On 6 August 2014, European Space Agency (ESA)’s Rosetta spacecraft arrived at its comet destination after a 10 year-journey through space. Rosetta is the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.
Why is the Rosetta mission such a big deal? Comets are regarded as the primitive building block of life and may have helped “seed” Earth with water – and maybe even life. By studying the nucleus of Comet 67P/Churyumov–Gerasimenko and its environment in detail, Rosetta will help scientists learn more about the role of comets in the origin and evolution of the Solar System.
Rosetta will follow Comet 67P/Churyumov–Gerasimenko as it heads towards the inner Solar System, measuring the increase in activity as the frozen comet is warmed by the Sun. The comet will develop the so-called “coma” (essentially its atmosphere comprising of gas and dust) and the characteristic ion and dust tails.
The spacecraft will land a probe – the Philae Lander – on Comet 67P/Churyumov–Gerasimenko, which will focus on the composition and structure of the comet’s dust and gas. Philae will drill into the subsurface to collect samples for inspection by its onboard lab.
“Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land,” says Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager.
As many as five possible landing sites will be identified by late August, before the primary site is identified in mid-September. The final timeline for the sequence of events for deploying Philae – currently expected for 11 November – will be confirmed by the middle of October.
After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun – in August 2015 – and as it moves back out towards the orbit of Jupiter.
On its approach, Rosetta already observed a wealth of information about Comet 67P/Churyumov–Gerasimenko:
* Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet’s coma became rapidly brighter and then died down again over the course of those six weeks.
* In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter (MIRO) suggested that the comet was emitting water vapour into space at about 300 millilitres per second.
* On 1 August, the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) measured the comet’s average temperature to be about -70 degrees Celsius, indicating that the surface is predominantly dark and dusty rather than clean and icy.
* Then, stunning images taken from a distance of about 12 000 km began to reveal that the nucleus comprises two distinct segments joined by a ‘neck’, giving it a duck-like appearance. Subsequent images showed more and more detail – the most recent, highest-resolution image was taken by the Rosetta navigation camera (NAVCAM) on 9 August 2014 at about 99 km from Comet 67P/Churyumov-Gerasimenko.
Rosetta mission timeline
Launch: 2 March 2004
1st Earth swingby: 4 March 2005 (distance from Earth: 1955 km)
Mars swingby: 25 February 2007 (distance from Mars: 250 km)
2nd Earth swingby: 13 November 2007 (distance from Earth: 5301 km)
Asteroid Steins flyby: 5 September 2008 (distance from Steins: 802.6 km)
3rd Earth swingby: 13 November 2009 (distance from Earth: 2480 km)
Asteroid Lutetia flyby: 10 July 2010 (distance from Lutetia: 3162 km)
Enter deep space hibernation: 8 June 2011
Exit deep space hibernation: 20 January 2014
Comet rendezvous manoeuvres: May-August 2014 (distance from comet: 600 000-100 000km)
Arrival at comet: 6 August 2014
Philae lander delivery: November 2014 (distance from comet: 3 km)
Comet escort phase: From Dec 2014
Closest approach to Sun: 13 August 2015
End of mission: December 2015
* Interactive 3D visualisation of Rosetta’s journey to Comet 67P/Churyumov–Gerasimenko (from launch in 2004 to beyond the end of its normal mission in 2015)