms in the ocean, PACE will view the expanses of water on Earth to measure phytoplankton – the P in its name. With its ability to measure a wide spectrum of colors, PACE will now not only be able to see more across the surface of the ocean but will also help scientists differentiate between phytoplankton species.

“It’s like you were making a painting with really coarse brushes, and now you have thin, fine brushes that help explain so much more in greater detail,” said Ivona Cetinić, an oceanographer in the Ocean Ecology Lab at NASA Goddard.

Phytoplankton, small organisms that live on the surface of the ocean, play a critical role in the food chain and the global carbon cycle. Each type of phytoplankton provides a different pathway in that expansive web of routes that carbon can take, all depending on the characteristics of the plankton. One pathway may lead to the carbon becoming food for a larger species, while another may lead to carbon becoming waste, sinking deeper into the ocean.

Scientists conducting field work have found that types of phytoplankton vary slightly in color and have identified these phytoplankton on small scales. PACE’s ability to measure a full spectrum of color will help scientists tell the difference between phytoplankton on a global scale by seeing more of these colors, deepening the understanding of carbon pathways and quantities.

Though one of PACE’s key goals is to view the ocean, its line of sight looks over the atmosphere and land as well. With these expansive observations, and the massive quantities of data collected, PACE provides the ability to see in what ways the atmosphere, land, and ocean are connected, including with the complex web of carbon pathways. 

“I’m energized for this opportunity for discovery that this observatory is offering,” Werdell said. “I have every expectation the world is going to do great things with these data.”

By Erica McNamee, Science Writer at NASA’s Goddard Space Flight Center

Observatory, assembled!

The Ocean Color Instrument (OCI) is integrated onto the PACE spacecraft in the cleanroom at Goddard Space Flight Center. Credit: NASA’s Goddard Space Flight Center.

The PACE satellite now has all three of its scientific instruments attached to the spacecraft, as the integration crew bolted the Ocean Color Instrument into place with its two polarimeter neighbors.

With the assembly completed Nov. 21 at NASA’s Goddard Space Flight Center, the team will now be working on the electronic and other connections between the different components of the satellite, then putting the complete observatory through tests to make sure it can work in the harsh environment of space.

By Kate Ramsayer, Science Writer at NASA’s Goddard Space Flight Center

NASA’s PACE Mission Undergoes Milestone Testing

NASA’s PACE mission, which will provide a major boost to scientists studying Earth’s atmosphere and ocean health, completed a milestone test in October at the agency’s Goddard Space Flight Center in Greenbelt, Maryland.

The Ocean Color Instrument (OCI) on the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission passed thermal vacuum tests to ensure it can withstand the harsh space environments.

As we prepare the Plankton, Aerosol, and cloud Ecosystem satellite for launch, we’re gathering all the ingredients, um…instruments, and baking ourselves a fresh new satellite. Credit: NASA’s Goddard Space Flight Center/Scientific Visualization Studio. Video descriptions available

PACE will view the atmosphere and ocean surface from space. While highly useful for studying atmospheric aerosols, OCI is specifically designed to look for small aquatic organisms called phytoplankton that can be so numerous they influence the colors of the ocean. Phytoplankton play a large role in the ocean ecosystem — not only are they food sources for larger species, but they also convert carbon dioxide into organic matter through photosynthesis, playing an active role in moving carbon from the atmosphere into the ocean.

The PACE mission will help scientists learn more about the relationships between phytoplankton and the surrounding environment by measuring how light reflects off the ocean and through the atmosphere. Scientists can see these organisms in the ocean using satellites, but currently can’t differentiate the phytoplankton by type easily. Identifying types of phytoplankton help scientists to detangle some of the complex ecological systems in the oceans.

“When you look down at the ocean, you can see phytoplankton there and for the first time, with PACE, the scientists will be able to see what type of phytoplankton there are from space,” said Gary Davis, mission systems engineer at Goddard for the PACE mission. “Hopefully this mission will be able to communicate the importance of ocean health and the health of plankton to the whole world.”

To ensure the satellite is ready to gather this data, engineers put the satellite through, well, its paces. The thermal vacuum test that was just completed reduces atmospheric pressure as close to the vacuum of space as possible and then cycles through a wide range of temperatures. During the sunlit part of a spacecraft’s orbit, it can get very hot, up to approximately 50 degrees Celsius (122 degrees Fahrenheit); at other parts of the orbit, zero solar exposure means extremely low temperatures, as low as -90 degrees Celsius (-130 degrees Fahrenheit).

OCI, which was built at Goddard, can measure light in a multitude of colors, far more than previous satellites that share its frequent global coverage. Light variation by wavelength, the character of light by which it is defined, provides the color we see. OCI can detect a continuous spectrum of different wavelengths of light, and can even see colors beyond what the human eye can detect. By detecting more wavelengths, the instrument will allow scientists to tell the difference between types of phytoplankton from space. This is helpful in understanding the pathways of the carbon cycle in the atmosphere, land, and ocean, and characterizing the phytoplankton as harmful or helpful.

“OCI is really a stretch of the state of the art of what we can do right now,” said Davis. “It’s probably the most advanced thing we have on the observatory.”

Former ocean-observing satellites had the ability to measure light at a small set of wavelengths through the development of multi-spectral instruments. OCI has the ability to measure color continuosly at many ultraviolet, visible, and near infrared wavelengths, also known as hyperspectral imaging.

The previous missions can be imagined as a regular 8-color box of crayons, said Jeremy Werdell, project scientist for the PACE mission. Though still highly valuable for creating a complete picture, there are gaps in between the shades of colors. For PACE, OCI can be imagined as a 128-color box of crayons, filling in those gaps using smaller and continuous intervals of wavelengths.

“With all of the colors of the rainbow here, most of us don’t know what we’re going to discover, because we’ve never had that chance on global scales,” Werdell said. “It’s the only mission planned at NASA or elsewhere that provide global hyperspectral, full colors of the rainbow everywhere, everyday.”

When light from the sun reflects off the ocean, that light has already traveled from the sun, through the atmosphere – clouds and aerosols that compose Earth’s atmosphere – and water before it reaches the plankton in the ocean. The light then bounces off the plankton and travels back through the water and atmosphere again. The light that makes its way through all those stages can tell a story through color but still needs to be analyzed and accounted for any atmospheric effects, which is where the polarimeters on PACE come into play.

The Hyper-Angular Rainbow Polarimeter 2 (HARP2) also recently completed TVAC testing, earlier in September. The instrument is one of two multi-angle polarimeters on PACE, which act as polarized sunglasses for the spacecraft, measuring how light bends as it travels through the water droplets, clouds, and aerosols in Earth’s atmosphere, informing scientists more about their physical properties, as well as providing another source of color measurements. HARP2 was built at the University of Maryland, Baltimore County.

SPEXone, the other multi-angle polarimeter, was built in the Netherlands by engineers from SRON Netherlands Institute for Space Research, Airbus Netherlands and NASA. Each of the three instruments will be integrated into the spacecraft as they complete their individual tests – and in fact, OCI was just lifted onto the spacecraft on November 21.

“We have an observatory!” said Werdell.

As the timeline of events for PACE ticks on, the days are being counted down, all leading to the launch scheduled for early 2024.

For more information on PACE, visit

By Erica McNamee, Science Writer at NASA’s Goddard Space Flight Center