Space-ground asteroid monitoring network mulled

Chinese scientists and engineers are conducting feasibility studies on developing a space-ground integrated monitoring and early-warning network to address risks posed by near-Earth asteroids, according to a project leader.

"By now, more than 40,000 near-Earth asteroids have been discovered and cataloged worldwide. No asteroid has so far been identified that will definitely collide with Earth in the foreseeable future, but concerns over impact risks are not unfounded. A large number of near-Earth asteroids remain undetected," said Li Mingtao, chief scientist at the asteroid monitoring and early-warning research center under the China National Space Administration.

"Major space powers are continuously improving their asteroid monitoring and early-warning capabilities. We must never let our guard down, but there is also no need for excessive anxiety," Li said.

He noted that near-Earth asteroid impacts are a common challenge for all people across the world. As a responsible major space power, China is carrying out feasibility studies on a space-ground integrated monitoring and early-warning network as a core component of its planetary defense system.

For ground operations, according to scientists, the country will select suitable sites to build multiple large-aperture optical telescopes, forming a geographically balanced ground-based monitoring system that can detect distant objects across a wide expanse of the night sky with high precision.

Li explained that several factors would be considered in choosing optimal sites.

"First, since optical telescopes only operate at night, candidate locations must have a high rate of clear skies. Second, asteroid observations require stable atmospheric conditions — a measurement known as astronomical seeing. Areas with excellent astronomical seeing, typically high-altitude regions, are preferred because a thinner atmosphere causes less interference with observations," he said.

In short, the ideal sites have a high clear-sky rate, good astronomical seeing, and high elevation. That is why the telescopes in the monitoring network will most likely be located in remote, sparsely populated areas, he said.

In outer space, he added, scientists plan to deploy a space-based monitoring constellation. Free from atmospheric interference and the constraints of the day-night cycle, these orbiting instruments will focus on filling the blind spot of threats approaching from the sun's direction, enabling round-the-clock observations through coordinated ground and space operations.

Li noted that telescopes in the space-based constellation will be positioned slightly farther from Earth, so they can monitor a wider perimeter around Earth and provide longer early-warning lead time.

Once completed, the constellation will complement ground-based telescopes: ground-based instruments mainly monitor the night sky, while space-based telescopes cover the blind zone toward the sun. Together, they will deliver seamless, all-sky monitoring with no blind spots.

According to Li, once the monitoring network enters operation, its priority will not be known individual celestial bodies, but the yet-undiscovered near-Earth asteroids.

"For near-Earth asteroids larger than 1 kilometer in diameter, which could trigger global catastrophes, it is estimated that more than 95 percent have been discovered worldwide. So far, none of them are on course to hit Earth in the next 100 years," he said. "But for asteroids around 140 meters across — capable of destroying a small or medium-sized country — only about 45 percent are estimated to have been found, meaning more than half remain undetected. The discovery rate is even lower for asteroids tens of meters in size."

These undiscovered near-Earth asteroids pose the greatest risk. That is why major space powers are accelerating efforts to build monitoring and early-warning capabilities and catalog these asteroids as soon as possible, Li added.

China has made breakthroughs in models and algorithms for asteroid impact risk analysis, and is developing an early-warning system. The idea is that once a telescope detects a suspicious object, the system will automatically calculate its orbit and assess the impact probability.

zhaolei@chinadaily.com.cn