NASA is searching for evidence of life on other planets. What characteristics make life possible? Water is essential to all known forms of life on Earth. NASA scientists are looking for 'Goldilocks Planets' that have temperatures not too hot or too cold to allow liquid water. By looking within our own solar system, we identify reasons neighboring planets and our moon lack conditions for life. Then we look at Earth: how the presence of liquid water, reflective surfaces such as polar ice caps, and the chemical composition of our atmosphere all contribute to keeping Earth's energy budget in balance.
A 'Goldilocks Planet' is the right distance from its Sun to allow temperatures for liquid water. Not too hot, not too cold.
The Sun is our primary energy source. The energy Earth receives from the Sun is in balance with the energy our planet loses to space:
Earth reflects an average 30% of incoming solar energy back to space
Earth's atmosphere absorbs about 20% of incoming solar energy
About 50% of solar energy reaches the land and oceans and warms them
Earth emits 70% of incoming energy back to space as heat (infrared radiation)
Earth's energy budget is roughly in balance, but the addition of greenhouse gases from fossil fuel emissions since 1900 has resulted in less heat lost to space, a slight heat gain, and increasing average temperatures on Earth
Venus is too close to the Sun with an atmosphere that is mostly carbon dioxide, thus it is much too hot for water.
Mars is the right distance from the Sun, but does not have enough atmosphere and gets too cold at night. Water is frozen in polar ice caps. Curiosity rover is on Mars collecting samples and has found water in rock, but so far no evidence of life.
Our moon is the right distance from the Sun, but without an atmosphere it is too hot in the day and too cold at night.
There is also an introductory autorun movie available that gives an overview of NASA's Search for Goldilocks Planets without the depth of the docent show and is designed to stand on its own or can be used within a docent show as an introduction.