The divergent destinies of our solar system's closest neighbors
In short: Venus and Mars were once more like Earth than they are today. By studying how these two planets lost their ability to host liquid water, scientists can better understand the potential past and future scenarios for our own home planet.
Approximately 4.6 billion years ago, all planets in our solar system formed from a single swirling cloud of gas and dust surrounding the newborn Sun. Gravity caused dust to accumulate into boulders and eventually snowball into planet-sized entities. The rocky material survived the heat closest to the Sun, forming the innermost terrestrial planets like Venus and Mars. The leftover materials from this construction process created asteroids and comets. Gassy and icy components were pushed further away to form the outer gas giants.
As these young planets cooled from molten rock, they underwent 'outgassing'—a process where gases were released from the interior to form hot, dense early atmospheres. During this period, all three terrestrial planets experienced rains that formed their first oceans. However, the geological activity of Earth, Venus, and Mars eventually diverged, leading to vastly different environmental outcomes. Volcanic eruptions also contributed to early atmospheric composition. Small deliveries of water and other ingredients arrived via impacts from space debris.
Today, the differences are stark: Venus possesses a thick, poisonous atmosphere, while Mars has hardly any atmosphere at all. Space missions like ESA’s Venus Express (2006–2014) and Mars Express (since 2003) have confirmed that liquid water once flowed on both surfaces. On Venus, this water boiled away long ago; on Mars, it remains buried underground or trapped in ice caps. The current state of these atmospheres is intimately linked to the search for extraterrestrial life. These observations help reveal why Earth remains unique in its ability to support life today.
The study of these neighbors is not just about distant rocks. By examining the interplay between a planet's atmosphere, oceans, and rocky interior, researchers gain vital clues about the conditions required for life to flourish and how planetary environments evolve over billions of years. These planetary histories provide a framework for understanding how environments change over time. They offer a window into the mysteries of our solar system's evolution.
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Sources
- Summary by Intellect · source: Venus and Mars | How the Universe Works | Science Channel
- Also: How Venus and Mars can teach us about Earth
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