We need the existence of liquid water for life, as we know it, to form. 70.8% of our planet’s surface area is covered with water. Thinking about oceans makes us imagine the waves of the Pacific Ocean or the currents of the Atlantic. Little do we think about vast oceans on the other planets and moons in our Solar System.
All of us have looked at the Moon but have you done so attentively? Only a few people know that it is covered with seas. Of course these seas do not contain liquid water; nor have they ever been connected to water in any state. The term indicates dark basaltic plains on the Moon that early astronomers mistook for actual seas. The plains were formed during early volcanic eruptions and as a result of their iron-rich compositions they are less reflective than the higher parts of the Moon. Therefore, they appear darker to the naked eye.
Our Moon is rich in seas, bays, lakes and even marshes. Most importantly, it even has one ocean. Oceanus Procellarum, also known as the Ocean of Storms, is the largest of the maria (seas) on the Moon: its total surface area is 4,000,000 km2. That is approximately the size of the European Union.
Like all lunar seas, Oceanus Procellarum is covered in a nearly flat thick layer of solidified magma. But unlike the other lunar maria, Oceanus Procellarum may not be contained within one well-defined impact basin. There are several hypotheses about the formation of Oceanus Procellarum. One appealing hypothesis states that it was a result of an ancient impact on the near side of the Moon.
If you’re curious, Oceanus Procellarum can be observed without any additional equipment during the full moon. It is the vast dark area located in the western hemisphere of the Moon.
Early astronomers were also interested in observing our neighbouring planets, known as the Earth-like planets. It seemed only logical that if the planets resemble each other – which they seemed to considering their distance from the Sun and their composition – there should be water in some state found there.
Venus is thought to have had liquid water and perhaps even oceans during its early formation. However Venus is infamous for active geological processes; its entire area is constantly being resurfaced, so it is impossible to study these assumptions.
It is much easier to find evidence of the existence of liquid water on Mars. The main hypothesis is that Mars used to resemble Earth but has dried up during its development. Several basins on Mars have been proposed as dry seabeds, the largest of them being Vastitas Borealis (Northern Waste). There are currently discussions over whether Mars once had an ocean of water in its northern hemisphere. Recent findings by the Mars Exploration Rover mission indicate that Mars had some long-term standing water in at least one location, but its extent is not known.
Many of us have heard about dry channels on Mars. Long dark striations seen in the polar latitudes have been interpreted by some as irrigation channels for liquid water; but these straight line features can actually be explained as optical illusions.
The latest Martian studies concentrate on subsurface liquid water. The confirmation of former liquid water on Mars came by studying of minerals that include water molecules and geological formations induced by standing water. Now, researchers want to know why all the water disappeared, and where it is now. Currently, it is thought that liquid water on Mars can be found in polar caps and/or under the surface.
During recent years, there has been much dispute over the existence of water on Jupiter’s moon Europa. Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of water ice and is one of the smoothest in the Solar System. Theoretically, there may be a vast ocean under its icy surface.
The hypothesis for the ocean proposes that pressure from tidal flexing – the effect of tidal forces between a satellite and the planet it orbits, often producing heat – causes the ocean to remain liquid and drives geological activity similar to plate tectonics. Life could exist in this ocean, perhaps surviving in an environment similar to Earth’s deep-ocean hydrothermal vents. Conjectures on extraterrestrial life have ensured a high profile for Europa and have led to steady lobbying for future missions.
Excitingly, it is possible that two other moons of Jupiter, Callisto and Ganymede, exhibit water in some state as well. A moon of Saturn called Enceladus also appears to have a ocean of liquid water beneath its surface. Active eruptions of water vapour were observed on Enceladus in 2008 – analysis of the plume composition revealed salty particles that currently can only be explained by the existence of such a subsurface ocean.
As we are infinitely interested in extraterrestrial life, we keep searching for evidence of water on other planets and moons. Recently, extrasolar planetary systems have diverted much of our attention as many lie in the habitable region around their particular stars. It is believed that rocky planets and moons hosting water may be commonplace throughout the Milky Way.
We have a lot of oceans to discover in the universe and as Bob Bello, a visionary artist inspired by the universe once said, “The sky is the limit only for those who are not afraid to fly!” Or in our case, swim.