Nevertheless, the recent detection of biological phosphine in the clouds of Venus serves as a reminder that at least some of these components also exist elsewhere in the solar system. So, what are the most promising locations for life beyond Earth?
Mars
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Mars stands out as one of the most Earth-like planets in our solar system. It boasts a 24.5-hour day, polar ice caps that expand and contract with the seasons, and a diverse range of surface features sculpted by water over its history.
Mars becomes a fascinating contender for potential life due to the recent discovery of a subsurface water lake beneath its southern polar ice cap and the presence of methane in its atmosphere, which varies with seasons and even throughout the day. Methane is of particular significance as it can be generated by biological processes. However, the actual origin of methane on Mars remains a mystery.
Life might have potentially established itself on Mars, as evidence suggests that the planet once possessed a much more favorable environment. However, Mars now has a very thin and dry atmosphere primarily composed of carbon dioxide, leaving it susceptible to significant solar and cosmic radiation. Despite these harsh conditions, the existence of a subsurface water reservoir on Mars opens up the possibility for life to persist.
Euroра
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In 1610, Galileo Galilei discovered Europa along with three other larger moons of Jupiter. Europa is slightly smaller than Earth’s Moon and orbits Jupiter at a distance of approximately 670,000 kilometers, completing one orbit every 3.5 days.
Tidal flexing causes continuous squeezing and stretching of Europa due to the competing gravitational forces of Jupiter and other Galilean moons.
Europa is thought to be a geologically active world, similar to Earth, as the strong tidal forces heat the interior rock and partially melt it.
The surface of Europa is a vast expanse of ice. Many scientists believe that beneath the frozen surface lies a layer of liquid water, creating a global ocean on the moon.
Evidence for this ocean includes water plumes erupting through cracks on the icy surface. The weak magnetic field and chaotic terrain on the surface may have been distorted by subsurface swirling ocean currents. This icy shell isolates the subsurface ocean from extreme cold and the pressure of space, as well as the intense radiation belts of Jupiter.
At the depths of this oceanic world, scientists envision the possibility of finding hydrothermal vents and volcanoes. On Earth, such features often support highly diverse and abundant ecosystems.
Enсelаdus
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Similar to Europa, Enceladus is an icy moon with a subsurface liquid water ocean. It orbits Saturn and first gained attention as a potential habitable world after the unexpected discovery of massive water plumes near its south pole.
Water jets escape from large cracks on the surface and, due to Enceladus’ weak gravity, they spew out into space. They are clear evidence of a subsurface liquid water reservoir.
Not only has water been detected in underground reservoirs, but a range of complex organic molecules and importantly, small silicate rock particles that can only form if water beneath the ocean floor contacts the rock at temperatures of at least 90°C. This is strong evidence for the existence of hydrothermal vents beneath the ocean floor, providing necessary chemicals for life and energy sources.
Tіtаn
Titan is Saturn’s largest moon and the only moon in the solar system with a significant atmosphere. Its atmosphere consists of a thick orange haze layer composed of complex organic molecules and a weather system of methane gas instead of water, with seasonal rains, dry periods, and wind-sculpted sand dunes on the surface.
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The atmosphere is primarily nitrogen, a chemical element crucial for creating proteins in all known forms of life. Radar observations have revealed the presence of rivers and lakes of liquid methane and ethane, and possible cryovolcanoes, a type of volcano that erupts evaporating substances like water, ammonia, or methane, instead of molten rock. This suggests that Titan, like Europa and Enceladus, has a subsurface liquid water reservoir.
Titan’s surface temperature is -180°C due to its distance from the Sun, which is too cold for water to maintain a liquid form. However, the abundance of chemicals available on Titan has sparked speculation that alternative chemical forms for terrestrial life could exist there.
(According to The Conversation)