Advancements in space observation technology have led us to discover an increasing number of planets outside the solar system. The Kepler mission alone has so far confirmed the finding of over 2000 extracellular planets. But which of these have the potential to support at least some basic forms of life? Here is a quick overview of what we consider the five main conditions for a planet to be habitable. The right star! Life on Earth took nearly a billion years to develop and thrive. This would not have been possible if the Sun had not been providing heat and light for that amount of time. More massive stars tend to consume their fuel faster and stars over 10 times more massive than the Sun only lasted few hundred million years. Also, stars in transition evolutionary stages cannot provide a steady source of energy. In those conditions, life can't stand a chance. The right distance. Stars are surrounded by roughly circular strip, where temperatures are just right for liquid water to exist. Water in liquid form can dissolve and transport substances to and from cells, enabling the key chemical reactions of life. Depending on the size and surface temperature of the star, the location of the habitable zone can differ. In general, hotter stars have their habitability zone further away and vice versa. The right atmosphere. Did you know that without atmosphere, the mean temperature on the surface of the Earth would be about minus 20 degrees centigrade? Our atmosphere contains certain gases, called greenhouse gases, which trap some of the Sun's radiation and turn it into heat, therefore warming up our world. Smaller planets, such as Mars, have a lower gravity and are unable to keep a substantial atmosphere around them. While planets with an atmosphere that is too thick or contains an excess of greenhouse gases, will become like Venus, a dry, inhospitable furnace. In addition, atmospheres burn meteorites, which would otherwise heat the surface and bring havoc. A magnetic field. Meteorites are not the only thing that need to be shielded off. Our Sun spits out billions of high energy charged particles every second, forming the so-called solar wind. If the Earth did not possess a magnetic field, this radiation would literally burn up every life form. Magnetic fields deflect charged particles, therefore protecting life forms on a planet's surface. The right chemicals. Life needs the right elements to form those organic compounds that are indispensable to drive physiological processes. Some of these elements, like iron, calcium, sodium and magnesium, are present in the Earth's crust and get refurbished over time. Plates get pushed under each other by tectonic movements. The rocks melt and later return to the surface through volcanic phenomena. Therefore, a planet that shows signs of geological activity is also potentially interesting for life. Thank you for watching!