Every country that has ever explored space has sent robotic probes first. The robots have become more sophisticated over time, so now they can make their own decisions without having to wait for instructions from Earth by radio. The robots are built to withstand extreme temperatures and hard radiation environments and still get the job done. 

The robotic probes that are closer to the sun than Jupiter use solar panels to create electricity to do their missions.  However, if they go past the distance of Jupiter, the sun appears to be very dim and so there’s not enough sunlight for solar panels. Because the element plutonium can stay hot for many years, it can be used to create electricity for the robots that are far from the sun, such as Voyager.

Every planet has been visited by a robotic space probe, as well as the dwarf planets Ceres and Pluto.  Every time people have sent robots to new places, there is always a surprising new scientific discovery.

Some robots like the Voyager probes have recordings and images on them so that if an alien race were ever to find them someday, they could learn about humans and the earth. Any alien life would most likely be very different from any life on earth, but hopefully intelligent alien beings might be able to understand our messages.