Mission typeJupiter and Callisto orbiter
Uranus flyby
Spacecraft properties
Launch massTotal: 5,000 kg (11,000 lb)[1]
Jupiter-Callisto Orbiter: 4,000 kg (8,800 lb)
Interplanetary flyby probe: 1,000 kg (2,200 lb)
Start of mission
Launch dateSeptember 2029 (proposed)[2]
RocketLong March 5
Launch siteWenchang
Flyby of Venus (gravity assist)
Closest approachApril 2030 (proposed)
Flyby of Earth (gravity assist)
Closest approachFebruary 2031 (proposed)
Flyby of Earth (gravity assist)
Closest approachMay 2033 (proposed)
Jupiter orbiter
Orbital insertionDecember 2035 (proposed)[3]
Orbital departureFebruary 2038 (proposed)
Callisto orbiter
Orbital insertionFebruary 2038 (proposed)[4]
Flyby of Uranus (Interplanetary flyby probe)
Closest approachMarch 2045 (proposed)[3]

Tianwen-4, (Chinese: 天问四号) formerly known as Gan De, (Chinese: 甘德)[5] is a planned interplanetary mission by China to study the Jovian system and its environs, sharing a launch with a spacecraft which will make a flyby of Uranus.[6]


The goals of the planned Tianwen-4 Jupiter mission were detailed in an article published in a Chinese academic journal, they include the following: study of the interaction between magnetic fields and plasma present in the Jovian system, examination of the compositional variations in the Jovian atmosphere, exploration of the internal structures and surface characteristics of either Ganymede or Callisto, as well as investigation of the space environment surrounding the aforementioned Galilean satellites.[7]

According to reports in the Western media, there are two competing mission profiles as of January 2021: the 'Jupiter Callisto Orbiter' (JCO) and the 'Jupiter System Observer' (JSO).[5] 'JCO' would involve a spacecraft conducting fly-bys of Jupiter's irregular satellites before it enters into a polar orbit about Callisto; this mission profile also may include a Callisto lander. In contrast, the 'JSO' mission profile, while broadly similar to that of 'JCO', would forgo an attempt by a spacecraft to orbit Callisto and instead would focus on more intensive studies of the Galilean moon Io (the 'JSO' mission profile also does not appear to include a lander though it may involve sending the spacecraft to the Sun-Jupiter L1 point at the conclusion of its tour of the Jovian system). Finally, presentations by Chinese researchers suggest that the Tianwen-4 Jupiter mission may include an additional probe that would conduct a fly-by of Uranus sometime after 2040.[8] As of December 2023, it appears that the JCO Profile has been selected, with the Uranus flyby as well.[9]

The original name of this mission referred to the fourth century BCE Chinese astronomer Gan De, who made early planetary observations and reputedly first observed the Galilean moons with the unaided eye.[5]


On October 15, 2003, CNSA launched China's first independent crewed orbital mission; subsequently it prosecuted successful robotic lunar orbital missions (Chang'e 1 and Chang'e 2) and a robotic lunar lander/rover mission (Chang'e 3). In the hope of building upon these achievements, CNSA began to contemplate more ambitious interplanetary missions in the 2020s and beyond. In 2018, Pei Zhaoyu, the deputy director of CNSA's Lunar Exploration and Space Program Center stated that China was planning to conduct four major interplanetary missions before the end of the 2020s;[10] the four missions include a mission to Mars (Tianwen-1), a main-belt comet and asteroid sample-return mission (Tianwen-2), a Mars sample-return mission (Tianwen-3), and a Jupiter system mission. As of early 2021, the aforementioned JCO and JSO mission profiles are competing to be realized as the Tianwen-4 Jupiter system mission.[5]

Possible mission timeline

One possible Earth-Jupiter mission trajectory and timeline was presented at the 2020 General Assembly meetings of the EGU.[11] Under this scenario, the Tianwen-4 probe would launch in September 2029,[2] conduct a Venus fly-by six months later in April 2030,[a] then proceed to encounter Earth twice (the first encounter occurring in February 2031[b] and the second in May 2033[c]). Before arriving at Jupiter, the sub-probe will separate from the main probe and continue towards Uranus for a flyby in March 2045.[1][3]

The main probe will enter Jupiter orbit in December 2035. After 1 or 2 braking passes, the probe will stay in a large elliptical orbit around Jupiter with a period of 30 days, making flybys of irregular moons.[9] It will conduct 10 orbits over about a year before entering its second phase with two gravity assists of Callisto. In February 2038, Tianwen-4 will enter orbit around Callisto with an altitude of 300 km and an orbital period of 17.7 hours, and an impact probe will then be released to impact the surface of Callisto.[4][3]

Mission architecture

As of 2021, one of the two following mission profiles (JCO and JSO) is likely to resemble the final mission architecture:

Jupiter Callisto Orbiter (JCO)

JCO would fly by several irregular Jovian satellites before entering a polar orbit around Callisto. This scenario includes a possible lander which, like the Chang’e lunar landers, would provide unprecedented insights into the moon's formation and evolution. Callisto is the outermost of the four Galilean moons. Its interior experiences less heating due to gravity from the other moons and Jupiter. It likely formed with leftover Jupiter material and has sat mostly dormant since, with only asteroid impacts to modify its surface. The moon thus preserves a history of the early Jupiter system and the Solar System at large for a lander to study. Callisto also has a thin atmosphere with small amounts of oxygen, increasing its scientific allure despite being less glamorous than fellow subsurface ocean moons Europa and Ganymede and volatile, active Io. Callisto is also the least challenging Jovian moon to land on. A spacecraft requires less fuel to reach it, and it sits outside Jupiter's intense radiation field. These are rationales that argue for Callisto as the main mission target. JCO also includes a secondary spacecraft that would independently fly towards and encounter with Uranus sometime in the late 2040s.[5]

