Europa Clipper heads to Jupiter: Can its icy moon support life?

The Europa Clipper has unfurled its solar panels and is on its way to Jupiter, but it’s taking a circuitous route by way of Mars.

The launch itself went off without a hitch, much to the relief of the assembled scientists, engineers, and mission specialists. Millions of hours of work could have been blotted out in an instant if the Falcon Heavy hadn’t kept its 100 percent success rate.

“It’s highly stressful, I never enjoy the launches,” Dr Sascha Kempf, principal investigator for one of the nine instruments on board, told The Register. Kempf has spent the last 20 years on the team and is acutely aware that all that time could be in vain.

This is NASA’s largest and best equipped interplanetary probe yet. Even with the initial boost from Falcon Heavy’s thrusters, it’ll take over five years for the circa 6,000 kg (13,000 lb) Clipper to reach Jupiter, by way of gravity slingshots from Mars and the spacecraft’s home planet. Once at Jupiter, the surveyor will begin a four-year mission to map, sniff, and probe the ice moon of Europa, considered one of the best prospects for harboring the conditions necessary for life in the Solar System.

Jupiter’s fourth-largest moon, about 90 percent the size of our own, is entirely covered by a thick shell of ice (believed to be 15 to 25 kilometers deep), which hides a vast ocean of liquid water beneath. This ocean is kept warm by the constant gravitational tugging and kneading from its close orbit around the largest planet in the Solar System. Plumes of liquid erupt from its surface, which could provide evidence about whether Europa’s ocean has the conditions necessary to support life.

Europa Clipper – click to enlarge

NASA has been planning this trip for decades, and these included landing, boring a submarine into the waters below, and now nine carefully designed instruments that will hopefully map the moon’s surface, scan its underwater oceans, and find out what Europa’s made of.

We can’t build a spacecraft that could survive orbiting Europa, given Jupiter’s fearsome radiation belts that encircle the moon. So, the Clipper will dive through them with most of its hardware encased in a shielded cage. Once out of the danger zone, the data will be trickled back to Earth and we’ll find out if Europa is a source of life in the Solar System and its resources.

The shining potential city on the hill
The launch was something Europa’s discoverer 17th Century astronomer Galileo Galilei would have loved to see.

He’s credited with first sighting the moon on January 8, 1610, although a fierce plagiarism fight determined German astronomer Simon Marius may also have spotted it around the same time but not broadcast his notes on time – broadband speeds being someone on a horse in the seventeenth century. Its highly reflective icy surface and size made it an easier spot, and the constantly shifting ice crust makes it one of the smoothest objects in the Solar System, and one of the brightest.

Humanity received the first blurry photos of Europa in 1973, when Pioneer 10 shot past, and again a year later with Pioneer 11. The Voyager spacecraft got slightly better images, showing the surface riven with cracks in the ice and – critically – no impact craters, suggesting a surface that was constantly shifting and reforming.

Europa in color from Voyager. Source: NASA – Click to enlarge

These images inspired Arthur C Clarke to write a sequel to his classic book 2001, named 2010, which postulated using the moon as a possible refueling station for spacecraft. An attempt by Chinese astronauts to do so tragically fails with primitive life under the ice overwhelming the spacecraft.

It was – appropriately enough – the Galileo probe in 1995 that sent back the first really good shots of the moon’s surface shortly afterward – from a distance of 33,000 kilometers (20,000 miles,) making a total of 11 flybys in all over its eight-year mission – more than any other Jovian satellite.

Galileo’s magnetometer revealed that Europa likely has a subsurface ocean beneath its icy shell, and also that significant amounts of water can be found on its sister moons Callisto and Ganymede. The three moons also have what’s called a ‘surface-bound exosphere,’ which is a tenuous atmosphere extending above the surface.

It’s this exosphere that scientists like Kempf and the rest of the team behind the Clipper want to explore, but first they have to get there, and the rest of the Solar System is going to lend a helping hand.

First stop, Mars!
The probe’s trip to the largest planet in the Solar System is a circuitous one. First the spacecraft is heading off to Mars to pick up some speed.

