Gas giants

v0.2 - 25-04-2020

Gas giants

The outer planets are called gas giants. They are Jupiter, Saturn, Uranus and Neptune respectively. So far only one mission, Galileo,  dove into the thick atmosphere of these gas giants. The term lander for a gas giant is somewhat abstract as there is no real hard surface to land on, a better term would be "atmospheric probe". However, the moons of gas giants do have a solid surface that can be landed on. 

Galileo entry probe

Operator: NASA

Target:  Jupiter

Landing date:  2003

Status:  Completed

The Galileo atmospheric probe was part of NASA’s 1989 Galileo mission to Jupiter. As part of the mission, a 337kg probe was deployed from the spacecraft tasked with collecting data from the Jovian atmosphere. The probe endured a maximum deceleration of 228g and temperatures in excess of 16,000°C but was still able to transmit useful data for 58 minutes before ultimately succumbing to the intense pressures of Jupiter’s atmosphere.


The probe used a two-stage parachute system to control its descent into the Jovian atmosphere. Shortly after atmospheric entry once the vehicle had passed the period of maximum heating and deceleration having burnt off over 100kg of ablator material from the heat shield the parachute system was activated. First, a pilot chute was deployed from the top of the vehicle using a mortar system. This pilot chute was used to pull off the vehicles back cover deploying the 2.47m projected diameter conical ribbon main parachute. This parachute was designed to help control the vehicles descent rate through the atmosphere rather than to allow the vehicle to land. Finally, the heat shield was jettisoned exposing the vehicles sample analysis instruments to the atmosphere and allowing the probe to start transmitting the data it had collected to the orbiter. In order to survive the harsh conditions on Jupiter, the main parachute canopy and suspension lines were made from the temperature-resistant polymer, Dacron with the parachute riser made from the aramid, Kevlar.

Although the Galileo Jupiter Atmospheric Probe’s mission was relatively short, it gathered a lot of valuable data about Jupiter’s atmosphere. It gave an insight into the composition of the atmosphere and detected winds in excess of 640m/s. [12]

v0.2 - 25-04-2020

Galileo probe during integration

Triton Hopper

Operator: NASA

Target:  Neptune's moon, Triton

Landing date: 2040

Status:  Proposed

Although there are a lot of landers going to our nearest neighbours, NASA is also looking further into the solar system with the dragonfly and Triton hopper. These are proposed to go to a moon of Saturn and Neptune, respectively. As the name suggests, the Triton hopper is proposed to land on Triton, one of Neptune’s moons. Although the project is currently in development, it has already completed its phase I study, and a conceptual design was drawn up [99].

When landing on Triton, the Triton hopper would be landing on a moon in a retrograde orbit around its parent planet about 30AU from the earth (1AU=distance earth-sun). This retrograde orbit is most likely because Triton is a captured object from the Kuiper Belt. Making the Triton hopper the first human-made object to land on a Kuiper belt Object when it would land in 2040 [99].

The vehicle would land using propulsion since the atmosphere on Triton is only 14-40 microbar (~1 Pa), mainly consisting of Nitrogen. To get to the point, a landing can be attempted, the entire system would first be inserted with a solid stage into a 200km parking orbit around Triton. Then the lander would separate and using a bi-propellant stage would descend to an altitude of 250m, where the hopper would make its first hop to the surface [99].

The Triton Hopper is estimated to have a dry weight of 325kg and 450kg when fully fuelled with Nitrogen. The engine used for hopping would use Nitrogen which is sourced after the first hop from the atmosphere and surface of Triton because the atmosphere is made mostly of Nitrogen. The hops it would make will be 1.3 km heigh and 5.2 km downrange, during which it will gather data on the atmosphere of Triton. Besides this, it will take along a wide range of sensors and cameras to analyse and photograph Triton [99].

The Triton hopper

Europa Lander

Operator: NASA

Target:  Jupiters's moon, Europa

Landing date: 2030+

Status:  Proposed, not selected?

Europa is one of the ice moons of Jupiter. The moon is considered one of the candidates for life in our solar system due to the presence of water and geological activity. This could be a possible site for extremophiles to live. To explore this a mission was proposed already in 2005 to land a small lander on Europa. Originally the lander would be combined with the Europa Clipper mission, but these two missions were separated to reduce risks. The mission was considered by the planetary Science Decadal Report of 2023-2032 but rejected.