For the European Space Agency (ESA), tomorrow will hold a nerve-shredding 6 minutes. At 4:42 p.m. local time, the agency’s Mars lander Schiaparelli will begin its furious descent through the Red Planet’s thin atmosphere. Six minutes later, mission managers will know whether they have joined the select club of agencies that have successfully landed a spacecraft on Mars. NASA has landed seven working craft, and in 1971 Russia gleaned 20 seconds of data from its Mars 3 lander. ESA carried the U.K.-built Beagle 2 to Mars in 2003 but it failed to deploy its arrays and never called home. Tomorrow, it is hoped, Schiaparelli will not only provide ESA entry to the club, but will also pave the way for a more ambitious rover in 4 years’ time. Once its job of landing is done, Schiaparelli will devote its few remaining days of battery power to studying the atmosphere above the Meridiani Planum.

Schiaparelli is part of a multielement mission called ExoMars. In the first phase that launched in March, Schiaparelli shared a ride with the Trace Gas Orbiter (TGO), which will search the martian atmosphere for methane and other gases that could signal life. These will be followed in 2020 by a much larger lander with a rover that can drill up to 2 meters below the surface in search of ancient, or even current, microbes.

The ExoMars program has had a long and difficult gestation. Originally a solo ESA project, NASA came on board but had to jump ship again in 2012 because of budget problems. ESA then teamed up with Russia’s Roscosmos, which offered to provide launchers and some contributions to the project’s hardware.

At ESA’s mission control center in Darmstadt, Germany, ExoMars managers will be waiting with bated breath tomorrow afternoon as the two spacecraft arrive at the Red Planet, having separated from each other 3 days earlier. “Right now, I’m nervous about everything,” says the lander’s mission manager Thierry Blancquaert.

ESA is aiming for the TGO to be captured by Mars’s gravity in a highly elongated orbit. Over several months, the spacecraft will slowly circularize its orbit, dipping in and out of the atmosphere, and using that friction to reach a circular orbit 400 kilometers above the surface. The spacecraft will then begin its scientific work.

In contrast to the TGO, Schiaparelli is a technology demonstrator: It will test some of the techniques that will be needed in 4 years to get the larger ExoMars 2020 mission (2000 kilograms compared with Schiaparelli’s 600 kilograms) onto the surface. Like all landers, Schiaparelli’s big challenge is to slow down: In the space of 6 minutes it must shed the speed of interplanetary travel (21,000 kilometers per hour), descend through 121 kilometers of atmosphere, and reach a slow enough pace to touch down gently on the surface. Losing that speed is much harder than on Earth because the martian atmosphere is so thin. “There’s just enough atmosphere to be annoying, but not enough to be helpful,” says Allen Chen, who heads the entry, descent, and landing team for NASA’s Mars 2020 mission at the Jet Propulsion Laboratory in Pasadena, California.

Like its predecessors, Schiaparelli will first decelerate using the atmospheric drag on its heat shield, causing it to glow red hot and partially vaporize. The heat shield is bristling with sensors measuring temperature and heat flux to assess how well it performs. Once slowed to 1700 kilometers per hour, at an altitude of 11 kilometers, Schiaparelli will deploy a parachute to bring its speed down to 250 kilometers per hour. Then, like a butterfly fully grown, Schiaparelli will cast off its heat shield and drop to the surface. Nine thrusters will kick in for this last kilometer, guided by a radar altimeter. “This is the most delicate phase,” Blancquaert says. “It has to deal with atmospheric and environmental conditions, vertical and horizontal wind, and the slope of the terrain.” At just 2 meters above the surface, the thrusters cut out and Schiaparelli drops, cushioning its landing with a collapsible aluminum honeycomb on its underside. Landing on Mars has many challenges, Chen says. “Everything has to go right. There’s no partial success in a Mars landing.”

Heat shields and parachutes are common to all Mars landers, but NASA has tried different approaches for the final stage of descent. Smaller landers like Pathfinder, Spirit, and Opportunity were nestled among protective airbags that bounced across the surface to a stop. For the larger Curiosity rover, NASA developed a “sky crane,” which hovered above the surface with rockets while the rover was lowered gently to the surface with a winch.

Blancquaert says ExoMars 2020 will largely follow Schiaparelli’s lead, but with a two-phase parachute (small followed by large) and it will have variable thrusters—currently being developed by Russian spacecraft builder Lavochkin Association—so it can gently touch down on spring-loaded legs. “ExoMars 2020 should be able to do a real soft landing,” Blancquaert says.

ESA and Roscosmos engineers alike will have fingers crossed that everything performs as planned because if something goes seriously awry, there is little time before 2020 to fix it. “We can do fine tuning,” Blancquaert says. “If modifications are needed, that’s a different ballgame.”

Although getting safely onto the surface is Schiaparelli’s primary goal, its designers did squeeze in a little science. During the descent, its engineering sensors will take time out to probe the state of the atmosphere. On the surface, the lander’s first job is to beam up all the descent data to an orbiting craft for relay back to Earth—not the TGO, which will be far out of range by then, but one of the other several NASA and ESA spacecraft on station. Once that is done, most of the lander’s systems are shut down to conserve battery power—it has no solar arrays—and a small package of meteorological instruments called the Dust Characterization, Risk Assessment, and Environment Analyzer on the Martian Surface (DREAMS) comes to life.

The DREAMS will measure wind speed and direction, temperature, pressure, humidity, and the transparency of the atmosphere. But its unique selling point is that it will measure for the first time the planet’s electric field. Because of the available launch window, the spacecraft are arriving at Mars in the middle of its global dust storm season. A storm isn’t forecast for Schiaparelli’s time of arrival, but the timing does give it a chance to study the role of dust in the martian atmosphere and the part played by electric field.

On Earth, when wind blows dust off the surface, the swirling particles collide and exchange electric charge. In the most violent cases, like Saharan dust storms, the charge can build up from a typical 50 volts per meter to 20,000 volts per meter. “We want to understand the dust cycle,” says DREAMS Principal Investigator Francesca Esposito of the Astronomical Observatory of Capodimonte in Naples, Italy. “Is it the same phenomenon as on Earth? How does it affect climate? Will electrical disturbances affect future missions?”

Unfortunately, Esposito and her team may only have a few days to answer those questions. With no way to charge them, Schiaparelli’s batteries won’t last for long, especially if it is very cold and heaters are needed to keep the instruments functioning. “We’ll still be able to produce new science,” she says.