Final answer:
Helium-3 is hypothesized to be used as a fuel for clean nuclear fusion reactions that could provide energy for propelling spaceships and for sustaining human presence on Mars. It's not currently harvested from Mars, but its potential uses in space exploration and settlement are significant. Option a is the answer.
Step-by-step explanation:
The Helium-3 harvested from Mars is theorized to be a potential fuel for future nuclear fusion reactors. Currently, no Helium-3 is being harvested from Mars, as the technology and missions required to do so have not yet been established. However, the concept is based on the idea that Helium-3 could be an ideal fuel for clean nuclear fusion, providing a powerful energy source that releases very little radioactive waste compared to current nuclear fission reactors.
Propelling spaceships is one of the potential uses of Helium-3 if we were to harvest it from extraterrestrial bodies. It's essential for long-duration space travel because of its potential for high-energy yield and low environmental impact. Exploring options for in-situ resource utilization, such as mining Helium-3, could be crucial for sustaining human presence on Mars or other celestial bodies by providing necessary construction materials and potentially addressing the long-term health of astronauts' muscles and bones in low gravity environments.