On July 2, 2026, the Tenbun-2 spacecraft made a remarkable approach, coming within just 20 km (12.4 miles) of the near-Earth asteroid 2016 HO3. As one of the seven identified Earth quasi-satellites, this celestial body has sparked a science campaign in preparation for the final sample return attempt.
Tianwen-2 captured this image of 2016 HO3 on July 2, 2026, from roughly 20 km away. Image credit: CNSA.
Discovered on April 27, 2016, by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at Haleakala Observatory in Hawaii, 2016 HO3—also known as Kamo’olewa (Hawaiian for “vibrating celestial fragment”)—is approximately 30 meters (98 feet) in diameter and has a one-year orbital period.
“Of all known near-Earth asteroids, 2016 HO3 is a unique co-orbital object with Earth,” stated Dr. Rongqiao Zhang and colleagues from the Lunar Exploration and Space Engineering Center.
“As a quasi-Earth satellite, its orbital period closely matches Earth’s, enabling low-energy transfers and maintaining a stable distance of approximately 0.1-0.3 astronomical units (AU) from Earth. This allows for optimal tracking, control, and communication.”
“Its unusual orbital characteristics, mysterious origin, and poorly understood physical properties make this satellite a strong candidate for addressing fundamental questions about the origins of Earth’s quasi-satellites and the dynamic evolution of their orbits.”
“Orbital dynamics models suggest that the current quasi-satellite state began around 100 years ago and is expected to continue for about 300 years,” researchers noted.
Currently, 2016 HO3 holds the title of the closest quasi-satellite to Earth (minimum distance 0.2 AU, with stable dynamics not exceeding 0.3 AU) and is the most stable target of its kind.
Possible origins for this asteroid include local formation, gravitational capture, or ejection from the lunar surface due to a collision with another celestial body.
2016 HO3 serves as the primary target for the China National Space Administration (CNSA) Tianwen-2 small celestial body exploration mission.
“Launched from the Xichang Satellite Launch Center on May 29, 2025, using a Long March 3B/G2 rocket, Tianwen-2 represents China’s commitment to planetary exploration,” researchers said.
China’s planetary exploration initiative, dubbed the Astronomical Project, outlines an ambitious vision that encompasses a series of four flagship missions: Tianwen-1 for Mars, Tianwen-2 for small celestial objects, Tianwen-3 for returning Martian samples, and Tianwen-4 for exploring the Jupiter system.
Notably, Tianwen-2 serves dual purposes: conducting in-orbit observations and sample collection from the near-Earth asteroid 2016 HO3, while also investigating the subsequent main-belt comet 311P.
After a 400-day journey covering about 1 billion kilometers (600 million miles), Tianwen-2 approached within approximately 20 kilometers of 2016 HO3 on July 2, 2026.
“During its journey, Tianwen-2 executed a series of deep space maneuvers and mid-course adjustments,” mission scientists reported.
“The spacecraft identified the asteroid on June 6, performed acquisition control from a distance of 30,000 km on June 7, and achieved co-orbital flight by June 19, when it was within 2,000 km.”
“Using the optical navigation data, we refined the asteroid’s ephemeris, improving positional accuracy to just a few kilometers compared to hundreds based solely on ground observations.”
Tianwen-2 is now set to enter a more detailed scientific investigation phase, characterizing the asteroid’s shape, surface composition, and internal structure, laying the groundwork for future sample collection.
Source: www.sci.news
