According to NASA, a habitable planet is one that can sustain life for a significant period of time. Here are three characteristics or elements that a habitable planet should have and how they support life:

Liquid water: Water is essential for life as we know it, and a habitable planet should have liquid water. Liquid water allows for the transportation of nutrients, removal of waste, and regulation of temperature in living organisms. Water is also a key ingredient in the formation of organic molecules, which are building blocks for life.

Atmosphere: A habitable planet should have an atmosphere that can support life. An atmosphere can help regulate the planet's temperature, protect the planet from harmful radiation and meteorites, and provide the necessary gases for respiration and photosynthesis. A stable atmosphere also helps maintain a stable climate, which is important for the survival of living organisms.

Suitable energy source: A habitable planet should have a suitable energy source for life to thrive. This energy source could be from the planet's star or other sources such as geothermal or chemical energy. This energy is necessary for the production of food through photosynthesis, and for the metabolism of living organisms. A stable energy source also helps maintain a stable ecosystem, which is important for the survival of the planet's biodiversity.

These characteristics or elements are important for a habitable planet to support life as we know it. However, it is also possible that life could exist in environments that do not have these characteristics, and scientists continue to search for signs of life beyond what we currently understand as habitable planets.