In our universe, there are many planets which could possibly contain life. However, there are multiple criteria a planet must be able to meet in able to be considered “habitable.” First of all, it should be in its solar system’s habitable zone, also called the Goldilocks zone. This is the area in a solar system where the planet(s) in it are most likely to meet the criteria for containing life as we know it. For example, in our solar system, Venus, Earth, and Mars are in the habitable zone. Another criteria is temperature, partly determined by a planet’s location in a solar system (ex: Venus, being closer to the Sun, is very hot, while Mars, being farther from the Sun, is much colder). Earth has temperatures which are able to sustain life, which is why climate change is such a big problem for life on Earth as we know it. This directly connects to another criteria, which is liquid water. While there is possibly water in the form of ice on Mars, it is too cold to sustain life. While there are definitely more factors in defining life as we know it, these are some of the most major ones.

1. Mars

Surprisingly for many, Mars may once have had life. It is believed that Mars was habitable ending 3.5 billion years ago. During this time period, Mars would have received rain in the form of liquid water, a vital element for life. Life on Earth developed earlier than this time, so assuming the then-habitable Mars followed similar patterns, there was definitely more than enough time during Mars’ habitable period for life to develop.

2. Kepler-22b

This exoplanet orbits the star Kepler 22, in the constellation of Cygnus, about 600 light-years away from Earth. Kepler 22 is a star which is actually similar to our own Sun. Both our own Sun and Kepler 22 have similar sizes and temperatures. It is about 2.4 times Earth’s size. Not only is the planet in the habitable zone, but some studies also suggest that it could have temperatures very similar to Earth, at about 72 degrees Fahrenheit, or 22 degrees Celsius.

3. Proxima Centauri B

Proxima Centauri B is one of the closer potentially habitable planets at just about 4.24 light-years away. It is similar in size to Earth, at about 1.17 Earth masses. However, it orbits its star much more quickly than Earth orbits its Sun. It takes Proxima Centauri B only about 11 days to orbit its star, Proxima Centauri, a part of the triple star Alpha Centauri System. Proxima Centauri B is within the habitable zone, so it is definitely a plausible candidate for extraterrestrial life and habitability.

While there are many candidates for extraterrestrial life on exoplanets, it is important to remember that these are only the one’s considered habitable due to similarity with Earth. Therefore, there may actually be many more exoplanets which possibly contain life. Our lists of “habitable” exoplanets are only based on our knowledge of what life on our planet, Earth, needed to develop.

-Peri A.