Mars is often thought of as the nearest planet that could support life, as its soil contains nutrients, there’s water locked up in ice caps, and its atmosphere offers protection from solar and cosmic radiation.
But living conditions there can be harsh. Toxic soil can suffocate you and temperatures are too cold to support comfortable living conditions.
Mars
Mars, our fourth planet from the sun, is dry, rocky, and freezing cold – an easy planet to spot at night when looking skyward; looking like a red point of light in the night sky. NASA rovers such as Perseverance and Curiosity have explored its surface in order to discover whether life existed there previously or could exist again today.
Red Planet boasts some of the most stunning landscapes in our solar system. From its majestic mountains and valleys to Olympus Mons’ peak that rises more than 17 miles (27 kilometers), its scenery will astound you. Additionally, Valles Marineris cuts through its southern half with over 2,500 miles (4,000 km).
Mars’ thin atmosphere of carbon dioxide and nitrogen allows heat to escape the planet easily, leading to temperatures ranging from summer at the equator to winter at its poles. Due to Mars’ elliptical orbit, its distance from the sun also fluctuates – when closest, called “perihelion”, and farthest away when at “aphelion”. These variations in sunlight cause different seasons on this distant world.
Over millions of years, solar radiation eroded most of Mars’ original atmosphere away, leaving only a thin blanket of gases lingering behind. Due to this change, Mars is much drier than Earth and lacking a magnetic field makes retaining water harder for Mars than for Earth.
Scientists remain hopeful of discovering life on Mars, though it likely wouldn’t be as complex as that found here on Earth due to concentrations of highly toxic chemicals that might exist there and wipe out any attempts at colonisation by life forms that found foothold on its surface.
But if we could locate an exoplanet within Proxima Centauri’s habitable zone, that might change. At least 1.3 times larger than Earth and most likely composed of rocks – researchers believe its proximity to its star increases its chance of possessing liquid water reserves than planets farther from it in our galaxy.
Venus
Venus, the second planet from the Sun, is an atmospheric carbon dioxide giant with the hottest surface temperature in our solar system and an increased greenhouse effect due to greenhouse effect.
Venus’ high temperatures and dense cloud cover make its study difficult, yet some probes have managed to penetrate its atmosphere and map its surface using radar technology. Both Soviet Venera orbiters and NASA’s Magellan spacecraft utilized this approach, giving scientists insights into what its surface once looked like; with wide plains and mountainous regions.
But the process remains mysterious; Venus is now covered with thick sulfuric acid clouds that obscure its surface from optical observation by both Earth-based and orbital sensors, leaving scientists no explanation as to their origin or persistence of their dark streaks.
The popular theory posits that Venus’ temperature skyrocketed due to an out-of-control greenhouse effect caused by the evaporation of water, leading to increased CO2, as a result. But an environment capable of supporting life likely wouldn’t rely on CO2, as seen on Venus, where solar radiation provides far more energy than on Earth.
Venus resembles Earth in many respects; it contains a metal core, thick rocky mantle, and less-dense crust. However, unlike Earth, tectonic plates on Venus have seemingly fused together preventing any movement of its mantle layer, potentially recycling old layers of crust instead.
Thirty miles above Venus’ surface (roughly 50 kilometers), temperature and atmospheric pressure are comparable to Earth. This zone, known as the thermosphere, makes an excellent environment for hosting “extremophile” bacteria capable of withstanding extreme temperatures.
Venus takes approximately 243 Earth days to rotate on its axis and 227 to orbit the Sun. Because of this slow orbital cycle, its polar hemisphere warms faster than its equator due to the greenhouse effect, leading to bizarre surface features on Venus such as “pancake” domes with flat tops and steep sides, “tick” domes that resemble blood-feeding ticks from above, and tesserae which feature raised areas with many ridges and valleys arranged in different directions.
Triton
In the outer solar system, Triton is second only to Europa in its potential as a site for alien life. But its story is even more intriguing than that of its icy neighbor.
Its reddish surface is geologically young, with very few craters. And unlike the Everest-sized peaks on our Moon and Saturn’s Iapetus, its youth wasn’t fueled by tectonic shifts or regions crashing together to push up mountains. Instead, it seems to be the result of material seeping from below and spreading out. And not hot things like lava, but cold ones, such as a water-ammonia mix that oozes from volcanoes and then freezes solid.
That’s why Voyager 2 saw ice-rocket-like plumes that shoot nitrogen, dust and chemicals containing methane into the sky. It’s one of only four bodies in the solar system to have these plumes, after Earth, Io and Enceladus. And that tells scientists that there may be an underground ocean on Triton, with liquid methane and ethane and organic molecules circulating within it.
Triton is not believed to have formed around Neptune, but instead probably in the Kuiper Belt, where dwarf planets Pluto, Haumea and Makemake hang out. Its orbit and rotation tell us it was captured by Neptune, perhaps early in its history. That’s supported by its high rock-to-ice ratio—indicating it wasn’t a home-grown Neptunian moon.
Scientists don’t know why the surface of Triton gets refreshed so frequently, but they suspect it involves an interplay of tidal dissipation (the energy from Neptune’s gravity), radiogenic heat (from decaying radioactive isotopes) and thermal insulation from overlying ice.
There’s a lot more to explore on Triton, but getting there isn’t easy. The window for a flyby opens only every 13 years, and the next one won’t happen until 2026, when NASA plans to send the Trident spacecraft to Neptune and Triton. The European Space Agency’s upcoming JUICE mission to Jupiter, which will make several close flybys of the icy moons Ganymede and Callisto, may also help researchers learn more about Triton and its chances for life. But even if the world isn’t hospitable to life, studying it can give us insight into how life did or didn’t evolve on other planets—and maybe point out the path our own civilization could take in the future.
Enceladus
Enceladus, located within Saturn’s rings, is one of the most fascinating worlds in our Solar System. Among its features are a rocky seabed beneath its icy shell and geyser-like activity that sends plumes of water ice and organic compounds shooting out from deep within. Scientists speculate that Enceladus’ subsurface ocean may provide ideal conditions for life to begin as it contains many ingredients necessary for life to exist on planet Earth.
Enceladus’ most striking characteristic is its signature ice-smoothed jets, which regularly shoot from fissures on its surface and contain water, hydrogen and carbon dioxide. Researchers have long recognized these jets’ presence of organic molecules – precursors to many essential chemicals for life – but recently, scientists made an exciting discovery – hydrogen cyanide within these jets can combine with other molecules to form amino acids which suggests life might exist on Enceladus!
Prior research has determined that Enceladus’ geysers emerge from four regions known as “tiger stripes.” These regions consist of tectonic fractures with fields of ice boulders. When geysers erupt from these four spots on its surface, cryovolcanism occurs – eruptions which don’t involve melting rock but instead spew water and ice as their by-product. Scientists have discovered these plumes contain salts essential to life such as phosphorus.
Scientists have also observed that the ice-rock forming the tiger stripes is rich in sulfur, an essential element for many chemical processes including photosynthesis and protein formation as well as providing energy sources to any microorganisms living there.
These discoveries suggest that Enceladus may be more likely than other icy worlds like Jupiter’s Europa and Neptune’s Triton to support life than others such as Europa or Triton, which would mark an enormous step in our search for extraterrestrial life, as well as answering one of Earth’s deepest mysteries about how life began in either ocean or terrestrial environments. It would also mark a breakthrough in debates regarding which is more likely – ocean life vs land life origins!