Europe's pioneering spacecraft Rosetta headed for a suicide crash with the comet it has stalked for two years, nearing the end of an audacious quest to unravel the Solar System's mysteries. Sent by ground controllers on a leisurely, 14-hour freefall, Rosetta launched into a last-gasp spurt of science-gathering on the 19-kilometre journey to its icy comet tomb.
"Next stop #67P!" the European Space Agency (ESA) tweeted, using a shortened version of Comet 67P/Churyumov-Gerasimenko's full name. It confirmed that the command for Rosetta to exit the galactic wanderer's orbit was received at a distance of 450 million miles from Earth. The craft was programmed to terminate its 12-year space odyssey, joining long-spent robot lander Philae on the comet for a never-ending journey around the Sun. "We're all very excited," Rosetta project scientist Matt Taylor said at the mission control centre in Darmstadt.
Rosetta's science instruments were primed to sniff the comet's gassy coma, or halo, measure its temperature and gravity, and take pictures from closer than ever before. "In the final descent, we will get into a region that we have never sampled before. We've never been below two kilometres, and that region is where the coma, the comet atmosphere, becomes alive, it's where it goes from being an ice to a gas," said Taylor.
With the comet zipping through space at a speed of over 14 kilometres per second, Rosetta was programmed to make a "controlled impact" at human walking speed, about 90 cm (35 inches) per second. Confirmation of the mission's end is expected in Darmstadt around 1120 GMT when Rosetta's signal, which takes 40 minutes to travel, vanishes from ground controllers' computer screens. "It's mixed emotions," Taylor said of the impending end. While it will all be over for mission controllers, scientists will be analysing the information gleaned for "years if not decades" to come.
The first-ever mission to orbit and land on a comet was approved in 1993 to explore the origins and evolution of our Solar System -- of which comets are thought to contain primordial material preserved in a dark space deep freeze. Rosetta and lander probe Philae travelled more than six billion kilometres over 10 years to reach 67P in August 2014. Philae was released onto the comet surface in November of that year, bouncing several times, then gathering 60 hours of on-site data which it sent home before entering standby mode.
Insights gleaned from the 1.4-billion-euro mission have shown that comets crashing into an early Earth may well have brought amino acids, the building blocks of life. A highlight of the final hours will be a one-off chance to peer into mysterious pits dotting the landscape for hints as to what the comet's interior might look like.
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The numbers
6.5 billion: Kilometres travelled from Rosetta's launch in March 2004 until it reached Comet 67P/Churyumov-Gerasimenko, aided by gravity boosts on Earth and Mars flybys. By now, the accumulated distance is 7.9 billion km.
12 years, six months, 28 days: Mission duration from launch to end.
786: days Rosetta spent circling 67P, sniffing and tasting its atmosphere and photographing it from all angles.
19: kilometres -- the altitude from which Rosetta was set on a collision course with the comet.
14: hours -- the duration of Rosetta's freefall.
90: centimetres per second -- the speed at which Rosetta is to make a "controlled impact" with the comet.
720 million: kilometres -- Rosetta's distance from Earth when it received its suicide command.
14.2: kilometres per second -- the speed of the comet, with Rosetta and Philae on deck, zipping around our Sun on a near seven-year elongated orbit.
40: minutes -- the time it took for signals to travel between mission control in Darmstadt and Rosetta.
11: Science instruments onboard Rosetta, added to another 10 on Philae.
100 kilograms -- Washing machine-sized Philae's weight on Earth, compared to one gram on the low-gravity comet. Rosetta weighs some three tonnes.
500: Number of scientists and engineers involved in the project.
