Scientists Finally Retrieved A Space Probe's Astonishing Last Photo

By 2017, nearly a year had passed since the European Space Agency’s Rosetta spacecraft crash-landed on the comet it had taken a decade to reach. Since then, scientists have continued their painstaking work of combing through the reams of imaging data transmitted by the probe. Much to their surprise, they discovered an eerie photo they’ve never could've suspected.

OSIRIS

Rosetta had previously been fitted with the highly sophisticated camera OSIRIS. The German-made device was equipped with both a wide-angle and a narrow-angle lens capable of producing high-definition images, meaning it was able to take some 100,000 shots during Rosetta’s 12-year mission.

A beautiful subject

Of that staggering tally, around one-fifth of the images were captured as Rosetta made its way through space towards Comet 67P. Other photos taken during the journey to 67P included some of Mars and of a couple of asteroids that Rosetta passed on its trajectory.

Working the camera

Even as Rosetta neared the end of its mission, the camera shutter kept clicking. And although some of the photographs suffered from an unexpected data corruption caused by a break in transmission, researchers were nevertheless able to interpret this information. The process then led the team to some quite astonishing shots of space – including the very last one that OSIRIS was able to take.

67P/Churyumov–Gerasimenko

But what of the comet that Rosetta was studying? Well, its full name is 67P/Churyumov–Gerasimenko, although for simplicity’s sake we’ll just call it 67P. And, in case you were wondering, the last part of that moniker honors the two Soviet astronomers who originally discovered the comet in 1969.

What Churyumo saw

At the tail-end of the ’60s, Svetlana Gerasimenko captured images of a comet called 32P/Comas Solà using a powerful telescope. But, upon further inspection, her colleague Klim Churyumo realized that the astronomer had actually spotted an entirely different astronomical body. The “67P” designation comes, meanwhile, from the systematic comet-naming protocol.

Not NASA

And the origins of the Rosetta mission can be traced right back to 1986. That year, spacecraft were dispatched to investigate Halley’s Comet at a time when it could be observed from Earth. Launches came from Russia and Japan as well as the European Space Agency (ESA), which would later send off the probe to investigate 67P.

Developing plans

Scientists’ appetites for knowledge about comets were whetted by that encounter with Halley, and experts ultimately realized that there was much more to learn about these rocks speeding through space. Expanding our knowledge about comets could even throw light on other intriguing scientific questions, in fact. So, ESA and NASA began to cooperate in developing mission plans, although NASA’s financial constraints obliged it to withdraw from the project in 1992.

Project manager

At first, the idea had been to launch a probe that would take samples from the surface of a comet and actually return them to Earth. That concept was subsequently deemed to be over-ambitious, however. And while speaking to The Guardian in 2016, Gerald Schwehm, Rosetta’s original project manager, described the thought process that led to the mission’s final form.

No small flying object

“We decided [that] if we could not get the comet to the laboratory, we’d get the laboratory to the comet,” Schwehm told The Guardian. “Surprisingly, it worked.” This approach meant, though, that the probe would have to carry scientific equipment – including radar, some optical spectrometers and the OSIRIS camera – weighing in at more than 350 pounds.

A feat of engineering

The full weight of Rosetta was in excess of 6,500 pounds, of which the 220-pound lander Philae was part. And those necessary scientific instruments were housed in what was dubbed the payload support module, which sat at the summit of the spacecraft.

Not-so lightspeed

To stop Rosetta from freezing up when it was far from the Sun, the probe was also fitted with a heating system. Yet while communications equipment was similarly on board, the distances involved in the mission meant that there was a considerable lag in transmitting and receiving signals to and from Earth. When Rosetta was about 250 million miles from Earth and nearing 67P, this delay came to more than 20 minutes.

Moving quickly

And to get Rosetta to the comet, engineers installed clusters of silicon solar panels that spread across nearly 700 square feet. These were accompanied by 24 pairs of thrusters, which were capable of propelling the spaceship at a velocity of an astonishing 7,500 feet per second.

