Nasa
Nasa is gearing up to launch a new Earth-observing satellite that will offer important insights on airborne particles of sea salt, smoke, human-made pollutants and dust – collectively called aerosols – by observing how they interact with light.
The satellite, called Plankton, Aerosol, Cloud, ocean Ecosystem (PACE), is set to launch on 6 February 2024 on a SpaceX Falcon 9 rocket, the space agency announced.
Once launched, it will scan the Earth every two days and gather data on the chemical composition, movement and interaction of aerosols and clouds through the use of two cutting-edge polarimeters – instruments that measure light properties.
Light leaving the Sun moves in different directions like a wave, an effect that is known as unpolarised light.
When it interacts with something like a cloud or an aerosol particle, however, light can oscillate more in one direction than the other, which makes it polarised light. This quirk of light behaviour can help scientists learn more about the characteristics and interactions of aerosols and water droplets in the sky.
The two polarimeters on PACE – HARP2 and SPEXone – each have slightly different roles. HARP2, built at the University of Maryland, will observe four wavelengths of light from up to 60 different angles.
SPEXone, built at the Netherlands Institute for Space Research (SRON) and Airbus Netherlands, will peer down at a narrower swath, using five viewing angles but looking at light at hyperspectral resolution – the full range of colours in a rainbow. Together the polarimeters will offer a picture of Earth’s atmosphere in unprecedented detail.
Scientists have been observing aerosols from space for decades, although the community has not had polarimetry data for a decade. PACE will provide this data from multiple vantage points and, because of technological advancements in the instruments, the data will be of better quality than ever before.
“We want to measure properties of aerosols because aerosols affect climate,” said Otto Hasekamp, senior scientist at SRON.
Aerosols reflect light back into space and can also absorb it, which plays a role in how much of the Sun’s energy reaches Earth’s surface. They also affect cloud formation and properties, but the details of these relationships are not fully known to scientists. The data PACE collects will help to clarify some of these unknowns.
The new polarimetry data will also offer real-time insights on air pollution. “PACE measurements will not only answer fundamental science questions, but will also improve people’s quality of life,” said Marcela Loría-Salazar, assistant professor at the University of Oklahoma.
She is particularly interested in how aerosols change over time and with location, with an extra emphasis on the altitude of aerosols over the middle of the US. There, PACE will allow scientists to identify aerosols, while also deciphering what they mean for air quality.
