Rosetta

Europe's comet chaser

Rosetta orbiting Comet 67P/Churyumov-Gerasimenko

In November 1993, the International Rosetta Mission was approved as a Cornerstone Mission in ESA's Horizons 2000 Science Programme.

Since then, scientists and engineers from all over Europe and the United States have been combining their talents to build an orbiter and a lander for this unique expedition to unravel the secrets of a mysterious 'mini' ice world – a comet.

Initially scheduled for January 2003, the launch of Rosetta had been postponed due to a failure of an Ariane rocket in December 2002. The adventure began March 2004, when a European Ariane 5 rocket lifted off from Kourou in French Guiana.

During a circuitous ten-year trek across the Solar System, Rosetta will cross the asteroid belt and travel into deep space, more than five times Earth’s distance from the Sun. Its destination will be a periodic comet known as Comet 67P/Churyumov-Gerasimenko.

The Rosetta orbiter will rendezvous with Comet 67P/Churyumov-Gerasimenko and remain in close proximity to the icy nucleus as it plunges towards the warmer inner reaches of the Sun’s domain. At the same time, a small lander will be released onto the surface of this mysterious cosmic iceberg.

More than a year will pass before the remarkable mission draws to a close in December 2015. By then, both the spacecraft and the comet will have circled the Sun and be on their way out of the inner Solar System.

Historic mission

The Rosetta mission will achieve many historic firsts.

• Rosetta will be the first spacecraft to orbit a comet’s nucleus.
• It will be the first spacecraft to fly alongside a comet as it heads towards the inner Solar System.
• Rosetta will be the first spacecraft to examine from close proximity how a frozen comet is transformed by the warmth of the Sun.
• Shortly after its arrival at Comet 67P/Churyumov-Gerasimenko, the Rosetta orbiter will despatch a robotic lander for the first controlled touchdown on a comet nucleus.
• The Rosetta lander’s instruments will obtain the first images from a comet’s surface and make the first in situ analysis to find out what it is made of.
• On its way to Comet 67P/Churyumov-Gerasimenko, Rosetta will pass through the main asteroid belt, with the option to be the first European close encounter with one or more of these primitive objects.
• Rosetta will be the first spacecraft ever to fly close to Jupiter’s orbit using solar cells as its main power source.

Scientists will be eagerly waiting to compare Rosetta’s results with previous studies by ESA’s Giotto spacecraft and by ground-based observatories. These have shown that comets contain complex organic molecules - compounds that are rich in carbon, hydrogen, oxygen and nitrogen.

Intriguingly, these are the elements which make up nucleic acids and amino acids, the essential ingredients for life as we know it. Did life on Earth begin with the help of comet seeding? Rosetta may help us to find the answer to this fundamental question.

Why rosetta?

The Rosetta Stone, discovered in 1799

The European Space Agency's unprecedented mission of cometary exploration is named after the famous 'Rosetta Stone'. This slab of volcanic basalt - now in the British Museum in London – was the key to unravelling the civilisation of ancient Egypt.

French soldiers discovered the unique Stone in 1799, as they prepared to demolish a wall near the village of Rashid (Rosetta) in Egypt's Nile delta. The carved inscriptions on the Stone included hieroglyphics – the written language of ancient Egypt – and Greek, which was readily understood. After the French surrender in 1801, the 762-kilogram stone was handed over to the British.

By comparing the inscriptions on the stone, historians were able to begin deciphering the mysterious carved figures. Most of the pioneering work was carried out by the English physician and physicist Thomas Young, and the French scholar Jean François Champollion. As a result of their breakthroughs, scholars were at last able to piece together the history of a long-lost culture.

Just as the Rosetta Stone provided the key to an ancient civilisation, so ESA's Rosetta spacecraft will unlock the mysteries of the oldest building blocks of our Solar System – the comets. As the worthy successor of Champollion and Young, Rosetta will allow scientists to look back 4600 million years to an epoch when no planets existed and only a vast swarm of asteroids and comets surrounded the Sun.

History of cometary missions

International cometary explorer ( ICE )

                                                      International Cometary Explorer (ICE)

Launched on 12 August 1978, ICE achieved the first-ever comet encounter. This NASA spacecraft was originally known as ISEE-3 (International Sun-Earth Explorer). Having completed its original mission, it was reactivated and diverted to pass through the tail of Comet Giacobini-Zinner on 11 September 1985, coming within approximately 7860 kilometres of the comet at closest approach. It also flew through the tail of Comet Halley on 28 March 1986, at a distance of 31 million kilometres from the comet's nucleus.

