Villanueva was on the team that reported discovery of methane in the atmosphere of Mars. This discovery is important because methane is thought not to stick around too long on Mars (< 300 years), and so something has to actively produce it for methane to be there now, such as microbial life.
Detecting methane on Mars is difficult from telescopes on the ground on Earth because the Earth’s atmosphere also has a lot of methane in it. In order to see the Martian methane, Villanueva has to do a lot of observing and modeling to rescue the tiny spectral signal of Martian methane from underneaththe whopping terrestrial signal.
According to Villanueva, current observations suggest that, if methane is released into the Martian atmosphere, it is released rarely and not seasonally. In his most recent work, Villanueva did not detect any methane, possibly indicating that methane has an even shorter lifetime in the Martian atmosphere than previously thought. And so work continues to understand this puzzling but tantalizing discovery.