Last week, NASA launched its MAVEN mission to study Mars’ atmosphere. This though is one of the last NASA missions to another planet for the foreseeable future. The space agency currently only has three other such missions in development. These are:

• The InSight mission to Mars, which is set to launch in March 2016.

• OSIRIS-REx, an asteroid sample return mission set for launch in September 2016. The samples are due back on Earth in 2021.

• Then in 2020, NASA will launch another big rover to Mars. The rover, like the Curiosity rover that’s currently operating on Mars, will again need to make use of a radioisotope thermoelectric generator. RTG produces energy from the decay of radioactive elements, usually plutonium 238 (Pu 238). Pu 238 is in limited supply. The good news is that the the U.S. has just restarted Pu 238 production. The bad news is that NASA is ending its efforts to develop a better technology for transforming radioactive decay in power, an Advanced Stirling Radioisotope Generator, which requires a quarter as much PU 238 to generate the same amount of energy.

NASA also has probes en route to Jupiter (Juno) and Pluto (New Horizons).