The concept of using a planet for a free speed boost came from UCLA mathematician Michael Minovitch, who used NASA JPL’s IBM 7090 – then the fastest supercomputer of its time in 1961 – to solve the three-body problem of orbital computing a year later. Calculating orbits based on two objects, such as the Moon and the Earth, was relatively straightforward, but add another body into the equation – such as the Sun – and there was the potential for some really interesting orbital mechanics. Minovitch’s equations were used to boost some of humanity’s earliest space probes and the Clipper is no exception.

By diving into Mars’ gravity well the probe will gain two kilometers a second’s worth of velocity, Stefano Campagnola, mission design manager of the mission told The Register. In return the planet will lose an infinitesimal amount of momentum.

“Mars orbit is technically not in the optimal place to leverage our initial orbit, but we can use its gravity for free (if the timing works), and that saves a lot of propellant.” he explained.

NASA’s Europa Clipper leaves for Jupiter’s moon atop Falcon Heavy

The Europa Clipper stretches its wings as launch nears

That’s gas: CO2 found on Europa surface may hint at some possible sign of life

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Once the probe has been slingshotted around Mars it’ll head back to Earth for another gravity assist. That will power it off to Jupiter with enough propellant saved to allow the probe to maneuver into orbit around the gas giant and allow it to swing close to Europa without having to hang around in the dangerous belt of radiation.

Campagnola explained how, once in orbit, the Clipper team will use the gravitational influence of Jupiter’s four largest moons to adjust the spacecraft’s trajectory and allow it to scan most of Europa’s surface and swoop down over the surface to sample the conditions. This will preserve the spacecraft’s fuel and allow it to possibly extend the mission if the kit on board can hold out long enough.

Protecting the hardware, for a while
An unshielded human would absorb a killing dose of charged particle radiation every day they were on the surface. But the radiation also causes serious problems for instrumentation, so the Clipper design seeks to put as many of the critical components of the spacecraft in a radiation-hardened repository in the center of the vehicle.

For example, Dr Kempf has been on the team designing the SUrface Dust Analyzer (SUDA) for the flight, a sniffing device designed to find out what is lurking near Europa’s surface. The instrument will store its findings in 8GB of Flash memory housed in the repository and then, as the spacecraft leaves Europa and the radiation shielding, will fire that data back towards Earth.

SUDA sniffer is on its way. Source: NASA – Click to enlarge

There’s not a lot the team can do to protect some of the instrument’s components, but everything that can be put in the repository is, he explained. With this design, the whole Clipper team is hoping to extend the life of the probe.

Another problem is everyone getting their instruments in the right place. The MAss Spectrometer for Planetary EXploration/Europa (MASPEX) will be used on flights that will go as low as 25 kilometers from the moon’s surface, he said, but for the cameras used to map the surface that’s too low and the probe will be going too fast – leading to a phenomenon called pixel smearing.

The same issues will affect MASPEX instrument, designed to sniff out particles surrounding the moon, or even from inside it, Kelly Miller, group lead at Southwest Research Institute that built the instrument, explained.

Eruptions from within Europa have been spotted by the Hubble Space Telescope and it’s hoped, if the team is very lucky, that the spacecraft might intercept either one of the plumes or its aftereffects. Doing so would show a lot of information about whether or not Europa could actually be suitable for life.

The Clipper is planned to fly by the moon 49 times in the original mission plan, but Miller told The Register that she was hopeful that the instrumentation would hold up for many more flybys. After all, previous NASA missions have extended well past their original planned shutdown dates.

But at the end, the Clipper will be destroyed – deliberately. Once all the useful science has been achieved, the team don’t want to risk the spacecraft crashing into Europa and contaminating the moon, so instead the spacecraft will be put on a collision course with one of Jupiter’s other satellites, Ganymede.

It’ll be a sad end for a probe that represents possibly our best chances to date for studying the habitability of environments beyond Earth, but the volumes of data transmitted back could reveal vital clues that we are not alone in the Solar System. ®