How Hot Would the Earth Be if the Sun Came Nearer?
- As a quick survey of the planets will show, planets closer to the sun tend to have higher mean temperatures than planets farther out in the solar system, due to different levels of exposure to solar radiation. However, the planet with the highest mean temperature is Venus, which, at around 67 million miles, is much farther from the sun than Mercury (29 million miles). This discrepancy can be explained by the greenhouse effect caused by Venus' thick atmosphere of carbon dioxide. This highlights some of the difficulties in calculating planetary temperatures based solely on distance from the sun.
- The Earth's distance from the sun actually varies by about 3 million miles over the course of a year due to the elliptical nature of its orbit. Earth is closest to the sun in January (perihelion) and farthest in June (aphelion). This causes a small temperature difference, which is largely eliminated by the concentration of landmass in the Northern Hemisphere. When the Earth is closest to the sun, it is summer in the Southern Hemisphere, which is dominated by oceans. Oceans absorb heat more slowly than land, which counterbalances the additional heat of perihelion.
- The inverse square law states that solar radiation decreases by half as the distance from the sun is doubled. Therefore, if Earth orbited the sun at half its current distance, it would absorb twice the solar radiation. Based on Earth's current rates of absorption, this would raise the mean temperature of Earth by about 40 percent. This increase would be applied to the scale of absolute temperature, beginning at absolute zero, or 460 degrees below zero Fahrenheit. Earth's current mean temperature is 13 degrees Celsius (55 degrees F), which translates to 510 degrees F above absolute zero. A 40 percent increase would result in a mean temperature of 124 degrees C (255 degrees F).
- Due to the complicated nature of the Earth's heat exchange mechanisms, the temperature would likely change even further over time if the orbital distance were halved. The new temperature would be well above the boiling point of water, which would cause the oceans to evaporate. The planet would get hotter still as it lost the temperature regulation of the oceans and gained substantially more greenhouse gas in the form of water vapor. Since Earth's new orbit would be close to Venus' current orbit, it is possible that Earth's new greenhouse atmosphere would reach similar temperatures: 454 degrees C (850 degrees F.)