From Canals to Rovers: What Science Has Established About Mars

The search for life on Mars has moved from fiction and speculation into a long-running scientific investigation. Since Percival Lowell's 1890 claim of canals built by intelligent beings, astronomers have replaced telescope sketches with orbiters, landers and rovers. NASA's Odyssey spacecraft confirmed water ice at the poles in 2002, Mariner 9 photographed ancient water-carved beds in the 1970s, and later work suggested Mars may once have held an ocean comparable in size to the Arctic Ocean.

Those findings point to a planet that was once far more hospitable than it is today. Mars is rocky and sits in the Sun's habitable zone. Evidence indicates it had a thicker atmosphere, liquid water, a more geologically active surface and, based on soil tests such as Phoenix's pH measurement of 8 to 9, chemistry compatible with microbes and even plant life. The Curiosity rover has detected nearly two dozen organic molecules and a seasonal methane signal near Gale Crater, while the Perseverance rover collected a sample in 2025 containing possible biosignatures in Jezero Crater.

None of this yet proves life existed. The organic molecules and methane could have geological origins, and the rovers cannot settle the question on their own. Scientists argue the decisive step is returning Martian samples to Earth, where far more advanced laboratories can measure ancient temperatures, pressures and water availability. The first planned sample-return mission is China's Tianwen-3, slated for launch in 2028. In the meantime, researchers also track promising exoplanets such as LHS 1140 b, a rocky world in its star's habitable zone with a confirmed atmosphere.

What the Evidence Can and Cannot Yet Prove

Sixty years of orbital and surface data have shifted the question from whether Mars was once habitable to how habitable it was, and for how long. The planet is rocky, sits in the Sun's habitable zone and shows clear evidence of past liquid water, a thicker early atmosphere and the chemical ingredients associated with life. That combination makes it a more credible target than Venus, where surface conditions remain prohibitively hostile.

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Why the "maybe" evidence keeps accumulating

The most tantalizing findings are suggestive rather than conclusive. Curiosity's organic molecules and the seasonal methane signal at Gale Crater are consistent with biology, but both can also be produced by geological processes. The 2025 Perseverance sample from Jezero Crater contains possible biosignatures, yet the rover cannot verify them on site.

What sample return would change

Earth-based instruments are far more capable than anything sent to Mars. Researchers quoted by CNET argue returned material would allow direct measurement of ancient temperature, pressure and water availability, and could help explain why Mars's climate deteriorated. China's Tianwen-3 mission, scheduled to launch in 2028, is currently the first planned attempt to return samples.

The exoplanet back-up list

Outside the solar system, LHS 1140 b is notable as a rocky planet in its star's habitable zone with a confirmed atmosphere. TOI-700 d and Trappist-1e remain candidates, but their atmospheres are unconfirmed. These worlds widen the search but are far harder to study directly in the near term.