Japan is on the moon - at least for a few hours.
The country's robotic SLIM spacecraft landed on the lunar surface this morning (Jan. 19), marking a huge success for Japan, becoming only the fifth country to land softly on Earth's nearest neighbor.
"First and foremost, the landing was successful," Yamakawa Hiroshi, chairman of the Japan Aerospace Exploration Agency (JAXA), said today at a post-landing press conference (in Japanese; English translation provided by a translator during the briefing).
In the future, we should have access to the moon's surface, Hiroshi added. "I believe a path to that is now opening up."
The other countries in the moon landing club are the Soviet Union and the United States, which made their first trips to the moon's surface during the Cold War space race; China, whose first landing took place in December 2013; and India, whose lander-rover duo Chandrayaan-3 landed last August.
But it wasn't all good news for SLIM: The probe's solar panels will not generate electricity as planned on the lunar surface, JAXA officials said during today's briefing. If the problem is not resolved quickly, SLIM may remain silent forever. The battery can only support operations on the moon for a few hours.
Related: Missions to the moon: past, present and future
SLIM (short for "Smart Lander for Investigating Moon") was launched last September, along with an X-ray space telescope called XRISM. The telescope was deployed into low Earth orbit shortly after launch (and recently sent home the first test images), but SLIM headed to more distant celestial shores.
The probe followed a long, looping route towards the moon, finally arriving in lunar orbit on Christmas Day. Its initial orbit was highly elliptical, bringing SLIM within 600 kilometers of the moon's surface at its closest point and 4,000 kilometers at its farthest point.
Early Sunday morning (Jan. 14), SLIM performed a crucial engine burn, spinning its orbit at an altitude of 373 miles and setting the stage for descent and landing operations.
Those operations continued this morning with another burn, which dropped SLIM's orbit to about 9 miles (15 km) above the moon's surface. And they culminated in the landing attempt, which began today at about 10 a.m. EST (3 p.m. GMT; midnight on Jan. 20, Japan time) and ended 20 minutes later.
Everything seemed to go smoothly: SLIM reached its various milestones during the descent, and the lander communicated with its handlers during and after the historic touchdown. However, JAXA could not immediately confirm SLIM's status after landing. About an hour later, the agency gave us an update via the press conference, explaining the probe's power issues.
It's unclear why the solar cells aren't working, JAXA officials said. But it's unlikely they were damaged during the touchdown, as SLIM's other hardware seems fine and functional. According to JAXA, the lander may not be aimed at the sun as expected.
Related: Facts about JAXA, the Japanese space agency
SLIM's goal was to land within 100 meters of its target location on the rim of the Shioli Crater, which explains the probe's nickname "Moon Sniper".
"While impressive in their own right, this mission's landing ambitions are also key to the future of scientific lunar exploration," The Planetary Society wrote in a mission description.
"Global interest in the moon is growing and many countries and commercial entities are entering the field," added the nonprofit, which is led by former TV "Science Guy" Bill Nye. "As lunar exploration progresses, so will the need to target specific locations to answer salient scientific questions. SLIM's mission architecture hopes to change the norms of lunar landing missions, from countries where it is easy to drop exactly where desired. "
It appears that SLIM has achieved the desired landing precision, JAXA officials said at the press conference, although it could take about a month for the mission team to confirm that conclusion.
SLIM also wanted to show that small, relatively cheap spacecraft can deliver impressive exploration performance. The probe weighs just 200 kilos without propellant, and it cost about 18 billion yen ($120 million US) to develop, according to The Planetary Society.
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Although SLIM is primarily a landing technology demonstrator, it was designed to perform some scientific work during its surface mission, which was expected to last one Monday, or about two Earth weeks. (SLIM has no heater to protect the electronics from the frigid moon night.)
SLIM wanted to study the environment - a patch of Mare Nectaris ("Sea of Nectar"), which is located about 15 degrees south of the lunar equator - using its built-in spectrometer. The instrument's data could reveal insights into the region's composition, which could in turn shed light on the moon's formation and evolution - but it won't have the chance to do so unless SLIM's solar panels become operational.
SLIM also carried two small rovers: a small hopper called LEV-1 and a spherical craft known as LEV-2. ("LEV" is short for "Lunar Excursion Vehicle.") These little robots are designed to deploy from the SLIM mothership, collect some data and take pictures on their own.
The data shows that both LEV-1 and LEV-2 deployed as planned, JAXA officials said today. And LEV-1 is known to work, contributing to mission performance.
SLIM was not the first Japanese spacecraft to aim for a moon landing. The nation placed a small lander named OMOTENASHI on NASA's Artemis 1 mission, which sent an unmanned Orion capsule to lunar orbit in late 2022. But OMOTENASHI's handlers were unable to establish communication with the probe and the landing attempt was abandoned.
The privately owned Hakuto-R lander made a swing in April 2023, but was unsuccessful. Hakuto-R, built and operated by Tokyo company ispace, reached lunar orbit but crashed during its landing attempt after being confused by the rim of a lunar crater.
Editor's Note: This story was updated on January 19 at 1:00 PM EST with news that SLIM has landed successfully, but is experiencing a power issue.