The earth’s biosphere contains all of the known constituents necessary for life as we know it. Broadly speaking, these are: liquid water, at least one source of energy, and an inventory of biologically useful elements and molecules.
But the recent discovery of possibly biogenic phosphine in the clouds of Venus reminds us that at least some of these ingredients are also found elsewhere in the solar system. So where are the other most promising places for extraterrestrial life?
Mars is one of the most Earth-like worlds in the solar system. It has a 24.5 hour day, polar ice caps that expand and contract with the seasons, and a large number of surface features that have been shaped by water during the planet’s history.
The detection of a lake below the south polar ice cap and methane in the Martian atmosphere (which varies with the seasons and even the Time ) make Mars a very interesting candidate for life. Methane is important because it can be produced through biological processes. However, the actual source of methane on Mars is not yet known.
It is possible that life has taken hold in the face of the fact proofs that the planet once had a much more harmless environment. Today Mars has a very thin, dry atmosphere that consists almost entirely of carbon dioxide. This hardly offers any protection from solar and cosmic rays. If Mars has managed to hold some reserves of water below its surface, it is not impossible for life to still exist.
Europe was discovered in 1610 by Galileo Galilei along with Jupiter’s three other larger moons. It is slightly smaller than Earth’s moon and orbits the gas giant every 3.5 days at a distance of about 670,000 km. Europe is constantly being squeezed and stretched by the competing gravitational fields of Jupiter and the other Galilean moons, a process known as tidal flexing.
The moon is believed to be a geologically active world, like the earth, because the sharp tidal curvature heats its rocky, metallic interior, keeping it partially melted.
The surface of Europe is a huge area of water ice. Many scientists believe that beneath the frozen surface there is a layer of liquid water – a global ocean – that is prevented from bending by the heat and may be over 100 km deep.
Evidence of this ocean are geysers breaking through Cracks in the surface ice, one weak magnetic field and chaotic terrain on the surface, which may have been deformed by ocean currents swirling underneath. This icy shield isolates the underground ocean from the extreme cold and vacuum in space, as well as from Jupiter’s wild belts of radiation.
At the bottom of this ocean world, it is conceivable that we could find hydrothermal vents and sea floor volcanoes. On Earth, such features often support very rich and diverse ecosystems.
Like europe, Enceladus is an ice-covered moon with an underground ocean of liquid water. Enceladus orbits Saturn and was first known by scientists as a potentially habitable world after Saturn surprising discovery of giant geysers near the south pole of the moon.
These jets of water escape from large cracks on the surface and spray into space in the face of Enceladus’ weak gravitational field. They are clear evidence of an underground reservoir of liquid water.
Not only has water been detected in these geysers, but also a number of organic molecules and, above all, tiny grains of rocky silicate particles that can only be present when the underground seawater is in physical contact with the rocky seabed Temperature of at least 90 ° C.. This is very strong evidence of the existence of hydrothermal vents on the sea floor that provide the chemistry and localized energy sources needed for life.
Titan is Saturn’s largest moon and the only moon in the solar system with a sizable atmosphere. It contains a thick orange haze of complex organic molecules and a methane weather system instead of water – including seasonal rains, dry spells, and wind-created surface sand dunes.
The atmosphere is mostly made up of nitrogen, an important chemical element used in the construction of proteins in all known life forms. Radar observations have determined the presence of rivers and lakes of liquid methane and ethane and possibly the presence of cryovolcanoes – volcano-like features that erupt in liquid water rather than lava. This suggests that Titan, like Europa and Enceladus, has an underground reserve of liquid water.
At such an enormous distance from the sun, the surface temperatures on Titan are cool -180 ° C – much too cold for liquid water. However, the numerous chemicals available on Titan have led to speculation that life forms are forming – possibly with a fundamentally different chemistry than terrestrial organisms. could exist There.