Although NASA officially ceased contact with ICE in 1997, on 29 May 2014 a group named the ISEE-3 Reboot Project reestablished two-way communication with the spacecraft, finding it to still be in good working order.

Vega 1 and Vega 2

Launched on 15 and 21 December 1984, these two Russian probes each left a lander on the surface of Venus as they flew past it in June 1985 on the way to investigate and photograph Comet Halley.

Vega-1 made its closest approach to the comet on 6 March 1986 at a distance of 8890 kilometres. Vega-2 flew in closer to the comet nucleus at a distance of 8030 kilometres on 9 March 1986.

Sakigake and suisei

Launched on 7 January 1985 and 18 August 1985, these twin spacecraft were Japan’s first deep-space missions and aimed to explore comet Halley on its journey into the inner Solar System in 1986.

Suisei approached to within 151 000 kilometres of Comet Halley on 8 March 1986 to observe its interactions with the solar wind. Sakigake approached to within seven million kilometres of the comet on 11 March 1986.

Giotto

Launched 2 July 1985, ESA’s Giotto was the first European deep space mission. This spacecraft obtained the closest pictures ever taken of a comet.

Giotto flew past the nucleus of Comet Halley at a distance of less than 600 kilometres on 13 March 1986.

Images showed a black, potato-shaped object with active regions which were firing jets of gas and dust into space. Giotto then became the first spacecraft to visit two comets when it passed within 200 kilometres of Comet Grigg-Skjellerup on 10 July 1992.

Giotto was placed in hibernation on 23 July 1992, and the spacecraft has since been inactive. Giotto returned to the vicinity of the Earth on 1 July 1999. The distance of its closest approach was very uncertain, the estimate being about 220 000 kilometres, just over half the Earth-to-Moon distance. No communication with the spacecraft took place at this time.

Giotto will continue to orbit the Sun for the foreseeable future, completing six revolutions roughly every seven years.

Deep space 1

This was the first spacecraft in NASA’s New Millennium programme. Launched on 24 October 1998, its primary mission was to test 12 new advanced technologies. It approached within 26 kilometres of Asteroid 9969 Braille on 29 July 1999.

The few pictures returned showed that Braille's longest side is about 2.2 kilometres across and its shortest side appears to be about one kilometre. In an extended mission, Deep Space 1 encountered Comet Borrelly on 22 September 2001 and returned images and other science data. The spacecraft was retired on 18 December 2001.

Stardust

Launched 7 February 1999, this NASA mission travelled into the cloud of ice and dust that surround the nucleus of Comet Wild 2, coming to within 240 kilometres (150 miles) of the nucleus itself on 2 January 2004. There, it gathered comet dust particles and delivered them back to Earth in 2006.

In an extended mission phase known as Stardust-NExT (New Exploration of Tempel 1), the spacecraft visited Comet Tempel 1 in 2011, the comet that was the target of the Deep Impact mission (see below).

Contour ( comet nucleus tour)

Launched on 3 July 2002, Contour was a NASA mission to improve our understanding of comet nuclei. Encounters were planned with two comets.

The spacecraft remained in orbit around the Earth until 15 August 2002, when it began manoeuvres to move onto a heliocentric, comet-chasing orbit. NASA controllers were not able to re-establish contact with the spacecraft following this and concluded that Contour was lost.

Deep impact

NASA's Deep Impact mission launched on 12 January 2005. It consisted of two craft. The main spacecraft performed a flyby of Comet Tempel 1 and recorded images and data. The second craft was the ‘impactor’, which was propelled into a target site on the comet in July 2005. The impact excavated debris from the comet, allowing the main spacecraft to analyse the composition of surface and interior materials of a comet.

In an extended mission phase, Deep Impact was reassigned as EPOXI, a combination of two missions: DIXI, Deep Impact Extended Investigation Mission, and EPOCh, Extrasolar Planet Observation and Characterisation. The EPOCh phase was carried out en route to Comet Hartley 2, which it flew past on 4 November 2010.

EPOXI went on to observe Comet Garradd from afar in February and April of 2012, studying its orbit and surface activity. In February 2013 the spacecraft also observed Comet ISON.

NASA lost contact with the probe in August 2013, and ceased attempts to re-establish communications the following month.

Rosetta

ESA's Rosetta mission was launched on 2 March 2004. It has spent ten years in space, passed by two asteroids (2867 Steins in 2008 and 21 Lutetia in 2010) and will reach Comet 67P/Churyumov-Gerasimenko in 2014. Rosetta will follow the comet as it orbits around the Sun, and will be the first mission to attempt a landing onto a comet nucleus.

Why