What goes up…must come down, but not in the case of the space probes stranded on alien worlds for all eternity. As Comet 67P nears the Sun, increasing the chance of the Philae lander waking up, Richard Hollingham tracks down the space adventurers who will never see home again.

Beneath the toxic petrochemical clouds of Saturn’s moon Titan lies one of mankind’s greatest achievements – the tiny Huygens space probe, packed with instruments and electronics but destined never to return to Earth.

These space probes are monuments to humanity -       John Zarnecki, International Space Science Institute

Other spacecraft are stranded on the dusty plains of the Moon and Mars, while Philae is resting in a gully on comet 67P/Churyumov–Gerasimenko currently speeding at 55,000km/h (34,000mph) towards the Sun.

“These space probes are monuments to humanity,” says John Zarnecki, Director of the International Space Science Institute in Bern, Switzerland.

Emeritus Professor at the Open University, Zarnecki is probably the only scientist in the world to have worked on three spacecraft now resting on a comet, Mars, and a moon of Saturn.

Like other lonely landers – our avatars at the frontiers of knowledge – these probes took years to develop and build, survived perilous journeys around the solar system and some only lasted a matter of minutes before shutting down.

It is hard not to feel affection and, maybe even, a sense of guilt that we abandoned them.

“You spend years of your life living with these things – you eat, sleep and breathe them,” says Zarnecki. “You do become emotionally attached.”

Here is what happened to some of them:

Huygens

On 14 January 2005, the European Space Agency’s (Esa) biscuit-tin–shaped, 2.7m-diameter Huygens probe began its descent through the hydrocarbon smog that envelops Saturn’s moon, Titan. Suspended from the strings of a parachute – a landing system that had somehow survived a seven-year 3.5 billion kilometre (2.2 billion mile) journey – the European spacecraft captured the first-ever views of the alien world.

Two and a half hours later, Huygens was on the surface – relaying data back via its Cassini mothership, in orbit around Saturn. And 72 minutes after that, the lander was dead – its contact with Earth lost and its battery depleted.

“We think Huygens probably transmitted for another 10 minutes after Cassini disappeared over the horizon but there was no-one there to listen to it,” reveals Zarnecki. “Its last bit of data is still winging its way across the galaxy for someone else to pick up.”

Ten years on we can only guess at what state the lander is in now. “I do think about it sitting there,” says Zarnecki. “On Titan there’s this mist and rain – an organic goo that settles on the surface – so it’s probably got this covering of goo but is still recognisable.”

Zarnecki is optimistic that we will see the little lander again. “We’ll probably go back to Titan with a balloon flying around doing a survey,” he says. “So it’s not beyond the bounds of possibility that during my lifetime I will get images of Huygens.”

Beagle 2

Mars is littered with landers, with two – Nasa’s Opportunity and Curiosity – still trundling across the surface doing their bit for human knowledge. With the exception of the probes that missed the planet completely, such as the Soviet Union’s Mars 7 lander, or crashed into the surface, including the US Mars Polar Lander, most have worked for several days, weeks or months sending back valuable scientific data before succumbing to the harsh conditions.

There is, however, one lander that never got to perform: the UK-built Beagle-2. Recent images show it reached the Martian surface intact but the panels enclosing its transmitter failed to open. It may even have started to take pictures and record data.

“Someone just needs to kick it to open it up,” says Zarnecki, a scientist on the mission. “It would be possible to send a mission to fix it – although I can’t see the space agencies approving that.”

Still, with all eyes on Mars, and a future human mission a distinct possibility, it is certainly conceivable that people will one day visit these remnants of Earth technology. And maybe an astronaut will be tempted to give it a kick. Zarnecki says we should be cautious.

“These are akin to archaeological sites,” he says. “So if we go back and start strip mining Mars or whatever, the Beagle landing site should be given protection to stop Martian settlers plundering landers for spare parts.”

Lunokhod 2

Many people have similar concerns about preserving the historic missions scattered across the surface of the Moon.

From the first successful lunar lander, the Soviet Luna 9 of 1966, to the Apollo landers and China’s latest robotic rover, there is no shortage of history littered across the Moon’s surface.

Remarkably one of the oldest rovers – the 40-year-old Lunokhod 2 – is still in use. This tubby, eight-wheeled Soviet machine was one of a pair of vehicles that pioneered the successful use of robotic rovers on alien worlds, sending back images of the landscape and data on the composition of lunar soil.

However, four months after landing in January 1973, Lunokhod 2 overheated and shut down. In 1993, despite no-one knowing exactly where it was on the lunar surface, the rover was put up for auction. It was bought for $68,500 by video game developer Richard Garriott (who would go on to become a space tourist flying to the International Space Station in 2008).

Then, in 2010, Nasa spotted the rover from its Lunar Reconnaissance Orbiter spacecraft. Today, astronomers use Lunokhod 2’s reflective surface to measure the distance between the Earth and Moon.

Controversially, Garriott claims that area of the Moon as his.

“My lunar rover not only tilled the surface of the Moon, surveyed many kilometres during its travels but it’s still in active use,” he said last year. “My location on the Moon is still in active use and I’m the owner and so I think there’s some legitimacy in claiming that area of the Moon.”

Philae

Another lander that may yet live to fight another day is currently 322 million kilometres away, somewhere on 67P/Churyumov–Gerasimenko. After bouncing across the comet’s surface, Esa’s Philae probe settled in a gully – transmitting 56 hours and 15 minutes of data, including a spectacular selfie, before shutting down.

As the comet nears the Sun, and sunlight and temperature increase, there is a chance that the lander could awake to continue its research. In fact Philae’s technical manager Koen Geurts recently told the Space Boffins podcast that the odds are looking good.

“We have a good chance that Philae will be able to boot,” says Geurts. “Up until mid-August, everyday our chances are increasing.”

I think they should get as much publicity as the Kardashians -        John Zarnecki

After that, as the comet’s elliptical orbit takes it away from the Sun and out towards Jupiter, things do not look good for the lander’s long term survival. Although the comet returns to the Sun every seven years, Philae is unlikely to recover.

“Unfortunately,” says Zarnecki, who worked on one of Philae’s instruments, “it’s going to get so cold that it will suffer catastrophic damage.”

But when it comes to total isolation, all these missions pale in comparison to the Voyager probes. Voyager 1 is currently 19.5 billion kilometres from Earth. It is unlikely we will ever get it back.

Zarnecki suggests it is worth thinking about how remarkable these spacecraft – and the people who built them – are.

“I think they should get as much publicity as the Kardashians,” he says.

“The people who send these probes to distant places should be more highly credited and praised – they are our first tentative steps into the Solar System and beyond.”

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