China plans to venture farther into deep space

China has achieved remarkable accomplishments in the field of deep space exploration and is advancing its next ambitious missions, such as a Mars sample-return adventure and a Jupiter system expedition.

Chinese space scientists are also setting their sights on farther destinations that have never been closely observed by any Earthly spacecraft — ice giants in the solar system, particularly Neptune.

"Ice giants preserve pristine gaseous materials that record the evolutionary history of protostellar clouds and crucial information about planetary formation. These planets serve as vital subjects for studying the solar system's origins and exoplanets," Yang Mengfei, a senior scientist at the China Academy of Space Technology in Beijing and chief designer of the Chang'e 5 lunar mission, told China Daily in an exclusive interview.

An ice giant is a colossal planet composed mainly of elements heavier than hydrogen and helium, including oxygen, nitrogen, carbon and sulfur. Two planets in the solar system, Uranus and Neptune, are categorized as ice giants.

According to Yang, Uranus has the coldest atmospheric temperature in the solar system, with a minimum of about minus 224 C, and the most tilted rotation axis among all planets in the solar system.

Meanwhile, Neptune, the farthest planet from the sun, has the strongest surface winds, reaching speeds of up to 2,100 kilometers per hour.

Moreover, Triton, Neptune's largest moon, is considered "the most likely extraterrestrial body in the solar system to host microbial activity", and may provide key clues to life's origins.

"The formation and evolution of ice giants represent a cutting-edge frontier in planetary science. These planets remain among the least explored realms in our solar system. Their unique properties pose significant challenges to existing planetary formation theories, which struggle to adequately explain their mass and gas-to-solid ratios," Yang said.

Yang, who is also an academician of the International Academy of Astronautics and the Chinese Academy of Sciences, added that "limited observational data means the current understanding of Uranus' and Neptune's composition and internal structure relies heavily on planetary models, which have substantial uncertainties".

Therefore, he said, ice giant exploration has become an international priority in deep space research, and has been highlighted in the space exploration plans of Europe and the United States.

With China's advancing deep space exploration capabilities and critical progress in space-based nuclear power technology, the nation is basically ready to conduct orbital and close-in missions to ice giants, Yang said.

"China should strive to become the first to achieve orbital exploration of an ice giant," he suggested.

So far, only the US' Voyager 2 probe, launched by NASA in August 1977, has approached Uranus and Neptune and carried out flyby observations.

The spacecraft, which is now on an extended mission to study interstellar space, was about 20.8 billion kilometers away from Earth as of May this year.

Mission 'very necessary'

Another distinguished scientist, Wang Chi, director of the Chinese Academy of Sciences' National Space Science Center, said that except for the brief flybys by Voyager 2 in the 1980s, no spaceships have been sent to the two planets, resulting in an inability to improve the understanding of the Uranian and Neptunian systems.

"A dedicated, integrated mission to explore the ice giants is therefore very necessary, as it holds tremendous scientific value. Scientific studies suggest that a joint mission to Neptune and its largest moon, Triton, will be an ideal opening chapter to start our ice giant exploration," he said.

Wang noted that Triton is the only large moon in the solar system that orbits in the opposite direction of its host planet's rotation, which indicates that Triton is likely an object captured from the Kuiper Belt, a region of icy objects beyond the orbit of Neptune.

Crucially, Triton may possess a subsurface liquid ocean, making it one of the prime targets in the search for extraterrestrial "ocean worlds" and the quest for life beyond Earth.

The search for signs of life in the oceans of icy moons like Triton has become an international frontier in space-based life detection and a key to unraveling the mysteries surrounding the origins of life, according to Wang.

He noted that in China's first-ever national plan for space science development, which was published in October last year, the quest for habitable environments and life signs on ice giants was listed as an important scientific issue. The document suggests that Chinese scientists could need eight years, starting in 2028, to carry out feasibility research regarding the tasks of ice giant exploration.

Yang, the senior scientist from the China Academy of Space Technology, said that considering factors such as its 15-year duration, the Neptune mission should be conducted as early as possible after China launches its Jupiter probe. He suggested that the year 2033 could be a reasonable option for the Neptune explorer's launch window.

"Using a single mission to perform orbital observations of Neptune and then fly through its atmosphere would yield data on its magnetosphere, atmospheric structure and internal activity. This would reveal how outer heliospheric space weather affects atmospheric and water loss, examine the interactions between Triton and solar wind-magnetosphere energy transport, and look for signs of life in Triton's subsurface ocean," Yang said.

"This will deliver a groundbreaking scientific achievement ... and will help to establish China's reach across the entire solar system, elevate our overall technological prowess in the space industry, and position China at the global forefront of space exploration," he added.

In order to promote ice giant exploration and draw more attention to their suggestions, the two top scientists and a group of fellow researchers published two articles in the latest issue of the academic journal Chinese Space Science and Technology, elaborating on necessities, scientific and technological issues, and the challenges of an ice giant expedition, as well as possible solutions.