Is there life beyond Earth? If NASA wants to answer this age-old question, we’ll need to start looking in the right place. That means sending a probe to Enceladus — a moon of Saturn.

In planetary exploration, the search for extraterrestrial life begins with the search for extraterrestrial habitats, locales that contain the foundational ingredients critical to life on Earth, the only form of life we know. These ingredients include liquid water, organic materials, chemical and energy sources and gradients strong and stable enough to sustain the processes of life.

Over the last 60 years, our robotic spacecraft have completed the reconnaissance of the solar system and have found several worlds meeting, or believed to meet, the first criterion of liquid water. Two leading contenders for water-based life are Enceladus and Jupiter’s moon Europa.

In 2015, Congress directed NASA to land on Europa with a flagship-sized mission — the biggest, most expensive and therefore rarest mission possible. This mission would coincide at Jupiter with another Europa Flagship mission already under development — the Jupiter-orbiting Europa Clipper.

Meanwhile, Enceladus has gone ignored.

Instead of doubling-down on Europa, NASA should send our next planetary flagship mission to search for evidence of life on Enceladus. Why? Because abundant evidence collected from the recently concluded Cassini mission — a robotic spacecraft that explored the Saturn system for more than a decade — points to Enceladus as the more promising site for advancing our understanding of life’s distribution in the cosmos.

In early 2005, Cassini first sighted an extensive plume of frozen mist formed by over 100 geysers erupting from deep fractures on Enceladus. More than 12 years of observations, including high-resolution imaging and repeated fly-throughs with direct chemical sampling, have revealed the plume’s source to be a global ocean of liquid water under the moon’s outer ice shell, with salinity comparable to that of the Earth’s oceans.

Moreover, the plume’s tiny ice particles were found to contain large organic compounds, as well as evidence of hydrothermal activity, presumably on the moon’s seafloor. Scientists estimate that the heat from the moon’s core into the ocean could be comparable to the average heat passing up through the seafloor of the mid-Atlantic Ocean. The localized hydrothermal regions in the Atlantic are sites of hot, erupting fluids with abundant minerals and diverse communities of organisms that thrive on those minerals and live without sunlight. It raises the obvious question: Do organisms exist at similar sites on Enceladus too?

All together, these results constitute a standard of evidence that is not presently available for any other candidate habitable world — even Europa.

Although an intermittent plume of material has recently been discovered on Europa, it is not yet established that the plume comes from the moon’s ocean or contains organic material. And there is no evidence of organic materials on Europa’s surface, either. In fact, while it is possible that seawater reaches all the way to the surface on Enceladus, it is suspected that fractures in Europa’s ice shell do not open from surface to ocean, making its ice shell impenetrable.

Simply put, Enceladus presents the solar system’s best documented, best understood and, because of its plume, most accessible extraterrestrial ocean. There is no other ocean world about which we are better informed to decide which biosignatures are key to a well-designed search or better prepared to develop focused mission and measurement strategies to detect them.

Clearly the decision to send a lander to Europa was premature. It should not have been made until Clipper arrives at Jupiter in the late 2020s, conducts Cassini-like fly-throughs of the plume, and returns information with the scope and detail we have today on Enceladus. Only then will we know the status of any organic or ocean signatures, either in the plume or on the moon’s surface, and whether a follow-on lander makes sense.

In the meantime, let’s get started now designing a lander mission for Enceladus. Some 90 percent of the frozen mist in its plume falls back to the ground. Those falling particles could over time accumulate on a surface collector to a mass sufficient to permit very sensitive measurements, by a suite of onboard instruments diverse enough to offer as unambiguous an answer as possible regarding the presence of life in the moon’s ocean. After a dozen years of mapping the surface of Enceladus, we know today the locations of the most active geysering areas and, hence, the best places to land. Moreover, while a probe on Europa would last at most a few months, a lander on Enceladus could operate for many years before suffering fatal radiation damage.

For decades, NASA has held the search for life beyond Earth as its most urgent quest. It follows, then, that we should urgently build upon the expansive knowledge gained by Cassini’s exploration and return to the place that offers the opportunity to probe deepest and farthest for an answer.

It could be snowing microbes on Enceladus right now. What are we waiting for?

Carolyn Porco is the leader of the imaging team on the Cassini mission at Saturn, a former member of the Voyager imaging team, and currently a visiting scholar at the University of California at Berkeley.