46P/Wirtanen

Then, once the probe’s sophisticated systems and instrumentation had been assembled to the satisfaction of the ESA engineers and scientists, it was time to schedule take-off. But, unfortunately, the first mooted attempt at launching was a bitter disappointment. Originally, the event was scheduled for January 12, 2003, with the chosen target being another comet named 46P/Wirtanen.

Ariane 5 ECA

In December 2002, however, the ESA was forced to cancel this plan when another launch using an Ariane 5 ECA carrier was unsuccessful. Crucially, the Ariane was the model of rocket that had been selected to send Rosetta out of Earth’s atmosphere and on into space, meaning there was ultimately no choice but to postpone the mission.

The mission remains

As a result, the ESA experts had to come up with a new scheme. The launch was set instead for February 26, 2004, with the target comet this time around being 67P. And although some modifications to Rosetta were required before launch, much of the mission remained largely the same.

Guiana Space Centre

So, after another brief delay of just a few days, Rosetta finally set off from the Guiana Space Centre in French Guiana on March 2, 2004. And, happily, Churyumov and Gerasimenko, the two astronomers who’d originally identified 67P, were both on hand to witness the event.

Over big red

No doubt to everyone’s relief, Rosetta blasted off into space without a hitch. The probe then followed a route through the inner Solar System that allowed it to use the power of planetary gravity in its journey. This included a flight past Earth in March 2005 as well as a fly-by near Mars two years later. The tour over the Red Planet was designed to put Rosetta on the right trajectory to intercept 67P.

No sunshine? Big problem

Skirting close to Mars was a tricky process, however, as it entailed Rosetta being in the shadow of the planet for a quarter of an hour. Shielded from the Sun, the craft’s solar panels would therefore be inoperative for that period, resulting in a worrying decrease in power for the ship’s systems; communication with Earth would be interrupted, too. In the event, though, the operation went smoothly.

High above

In fact, this part of the mission went so well that Rosetta was able to transmit some excellent images of Mars’ surface back to the European Space Operations Centre in Germany. Then, after another fly-by over Earth during November 2007, Rosetta headed off into deeper space – but not before there was a strange case of mistaken identity as the probe edged closer to our planet.

Denis Denisenko's observation

You see, as Rosetta sped by Earth, an astronomer at the University of Arizona’s Catalina Sky Survey in Tucson mistook the spacecraft for a previously unidentified asteroid. This object was even given the name 2007 VN84, and fears arose that it might crash into our planet. Fortunately, though, respected Russian astronomer Denis Denisenko spotted that the new asteroid was actually Rosetta – thus bringing an end to the panic.

Hibernation

As Rosetta subsequently sped through space towards its target, it passed the asteroid 21 Lutetia and took the opportunity to take photographs and register various scientific measurements. After that, in the summer of 2011, it was time for the craft to go into hibernation – a necessary power-saving measure.

The tensest moments

The shutdown meant that the probe – now almost half a billion miles from the Sun – was powered solely by its solar panels. And as the majority of systems, including communications, were turned off, there was consequently a lengthy period when mission control had no contact with Rosetta. Understandably, this made the moment when these elements were due to be switched back on a tense one for the ESA scientists and engineers.

Revival

Yes, after some 31 months, the time came to awaken Rosetta from her slumber, with the big day arriving on January 20, 2014. And nerves at mission control weren’t exactly calmed by the fact that the expected first communication from the craft was 18 minutes late. Then, to jubilation among the ESA staff, Rosetta ultimately revived and, in time, sent a transmission.

The right position

Now that Rosetta was back online, all of its systems needed to be checked as it sped towards its rendezvous with 67P. Mission control also put the probe through a series of maneuvers using the ship’s thrusters. These were executed so that Rosetta was in exactly the right position as it approached the comet.

No potatoes here

Now, Rosetta was able to get a much better look at 67P. But what the cameras ultimately captured turned out to be a major surprise for the scientists back in Germany. You see, they’d expected that the comet would most likely be potato-shaped; as it happens, though, 67P appeared nothing like an everyday vegetable.

Rubber duckies

Instead, what the astonished experts saw in the images Rosetta was sending back was a rock with two distinct lumps that were joined by a neck-like structure. For all the world, it looked like a child’s bathtime rubber duck. And “rubber duck” quickly became the accepted – although hardly scientific – description of the comet’s shape.

