NASA and the European Space Agency will release next month the first solicitation for science instruments on a Mars orbiter mission scheduled for launch in 2016, signaling closer cooperation in a joint Mars exploration program.

Artist's concept of the 2016 Mars orbiter. Credit: NASA

The first-of-a-kind announcement of opportunity will request proposals for a suite of sensors designed to detect trace gases and map methane concentrations in the Martian atmosphere.

Methane is a key indicator of biological or geological activity. It can be produced by living organisms or natural processes like the oxidation of iron, according to scientists.

The methane mystery at Mars will be the focus of the first joint mission in a new robotic exploration program.

Scheduled for release in the middle of January, the announcement will bring NASA and ESA plans for a cooperative Mars program closer to reality.

The agencies established the Mars Exploration Joint Initiative earlier this year, laying out plans for combined missions in 2016, 2018 and 2020, eventually leading to a Mars sample return mission in the 2020s.

The missions will marry ESA's long-delayed ExoMars architecture with NASA know-how in entry, descent and landing technology.

The Mars agreement was signed as NASA and ESA struggled funding their individual exploration plans.

The Trace Gas Orbiter would launch on a NASA-provided Atlas 5 rocket in January 2016, arriving at Mars nine months later with payloads from the United States and Europe. The European-led probe would combine elements from a previous ExoMars orbiter with NASA's plans for a science mission in 2016.

The ESA Council, the space agency's governing body, still has to formally approve the mission after receiving cost estimates. ESA member states gave a provisional go-ahead earlier this year.

According to a preview of the January announcement, officials hope to select winning instrument proposals by next July.

Europe is also studying a small demonstrator to test their own entry, descent and landing systems. If ESA secures funding for the project, the demonstration could land a weather station on Mars as a piggyback to the ExoMars Trace Gas Orbiter.

The ExoMars rover, approved by ESA in 2005, would launch on another Atlas 5 rocket during the next Mars flight opportunity in early 2018. It would land utilizing a NASA-built sky crane system currently being developed for the Mars Science Laboratory mission in 2011.

NASA plans a smaller rover to launch with ExoMars in 2018 to study the planet's habitability and collect samples for a future sample return mission.

Under the agreement, another undefined joint mission would follow in 2020.