This article is from the source 'bbc' and was first published or seen on . It will not be checked again for changes.

You can find the current article at its original source at http://news.bbc.co.uk/go/rss/-/1/hi/sci/tech/7015259.stm

The article has changed 4 times. There is an RSS feed of changes available.

Version 1 Version 2
Asteroid mission gets its chance Successful launch for Nasa probe
(about 2 hours later)
Nasa's Dawn mission to the asteroid belt is set for an imminent further launch attempt, after giving up its previous slot to a Mars probe. Nasa's Dawn space probe has begun an eight-year journey to the Solar System's asteroid belt.
The US spacecraft, which will visit the small worlds of Ceres and Vesta, will launch atop a Delta rocket from the Cape Canaveral Airforce Station. The US spacecraft, which will visit the small worlds of Ceres and Vesta, blasted-off at 1134 GMT (1234 BST) from the Cape Canaveral Airforce Station.
Its journey of eight years and nearly five billion kilometres will help decipher how the Solar System formed. The probe's journey of nearly five billion kilometres will hopefully help scientists decipher how the Solar System formed.
The asteroids are thought to be the leftovers after the planets were made.The asteroids are thought to be the leftovers after the planets were made.
Dawn will reach Vesta in 2011 before going on to visit Ceres in 2015. Dawn will reach Vesta in 2011 before going on to visit Ceres in 2015.
See Dawn's mission profileSee Dawn's mission profile
Ceres is almost spherical and is thought to harbour a layer of water ice some 60 to 120km (40 to 80 miles) thick beneath its hard surface.Ceres is almost spherical and is thought to harbour a layer of water ice some 60 to 120km (40 to 80 miles) thick beneath its hard surface.
At a meeting of the International Astronomical Union (IAU) last year, Ceres was elevated in status from merely the biggest body in the asteroid belt to a "dwarf planet" - the same designation now held by Pluto.At a meeting of the International Astronomical Union (IAU) last year, Ceres was elevated in status from merely the biggest body in the asteroid belt to a "dwarf planet" - the same designation now held by Pluto.
CERES AND VESTA At 930km (580 miles) across, Ceres (L) is the biggest object in the asteroid beltIt is almost spherical and is classed as a dwarf planetVesta (R) is 525km (326 miles) across and has been resurfaced by volcanic flowsCeres is thought to have an icy layer beneath its dusty surface; Vesta was resurfaced by ancient lava flowsPieces of Vesta have fallen to Earth as meteorites Vesta is very different. It is devoid of any water and appears to have been resurfaced by ancient lava flows.CERES AND VESTA At 930km (580 miles) across, Ceres (L) is the biggest object in the asteroid beltIt is almost spherical and is classed as a dwarf planetVesta (R) is 525km (326 miles) across and has been resurfaced by volcanic flowsCeres is thought to have an icy layer beneath its dusty surface; Vesta was resurfaced by ancient lava flowsPieces of Vesta have fallen to Earth as meteorites Vesta is very different. It is devoid of any water and appears to have been resurfaced by ancient lava flows.
Of particular interest is the giant crater - 460km (285 miles) across and 13km (eight miles) deep - at the object's southern pole. The massive collision that created this crater gouged out 1% of the asteroid's volume. Many of the meteorites that have fallen to Earth are thought to have originated in this space smash.Of particular interest is the giant crater - 460km (285 miles) across and 13km (eight miles) deep - at the object's southern pole. The massive collision that created this crater gouged out 1% of the asteroid's volume. Many of the meteorites that have fallen to Earth are thought to have originated in this space smash.
"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn's principal investigator, Christopher Russell, of the University of California, Los Angeles."Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn's principal investigator, Christopher Russell, of the University of California, Los Angeles.
"One is rocky, and is representative of the building blocks that constructed the planets of the inner Solar System; the other may very well be icy, and represents the outer planets."One is rocky, and is representative of the building blocks that constructed the planets of the inner Solar System; the other may very well be icy, and represents the outer planets.
"Yet, these two very diverse bodies reside in essentially the same neighbourhood. It is one of the mysteries Dawn hopes to solve.""Yet, these two very diverse bodies reside in essentially the same neighbourhood. It is one of the mysteries Dawn hopes to solve."
The mission's objectives include:The mission's objectives include:
  • study internal structure and density
  • determine size, composition, shape and mass
  • examine surface features and craters
  • understand the role of water in controlling asteroid evolution
  • study internal structure and density
  • determine size, composition, shape and mass
  • examine surface features and craters
  • understand the role of water in controlling asteroid evolution
Dawn is expected to send back high-resolution images of these worlds, showing not just craters but also mountains, canyons, and clear evidence of volcanism.Dawn is expected to send back high-resolution images of these worlds, showing not just craters but also mountains, canyons, and clear evidence of volcanism.
Dawn will make a fly-past of Mars on its long journey. The spacecraft will orbit Vesta for about nine months, and Ceres for at least five months. The mission is scheduled to end in July 2015.Dawn will make a fly-past of Mars on its long journey. The spacecraft will orbit Vesta for about nine months, and Ceres for at least five months. The mission is scheduled to end in July 2015.
Visiting two objects and orbiting both is a capability that is only now becoming possible through the development of solar-electric engines.Visiting two objects and orbiting both is a capability that is only now becoming possible through the development of solar-electric engines.
Unlike the chemical rockets of yesteryear which gave probes a short, sharp impulse, the new generation of ion thrusters provide gentle but sustained propulsion. They work by ejecting charged atoms (ions) of xenon.Unlike the chemical rockets of yesteryear which gave probes a short, sharp impulse, the new generation of ion thrusters provide gentle but sustained propulsion. They work by ejecting charged atoms (ions) of xenon.
They take time to build up speed - hence Dawn's long mission profile - but they are very efficient and flexible, allowing spacecraft to hop from target to target.They take time to build up speed - hence Dawn's long mission profile - but they are very efficient and flexible, allowing spacecraft to hop from target to target.
Click here to returnClick here to return