Solar winds from the sun constantly slam into the planet and strip away the atmosphere's outer layers. That's about a quarter-pound a second.
Other scientists who were involved in the project say they were kicking themselves that they hadn't solved the riddle sooner. Its goal is to help scientists understand one of the solar system's biggest mysteries - what happened to the water on Mars and the carbon dioxide in its atmosphere several billion years ago?
Data from MAVEN, an unmanned spacecraft that has been circling Mars for the past year, was published in scientific studies, including four in the journal Science and 44 more in Geophysical Research Letters.
Ever since discovering that liquid water once existed in lakes and oceans on the surface of Mars, space scientists from the National Aeronautics and Space Administration (NASA) have not stopped determining why the planet became cold and dry.
In addition, a series of dramatic solar storms hit Mars' atmosphere in March 2015, and MAVEN found that the loss was accelerated.
"Understanding what happened to the Mars atmosphere will inform our knowledge of the dynamics and evolution of any planetary atmosphere", John Grunsfeld, astronaut and associate administrator for the NASA Science Mission Directorate in Washington, said in a statement.
Scientists say a prime suspect is the solar wind - a stream of particles, mainly protons and electrons, flowing from the sun's atmosphere at about a million miles per hour. "It tells us that solar particles are streaming directly into the Mars atmosphere, where they can have an impact".
This week, NASA research revealed that eons of solar storms stripped ions from the planet's upper atmosphere, transforming a formerly warm and wet environment that might have supported surface life to the cold, arid body Mars is today.
"We think that all of the action took place between about 4.2 to 3.7 billion years ago", explains MAVEN principal investigator Bruce Jakosky, with the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado in Boulder.
"However, when we account for the greater loss rates early in history, we think (the) loss to space by the stripping by solar wind was an important process in the changing climate of Mars".
New results indicate that the loss is experienced in three different regions of the Red Planet: down the "tail", where the solar wind flows behind Mars, above the Martian poles in a "polar plume", and from an extended cloud of gas surrounding Mars.
Artist concept of the solar wind interacting with the Mars upper atmosphere (L). Just over a month ago, the Mars Reconnaissance Orbiter revealed evidence of salt water trickling down Martian slopes, at least in the summer.
As the field passes past Mars, it generates an electric field around the planet in the same way that a turbine can produce electricity here on Earth.
For the first time, NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has observed this process in action - by measuring the speed and direction of ions escaping from Mars.
Knowing why the so-called Red Planet lost its atmosphere is essential for understanding why Mars is not a lush planet with liquid water.
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