BOULDER, August 4 — Our celestial neighbor, Mars, once held flowing rivers and perhaps even an ocean, a stark contrast to the cold, arid desert it is today. Geological evidence from orbiters and rovers paints a picture of a planet with abundant surface water between roughly 4.1 and 3.7 billion years ago, featuring lake deltas and extensive waterways, possibly even an ocean covering much of its northern hemisphere.
Today, Mars, the fourth planet from the Sun, has a diameter of about 6,779 kilometers, with a day length of 24.6 hours and a year of 687 Earth days. Its average surface temperature hovers around −62 °C (−80 °F), and its atmosphere is only about 0.6% as dense as Earth’s at the surface.
Understanding this dramatic transformation offers valuable insights for communities across the region, reminding us of the delicate balance that allows life to thrive on a planet.
The Solar Wind’s Relentless Force
The leading explanation for this profound change, backed by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission, points to the solar wind stripping away most of Mars’ early atmosphere. The MAVEN mission, led by principal investigator Bruce Jakosky of the University of Colorado Boulder’s Laboratory for Atmospheric and Space Physics, launched on November 18, 2013, from Cape Canaveral Air Force Station aboard an Atlas V 401 rocket. It successfully entered orbit around Mars on September 22, 2014.
MAVEN carried 10 instruments specifically designed to measure how the solar wind removes gas from Mars’ upper atmosphere. Its detailed measurements have shown that this supersonic stream of charged particles erodes Martian gas at an average rate of about 100 grams per second.
During periods of increased solar activity, such as coronal mass ejections and solar storms, that escape rate can jump by 10 to 20 times. A key factor in Mars’ atmospheric loss is its lack of a global magnetic field. Without this protective shield, the solar wind directly interacts with the planet’s ionosphere, accelerating oxygen and carbon dioxide ions away into space.
This relentless process, occurring over billions of years, gradually thinned the atmosphere to a point where liquid surface water could no longer survive. Furthermore, ultraviolet sunlight then split any remaining water vapor, allowing hydrogen to escape into space.
Lessons for Our Home Planet
What this means for people, even those far from scientific observatories, is a clearer picture of how vital it is to understand and protect our own planetary environment, making the lessons from Mars feel closer to home. Mars stands as a critical case study for how a planet once capable of hosting
