The Road Trip That Would Break Every Record

Imagine loading up a rover and pointing it west along the longest canyon in the solar system. Valles Marineris spans approximately 3,900 kilometers from end to end — about the distance from Los Angeles to New York City — and in places plunges more than 7 kilometers deep. Earth's Grand Canyon, impressive as it is, would fit inside one of Valles Marineris's smaller side chasms and still have room to spare.

No rover has yet explored the canyon floor. But the science case for sending one there is enormous, and mission planners at NASA and ESA have studied the region seriously. So let's take a hypothetical drive — grounded in real Martian geology — and see what we'd actually encounter.

Departure: The Eastern Chasmata

Our trip begins at the eastern end, where the canyon system fractures into a chaotic jumble of collapsed terrain called the Chaotic Terrain or Chaos regions — specifically Eos Chasma and Capri Chasma. These regions sit near 15°S, 330°E and show evidence of ancient catastrophic flooding. Towering layered deposits here record hundreds of millions of years of Martian geological history in their strata.

Orbital data from NASA's Mars Reconnaissance Orbiter (MRO), particularly from its CRISM spectrometer, has confirmed deposits of hydrated sulfates and phyllosilicates (clay minerals) throughout the canyon system. Both mineral families require liquid water to form — making the walls of Valles Marineris one of the most scientifically compelling targets for astrobiology on the planet.

The Central Chasms: Where the Canyon Gets Serious

Heading west, we roll into the main trough — a parallel set of chasms collectively called Melas, Candor, and Ophir Chasma. This is where Valles Marineris earns its reputation. The canyon here is roughly 600 kilometers wide, and the walls rise 5 to 7 kilometers above the floor.

Melas Chasma alone contains what researchers believe may be ancient lakebed sediments. Light-toned layered deposits visible in HiRISE imagery from MRO show remarkably regular banding — the kind geologists associate with cyclical deposition in standing water. A 2021 study using MRO data identified chloride salt deposits in the region consistent with evaporated brines.

Interior Layered Deposits (ILDs) — distinctive mesas of sedimentary material rising from the canyon floor — are another highlight. Scientists debate their origin, but leading hypotheses involve ancient lakes, windblown dust accumulation, or volcanic ash settling over millions of years. Any one of those histories would be scientifically revolutionary to confirm on the ground.

Pit Stop: Melas Basin

If our road trip has a must-stop destination, it's Melas Basin, which sits at approximately 1.5 kilometers below the Martian datum (the equivalent of sea level on Mars). This makes it one of the lowest points on the planet — and therefore a place where, in Mars's warmer and wetter past, liquid water would have persisted longest.

  • Depth below Martian datum: approximately 1.5 km
  • Evidence of ancient lake deposits detected by orbital spectrometers
  • Potential for preserved organic material in sedimentary layers
  • Relatively sheltered from solar radiation compared to open plains

Atmospheric pressure at the floor of Melas Basin is meaningfully higher than at the Martian surface average — roughly 1,155 Pa compared to the planetary average of around 610 Pa. Still far too thin for humans without pressurized suits, but enough to matter for future in-situ resource utilization calculations.

Western Approach: Ius and Tithonium Chasma

The western chasms — Ius Chasma and Tithonium Chasma — are narrower but show spectacular spur-and-gully wall morphology. Landslides here have created debris aprons that would be slow going for any rover. ESA's Mars Express orbiter has captured some of the sharpest stereo imagery of these regions, revealing layered walls carved by tectonic forces stretching back 3.5 billion years.

Journey's End: Noctis Labyrinthus

The western terminus spills into Noctis Labyrinthus — the Labyrinth of the Night — a chaotic network of intersecting valleys and plateaus near the Tharsis volcanic rise. The same volcanic activity that built Olympus Mons and the Tharsis Montes volcanoes likely played a central role in cracking the Martian crust to form Valles Marineris in the first place, through a process of tectonic rifting and subsidence.

Why We Haven't Gone Yet — And Why We Should

The canyon's extreme terrain makes it a navigation challenge for current rover technology. Curiosity and Perseverance were designed for relatively flat, open terrain. Descending canyon walls that rival Earth's tallest mountains would require new engineering approaches — possibly including aerial assets like an advanced successor to the Ingenuity helicopter.

But the scientific return would be extraordinary. Nowhere else on Mars offers such a deep, continuous cross-section of the planet's geological and potentially biological history. When the first rover — or astronaut — finally reaches the floor of Valles Marineris, it will be one of the most significant moments in the history of planetary exploration.