The most promising places to look for life in the Solar System are in the ocean moons Europa and Enceladus. But all that warm, salty, potentially life-supporting water is under thick sheets of ice: up to 30 km thick on Europa and up to 40 km thick for Enceladus.
The main obstacles to exploring all that water are the thick ice barriers. Assuming a spacecraft can be designed and built to melt its way through all that ice, what then?
Submarines can do the actual exploring, and they needn’t be large.
If we ever detect an Extraterrestrial Civilization (ETC) and start communicating with them, the messages could take years, decades, or even centuries to travel back and forth. We face a challenging 49-minute long delay just communicating with the Juno spacecraft orbiting Jupiter, and that’s well within our Solar System. Communicating with an ETC that’s hundreds of light-years away or even further is a daunting task.
As Carl Sagan once said, “The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars.” And our first emissaries to the stars will be robotic probes. These interstellar probes will be largely autonomous, but we will want to communicate with them. At the very least we will want them to phone home and tell us what they’ve discovered. The stars are distant, so the probes will need to make a very long-distance call.
The gravity of the Earth is a tough thing to escape, but breaking free from the gravity of the Sun is on a whole other level. But humans have achieved this amazing accomplishment, and right now there are several spacecraft leaving the Solar System and never coming back.