Goldilocks zone

A habitable zone, also called a Goldilocks zone, is the region around a star where orbiting planets similar to the Earth can support liquid water. It is neither too hot, nor too cold.

Scientists hunting for life in the Solar System and around other stars believe liquid water is an important ingredient necessary for life.

In September 2010 astronomers using the Keck telescope announced they had found an exoplanet, Gliese 581g2, about three times the size of Earth in the habitable zone of its star.

The Earth is a unique planet because it sustains life. Here are some more details:

1. The Earth lies between the orbits of Venus and Mars and the average distance from the Sun is about 148 million km. This gives it the optimum location with reference to the distance from the Sun. It is neither too hot like Venus nor too cold like Mars and the outer planets. The average temperature is about 17°C on the side facing the Sun.

2. The Earth has a favourable environment and presents optimum conditions for the origin, growth and survival of various life forms. If the heat received from the Sun

2 UPSC asked question on Gliese 581g

(insolation) increases or decreases by about 10 per cent, then a very large part of the Earth would become unsuitable for living organisms.

3. The rotation of the Earth around its axis, helps in keeping the extremes of temperatures between day and night well within tolerable limits.

4. The presence of adequate quantities of water in the oceans, seas, gulfs, rivers, lakes, etc., is a unique feature of our planet. Water occupies about 71 per cent of the total surface area of the Earth. These water bodies provide Ideal conditions for the origin and evolution of various life forms. The water cycle maintains the continuous flow of water on Earth.

5. The atmosphere acts as a shield and protects our planet from the harmful ultra-violet rays coming from the Sun. The atmosphere also absorbs terrestrial radiation from the Earth’s surface and thus keeps the Earth comparatively warmer during the night time and also during the winter season.

6. The presence of oxygen in the atmosphere has made life possible on Earth, as it is essential for respiration and survival of all living organisms.