The solar system hosts nine planets and countless moons. Is it conceivable that extraterrestrials could inhabit any of these celestial bodies?
The solar system has a few “hotspots” where life could have once existed or may still exist today.(Image credit: NEMES LASZLO/SCIENCE PHOTO LIBRARY via Getty Images)Subscribe to our newsletter
Who hasn’t gazed at the heavens and pondered the possibility of other life forms out there, observing us in return? Could alien life exist closer to home — within the confines of our solar system?
The concise response is affirmative; numerous locations within our solar system are under scrutiny by researchers searching for evidence of life, and certain indications suggest that life might be present in surprising locales.
Is there life on Mars?
While it appears unlikely that “little green men” inhabit Mars, the possibility of past microbial life cannot be dismissed. Mars is presently a frigid, arid desert, but data from Mars rovers studying the planet’s geology reveals that liquid water was once present — a crucial prerequisite for life.
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“The Curiosity rover was designed to seek out habitable environments, the types that could have sustained microbial life on Mars historically, should life have ever originated on the Red Planet,” stated Amy Williams, a professor of geology at the University of Florida and a participant in both NASA’s Curiosity and Perseverance science teams. “Curiosity’s instrument suite was chosen to achieve this objective by identifying conditions essential for life on Earth, such as liquid water, a carbon source, and chemical energy for metabolic processes,” she informed Live Science.
In addition to examining the Martian environment, the Perseverance rover has been gathering promising rock samples slated for return to Earth for in-depth analysis. The Mars Sample Return initiative, a joint project by NASA and ESA, is currently in development and aims to travel to Mars, collect sample cores, and transport them back to Earth. (However, the administration of Donald Trump has proposed budget cuts to NASA to fund this mission.)
“At least one of the collected cores exhibits characteristics consistent with a potential marker of ancient microbial life,” Williams commented on a particularly intriguing rock sample. “Returning samples to Earth via the Mars Sample Return framework would allow us to address some of humanity’s most fundamental questions, including our solitude in the universe.”
Could life be hiding in Venus’ atmosphere? (Image credit: NASA/JPL)Could there be life on Venus?
Despite being often referred to as Earth’s “twin,” Venus is likely not the initial candidate for life exploration within the solar system. Its surface temperature is sufficient to melt lead, and the ambient surface pressure exceeds Earth’s by over 90 times. It is enveloped in dense, thick clouds primarily composed of sulfuric acid, a highly corrosive compound that forms acid rain on Earth when combined with water, harming flora, fauna, and soil.
Notwithstanding these harsh conditions, extremophile microorganisms might potentially survive at high altitudes within Venus’ atmosphere, where temperatures and pressures are less extreme; perhaps life could devise mechanisms to shield itself from the destructive effects of sulfuric acid. To investigate this, MIT is assembling the Morning Star Missions, which will journey to Venus’ atmosphere with the ultimate objective of collecting a sample of the planet’s clouds and returning it to Earth for more thorough analysis.
“Microbial life could exist in Venus’ clouds, despite their composition of concentrated sulfuric acid,” asserted Sara Seager, a professor at MIT and the director of the Morning Star Missions, to Live Science. “If we uncover compelling evidence of life on Venus, it would revolutionize our comprehension of habitability and demonstrate that life can thrive in non-aqueous solvents, thereby broadening the spectrum of worlds where life is feasible.”
When searching for life, scientists frequently concentrate on the quest for liquid water, as it is indispensable for life as we know it on Earth. Discovering life on Venus would dismantle this constraint, implying that alien life could be far more peculiar than previously imagined, and that there might be numerous additional locations to explore.
In 2020, a potential detection of phosphine gas in Venus’ clouds sparked a debate regarding signs of life on Venus. The phosphine gas discovery was unexpected, as most known chemical processes generating it are linked to living organisms or extreme pressures found on gas giants. However, the signal was faint, and critics suggested it might have been an artifact of the data. The Morning Star Missions to Venus are expected to provide substantially more insight into the planet’s chemistry and potentially confirm the presence of phosphine in its clouds.
Could life be hiding in a subsurface ocean on Europa? (Image credit: Image data: NASA/JPL-Caltech/SwRI/MSSS; Image processing: Kevin M. Gill CC BY 3.0)Is there life on the moons of Saturn and Jupiter?
In the outer reaches of the solar system, several moons orbiting Saturn and Jupiter, notably Enceladus and Europa, present potential environments for life.
Enceladus, a moon of Saturn, harbors a global subsurface ocean concealed beneath a thick icy crust. The moon consistently expels massive plumes of saline water into space, offering scientists a rare chance to directly sample the interior of a celestial body beyond Earth. The Cassini mission conducted numerous flybys of Enceladus between 2005 and 2017, capturing images and even collecting direct samples from the plumes, which are still undergoing analysis. A 2023 publication in Nature announced the detection of phosphates on Enceladus, meaning scientists have now identified all the fundamental chemical elements necessary for life within the moon’s ocean.
Several missions focused on astrobiological research on Enceladus, aiming to collect additional samples from the plumes, are in development by teams at ESA and NASA, though they are still far from their launch phases.
Similar to Enceladus, Jupiter’s moon Europa is an icy celestial body featuring a global subsurface ocean and water geysers erupting from its surface. The substantial gravitational influence of Jupiter on Europa generates energy and motion that drives active geological processes, and is believed to be the primary factor maintaining the ocean’s liquid state. Interactions between the briny ocean and the rocky interior could potentially support life analogous to that found near hydrothermal vents on Earth.
The European Space Agency’s Jupiter Icy Moons Explorer (Juice) was launched on April 14, 2023, with an anticipated arrival at Jupiter in July 2031, where it will investigate Jupiter and three of its moons: Europa, Callisto, and Ganymede. NASA’s Europa Clipper mission, launched on October 14, 2024, is expected to reach Jupiter in 2030 and perform flybys of Europa to determine if conditions conducive to life are present.
Titan, another moon of Saturn, represents an exceptionally unique location within the solar system. It possesses a methane cycle comparable to Earth’s water cycle and boasts a dense atmosphere composed of nitrogen and methane. The Cassini mission undertook more than 50 flybys of Titan between 2004 and 2017 and deployed the Huygens probe, which successfully landed on the moon’s surface in 2005. These missions gathered data suggesting that Titan’s atmosphere could likely synthesize complex molecules serving as the foundational elements for life. NASA is developing a vehicle the size of a car, an octocopter, designed to navigate Titan’s atmosphere and collect samples from various landing sites.
Where else could life be in the solar system?
Several other potential locations exist for finding life within the solar system, including dwarf planets such as Ceres. Ceres is believed to contain significant quantities of liquid water beneath its icy and rocky exterior, according to data from NASA’s Dawn mission, which visited the dwarf planet in 2015.
The more we explore the solar system, the more environments we discover that possess conditions capable of sustaining life. If life exists beyond Earth, it is unlikely to have achieved a level of advancement enabling interstellar communication, thus requiring us to initiate contact.
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