If there's life swimming in the dark, frigid ocean of the Jupiter moon Europa, an upcoming NASA mission might be able to sniff it out.
The agency's Europa Clipper spacecraft is scheduled to launch in the mid-2020s on a mission to characterize the icy moon's subsurface sea and its life-hosting potential. But Clipper is capable of making even bigger discoveries, if everything falls into place just right.
"We're a habitability mission. We're trying to understand, Is Europa a habitable environment?" Europa Clipper project scientist Robert Pappalardo, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said Wednesday (Oct. 23) at the 70th International Astronautical Congress (IAC) in Washington, D.C.
"We're not a life-search mission," Pappalardo added. "But, if Europa's interior happened to be rich in organic microbes pouring out of it, we would be able to tell from the mass spectra — probably, possibly — that we're sensing life. That's a longshot, but it's not impossible."
Pappalardo was referring to measurements made by Clipper's mass spectrometer, one of nine science instruments the probe will carry. Mass spectrometers determine the masses of ions (charged atoms and molecules) in a sample, helping scientists identify what those ions are.
Clipper will collect these samples during dozens of flybys of Europa, which the probe will make from Jupiter orbit over the course of its 3.5-year operational life. Circling Europa itself was not a viable option, given the intense radiation environment around the moon, mission team members have said.
The samples will come from Europa's wispy atmosphere and, the team hopes, from plumes of water vapor and other material wafting from the icy moon's surface. Scientists have spotted evidence of such plumes on multiple occasions, but their existence has yet to be confirmed.
"Early in the mission, we'll be searching for plumes and trying to understand, Are they real? Are they there? Where are they? Are they sporadic or continuously active?" Pappalardo said.
"And maybe we'll fortuitously go through a plume, or maybe we'll be able to adjust the orbit slightly in order to go through a plume," he added. "And if we do, then our in situ instruments, especially the mass spectrometer and the dust detector, will be able to sample that material in extreme detail to search for organic materials and to understand the detailed chemistry of Europa's interior."
Pappalardo cautioned that Europa's plumes, if they do indeed exist, might be very different than the confirmed one emanating from the south polar region of Saturn's icy moon Enceladus. The Enceladus plume is generated by powerful geysers that are continuously blasting material from the Saturn satellite's subsurface ocean into space. Although the Europa material could be coming from its ocean, the source could also be lakes of liquid water within the moon's ice shell, Pappalardo said.
And he stressed that plume sampling won't make or break Clipper's mission.
"That's essentially bonus science, not required by the mission," Pappalardo said. "But I sure hope it happens."
The other instruments carried by the solar-powered Clipper, whose total mission costs are estimated at around $4 billion, include a magnetometer and a radar instrument, which will allow the team to characterize in detail Europa's ocean and ice shell, respectively. Scientists think the ocean is about 50 miles (80 kilometers) deep and the ice shell about 13 miles (20 km) thick, but those are estimates, and there will certainly be regional variation.
In case you just skimmed over that last sentence: A 50-mile-deep ocean is pretty amazing, considering that the deepest point on Earth's seafloor is just 7 miles (11 km) beneath the waves. At 1,900 miles (3,000 km) wide, Europa is smaller than Earth's moon but is thought to harbor twice as much liquid water as our planet's surface does.
Europa's ocean is also thought to be in contact with the moon's rocky core, potentially enabling a wide range of interesting and complex chemical reactions. As a result, Europa is widely regarded as one of the solar system's best bets for harboring alien life. Others on the short list include Enceladus and Saturn's huge moon Titan, which has hydrocarbon seas on its surface and likely a buried ocean of liquid water as well.
The Clipper will also tote powerful cameras, which will snap photos with a resolution of about 1.6 feet (0.5 meters) per pixel. That's 10 times sharper than the best existing images of Europa's surface, which were captured by NASA's Galileo spacecraft, Pappalardo said. Galileo orbited Jupiter from 1995 to 2003.
While Clipper's photos will be revelatory enough in their own right, they should also help pave the way for the next step in Europa exploration: a life-hunting lander that Congress has instructed NASA to develop. Clipper's data will help researchers identify good places for the lander mission to touch down, NASA officials have said. (The lander mission remains a concept for the moment, however; it's not officially on NASA's docket.)
NASA had long been targeting a 2023 liftoff for Europa Clipper. Congress has told the agency to launch the mission using NASA's powerful Space Launch System (SLS) megarocket, which would allow Clipper to travel directly to Jupiter and get there after just 2.4 years of flight.
But SLS is still in development and has experienced multiple delays and cost overruns. In addition, NASA plans to use the first three SLS vehicles for its Artemis lunar-exploration program. As a result, the first SLS available for use by Clipper won't be ready until 2025 at the earliest, NASA's Office of the Inspector General (OIG) recently concluded.
The OIG therefore recommended that NASA should be allowed to consider launching Clipper on a commercial rocket, such as SpaceX's Falcon Heavy or United Launch Alliance's Delta IV Heavy. These vehicles aren't as powerful as SLS is expected to be, so going the commercial route would require a different trajectory for Clipper — a roundabout one that employs planetary "gravity assists" and features a total transit time of nearly six years, according to the OIG report.
- NASA's Europa Clipper Mission to Jupiter's Icy Moon Clears Big Hurdle on Path to Launch
- Water Plumes on Europa: The Discovery in Images
- Photos: The Galilean Moons of Jupiter
Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.