1. We know of only one place in the Universe where life arose – our own planet Earth.
- We don’t know if life is common or rare in places where the conditions are right.
- We know of other places in our own Solar System (including Mars and several moons) where conditions may be (or once may have been) suitable for life, but we don’t know if life ever arose there.
2. We now know that planets around other stars are common.
- Some of these extrasolar planets are located in their parent star’s habitable zone.
3. Life as we know it requires organic materials, an energy source (e.g., sunlight), and liquid water.
- Current searches for extraterrestrial life focus on finding carbon-based life, though other forms of life may be possible.