Explained: How earth may appear to an alien from light years away

The scientists came up with the contour map pictured. They worked with 10,000 images of Earth taken by the Deep Space Climate Observatory (DSCOVR) satellite, which NASA has positioned so that it can see only the daytime side of Earth. The images were taken at 10 wavelengths every one to two hours during 2016-17.

For each wavelength, the scientists reduced the images into a single brightness reading, which produced light curves over the images to represent a prolonged view of Earth, Science magazine explained. The team then compared the constructed map with the original image, and was able to identify the specific light curves that represented land masses and cloud cover.

The idea is that a similarly created image for an exoplanet may allow astronomers to assess whether an exoplanet has oceans, clouds etc.

The scientists, from the California Institute of Technology, have made it clear this may not represent how a real alien would see Earth. “We present the first two-dimensional surface map of Earth reconstructed from light curve observations without any assumptions of its spectral properties,” they said in their paper, now on a preprint server at https://arxiv.org/abs/1908.04350.