Mars Scout: two focused paths into Mars science

Mars Scout provided a competitive route for relatively focused NASA investigations of Mars. Its two selected flight missions, Phoenix and MAVEN, asked different questions and used very different spacecraft. The line belongs in the history of NASA’s wider Mars exploration effort, while each mission retains its own scientific and operational identity.

The principal investigator — open definition and partner organizations had to turn a proposed question into a deliverable measurement plan. Phoenix brought together a surface investigation, a landing system and instruments for studying the polar environment. MAVEN connected university science leadership with NASA Goddard project management, spacecraft development and instrument teams to investigate atmospheric escape — open definition.

Phoenix landed in Mars’s northern polar region on May 25, 2008. Its robotic arm exposed and sampled icy ground, and its instruments studied water, soil chemistry and weather. The stationary lander supplied evidence at one location. Ice at that site did not by itself establish living organisms or a complete inventory of all Martian water.

MAVEN launched on November 18, 2013 and entered Mars orbit in September 2014. Its instruments investigated the upper atmosphere and interactions with the Sun and solar wind. Measurements of escape processes help scientists reconstruct atmospheric evolution through models and comparison. Observing a present-day process does not mean directly watching the planet’s entire ancient history.

Mars Scout was discontinued after Phoenix and MAVEN, with Mars investigations eligible to compete through Discovery. That change to the selection line did not retroactively move every historical mission into a different original program. It also did not mean that an already selected spacecraft had to cease operations on the same date.

Dated mission records matter when describing later operations. NASA declared MAVEN’s mission ended on June 3, 2026, following loss of contact on December 6, 2025. Its archived observations remain scientifically useful. A historical selection announcement explains what was proposed; the flight record and later research establish what was observed and how the interpretation developed.