Some of Earth's heat escapes into space in a form that satellites have so far observed rather poorly. Two small NASA satellites are now directly tracking this radiation above the Arctic and Antarctic. After two seasonal cycles, their measurements show how much these heat losses vary by region and season.
This heat is mainly emitted in the far infrared, a portion of invisible radiation beyond what our eyes can perceive. At the poles, this component represents a significant fraction of the energy sent back into space. Yet previous space-based observations did not directly cover this entire range of wavelengths.
NASA image
That is precisely the role of NASA's PREFIRE mission. It relies on two CubeSats, small satellites far less bulky than large Earth-observing platforms. Launched in 2024, they regularly pass over the high latitudes and measure thermal radiation emitted by the surface, clouds and atmosphere.
The data reveal particularly large differences between polar winter and summer.
To understand their significance, we need to look at Earth's energy budget. Our planet receives energy from the Sun and then sends it back into space. The amount that enters and the amount that leaves influence temperatures. The polar regions play a major role in these exchanges, even when they receive almost no sunlight during winter.
PREFIRE's instruments make it possible to distinguish more precisely the contributions of water vapor, clouds, snow and ice. These elements do not all allow heat to escape in the same way. Clear skies, for example, produce a different signal from an atmosphere covered by clouds above a snow-covered surface.
The two years of observations mainly provide useful continuity. A single pass shows the state of the atmosphere at a given moment. By repeating measurements over several seasons, scientists can track changes in radiation as sea ice forms, retreats or becomes covered with snow, and as atmospheric conditions evolve.
This information must now be used to test numerical climate and weather models. Models calculate heat exchanges using numerous equations and observations. Direct measurements in a previously underobserved range make it possible to check whether their estimates at the poles actually match what is leaving Earth.
The mission should also help better connect polar changes with the rest of the climate system. The next step is to incorporate more of these observations into models to determine which representations of clouds, ice and the atmosphere best reproduce the heat losses actually measured.