Mars' Atmosphere Loss To Be Measured By NASA's MAVEN Orbiter
May 15, 2014

Mars’ Atmosphere Loss To Be Measured By NASA’s MAVEN Orbiter

Brett Smith for - Your Universe Online

When NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission arrives at its destination later this year, an instrument on board could help to determine why Mars has slowly lost much of its atmosphere and become the barren planet we see today.

After MAVEN enters into an orbit above Mars, its Solar Wind Ion Analyzer (SWIA) will begin sampling the small electrically charged particles in and above the planet’s wispy atmosphere. The unmanned craft will also be sampling ions from the solar wind, a magnetic field that originates deep within the Sun and radiates out toward the planets. Particles from the solar wind interact with ions in Mars' upper atmosphere and energizes them enough to escape from Mars' gravitational pull.

Scientists have theorized that this process progressively strips Mars of its atmosphere and it has done so for billions of years. The mission scientists said they hope to confirm this theory through measurements taken by the SWIA and other on-board instruments that will detect gases leaving the atmosphere.

"By combining SWIA measurements with measurements of escaping gases we can parameterize the loss of atmospheric gases from Mars as a function of solar wind conditions," said Jasper Halekas, SWIA analyst at the University of California, Berkeley Space Sciences Laboratory (SSL). "Ultimately, we want to know where the atmosphere, especially water, went, how it left, and what Mars has looked like over its entire history."

The solar wind consists of both small, negatively-charged electrons and bigger, positively-charged ions. Halekas explained that both ions and electrons could start the process of particle escape by charging neutral particles in the atmosphere. Once the atmospheric particles come to be charged, they could interact with the solar wind's magnetic field and be transported away from Mars. The ionization step is essential, since original neutral particles don't interact with the solar wind's magnetic field and commonly have too little energy to break free.

The ionized plasma in the solar wind also interacts with the wind's magnetic field to form an electric field, which provides the newly-charged atmospheric particles with enough energy to escape. To determine the details of these interactions, SWIA will work in concert with the MAVEN magnetometer to measure the network of charged particles and magnetic field lines around Mars known as the magnetosphere.

"If there were no solar wind ions or magnetic field, the Martian atmosphere would just be a big ball of partially ionized gas sitting in space," Halekas said. "It is the incoming solar wind ions and magnetic field that compress and warp the ionized gas into the teardrop-shaped structure we call a magnetosphere, which any escaping particles must travel through to leave the system."

Halekas said he expected the mission to face numerous challenges, but said he is confident that SWIA will perform well and help to reveal the secrets of the Martian atmosphere.

"Every stage of the mission has been, and will continue to be, a learning experience and a new and exciting challenge," Halekas said. "I'll be ramping up to support the team's scientists in their investigations of all of our observations, with the goal of answering all the big picture questions of MAVEN, and more."


Image 2 (below): The MAVEN Solar Wind Ion Analyzer will study ions in the Martian atmosphere, a key component for better understanding the planet's evolution. Credit: University of Colorado at Boulder LASP