Two robotic spacecraft launched into space on a Russian Proton rocket on Monday, marking the beginning of a seven-month journey to Mars. This is the first phase of the ExoMars mission, a partnership between the European Space Agency and the Russian Federal Space Agency, or Roscosmos. The goal of the collaboration is to send probes to Mars to determine if the planet is — or has ever been — home to alien life. The launch took place at 5:31AM ET.

The ExoMars program consists of two launches to the Red Planet: today's and one in 2018. Today's rocket launch carries the Trace Gas Orbiter and the Schiaparelli EDM Lander into space, which will both arrive at Mars in October of this year, according to the ESA. Once there, the Trace Gas Orbiter will put itself into orbit around the planet and measure the types of gases in the atmosphere. Specifically, the orbiter is looking for traces of methane — a potential indicator of biological life on the planetary surface below.

Sending probes to Mars to determine if the planet is — or has ever been — home to alien life

The job of the Schiaparelli lander is to descend to the Martian surface and land intact. Its landing is meant to show that the ESA and Roscosmos have the right technologies to gently touch down an object on Mars. It’s kind of a trial run for the next ExoMars spacecraft: a rover that will launch in 2018. The rover is designed to explore the planet and dig up dirt samples to look for signs of biology. If Schiapearelli can land intact, the rover that follows it likely will too.

If the ExoMars mission does find evidence of life, the program's researchers hope the discovery will inspire a future trip to Mars that brings samples back to Earth. It's difficult to study samples of Martian soil remotely; the analysis must be done entirely by spacecraft and the resulting data can be hard to translate from afar. But if the samples can be safely returned to Earth, they can be studied in greater detail by experts in our planet's laboratories. "It would be the logical next step," said Hakan Svedhem, an ESA project scientist for the ExoMars mission. "If we find life now on Mars, we’ll want to understand what kind of life that is."

Solving the methane mystery

An artist rendering of the ExoMars Trace Gas Orbiter. (ESA)

The Trace Gas Orbiter will look for many gases in Mars' lower atmosphere, but researchers are particularly interested in finding methane in the planet's air, according to Svedhem. Up to 90 percent of the methane in Earth's atmosphere comes from the breakdown of biological materials, the ESA notes. The gas's presence surrounding Mars could indicate a past or present life source too.

Methane's existence on the Red Planet has been questioned for decades

Methane's existence on the Red Planet has been questioned for decades. NASA's Curiosity rover and the ESA's Mars Express satellite have detected traces of the gas in the planet's atmosphere, and ground-based telescopes spotted methane on Mars in 2003, according to NASA. The detections have been intriguing, since the gas seems to only appear in localized areas on Mars, according to Nick Schneider, a planetary scientist who works on NASA's MAVEN mission. "If you see it in one place, it’s a bullseye that says look here for something interesting," said Schneider. "Maybe it’s a colony of life that’s only survived in a certain region."

However, the methane measurements have also been temporary: the methane spotted by telescopes in 2003 all but disappeared by 2006. And Curiosity measured four big spikes of methane in late 2013, but it has yet to measure the gas again. That’s weird, since methane has a lifetime of about 300 to 600 years — the length of time it takes for the Sun to break the molecule apart. Scientists don't know why the methane measurements are behaving this way, and that's why some researchers aren't sure the gas is even on Mars. For instance, one expert thinks the Curiosity rover may have just detected methane leaking from the rover itself.

A Mars Express instrument found methane at this area on Mars, Elysium Planitia. (ESA)

The Trace Gas Orbiter is designed to provide better answers, according to Schneider. "It has the capability to make the detections no one is going to argue with." The spacecraft's instruments will observe the atmosphere against the Sun, analyzing how the light changes the transparency of the gases. This will indicate what the Martian atmosphere is made of, says Svedhem. He notes the instruments are so sensitive, they can even determine if the methane is potentially coming from a biological source. "It’s by far the most sensitive type of mission one can do with Mars," he said.

However, it's going to take a while to know what types of gases the Trace Gas Orbiter finds. When the spacecraft reaches Mars, it will spend over a year slowing down to reach the right speed and altitude for orbit — a process known as aerobraking. The probe will start studying the atmosphere once it reaches its intended orbit 250 miles (400 km) above the planet. That's slated to happen sometime in December 2017.

Exploring the floor

The ExoMars Schiaparelli lander. (ESA)

The Schiaparelli lander's mission begins as soon as it reaches Mars in October. It will first separate from the Trace Gas Orbiter and begin its dive to the Martian surface three days later, according to the ESA. A heat shield will protect the spacecraft during its initial descent through Mars' atmosphere, and then parachutes will deploy at an altitude of seven miles. Eventually, the heat shield and parachutes are jettisoned, as tiny thrusters on the bottom of the spacecraft ignite. These small engines will make the lander hover just 6.5 feet above the surface; the thrusters will then turn off and Schiaparelli will drop the rest of the way down.

A complicated process that slows the lander down from 13,000 miles per hour

It's a complicated process that slows the lander down from 13,000 miles per hour (21,000 km per hour). Mars' atmosphere is one-hundredth the pressure of Earth's, according to NASA, so there's less air to reduce the speed of a falling object. That's why both parachutes and thrusters are needed to prevent Schiaparelli from crashing into the surface. These landing techniques will all be used to land the future ExoMars rover in 2019 — but for a much larger object. The Schiaparelli lander weighs about 1,322 pounds (600 kg), but all the hardware needed to land the 2019 rover on Mars safely will weigh nearly 4,000 pounds (1,800 kg).

Schiaparelli won't have much to do once it lands, though. It doesn't have any solar panels for recharging and its internal battery is only expected to last two to five days. But the lander is still equipped with a few instruments that will measure the weather and surrounding atmosphere during the spacecraft's brief mission. All of the life-finding instruments have been saved for the next rover. That robot will carry a drill that can dig up soil samples up to 6.5 feet below the Martian surface, and a set of nine technologies on board the rover will then analyze those samples for signs of biology.

A prototype of the future ExoMars rover. (ESA)

If ExoMars does find biological samples, it still may not be enough to definitely say that there is life on Mars. "In the short term, if we find that, it’s an absolutely, astonishing achievement, but then we may need to characterize it," said Svedhem. It's possible that the rover will find samples of ancient Martian fossils, or it may be that the rover will mistakenly detect organisms brought over from Earth. Researchers would need to do a Mars sample return to know the true origins of any life found on the Red Planet. That way, experts could use laboratory tools here on Earth to pick apart the Martian dirt. But such a mission would be a massive undertaking, requiring an extra rocket that can take off from Mars and a spacecraft to bring the samples safely back to Earth.

Securing funding for a Mars sample return may be more likely depending on what ExoMars digs up. But it's always possible the program may show Mars to be a dead space rock. "I think we’d have to be extremely lucky to find [life]," said Schneider. "And the jury’s still out on whether or not life has occurred on Mars even in the past."

Update Mar 14th, 5:58AM: This article has been updated to note a successful launch.

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