The question of alien life has long preoccupied astrobiologists and other scientists, but it could be that extraterrestrials are not the residents of a far flung solar system, but our next door neighbors. This is the purview of the European Space Agency’s just-launched Jupiter Icy Moons Explorer (JUICE) mission, which will survey three of the four large Galilean moons: Europa, Callisto, and Ganymede. The mission will assess whether these three moons demonstrate the prerequisites needed for life to form, namely to definitively confirm the existence of subsurface oceans.

The JUICE mission blasted off today on April 14, after being delayed a day due to poor weather conditions. Now that JUICE is underway, it has separated from the Ariane 5 rocket that carried it into space, and will now begin a 17 day process of deploying its various instruments and equipment as it readies for its long journey to Jupiter.

Whatever JUICE does find, it will be a long time before we have any answers. The probe will have quite the journey before it arrives at Jupiter — eight years in total. The spacecraft will make multiple passes by Earth, our moon, and Venus, building up gravitational momentum to slingshot itself past the asteroid belt and into the outer solar system, finally arriving in 2031. Why the long wait? Orbiting missions such as JUICE have to move at a slower velocity, to properly fall into Jupiter’s orbit upon arrival. The eight year wait is the price paid for detailed information on Jupiter and its moons.

During its tenure around Jupiter, JUICE will overlap with two other missions: NASA’s ongoing Juno mission, which has been orbiting the gas giant since 2016, and next year's Europa Clipper mission. These three follow a long tradition of studying the largest planet in our solar system. Pioneer 10 and 11, along with Voyager 1 and 2 performed flyby analysis while transiting past Jupiter, but it was Galileo's mission in 1995 that brought us much of what we know about the planet. It was this later mission that first brought evidence of the moons’ subterranean oceans, laying the groundwork for JUICE’s work today.

Europa in particular has long been a candidate for harboring microbial life, with its outer icy surface and the suggestion of liquid water below based on internal tidal heating. Unfortunately, Europa’s proximity to Jupiter’s magnetic field makes study difficult, so JUICE’s focus will be on Ganymede, which the probe will orbit after circling Jupiter. Ganymede is also a strong candidate for a subsurface ocean; the largest of Jupiter’s moons, Ganymede is the only known satellite to give off a magnetic field of its own. JUICE will also look to Callisto, but the moon’s greater distance from Jupiter and lack of an energy source makes it less likely to harbor life.

JUICE will make all these assessments with state-of-the-art equipment, including a magnetometer for studying the magnetic field, an optical camera system for photography, and a visible and infrared imaging spectrometer, to assess the composition of different materials. While the ESA is heading up this mission, the probe will also carry instruments from NASA and JAXA, the Japan Aerospace Exploration Agency, reflecting the collaborative nature of the mission. When JUICE does finally arrive at Jupiter in eight years, whatever findings it makes will hopefully be shared by this global community of scientific pursuit and discoveries.