China's Tianwen-2 Deep Space Mission: Asteroid Sample-Return & Comet Flyby
An illustration of China's Tianwen-2 spacecraft approaching an asteroid in deep space. The probe features large circular solar panels, a dish antenna, and an ion propulsion system emitting a blue glow. A small asteroid is visible in the background, set against the vast darkness of space.
The China National Space Administration (CNSA) is expected to launch its ion-engine powered Tianwen-2 deep space mission around May 28, 2025. The Tianwen-2 spacecraft is now being integrated with a Long March 3B rocket at the Xichang Satellite Launch Center in southwest China. This robotic spacecraft will first collect samples from a small near Earth asteroid called 469219 Kamoʻoalewa, also known as 2016HO3, and return them to Earth in 2027. The asteroid is roughly 40 to 100-meters in diameter. Then, Tianwen-2 will visit a main belt comet, named comet 311P/PANSTARRS. The next Tianwen mission after this one is a Mars sample return mission in 2028. Of course, Tianwen-2 is the second in the Tianwen (meaning “Heavenly Questions” or “Questions to Heaven”) exploration series. The first, Tianwen-1, included a Mars orbiter and surface rover, named Zhurong. Tianwen-4 will launch around 2030. It will include a solar-powered Jupiter orbiter which will observe the system and then enter orbit around the moon Callisto—potentially including a lander—and a smaller, radioisotope-powered spacecraft to make a flyby of Uranus. These missions are also part of a wider, planetary exploration roadmap focused on astrobiology and habitability, and a long-term plan for space science.
China's Tianwen-2 Mission follows similar missions by the United States, Russia, and Japan, except China will explore an asteroid and a comet in a single mission for the first time in history. China’s first asteroid flyby of 4179 Toutatis was in 2012, when the Chang’e-2 lunar orbiter made this an extended mission objective. Tianwen-2 aims to provide vital data to help us understand the nature of asteroids and comets. The Kamoʻoalewa asteroid travels in a similar orbit to Earth. A Tianwen-2 reentry module containing the samples will be released for atmospheric entry, descent and landing, but the main Tianwen-2 spacecraft will use the Earth’s gravity for a swingby, setting it on course for a six-year-voyage to comet 311P/PANSTARRS that orbits between 1.94 and 2.44 astronomical units from the Sun. Tianwen-2 carries multispectral and infrared spectrometers to study surface composition, while high-resolution cameras will map geological features. A radar sounder will probe subsurface structures, and a magnetometer will search for residual magnetic fields. Dust and gas analyzers will examine comet activity, and charged particle detectors will investigate solar wind interactions. The Space Research Institute of the Russian Academy of Sciences is understood to have contributed to the particle detectors.
Tianwen-2 Mission Timeline (Tentative):
Arrival at asteroid Kamoʻoalewa: July 4, 2026
👋 Departure: April 24, 2027
🌏 Reentry capsule landing: Nov. 29, 2027
☄️Arrival at comet 311P: Jan. 24, 2035
The CNSA has described 311P/PanSTARRS as a “living fossil”, making it useful for studying the early material composition, formation process and evolutionary history of the solar system. Comet 311P orbits in the main asteroid belt between Mars and Jupiter where most asteroids reside, containing over 90 percent of the asteroids in the solar system. It displays features of both comets and asteroids. It has become the seventh main-belt comet confirmed by human beings, and it is also the most peculiar one so far. According to the conventional theory, comets typically originate from the outer edges of the solar system and are rich in ice. As they approach the sun, the heat causes the ice to vaporize, forming their characteristic tails. However, Comet 311P, located in the asteroid belt—far closer to the sun than typical comets—faces intense solar radiation, making it unlikely to retain volatile substances like water ice. This comet challenges astronomers' traditional understanding.
Tianwen-2 will conduct remote sensing of the comet to characterize its orbit, shape, and rotation, examine its surface composition and volatile elements, and investigate dust emissions and activity mechanisms to understand cometary behavior in the main belt.
Comet 311P/PanSTARRS also known as P/2013 P5 (PanSTARRS) was discovered by Bryce T. Bolin using the Pan-STARRS telescope on August 27, 2013. Observations made by the Hubble Space Telescope revealed that it had six comet-like tails. The tails are suspected to be streams of material ejected by the asteroid as a result of a rubble pile asteroid spinning fast enough to remove material from it. This is similar to 331P/Gibbs that was found to be a quickly-spinning rubble pile as well.+
The Tianwen-2 Mission aims to advance China’s planetary exploration capabilities, provide new insights into the understanding of small planetary bodies and their evolutions, and potentially for planetary defense and the origins of life.
Asteroid 2016 HO3 was first spotted on April 27, 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii, operated by the University of Hawaii's Institute for Astronomy and funded by NASA's Planetary Defense Coordination Office. The size of this object has not yet been firmly established, but it is likely larger than 120 feet (40 meters) and smaller than 300 feet (100 meters).
While China has conducted two successful lunar sample return missions, the velocity of the reentry module will be greater for Tianwen-2, marking China’s first second-cosmic-velocity atmospheric reentry, at 12 kilometers per second, adding new challenges. The China Aerospace Science and Technology Corporation (CASC) conducted high-altitude parachute deployment tests for the mission in 2023. In contrast to the lunar sampling missions, Kamoʻoalewa will have negligible gravity, requiring specialized approaches for orbiting, approaching and sampling.
The spacecraft will attempt up to three methods of sampling: hover sampling, collecting samples with a robotic arm while matching the asteroid’s rotation; touch-and-go (TAG), using a rotating brush head; and anchored sampling. Its landing legs will use drills to press into the asteroid, if the surface composition and terrain allow. The TAG approach was used by both NASA’s OSIRIS-REx and JAXA’s Hayabusa2.
The asteroid is considered a quasi-satellite of Earth due to its co-orbital dynamics. Kamoʻoalewa is possibly a piece of the moon blasted into space following an impact event, according to researchers, based on spectral analyses. Analysis of the samples aims to reveal the nature and origin of the asteroid, analyze its mineral content and provide comparisons with other asteroids. Leah-Nani Alconcel at the University of Birmingham, UKShe says that the mission is daring, as Kamoʻoalewa is spinning. This will make landing harder. Navigation algorithms are likely to demand such powerful computers that images and sensor readings will be sent back to Earth for computation. “If we were to always pick lovely, cooperative objects, we wouldn’t learn a lot,” she says. “There’s a lot that could potentially go wrong.”
Image Credit: China National Space Administration (CNSA)
Text Credit: CNSA/CAS/SpaceNews/New Scientist
Release Dates: May 2025
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