Comets are the icy remnants of the phase of planet building in our solar system, some 4.5 billion years ago. Thousands of them have been seen orbiting our sun and hundreds have been studied by Earth-based astronomers. From these measurements we know that a large proportion of a comet is made of water-ice. This turns to vapour when heated by the sun, producing a transient atmosphere around the comet together with microscopic “dust” particles, eventually flowing into the the tails for which they are so well known.
Not only are comets fascinating bodies in their own right, they may also be the original source of much of the water on our planet. Many lines of research point to a hot, dry Earth in the early days of the solar system. While it is possible that some water was released from the Earth’s interior at this time, the suspicion has always been that comets delivered the rest when crashing into Earth.
Visiting a comet
We have been afforded a clearer picture of the composition and physical evolution of comets since 1986 when the European Space Agency sent the Giotto spacecraft to study Halley’s Comet. Several others have followed, but all have only provided fleeting glimpses. Now the robotic Rosetta spacecraft is carrying out the first proper rendezvous with a comet.
Rosetta launched in 2004 and completed three fly-bys of Earth and one of Mars en route to its destination. On August 6 this year it matched trajectories with comet 67P/Churyumov-Gerasimenko and arrived within 100 km of the icy nucleus. Since then European and American scientists have analysed the 4 km-long body via optical and infra-red imaging, and sampled the gas and small solid particles – comet dust – being released from its surface. The onboard spectrographs, mass-spectrometers, microscopes and plasma sensors have been used to characterise the nucleus of the comet and the material it is already releasing while still more than 402m km from the sun.
The first attempted landing on the surface of a comet is a huge landmark in the history of space exploration that will not only uncover further details about comets but could unlock further clues about the origins of our solar system and the development of life on Earth.
Comets are the icy remnants of the phase of planet building in our solar system, some 4.5 billion years ago. Thousands of them have been seen orbiting our sun and hundreds have been studied by Earth-based astronomers. From these measurements we know that a large proportion of a comet is made of water-ice. This turns to vapour when heated by the sun, producing a transient atmosphere around the comet together with microscopic “dust” particles, eventually flowing into the the tails for which they are so well known.
Not only are comets fascinating bodies in their own right, they may also be the original source of much of the water on our planet. Many lines of research point to a hot, dry Earth in the early days of the solar system. While it is possible that some water was released from the Earth’s interior at this time, the suspicion has always been that comets delivered the rest when crashing into Earth.
Visiting a comet
We have been afforded a clearer picture of the composition and physical evolution of comets since 1986 when the European Space Agency sent the Giotto spacecraft to study Halley’s Comet. Several others have followed, but all have only provided fleeting glimpses. Now the robotic Rosetta spacecraft is carrying out the first proper rendezvous with a comet.
Rosetta launched in 2004 and completed three fly-bys of Earth and one of Mars en route to its destination. On August 6 this year it matched trajectories with comet 67P/Churyumov-Gerasimenko and arrived within 100 km of the icy nucleus. Since then European and American scientists have analysed the 4 km-long body via optical and infra-red imaging, and sampled the gas and small solid particles – comet dust – being released from its surface. The onboard spectrographs, mass-spectrometers, microscopes and plasma sensors have been used to characterise the nucleus of the comet and the material it is already releasing while still more than 402m km from the sun.
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