NASA announced that it has moved back it’s next unmanned mission to Mars to 2018, after a component of the Mars spacecraft was found to have a leak in its key science instrument. The InSight mission — which stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport — is scheduling a new expected launch window beginning May 5, 2018, with a Mars landing scheduled for Nov. 26, 2018, according to NASA. The goal of the mission is to analyze the deep interior of Mars to determine how “rocky planets planets — including Earth — formed and evolved.”

The InSight mission aims to send a lander to Mars to study the planet’s interior and learn more about how the rocky world formed. The project had been on track for its intended March 2016 launch date, but everything came to a halt in December after scientists at NASA’s Jet Propulsion Laboratory discovered a problem with one of the lander’s two main instruments.

The instrument — called SEIS — was constructed by the French space agency Centre National d’Études Spatiales (CNES), and is designed to measure quakes on Mars, as well as extremely tiny ground movements. But the instrument must be sealed inside a vacuum chamber in order to be sensitive enough to work, and on December 3rd the agency discovered leaks in the chamber.

InSight would have been NASA’s first mission to the Martian surface since the Curiosity rover landed in 2012, and the third overall. (Two orbiters — NASA’s MAVEN and India’s Mars Orbiter Mission — reached the planet in 2014.) NASA says that InSight’s delay will not affect any of the agency’s other plans to go to Mars, which include landing another rover in 2020 and human missions in the 2030s.

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The European Space Agency and Roscosomos, Russia’s space agency, are sending two spacecraft — one orbiter and one lander — to Mars next week as part of the joint ExoMars mission.