To our understanding, Earth’s biosphere contains every necessary element to sustain life. These ingredients, broadly, are liquid water, a variety of elements and molecules useful for biology and at least one energy source.
In recent weeks, the discovery of phosphine on Venus has suggested that these life-sustaining elements can be found elsewhere in the universe.
If Venus could potentially hold life, what other worlds are promising for life in our solar system?
Mars
To our knowledge, Mars is the planet that is most like our own. The planet has a 24.5 hour day, seasons that contract and expand ice caps, and, throughout the planet’s known history, surfaces that were moulded by water.
For a while now, it is common knowledge that Mars is a very interesting possibility for life in space. To support this possibility, scientists have detected methane in the planet’s atmosphere as well as a lake beneath its southern polar ice caps. They have even found that the planet’s atmosphere varies with not only its seasons but with the time of day.
To our understanding, methane is an element that can be developed through biological processes, which is significant. However, researchers do not know what the source for methane on Mars is yet.
Researchers and scientists believe that Mars was once a very benign environment, but changes over time suggest that life on the red planet may be gaining traction. Mar’s current atmosphere is extremely dry and thin due to being composed of almost only carbon dioxide. These conditions offer virtually no protection from both cosmic and solar radiation.
If Mars can hold water, it is very possible that it can sustain life.
Europa
Jupiter’s moons were discovered by Galileo Galilei in 1610. The ‘gas giants’ smallest moon, Europa, is almost the size of Earth’s moon. The moon orbit’s Jupiter at a distance of approximately 670,000km every 3.5 days.
Through a process called tidal flexing, all of the Galilean moons are constantly being stretched and squeezed by competing gravitational fields.
Europa is thought to be a world that is, similarly to the Earth, geographically active. This is suggested by the way the tidal flexing heats the interior of the moon and keeps it partially molten.
On top of this, an un-ending expanse of icy water covers Europa’s surface. It has been suggested by scientists that, under this layer of ice, there is a global ocean that is being prevented from freezing because of the molten heat coming from the centre. They also believe that this ocean could be 100km deep.
This ocean has been discovered by geysers that erupted through the ices surface, turbulent surface terrain and a weak magnetic field, all of which could be warped by the ocean below.
On Earth, we understand that hydrothermal vents and volcanoes on ocean floors can sustain diverse and rich ecosystems, and scientists believe it is probable that these could be found in Europa’s ocean.
Enceladus
Enceladus is very similar to Europa, with an icy surface and subsurface ocean. This moon was first linked to the search for life-sustaining worlds when scientists discovered it held large geysers near the southern pole.
These geysers are a very clear indicator of liquid water being stored beneath the icy surface. Scientists found that jets of water escape the surface through cracks and fly into space due to the weak gravitational field of the moon.
There is really strong evidence that suggests life could be sustained on Enceladus.
Evidence supporting the chemistry that is needed for life and energy has been found on Enceladus. This includes a variety of organic molecules and grains of rocky silicate particles that means the ocean water has contact with a rocky ocean floor that is at least 90˚C.
Titan
Titan is Saturn’s largest moon. It is also the only moon in our solar system that has a substantial atmosphere.
The moon has complete seasons – rain and dry period and the entire surface is covered by sand dunes sculpted by the wind. Titan mostly consists of a nitrogen atmosphere, which is an important element to proteins in all life forms we know on Earth.
Similar to Europa and Enceladus, Titan is suspected of having a large reserve of sub-surface water. On Titan, this is observed through not only the presence of liquid methane and ethane but the strong possibility of cryovolcanoes.
According to scientists, Titan is too cold for liquid water due to its substantial distance from the Sun – it’s temperatures are approximately 180˚C. However, it is the bountiful chemical that scientists and researchers have found on the moon that allows them to speculate the presence of potential life forms.
