It's generally agreed that liquid water and a stable atmosphere are the minimal requirements for life. But new research shows that oceans play a vital role in stabilizing and moderating climates on Earth-like planets.
Mars is a good example of what the astrobiologists from the University of East Anglia are talking about. It's a planet that orbits within our solar system's habitable zone, plus it once fostered liquid water at the surface. But it has no oceans — an absent geological feature that causes the Red Planet's air temperatures to swing over a range of 100 degrees Celsius. Oceans, on the other hand, make a planet's climate more stable.
This is the thinking of a team of researchers from UAE's schools of mathematics and environmental sciences. The researchers created a computer simulated pattern of ocean circulation on a hypothetical ocean-covered Earth-like planet. The models considered various planetary rotation rates and how those variable factors might influence heat transport in the presence of oceans.
The researchers found that heat transported by oceans would have a major impact on the temperature distribution across a planet, thus potentially allowing a greater area of a planet to be habitable. Specifically, they found that...
...the dependence of the poleward ocean heat transport on planetary rotation period is significantly greater than that of the atmosphere at rotation periods longer than a day. The significance of the ocean transport at shorter rotation periods is also implied by the scale analysis detailed in this study. This highlights the importance of including this effect, through a dynamic ocean, to achieve more accurate modeling of the climates of terrestrial planets.
"Oceans have an immense capacity to control climate," noted mathematician and study co-author David Steven in a statement. "They are beneficial because they cause the surface temperature to respond very slowly to seasonal changes in solar heating. And they help ensure that temperature swings across a planet are kept to tolerable levels."
It's vital, therefore, that astrobiologists factor this in when scanning the stars for alien signatures. That said, they should still factor for extremophiles. What's more, models have shown that extreme forms of life can also survive on planets with weird orbits, which imply dramatic dynamic temperature ranges.