That may change as we continue exploring other worlds in the solar system using robotic vehicles, and potentially crewed spacecraft. Even if no living organisms are found on other worlds, our investigations will shed light on the processes of prebiotic chemistry and primordial geochemistry.25 The planet Mars, and the moons Europa, Enceladus and Titan, all have or had environmental conditions similar to parts of Earth. Future missions such as ExoMars and Europa Clipper will provide information about processes that are likely to have taken place on the young Earth.
A key challenge for the coming decades will be to send out sample-return missions that can bring high-quality samples back to Earth for detailed study. Because of the long development process for deep space missions, such a project would likely take more than 25 years to come to fruition.
The prospects for discovering life beyond the solar system remain remote. It is theoretically possible to find indirect evidence of life on an exoplanet, for example by detecting the presence of oxygen in the atmosphere through spectroscopic analysis. However, the technical challenges are considerable. Even if they are overcome, there is also the problem of interpretation: on Earth, oxygen is only produced by living organisms, but it is difficult if not impossible to rule out abiotic processes.26 This problem has already bedevilled researchers who detected methane on Mars and phosphine on Venus, and will be far worse when dealing with distant exoplanets for which information is more limited.27