The green light floating in the cloudy sky was something Daichi Fuji had never seen before. The museum curator’s motion-detection cameras were placed near Japan’s Mount Fuji to capture meteorites, allowing him to calculate the meteors’ positions, luminosity, and trajectories. But the bright green lines appearing in the video shot on September 16, 2022 were a mystery.

Then Fuji took a closer look. The beams were synchronized with a small green dot briefly visible among the clouds. He guessed it was a satellite, so he studied the orbital data and found a match. That night, NASA’s Ice, Cloud and Land Altitude Satellite 2, or ICESat-2, flew overhead. Fuji posted his findings on social media and eventually caught the attention of the NASA team.

Tony Martino, an ICESat-2 scientist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said the ICESat-2 team has seen for the first time images of the satellite’s green laser beams coming from orbit to Earth.

“ICESat-2 appeared almost directly above it, and the beam hit the low clouds at an angle,” Martineau said. “You have to be in the right place, at the right time, and in the right conditions to see a laser.”

ICESat-2 was launched in September 2018 to use laser light to measure the height of ice, water, and Earth’s surface from space. The laser device, called a lidar, fires 10,000 times per second, sending six beams of light to Earth. This is exactly a multiple of how individual photons bounce off the surface and return to the satellite. Computer programs use these measurements to calculate ice loss in Greenland and Antarctica, monitor how much of the polar oceans freeze, determine the height of freshwater bodies, map shallow coastal areas, and more.

Laser light emitted hundreds of miles in space is not harmful. In fact, it is difficult to notice. Martino said that if someone stood directly under the satellite and looked up, the laser would have had the power of a camera flash from more than 100 meters away.

People tried to take pictures of the satellite as it flew in, and they managed to take pictures several times – once from southern Chile and once from Oklahoma. He noted that capturing the beam is even more difficult because cameras and eyes need laser light to see the beam from the side. Here are the atmospheric conditions.

At night, ICESat-2 passed over Fuji City, but there were enough clouds to scatter the laser light so that it could be seen by the cameras, but not enough to completely block the light. There were actually two thin layers of clouds over Japan that night, information Martineau found by analyzing ICESat-2 data showing the clouds and the ground beneath them.