Tianwen-2: China closes in on Kamoʻoalewa

**Sarah Al-Ahmed** (0:03)
China's Tianwen-2 intercepts a bizarre companion world this week on Planetary Radio.
I'm Sarah Al-Ahmed of the Planetary Society, with more of the human adventure across our solar system and beyond. Earlier this month, China's Tianwen-2 spacecraft arrived at Kamo o Aleva, a tiny mysterious quasi-satellite of Earth. It may be a piece of the moon itself, or something else entirely. I sat down with Andrew Jones, a freelance space journalist who covers the China National Space Administration, to talk about Tianwen-2, what we hope to learn from the samples it returns to Earth, and where China's planetary exploration ambitions go from here. Then Bruce Betts, our chief scientist here at the Planetary Society, joins me for What's Up. With asteroid day just around the corner, we're going to be looking at some of the most exciting asteroid moments through the end of this decade. From a flyby that's happening just next month to 2029, when the asteroid Apophis passes closer to Earth than our geostationary satellites. If you love Planetary Radio and want to stay informed about the latest space discoveries, make sure you hit that subscribe button on your favorite podcasting platform. By subscribing, you'll never miss an episode filled with new and awe-inspiring ways to know the cosmos and our place within it.
Happy almost asteroid day, everyone. June 30th marks this annual global event. It's observed on the anniversary of the 1908 Tunguska impact when a small asteroid or comet exploded over a remote region of Siberia with the energy of a large nuclear weapon. It's a day to celebrate our growing understanding of these ancient travelers and to reflect on why finding and studying them matters so much. Right now, we're living through the most extraordinary chapter in the history of asteroid science. In just the last few decades, humanity has done something that would have seemed like science fiction just a generation ago. We've actually brought pieces of asteroids back to Earth. In 2010, Japan's original Hayabusa probe overcame massive solar flares, fuel leaks, and a near-fatal communications failure, but eventually brought home humanity's very first asteroid samples, about 1,500 microscopic dust grains from the stony asteroid Itokawa. That gritty proof of concept paved the way for a massive sample return that followed. In December 2020, Japan's follow-up mission, Hayabusa 2, returned pristine rocky material from a carbon-rich asteroid called Ryugu.
The results were absolutely stunning. Scientists found amino acids, organic molecules and water-bearing minerals. Chemical clues about the conditions that gave rise to life in our solar system.
Then, in September 2023, NASA's OSIRIS-REx delivered samples from asteroid Bennu, an asteroid with a name that was actually chosen through a student naming contest run by the Planetary Society. And Bennu's samples told a very similar story. A world rich in carbon and the chemistry of life's building blocks. And evidence that water-bearing minerals were once widespread in the early solar system.
These samples aren't just rock collections. They're time capsules, four and a half billion years old. And they're fundamentally changing how we understand where we came from. And now, China has entered this extraordinary chapter. On May 28th, 2025, the China National Space Administration launched Tianwen-2, its first asteroid sample return mission. On June 7th of this year, the spacecraft completed its first rendezvous maneuver and is now closing in on Kamau'o'alewa ahead of a sample collection attempt. After it completes its work there and drops the samples back at Earth, it's going to go visit a comet, making it a really ambitious mission.
Kamau'o'alewa takes its name from a Hawaiian creation chant, the Kumu Lipo, and translates to the oscillating fragment. It's a nod to the way that it appears to dance around the Earth as both it and the planet orbit the Sun. It was first discovered in 2016 by the Pan-STARRS survey, and it's just 40 to 100 meters wide, and spins about every 28 minutes. Unlike the moon, Kamau'o'alewa isn't gravitationally bound to the Earth. Instead, it orbits the Sun on a path so similar to ours that from Earth's perspective, it appears to loop around us in a slow stable waltz, what astronomers call a quasi-satellite. It's not a moon, but it's not quite a typical asteroid either. It's a companion. And here's the mystery at the heart of this mission, although it is also very much a tech demo.
Nobody is entirely sure where Kamau'o'alewa came from. Some scientists think it's a fragment of the moon that was blasted off into space by an impact. Others argue that it's a heavily space-weathered asteroid. Tianwen 2 is going to help us figure it out.
To get some perspective on this mission, I spoke with Andrew Jones, a freelance space journalist based in Finland, who covers China's rapidly growing space program. He's written a bunch of space-related publications, including for space.com, Space News, National Geographic, Sky and Telescope, New Scientist, and of course, the Planetary Society. Here's my conversation with Andrew Jones.