Of all the planets in the solar system, Venus most closely resembles Earth. Venus’s mass and radius are only 20% and 5% smaller, respectively. In addition, it orbits about 30% closer to the sun than Earth. A hypothetical observer outside the solar system might expect Earth and Venus to share an abundance of qualities in common.
But they would be wrong.
Compared to Earth’s pleasant global temperature which permits abundant liquid water, Venus’s surface measures a hellishly hot 800 degrees Fahrenheit. Where Earth’s thin atmosphere consists primarily of nitrogen and oxygen, a dense carbon dioxide atmosphere surrounds Venus. Further, a day on Venus lasts 243 times longer than an Earth day. Consequently, Venus presents a completely inhospitable environment for life. What caused the marked difference between these sister planets?
A paper published in the Earth and Planetary Science Letters journal (and summarized in a Science Daily article) proposes one explanation. Just as a collision during Earth’s formation impacted Earth’s future development, Venus might have experienced a collision from another planetary embryo. A head-on collision would have totally melted (and even vaporized some of) both bodies. The water released from such a collision would rapidly react with the iron in the merged body. The hydrogen produced from these reactions either escapes to space or is sequestered in the core. Either way, no hydrogen remains available to form water as Venus cools.
Such a head-on collision explains the lack of water on Venus as well as the absence of a moon and its slow rotation rate. In contrast, the embryo that collided with Earth impacted with a more glancing blow, resulting in three important differences. First, the glancing blow did not melt Earth entirely, which significantly diminished the hydrogen-removing water/iron reactions. Second, the impact blasted more of Earth’s primordial atmosphere into space so that, subsequently, a much thinner atmosphere replaced the denser one. Third, Earth’s impactor formed a large moon which has stablized Earth’s rotation over billions of years.
While Venus and Earth might have exhibited a family resemblance for a few million years, the different impact events directed them toward divergent futures. Earth’s large moon, thin atmosphere, and relatively quick rotation rate became the initial steps in its transformation from a “formless and void” planet to one teeming with life. In contrast, the proposed impact event destroyed any possibility of Venus ever supporting life.
This research raises questions about reports in the media where scientists claim to have found life-supporting planets outside the solar system. Those reports are based on finding planets with masses, radii, and orbits analogous to Earth’s. However, a truly habitable planet requires a large number of additional fine-tuned transformations. That all these transformations occurred here on Earth comports well with the idea that a supernatural Creator fashioned Earth specifically as a habitat for humanity.