On Wednesday morning, if all goes well, the European Space Agency’s Schiaparelli probe will alight on rusty Martian dirt. It’s been zipping through space for seven months now, and once it triggers its parachute, pops off its protective coverings, and lands, it’ll kick off a six-year mission to test Mars for signs of ancient (or current!) life.

Watch the livestream of the landing here; it starts at 11:40 am Eastern.

The European probe itself will be short-lived. For only a few Martian days, Schiaparelli will gather wind speed, humidity, temperature and other atmospheric data before its batteries die out—it’s really more of a test for the landing equipment ESA scientists have designed. But the spacecraft it hitched a ride on, the Trace Gas Orbiter, will orbit Mars until 2022, sniffing the methane, acetylene, and other trace gases in its atmosphere to see if they were produced by life or just chemistry.

But whoa there, Mars is the hottest destination this side of the Kuiper belt. NASA’s Curiosity is still ticking along on the Martian surface, and the agency is gunning to launch a super-slick improved rover in 2020. China, India, and the UAE are all working on their own forays to the Red Planet. And Schiaparelli is really more of an overture for the ESA’s next mission, a rover decked out with a drill and more heavy-duty scientific gear that’s also slated to launch in 2020. Also, Elon Musk. Does humanity need another science sniffing droid on the Red Planet?

Well, yeah. For one, “there’s no way to pack every analysis tool you want on every launch,” says Kevin Lewis, a planetary scientist at Johns Hopkins who works on the Curiosity mission. Each mission provides a different, valuable peek at the way things are on Mars—and looking at it from various angles helps scientists nail down what’s actually going on.

And, like Earth, Mars is complex. You wouldn’t be able to choose just one place to put a rover on Earth to get a sense of its sheer diversity. “If you sent one to Baltimore,” Lewis says, “it would teach you nothing about the Sahara desert or the Greenland ice sheet.” So scientists pick promising landing sites after years of deliberation and input from other researchers. Schiaparelli will touch down on a flat area called the Meridiani Planum, above a promising vein of hematite, a mineral that only forms around liquid water.

For all of the designs space agencies and ambitious entrepreneurs have on Mars, it’s still a whole planet’s worth of unknowns, far away and hard to reach. To start figuring it out, scientists are going to need all the data they can get.