Life in the Solar System

As billions of species come and go on our home planet Earth, we wonder, "Are we alone?"  Outside of our solar system, on extrasolar planets, life could be rare or bountiful.  But locally, here in our solar system, there are still candidates for life.  Recently, evidence of water, and possible evidence of bacteria, and other micro-organisms were revealed in trenches of ancient oceans on Mars, suggesting a habitable climate.  Two gigantic asteroids hit Mars right around the time that the fossils pinpointed the existence of water, leading some people to believe that these asteroids destroyed the magnetic field or some of the atmosphere of Mars.  Therefore, all life on the planet would go extinct, just like an extinction on Earth, but to a greater extent.  

Mercury has no atmosphere, Venus is too hot, the gas giants have no solid surface and objects farther out are too small or cold. So, the moons are the only possibilities left.  Europa, a Galilean moon of Jupiter has an icy surface floating above a freezing ocean, 2 to 100 km deep.  Tides from Jupiter and possible heat from Europa's core, keep this ocean from freezing.  Titan, the only moon in the Solar System with an atmosphere, also holds the ingredients to possible life, save the temperature.  Orbiting freezing Saturn, the only liquid on this moon is liquid nitrogen, collecting in pools on its surface.  Either of these moons could be subject to later spacecraft study, and as our knowledge of technology grows, it is only a matter of time, until we are no longer alone in the Universe...