Goldilocks Planets

A Goldilocks planet is one with conditions that are “just right” to sustain life. It must fall within a star’s habitable zone—neither too far nor too close from its star so that water can exist in liquid form on its surface. It also needs to be large enough with enough gravity to keep an atmosphere. Gravity is incredibly weak—our whole Earth doesn’t have enough gravitational pull to stop you from picking up a pebble. Yet it is enough to keep our atmosphere in place. The Moon, being only a fraction of Earth’s mass, doesn’t have enough gravity to hold an atmosphere. And without an atmosphere, liquid water can’t exist—it will just boil away into space. We also rely on our atmosphere to protect us from ultraviolet radiation and meteorites. Without it we would be cooked and pummeled, again, just like the Moon.

Sunset as seen on Mars through its thin atmosphere.

  The Earth’s liquid iron core generates a magnetic field which also protects us. This magnetosphere deflects solar winds that would otherwise strip us of our atmosphere. Mars, being much smaller than Earth, lost its magnetic field when its iron core cooled and as a result lost most of its atmosphere as well.

  Yet having an atmosphere does not a guarantee life either. Take Venus for example. Its atmosphere is the product of a runaway greenhouse effect. Its ocean’s boiled away from the heat and volcanic activity has left it an atmosphere that is mostly carbon dioxide. As a result, the planet that most closely resembles Earth is so hot that lead would melt on its surface.
  Goldilocks planets are of key interest to researchers looking for intelligent life or for a future home for the human race. Finding Goldilocks planets is an important part of the Kepler Mission (more here), which uses a space telescope to survey and compile the characteristics of such planets.


1) True or false: Mars is a Goldilocks planet.


2) Which of  following is not true about our atmosphere?
a) without it, we could not have liquid water  b) it protects us from ultraviolet radiation  c) it deflects solar winds  d) it protects us from meteorites


3) True or false: having an atmosphere guarantees that a planet can have liquid water.


4) Venus has an atmosphere that is mostly ______________.
a) nitrogen  b) carbon dioxide  c) argon  d) sulfuric acid


5) Finding Goldilocks planets is the primary goal of the _____________.

For additional content, musing and discussions follow us on Facebook.

To receive your Weekly Science Quiz by e-mail, request it here.