Jupiter Systems Observer (JSO)

JSO would substitute a possible Callisto landing with an in-depth investigation of the Jovian moon Io. The spacecraft would perform several Io flybys, studying how Jupiter's gravity tugs on the moon to power its volcanic activity. JSO would also study the mass, density, dynamics and chemical and isotopic composition of irregular satellites and would provide insights into these unique remnants of Jupiter's formation. As an option, JSO could release one or several small satellites to perform multi-point studies of the dynamics of the Jovian magnetosphere.

At the end of its tour JSO could be sent to orbit the Sun-Jupiter L1 point, where the planet's gravity balances with the Sun's in a way that spacecraft can remain there for long periods of time. From this unique perch where no spacecraft has ever visited, JSO could monitor the solar wind outside of Jupiter's magnetic field, and survey the irregular Jovian moons from afar.[11]

Mission instruments

Potential scientific instruments for the Tianwen-4 mission were discussed during a session of the 2020 General Assembly of the European Geosciences Union that took place in May 2020. The possible instruments were categorized into four payload packages designed to address the two main goals of the mission: answering questions on the formation and current "workings"[d] of the Jovian system (the actual instruments selected would depend on whether JCO or JSO is selected as the mission profile.) The four payload packages are: (A) plasma and dust analyzers, (B) multi-wavelength spectroscopic instruments, (C) geology/glaciology/geochemistry analyzers, and (D) radio/optical links and radio science instruments.[11]

Plasma and dust analyzers package

Multi-wavelength imaging/spectroscopy package

Geology/glaciology/geochemistry analyzers package

(fed-by sampling system for ice surface and by pyrolyser [for refractory component])

Radio + optical link + radio science package


  1. ^ The closest-approach to Venus is anticipated to be about 6,011 kilometers
  2. ^ Earth closest-approach: 5,482 kilometers
  3. ^ Earth closest-approach: 1,386 kilometers
  4. ^ These involve the Jovian system's energy transfer processes such as the tidal transfer and dissipation of gravitational energy between the planet, moons, the plasma torus, and the entire magnetosphere.

See also


  1. ^ a b 田百义,张磊,周文艳,朱安文 (February 2018). "《木星系及行星际飞越探测的多次借力飞行轨道设计研究》" (in Simplified Chinese). 《航天器工程》. Archived from the original on 2021-10-09. Retrieved 2021-10-09.
  2. ^ a b CNSA Watcher [@CNSAWatcher] (December 23, 2023). "Tianwen-4, launching Sept 2029, will journey to Jupiter using Venus & Earth gravity assists. Targeting Jupiter capture by Dec 2035 & a Uranus flyby in March 2045, the mission includes 2 probes, one exploring Jupiter's system and another flying by Uranus" (Tweet) – via Twitter.
  3. ^ a b c d Andrew Jones (2023-12-21). "China's plans for outer Solar System exploration". The Planetary Society. Retrieved 2023-12-27.
  4. ^ a b 张磊,田百义,周文艳,田岱,朱安文 (2018-02-28). "木星系多目标探测轨道设计研究" (in Simplified Chinese). 航天器工程,2018,27(01):31-36. Retrieved 2023-01-07.
  5. ^ a b c d e Jones, Andrew (12 January 2021). "Jupiter Mission by China could include Callisto Landing". Planetary.org. Retrieved 1 May 2021.
  6. ^ Andrew Jones published (2022-09-22). "China wants to probe Uranus and Jupiter with 2 spacecraft on one rocket". Space.com. Retrieved 2022-09-28.
  7. ^ Xu, Lin; Zou, Yongliao; Jia, Yingzhuo (2018). "China's planning for deep space exploration and lunar exploration before 2030" (PDF). Chinese Journal of Space Science. 38 (5): 591–592. Bibcode:2018ChJSS..38..591X. doi:10.11728/cjss2018.05.591. S2CID 256881663.
  8. ^ Jones, Andrew (14 July 2017). "Mars, asteroids, Ganymede and Uranus: China's deep space exploration plan to 2030 and beyond". FindChinaInfo. Archived from the original on 1 January 2022. Retrieved 1 May 2021.
  9. ^ a b "China's plans for outer Solar System exploration". EIN Presswire. 21 December 2023. Retrieved 24 January 2024.
  10. ^ "China outlines roadmap for deep space exploration – Xinhua | English.news.cn". www.xinhuanet.com. Archived from the original on April 25, 2018. Retrieved 2 May 2021.
  11. ^ a b c Blanc, Michel; Wang, Chi; Li, Lei; Li, Mingtao; Wang, Linghua; Wang, Yuming; Wang, Yuxian; Zong, Qiugang; Andre, Nicolas; Mousis, Olivier; Hestroffer, Daniel (2020-05-01). "Gan De: Science Objectives and Mission Scenarios For China's Mission to the Jupiter System". EGU General Assembly Conference Abstracts. 22: 20179. Bibcode:2020EGUGA..2220179B. doi:10.5194/egusphere-egu2020-20179. S2CID 235015121.