MAVEN, short for Mars Atmosphere and Volatile Evolution, was the US space agency's first mission devoted to observing the Martian atmosphere and its evolution.
NASA officials told reporters on Wednesday they last heard from MAVEN on December 6, when it experienced an unexpected loss of signal after passing behind Mars from Earth's vantage point, and was later determined to be in "an unrecoverable state".
A NASA review board is working to determine what caused the failure.
Launched in 2013, MAVEN began orbiting Mars in 2014 and exceeded its originally planned one-year mission by a decade.
MAVEN was involved in relaying Mars science data from assets such as the robotic surface rovers Curiosity and Perseverance to Earth. It explored the Martian atmosphere and studied atmospheric interactions with the sun and the solar wind - the relentless high-speed flow of charged particles from the sun - to better understand the loss of the planet's atmosphere to space.
Mars more than three billion years ago had a thicker atmosphere and large amounts of liquid water on its surface, with conditions that may have been conducive to microbial life. Studying current atmospheric loss provides insight into how Mars became the inhospitable place it is today.
MAVEN learned, for instance, that the erosion of the Martian atmosphere increases dramatically during space weather events - when solar storms erupt off the sun's surface.
MAVEN discovered several types of auroras that flare up when energetic particles from these storms plunge into the atmosphere. It also worked with Perseverance to observe an aurora on Mars in visible light for the first time, with the sky glowing softly in green.
NASA officials said MAVEN will remain in orbit for 50 to 100 years before falling to the Martian surface, and said it would not endanger any of the agency's other spacecraft.
MAVEN travels in a highly elliptical - oval-shaped - orbit around Mars, getting as close as around 180 to 220km and as far away as around 4000km.
