Most lunar explorers dispatched to the Moon can only operate through one lunar day—equivalent to about two weeks on Earth—before the extreme cold of the lunar night wreaks havoc on their electronic systems. However, in a remarkable feat, the Japan Aerospace Exploration Agency (JAXA) announced on March 27 that the Japanese lunar explorer SLIM has successfully weathered its second night on the lunar surface and continues to send images back to Earth.
From a tilted position on the SLIM lander, a view of the lunar surface. Photo courtesy of JAXA. SLIM marks Japan's inaugural lunar probe, positioning Japan as the fifth country to successfully land a spacecraft on the moon. Upon its landing on January 19, it settled at an angle, rendering its solar panels insufficient in powering it for more than a few hours. Nine days later, the sun had moved sufficiently across the sky to allow it to right itself.
Merely three Earth days after, the lunar night commenced. Temperatures on the moon plummet to minus 133 degrees Celsius during these periods, potentially damaging the probe's batteries and electronic components. Typically, lunar probes hibernate through the lunar night, never to awaken, but when the sun rose over SLIM on February 25, it powered back on.
This was a surprise in itself—the probe wasn't specifically designed to survive the lunar night; its initial mission was intended to conclude as darkness fell. Thus, when another lunar night approached, it seemed as though SLIM's journey was coming to an end.
However, on March 27, SLIM's official account shared an image of the lunar surface with a caption stating: "Last night, we received a response from SLIM, confirming it successfully endured a second lunar night. Due to solar heating, the equipment's temperature is currently high, hence the probe was only operated briefly to capture some standard landscape shots with its navigation camera." It appears that in the coming Earth days, the probe should be able to resume analyzing its surroundings.
Some probes use radioactive elements for warmth, but not SLIM, making its survival particularly remarkable. "They did not use radioactive isotope heaters, which is a significant achievement. Given that this is a primary design consideration for electronics to survive the lunar night, the result is very important and impressive," said Haym Benaroya of Rutgers University, noting that understanding how SLIM survived where many others have failed could aid in figuring out how to stay warm on the moon.
