Venus, the sister planet of Earth, is often overlooked in favor of Mars. However, Venus shares more similarities with Earth than Mars does. It is the second closest planet to the Sun in the solar system and is named after the Roman goddess of love and beauty, Venus. 

Venus is an inner planet, located closer to the Sun than Earth, with a faster orbital speed of 224.7 Earth days per revolution. Despite its proximity to the Sun, Venus has similar characteristics to Earth in terms of size, mass, volume, and distance from the Sun. Its diameter is only 650 kilometers smaller than Earth's, and its mass is 19.5% smaller. These similarities have led to Venus being called Earth's "sister" or "twin brother". 

Scientists speculate that Venus may have once harbored life because of these similarities, with primitive oceans and landforms similar to early Earth. However, a runaway greenhouse effect caused all surface water on Venus to evaporate, wiping out any potential life. Surprisingly, Venus also experienced a greenhouse effect, although it is more commonly associated with Earth. Similar to Earth, water vapor in Venus' atmosphere trapped radiation, causing the planet's temperature to rise. This rise in temperature led to increased evaporation and a vicious cycle of water vapor concentration. As a result, hydrogen escaped into space while oxygen reacted with the planet's surface rocks. This runaway greenhouse effect caused Venus' oceans to evaporate completely, leaving behind a thick atmosphere consisting mainly of carbon dioxide. 

Despite its inhospitable surface, astronomers believe that Venus' atmosphere, especially at an altitude of 50 kilometers, could potentially be habitable for humans. The pressure and gravity at this altitude are comparable to Earth, and the planet's thick atmosphere can shield against extreme solar radiation and solar storms. NASA has proposed a concept called the High Altitude Venus Operational Concept, where humans could float in helium-filled airships in Venus' atmosphere. 

This exploration of Venus is also seen as a precursor to future Mars missions, as it could provide valuable technological experience. In summary, Venus, Earth's sister planet, has many similarities to our planet but underwent a runaway greenhouse effect that turned it into an extremely hot and dry world. Despite this, scientists believe that the upper atmosphere of Venus could be a potential habitat for human exploration, providing valuable experience for future Mars missions.