Comets are frozen lumps of ice (often called volatiles) and rock that come from distant parts of our Solar System. As they move closer and around the Sun, the frozen materials start to melt and this causes a tail to form. The spectacular sight of a visible comet without the need for a telescope is one of the most sought after sights in the night sky. It is thought that on average one comet a year is visible. However, as previously seen last year with Comet ISON (or rather not seen), often these comets are dim and unimpressive. As a comet approaches the Sun, the icy nucleus becomes shrouded in the coma, an atmosphere of dust and gas making the nucleus difficult to observe from the ground. In order to study comets and find out what they’re really like up close, ESA is currently on track to land a spacecraft on one this year.
Originally launched in March 2004, the European Space Agency’s (ESA) Rosetta spacecraft has recently awoken from a 31 month slumber in order to prepare for touchdown on Comet 67P/Churyumov-Gerasimenko, in November of this year. There are almost 5000 comets catalogued, but there are potentially millions of pieces of other cometary material lurking out there. So in the initial planning of the mission, the right comet needed to be selected, it also needed to be one that would fit in with the timeline of the mission. Comet 67P/Churyumov-Gerasimenko was first discovered in 1969 and it is a regular visitor to the inner Solar System with an orbital period of 6.5 years. This comet was not meant to be Rosetta’s objective, originally it was to have encountered comet 46P/Wirtanen in 2011. After an initial delay in the launch of the Rosetta spacecraft due to problems with the Ariane 5 launch vehicle made this plan untenable, 67P/Churyumov-Gerasimenko was then chosen as the destination point for the mission.
The mission overview is to send an orbiter, Rosetta, to the comet, while it is still far from the Sun to explore in detail the surface of the nucleus. The Rosetta space craft is intended to release the Philae lander to descend to a gentle landing on the surface. Once there the lander will have to secure itself with the use of a harpoon-style anchor to prevent it drifting away as the comet’s surface gravity will be so low. The lander also has ten different instruments on board, which give it the ability to take panoramic images, drill up to 20cm beneath the surface to take samples, as well as the capacity to analyse the gases and organic materials present. These results will hopefully provide a detailed impression of the composition of a comet.
The Rosetta spacecraft was launched on board an Ariane 5 rocket in March 2004. It is a huge craft, its body, or bus, is 3m across with two outspread solar panels each 14m long (across the panels the spacecraft is as wide as the wingspan of a small airliner) and it weighs around 3000kg. The Rosetta spacecraft used the gravity of the Earth and Mars to slingshot its way towards the comet. The craft needed to use four gravity assist manoeuvres to enable this long journey and this has taken the craft on the scenic route so far, but this has allowed the craft to match speed with the comet.
A year after launch the spacecraft flew past the Earth, it was then hurled towards Mars. At this stage Rosetta was able to analyse the collision between NASA’s Deep Impact craft and the Comet Tempel-1. Two other flybys of the Earth in 2007 and 2009 sent Rosetta out to the asteroid belt. Rosetta flew past asteroid 2867 Steins in 2008 and flew within 3000 km of asteroid 21 Lutetia in 2010. This was a test for the on-board observing instruments whilst Rosetta got up close with these flying objects. It was after this stage, over two and a half years ago, when Rosetta was around 1 billion km from the Sun, that the European Space Agency placed their comet-hunting spacecraft into a period of hibernation in order to conserve power. Despite not having actually arrived at the final destination of Comet 67P just yet to carry out this new research, the craft has been recently awoken in order to prepare for landing this year. On 20 January 2014, Rosetta awoke with the aid of an on board alarm clock, with the message “Hello World”.
During the period of hibernation, Rosetta had no communication with ESA, but the computer with the vital on-board clock and several heaters remained on as the European emissary travelled ever further from the Sun, just to ensure it didn’t freeze. Rosetta was set to awaken at 10am UTC and the signal sent from Rosetta was detected by NASA’s 70m Goldstone dish just after 6pm GMT. The initial signal was a very basic but successful message that told Rosetta was awake. Since then ESA’s controllers are running a series of health checks to ensure all is looking good. So far it seems the spacecraft has come out of slumber as good as before. Over the next weeks all instruments will be tested and the lander Philae will be also taken out of hibernation in March. The last ten years of patience should pay off this year as Rosetta will manoeuvre close to the comet in May, arriving in August, and hopefully the lander will arrive safely onto the comet in November.
The Rosetta spacecraft takes its name from the Rosetta stone which was unearthed in the 18th century by French soldiers in French-occupied Egypt. It is thought to date back to 196BC and it was discovered near the town of Rosetta in northern Egypt. This stone has inscriptions in Egyptian hieroglyphics, Egyptian text as well as Greek. Translations of the hieroglyphics on the Rosetta stone became a missing puzzle piece and helped scholars learn more about the ancient Egyptian civilization. It is hoped that the Rosetta space craft will fulfil this role in the Solar System and help unlock some mysteries about the early stages of formation of the Solar System.
If the mission continues to plan, by the end of this year ESA with the help of the Rosetta spacecraft may start to unlock the mysteries of comets and reveal clues about the conditions in the early Solar System. This ambitious mission will be the first ever spacecraft to orbit and to land on a comet’s nucleus and the mission will continue until December 2015. Hopefully this mission will help us to understand what the Solar System was like 4.6 million years ago and it may even reveal if comets really could have deposited the main building blocks for the formation of life here on Earth. So good luck Rosetta!
(Article by Martina Redpath, Education Support Officer)