Top 5 deep space probes exploring Outer Solar System

While the orbit around Earth is positively crowded with satellites, and there is even a traffic jam on the Moon, there are few active probes beyond the Earth-Moon system. The twin Voyager probes continue to beam back data, although the spacecraft are old and degrading. These are the first interstellar missions from mankind, and have messages on board for any intelligent agents that might discover the probes in the distant future. The New Horizons mission is also exploring the outer Solar System, and the remote icy objects in the Kuiper Belt.

Illustration of the New Horizons spacecraft. (Image Credit: NASA). 

These missions are not considered for this list because they have already completed the primary objectives of their missions. NASA will continue to maintain contact with the Voyager probes for as long as possible, while New Horizons is on a modified, extended mission. There are active assets in orbit around Jupiter and Mars, as well as around the Moon, that are monitoring these worlds. Humans have dispatched robotic messengers that are still en route to their destinations. All these probes represent humanity’s ambitions of unraveling the mysteries of the Solar System. Here is a look at them.

The Juno spacecraft was launched on 5 August 5, 2011 on an Atlas V rocket. The Juno mission has the goal of studying Jupiter, the largest planet in the solar system, and better understand the formation and evolution of the system. Juno has mapped the magnetic and gravitational fields of the gas giant, and is probing its atmosphere and interior structure, peering through the thick layer of clouds blanketing the planet. The spacecraft entered Jupiter orbit in 2016, and has been studying the gas giant since then, executing close flybys of its moons regularly. The mission is set to retire by the end of the year, when it will crash into Jupiter to prevent any contamination of the ice moons that host water, and potentially life. Juno is the most distant operational planetary orbiter, and a NASA mission under threat by the proposed budget.

Illustration of the Juno mission to Jupiter. (Image Credit: NASA). 

The Psyche spacecraft was launched on 13 October, 2023 on a SpaceX Falcon Heavy rocket. The spacecraft is headed to the asteroid designated as 16 Psyche, which is a unique metallic object in the main belt between Mars and Jupiter. The goal of the spacecraft is to characterise the composition, structure and magnetic properties of the asteroid, using sophisticated payloads, including a multispectral imager, a spectrometer, a magnetometer and a gravity instrument. Scientists hope to shed light on the process of core formation and planetary differentiation during the course of the mission. The asteroid is believed to be primarily composed of iron and nickel. The spacecraft is expected to arrive at its destination in August 2029, after executing a gravity assist from Mars in 2026. Psyche is a NASA mission.

Illustration of the Psyche mission to the metallic asteroid. (Image Credit: NASA). 

There is another probe headed to the Jovian system. The Jupiter Ice Moons Explorer (JUICE) mission was launched on 14 April, 2023 on an Ariane 5 rocket. The probe will explore Ganymede, Callisto and Europa, three of the four Galilean moons of Jupiter. The JUICE mission will characterise the subsurface oceans on these ice moons, that are potential habitats for life outside of Earth. The payloads on board include a radar sounder, an ultraviolet spectrograph and a magnetometer. The JUICE mission is focused on astrobiology and geophysics. The mission is currently in the cruise phase, and is expected to reach the Jovian system in 2031. Juice is a mission by ESA, the only one on this list.

Illustration of the JUICE probe. (Image Credit: ESA). 

The Europa Clipper mission was launched on 14 October, 2024 on board a SpaceX Falcon Heavy rocket. This is a mission that is focused only on Europa, one of the most promising locations to find life elsewhere in the Solar System. The mission hopes to characterise the ice shell and the underlying ocean, examine the composition of the moon, and studying its geological features. It is equipped with an ice-penetrating radar, a thermal imager, a magnetometer, and plasma sensors. The spacecraft will orbit Jupiter and execute 49 flybys of Europa. Europa Clipper executed a Mars flyby on March 2025, and will return to the Earth in December 2026 to steal some of its rotational energy, necessary to reach Jupiter in April 2030. Europa Clipper is a NASA mission.

Illustration of the Europa Clipper mission to Jupiter. (Image Credit: ESA). 

The Lucy spacecraft was launched on 16 October, 2021 on an Atlas V rocket. This is the fourth mission on the list of five headed to Jupiter. The target of Lucy though, are still asteroids that have been captured by the gravitational influence of Jupiters. These ‘Trojan’ asteroids orbit the Sun along with Jupiter in two swarms, a leading swarm ahead of Jupiter in its orbit and a trailing swarm that follows the gas giant. The spacecraft will test the hypothesis that these Trojan asteroids originated in the outer solar system and then migrated inwards. The Lucy mission has a number of specific asteroid targets, and has already conducted observations. The spacecraft is expected to reach its first Trojan asteroid in August 2077. Lucy is also a NASA mission.

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Illustration of the Lucy mission. (Image Credit: NASA).