Life in the UniverseAnswer
How do astronomers find planets around other stars?
Distant worlds can reveal themselves through changes in starlight and the motion of their stars.
THE QUESTION LIBRARY LIFE IN THE UNIVERSE
Could there be life elsewhere in our solar system?
Mars and icy moons offer different evidence about possible habitats.
THE SHORT ANSWER
Possibly. Ancient Mars had conditions suitable for microbes. Europa’s inferred ocean and Enceladus’s plume chemistry offer reasons to investigate life under ice. But water, useful chemicals and possible energy supplies establish potential habitats, not inhabitants; candidate biological signals need further tests.
- Past habitability does not establish past life.
- An inferred ocean does not demonstrate microbes.
- Plume chemistry can test ingredients and energy sources.
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WHERE THE EVIDENCE STANDS
How sure are we?
- Ancient Mars had potentially habitable environments.Curiosity’s sampled minerals and chemistry support that interpretation.
- Sapphire Canyon confirms ancient Martian life.Nonbiological pathways have not all been excluded.
- Europa’s ocean could support microbes.Ocean evidence and possible energy sources motivate testing.
- Enceladus plume chemistry establishes life.Measured ingredients leave the biological question open.
WHAT WE DON’T KNOW YET
Whether life began or survives in these environments remains unresolved.
WHAT WOULD CHANGE THIS ANSWER
Independent biological evidence that survives contamination checks and nonliving alternatives would change the verdict.
Possibly. Mars had environments that could support microbes, and Europa and Enceladus are promising ocean worlds. The evidence described here establishes possible habitats and intriguing chemistry, not life. Whether anything lives—or once lived—there remains open.
THE LONG ANSWER
Free long answer 1 of 3 this month.
Was there ever life on Mars?
We do not know. In March 2013, NASA reported that Curiosity’s rock analysis at Yellowknife Bay supported an ancient wet environment with chemical ingredients and potential energy sources suitable for microbes. That is evidence of past habitability: conditions in which life could function, not a fossil or a detected organism.
A different question is whether a rock preserves a trace of biology. In September 2025, NASA described potential biosignatures in Perseverance’s Sapphire Canyon sample from Cheyava Falls. Carbon-containing organic material and small mineral patterns could be consistent with microbial reactions. But the minerals can also form without life; the study did not rule out every nonbiological pathway. The sample is a candidate for further testing, not confirmation that Mars had life.
Could microbes live under the ice?
Europa, Jupiter’s moon, likely has an ocean below its ice. While orbiting Jupiter from 1995 to 2003, Galileo measured a magnetic response best explained by salty water beneath the surface. Jupiter’s gravitational tug can generate internal heat. Chemical reactions could supply energy without sunlight, but whether the necessary ingredients mix in usable ways remains a question.
Enceladus, a moon of Saturn, offers a different kind of sample: jets of water vapor and ice escaping through cracks. Cassini sampled material associated with these plumes. A June 2023 analysis identified phosphorus-containing salts in ice grains from Saturn’s E ring, fed by the plume, adding an ingredient used by Earth life. Those measurements tell us about ocean chemistry, not whether cells are present.
A 2017 report described hydrogen measured during Cassini’s 2015 plume flyby. Reactions between water and rock are the proposed source. If microbes were present, some could gain energy by reacting that hydrogen with carbon dioxide. That shows a possible food supply; it does not show that anything has used it.
What would establish life?
Investigators must check the signal itself, exclude contamination carried from Earth, and test whether nonliving processes could make it. Independent evidence should then reinforce the interpretation. A habitable setting and a detected organism answer different questions.
Related questions explore how common life might be and how life on Earth began.
THREE THINGS TO REMEMBER
- Water, ingredients and life are separate claims.
Keep asking
Is life likely to be rare or common in the universe?
Nobody knows yet.
New here?
God Plays Dice answers big questions in plain words, with sources and one of six honest labels.
Words worth knowing (2)
- Habitability
- Conditions that could support life.
- Potential biosignature
- A feature that might have a biological origin.
Sources & further reading
(6)
- What Would It Take to Say We Found Life? ↗NASA; 10 September 2025Signal checks, contamination, alternatives and corroboration.
- NASA Rover Finds Conditions Once Suited for Ancient Life on Mars ↗NASA/JPL; 12 March 2013Yellowknife Bay minerals and inferred habitable conditions.
- NASA Says Mars Rover Discovered Potential Biosignature Last Year ↗NASA/JPL; 10 September 2025Sapphire Canyon observations and unresolved nonbiological alternatives.
- Why Europa: Ingredients for Life ↗NASA; updated 27 June 2025Galileo ocean inference and possible chemical energy.
- NASA Missions Provide New Insights into Ocean Worlds in Our Solar System ↗NASA/JPL; 13 April 20172015 plume hydrogen measurement and conditional microbial energy.
- NASA Cassini Data Reveals Building Block for Life in Enceladus’ Ocean ↗NASA/JPL; 14 June 2023, updated 23 October 2023Phosphorus-bearing E-ring grains and ocean chemistry.
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CONTINUE THE THREAD
Where this question leads.
Life in the UniverseAnswer
Could a planet without a star support life?
A world with no sunrise could still have internal heat. The question is whether it can keep water liquid and supply usable energy.
Life in the UniverseAnswer
How can identical twins with the same DNA turn out so different?
Identical twins develop from one fertilized egg and begin with almost the same DNA. Yet their conditions before birth, later environments and gene activity can differ. Shared DNA…