Venus: Earth's Twin?

Venus is the brightest planet in the night sky after the Moon and is often called the "morning star" or "evening star." Its similar size—about 12,100 kilometers in diameter—and mass, which is 0.82 times that of Earth, have led scientists to nickname it "Earth's twin." Yet, beneath this resemblance, Venus is one of the most extreme planets in our solar system, making scientists question what makes two similar planets so different.

Why Is Venus So Hot?

One of the most striking features of Venus is its surface temperature, which reaches 465°C (870°F)—hot enough to melt lead. This is hotter than Mercury, even though Venus is farther from the Sun. The main cause is Venus’s atmosphere, which is 96% carbon dioxide (CO₂) and about 90 times thicker than Earth’s. This dense atmosphere creates a runaway greenhouse effect: sunlight passes through the atmosphere and heats the surface, but the thick CO₂ traps the heat and prevents it from escaping back into space. Over millions of years, this process caused Venus to become a scorching world. The planet’s thick, yellowish clouds of sulfuric acid also block our view of the surface and add to the heat-trapping effect.

Rotation, Surface, and Exploration

Venus rotates in the opposite direction of most planets (retrograde rotation) and does so very slowly—one day on Venus lasts 243 Earth days, which is longer than its year (225 Earth days). Because of this rotation, a day on Venus (from one sunrise to the next) is about 117 Earth days. The surface is covered in volcanic plains, mountains, and impact craters. Scientists think volcanoes may still be active. Venus has no moons. Most of what we know about the surface comes from radar images, especially those taken by NASA's Magellan spacecraft, and data from Soviet Venera landers, which survived only a few hours in the hostile environment before being destroyed by the pressure and heat.

Why Are Venus and Earth So Different?

Even though Venus and Earth started out similarly, Venus’s closer orbit to the Sun and its thick CO₂ atmosphere led to very different outcomes. Scientists think Venus once had water, like Earth, but higher temperatures caused the water to evaporate and escape into space. As a result, carbon dioxide built up in the atmosphere instead of being locked away in oceans or rocks. This created the runaway greenhouse effect that now makes Venus so inhospitable. The study of Venus helps us understand planetary systems and the importance of atmospheric balance for life.

Venus remains a bright point in our sky and a warning of how planet-wide changes can transform a world.

Interesting Fact:
Venus is so bright that it can cast shadows on Earth and is sometimes visible in daylight!