About four billion years ago, Mars had rivers. Lakes. A thicker atmosphere and a magnetic field. Conditions that, by every measure scientists currently understand, could have supported life.
Then something changed. The planet's interior cooled, the magnetic field weakened, the atmosphere thinned, and Mars became the cold, dry, radiation-battered world we observe today. Whether anything lived during that earlier window โ and whether any trace of it survived โ is one of the deepest open questions in science.
A British-built rover launching in 2028 is going to look for the answer in a place no Mars mission has reached before: two metres underground.
The ExoMars Rosalind Franklin rover, built by Airbus in Stevenage for the European Space Agency, is targeting a landing at Oxia Planum in 2030 โ a region of ancient clay-rich rock formed during Mars' wetter period. Its drill will penetrate deeper beneath the Martian surface than any previous mission, reaching material shielded from the cosmic and solar radiation that has been destroying organic molecules on and near the surface for billions of years.
Every earlier Mars rover has sampled close to the surface, where preservation is far more difficult. Rosalind Franklin is designed to go below that destruction zone.
The instruments on board won't be looking for living organisms. They'll be looking for biosignatures โ chemical, molecular, or structural evidence of biological activity from a time when Mars was a very different place. Ground-penetrating radar will assess subsurface layering before drilling begins.
An infrared spectrometer will identify minerals associated with ancient water. A panoramic camera will characterise the surrounding terrain. The mission is designed to distinguish potentially biological signals from abiotic chemistry that can mimic them โ one of the hardest problems in astrobiology.
There's a question sitting behind all of this that goes even further. If ancient life existed on Mars, was it related to life on Earth? The early solar system was a chaotic place, and material was regularly exchanged between the two planets through impacts.
Panspermia โ the possibility that biological material or its precursors could travel between worlds on ejecta โ is no longer considered fringe science. As Susanne Schwenzer, professor of planetary mineralogy at the Open University and an interdisciplinary scientist on the mission, put it: "If life is the same there, it may be that we are all from the same ancestor."
Two separate origins of life within a single solar system would suggest biology emerges readily when conditions allow. A shared origin would suggest that life, or its ingredients, can travel between worlds. Either answer would change how we think about the galaxy.
The rover will operate largely autonomously. Communication delays of up to 21 minutes each way make real-time control impossible, so Rosalind Franklin must navigate, assess terrain, and execute drilling operations without waiting for instructions after every step. Teams have been rehearsing those procedures in the Tabernas Desert in Spain, where dry, rocky terrain approximates some of what the rover will encounter.
The mission launches in 2028. The answers, if they come, will arrive in the 2030s.
Some questions are worth waiting for.
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