Where will the next wave of space exploration take us?

The past few years have been a halcyon era for space exploration. In the span of little more than a decade, NASA’s New Horizons spacecraft whizzed by Pluto and the giant moon Charon, its Curiosity Mars rover rolled across a Martian crater looking for traces of once-habitable environments, and the European Space Agency’s Rosetta spacecraft rendezvoused with a comet. The Euro-American Cassini spacecraft orbited Saturn, dropping the Huygens lander on the giant moon Titan and providing close-up views of many of the ringed planet’s other moons. Other spacecraft orbited Mercury and the Moon, visited the Solar System’s two largest asteroids, skimmed Jupiter’s cloudtops, and returned dust samples from an asteroid and the tail of a comet.

Many of these missions have either ended or are about to. Even the workhorse Cassini mission, orbiting Saturn since 2004, finally ran out of manoeuvering fuel, taking a terminal swan dive into Saturn’s upper atmosphere in September. 

It feels like the end of an era. But that’s just part of the normal ebb and flow of a vibrant multi-decadal program, says Steve Squyres, a planetary scientist from Cornell University who heads up the science team for NASA’s Opportunity Mars rover. 

Opportunity has covered 45 km of Martian ground in the 13 years since its 2004 landing, and continues to make discoveries. It has outlived its 90-day design life by a factor of more than 50. 

“When a big mission like Cassini comes to an end, it can feel like the end of an era, but it’s not. It’s just the end of that one mission.”

A number of satellites continue to observe the Red Planet from orbit. There are talks of landing on one or the other of Mars’ tiny moons, and a plan for a new rover, potentially to be launched in 2020, better equipped and even more durable than those that came before. “Things are great at Mars,” Squyres says.

The reason it looks like the end of an era, he says, is that all missions have a natural lifecycle. “In a robust program, there will be missions at various states in their lifecycles, ranging from earliest formulation to mission end. When a big one like Cassini comes to an end, it can feel like the end of an era, but it’s not. It’s just the end of that one mission.”

Two of the most exciting missions on the planning board involve Jupiter. One is the Europa Clipper. This NASA mission would dive in and out of Jupiter’s punishing radiation belts to perform dozens of close flights past the icy moon Europa, which scientists believe holds a sub-surface ocean that might be suitable for life. Approaches would range from 2,700 km to as close as 25 km. There are even thoughts of a possible Europa lander, Squyres says. The launch date has not been locked in but is slated for some time in the 2020s.

Another Jupiter mission is JUICE, which stands for JUpiter ICy moons Explorer. This ESA mission could beat the Europa Clipper off the launch pad, arriving at the giant planet as early as 2030. It would then spend three years examining three of Jupiter’s four largest moons: Ganymede, Callisto and Europa. 

Other missions will stay closer to home. Japan’s space agency, JAXA, has a spacecraft called Hayabusa 2 already en route to one of the Apollo group of near-earth asteroids, 162173 Ryugu. 

In 2010, Hayabusa 2’s predecessor became the first mission to bring back samples from the surface of an extraterrestrial body other than the Moon when it visited another Apollo group asteroid, 25143 Itokawa. Unfortunately, due to mechanical problems with the probe’s sampling device, the Japanese were only able to collect tiny amounts of microscopic dust. 

This time the plan is to use an explosive device to dig a crater in the surface of 162173 Ryugu, to expose underlying material and collect somewhat larger samples, to be brought back to Earth in 2020. 

NASA is attempting something similar with a spacecraft called OSIRIS-REx, already heading for another Apollo group asteroid, 101955 Bennu. The asteroid is ranked as the third most dangerous potential Earth impactor, with eight chances of hitting us between 2169 and 2199. At 500 metres in diameter, it is big enough to pack a serious wallop; the asteroid that exploded above Chelyabinsk, Russia, in 2013, injuring nearly 1,500 people, was only 20 metres in diameter.

In part, the OSIRIS-REx mission’s goals are scientific – Bennu appears to be a “primitive” asteroid protentially providing clues to conditions at the dawn of the Solar System. But the primary goal is to find out what the asteroid is made of in case we have to attempt to deflect it someday. To determine that, the mission hopes to return a couple of kilograms of material back to Earth. If OSIRIS-REx and Hayabusa 2 both succeed, we will have surface samples from three different asteroids for comparative analysis.

New Horizons, meanwhile, isn’t dead. Its dramatic flyby of Pluto and Charon two years ago left it with enough fuel to adjust course for a 2019 rendezvous with another outer Solar System body. The new target, the Kuiper belt object 2014 MU69, is so distant it wasn’t even discovered until 2014, when astronomers were looking for interesting objects beyond Pluto toward which New Horizons could be directed. Nothing that far out in the Solar System has ever before been seen except as fuzzy dots in telescope images.

Heading in the opposite direction, a joint European-Japanese mission called BepiColombo, scheduled for launch in 2018, is aiming to reach Mercury in 2025. It comprises two orbiters that will work in tandem from different positions. At one point the mission planned to have a lander but that, sadly, was cancelled due to budget constraints.

Closer to home, China and India have Moon missions planned for the near future. China’s Chang’e 5 hopes to retrieve soil samples and is scheduled for lift-off in November. India’s Chandrayaan 2 mission to land a lunar rover is scheduled for 2018.

Meanwhile, Squyres says, there is fierce competition underway for the next NASA “New Frontiers” mission, the class that includes New Horizons, Juno and OSIRIS-REx. There are 12 proposals fighting for selection, he says. The details of these mission proposals aren’t publicly available but, all told, he is confident “the future looks as bright and exciting as it ever has”.