[ad_1]
Earth’s biosphere It contains all the known ingredients necessary for life as we know it. Generally speaking, this is 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 also exist in other parts of the solar system. So where are the other most promising places for extraterrestrial life?
Mars
Mars is one of the most Earth-like worlds in the solar system. It has a 24.5-hour day, polar caps that expand and contract with the seasons, and a wide variety of surface features that were sculpted by water during the planet’s history.
The detection of a lake below the South Pole ice sheet and methane in the Martian atmosphere (which varies with the seasons and even the time of day) make Mars a very interesting candidate for life. Methane is important as it can be produced through biological processes. But the actual source of methane on Mars is not yet known.
Life may have gained ground, given the evidence that the planet once had a much more benign environment. Today, Mars has a very thin, dry atmosphere made up almost entirely of carbon dioxide. This offers little protection against solar and cosmic radiation. If Mars has managed to retain some reserves of water below its surface, it is not impossible that life still exists.
Europe
Europa was discovered by Galileo Galilei in 1610, along with the other three largest moons of Jupiter. It is slightly smaller than Earth’s moon and orbits the gas giant at a distance of about 670,000 km once every 3.5 days. Europa is constantly compressed and stretched by the competing gravitational fields of Jupiter and the other Galilean moons, a process known as tidal bending.
The moon is believed to be a geologically active world, like Earth, because the strong bending of the tides heats its rocky and metallic interior and keeps it partially molten.
The surface of Europa is a vast expanse of water ice. Many scientists think that below the frozen surface there is a layer of liquid water, a global ocean, that does not freeze due to the heat of the bending and is perhaps more than 100 km deep.
Evidence for this ocean includes geysers erupting through cracks in the ice’s surface, a weak magnetic field, and chaotic terrain on the surface, which could have been warped by ocean currents swirling below. This icy shield insulates the subterranean ocean from the extreme cold and vacuum of space, as well as from Jupiter’s fierce radiation belts.
At the bottom of this ocean world, we conceivably find hydrothermal vents and ocean floor volcanoes. On Earth, such features often support very rich and diverse ecosystems.
Enceladus
Like Europa, Enceladus is an ice-covered moon with an underground ocean of liquid water. Enceladus orbits Saturn and first came to the attention of scientists as a potentially habitable world after the surprise discovery of huge geysers near the moon’s south pole.
These jets of water escape from large cracks in the surface and, given Enceladus’s weak gravitational field, spread out into space. They are clear evidence of an underground reservoir of liquid water.
Not only was water detected in these geysers, but also a number of organic molecules and, more importantly, small grains of rocky silicate particles that can only be present if groundwater ocean water was in physical contact with the bottom of the rocky ocean at a temperature of at least 90˚C. This is very strong evidence for the existence of hydrothermal vents at the bottom of the ocean, which provide the chemistry necessary for life and localized sources of energy.
Titan
Titan is Saturn’s largest moon and the only moon in the solar system with a substantial atmosphere. It contains a thick orange haze of complex organic molecules and a meteorological system of methane instead of water, with seasonal rains, dry spells and sand dunes on the surface created by the wind.
The atmosphere is made up primarily of nitrogen, an important chemical element that is used to build proteins in all known forms of life. Radar observations have detected the presence of rivers and lakes of liquid methane and ethane and possibly the presence of cryovolcanoes, volcano-like features that erupt from liquid water rather than lava. This suggests that Titan, like Europa and Enceladus, has an underground reservoir of liquid water.
At such an enormous distance from the Sun, Titan’s surface temperature is -180 ° C, too cold for liquid water. However, the abundant chemicals available on Titan have sparked speculation that life forms could exist there, potentially with fundamentally different chemistry than terrestrial organisms.
This article was originally published in The Conversation by Gareth Dorrian at the University of Birmingham. Read the original article here.