The flaw in the plan

Amusing though it may have been, the rubber duck shape wasn’t good news for the mission. That irregular profile meant it would be more difficult to calculate the weak but important gravitational force exerted by the three-mile-long comet. And as it happens, determining this information was crucial to the final part of Rosetta’s mission.

Philae

Specifically, once Rosetta was in the optimum position, the Philae lander would be launched. That way, Philae could actually touch down on 67P, take samples and analyze them on the spot. So, knowing how the comet’s gravity would influence the trajectory of the lander was exceptionally important.

Manuevering

Then, on August 6, 2014, Rosetta reached its destination. The probe was only around 60 miles from the comet, and mission control began to perform a series of complicated maneuvers to edge the craft even closer. The engineers also took the opportunity to analyze the comet’s complex gravitational pull in detail.

Closer

Cautiously, the scientists propelled Rosetta nearer to 67P until, on September 10, the spacecraft was less than 30 miles from the comet. At this point, Rosetta was actually within 67P’s gravitational field, although the gap between comet and craft was subsequently narrowed to just over five miles.

Touchdown

Then, finally, it was time to launch Philae towards the comet’s surface. On November 12, 2014, the lander was released from Rosetta and, around seven hours later, eventually touched the surface of 67P. But the operation didn’t quite turn out as hoped. You see, Philae was equipped with harpoons that were designed to fire and anchor the lander to the comet. These vital pieces of equipment malfunctioned, however, leaving Philae to actually rebound off 67P twice.

Readings

Nevertheless, Philae’s instrumentation was triggered, and so it began to take readings that were of considerable scientific value. Then another mishap occurred when Philae fell back towards the surface of 67P. In particular, the device became stuck in a shaded spot where its solar panels couldn’t operate, and this meant signals from the lander mostly stopped after just a couple of days.

Disappointment

This turn of events was a major disappointment, of course, as it had been hoped that the lander would continue to transmit data from 67P’s surface for much longer. Even so, the Rosetta mission managed to make not only several important scientific findings, but also some space travel breakthroughs. It marked the very first time that a probe had landed on a comet, after all.

Detection

And Philae operated for long enough to detect chemicals on the comet, including hydrogen sulfide, hydrogen cyanide and ammonia – a sour-smelling mixture, for sure. In addition, Rosetta’s instruments detected some organic compounds suspended in a mist around 67P, with this lending credence to the idea that life on Earth might have been seeded by comets.

Building blocks on Earth

So, despite the mishap with Philae’s landing, the mission was very far from a failure. In 2016 Professor Mark McCaughrean, the ESA’s senior science advisor, told BBC Radio 4, “It’s giving us a real insight into the building blocks of the solar system and the material which could have formed life on Earth – not life itself, but the raw building blocks. But more importantly for me, it’s engaged the public in a way [that] is just unparalleled for a robotics space mission.”

Life after death

As for Rosetta? Well, the ESA scientists decided to land the probe on the comet, too. This controlled descent came on September 30, 2016, and took more than half a day. And while Rosetta headed for the comet, the OSIRIS camera continued to take and transmit images, with the last captured at a height of just 80 feet above 67P’s surface.

Partial information

At least, everyone thought that shot was the last image from Rosetta. But, as it happens, it wasn’t. Towards the end of Rosetta’s last transmission of data back to Earth, there had been a disruption in the flow. Then, after technicians later discovered some pieces of data on the mission server, they recognized that this was partial information from a photograph.

Close up

Using these fragments and some specialized software, the scientists were then able to construct one more image. And, rather incredibly, it appeared that this shot had been taken from just 60 feet above 67P – making it the most close-up view of a comet ever seen to date.

A reason to celebrate

Indeed, there’s no overestimating the incredible achievements of Rosetta’s 12-year mission. And the ESA’s spacecraft operations manager, Andrea Accomazzo, summed these up in an interview with the The Guardian. “Rosetta has been comparable to the Moon landing,” she said. “It’s that order of magnitude. As a child, I could only have dreamt [of] something like this. It’s interesting to see how many emotions landing on a comet still trigger in very many people.”