After a journey of more than seven years, Nasa has confirmed that its Dawn spacecraft has successfully entered orbit around the dwarf planet Ceres – the first spacecraft ever to orbit a dwarf planet. The historic moment occurred today at 12.39pm GMT (7.39am EST).
Dawn was about 38,000 miles (61,000km) from Ceres when it was captured by its gravity, with a signal confirming that Dawn was healthy and its ion engine was thrusting – indicating it was in orbit.
‘Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet,’ said Dr Marc Rayman, Dawn chief engineer and mission director at JPL.
‘Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home.’
The mission will allow scientists to study the last major body between Earth and Jupiter that has yet to be explored.
While we won’t see any images for a few weeks, as the spacecraft will be on the dark side of the planet, the event will signal the start of more than a year of observations as the spacecraft spirals in closer and closer over the coming months.
And, crucially, we might finally discover what those two mystery bright spots on the surface are.
‘The mission is so exciting, because we’re exploring the last uncharted world of the solar system,’ Dr Rayman told MailOnline.
‘For me the opportunity to travel to this distant alien world that has been known of for two centuries, a mysterious world of rock and ice, perhaps with subsurface liquid water maybe stored as ponds, lakes or oceans, is very exciting.’
Ceres is actually Dawn’s second encounter, having orbited the large asteroid Vesta from 2011 to 2012. It is the first spacecraft to visit two separate significant bodies in the solar system in a single mission.
‘It happens in sci-fi all the time, go to a planet, beat somebody up or make out with them and then go somewhere else, but the reality is that such a mission is far beyond the capability of conventional chemical propulsion,’ Dr Rayman continued.
‘But Dawn is able to do this thanks to its advanced ion propulsion.’
To enter orbit around Ceres, Dawn fired its ion thruster to gently allow it to be captured by the dwarf planet’s gravity.
Ion propulsion is a form of electric propulsion that generates thrust by accelerating ions. Its bonus over regular chemical propulsion is it requires less fuel, and it can accelerate and decelerate over longer periods of time.
However, the amount of thrust ion propulsion produces is incredibly small – equivalent to the force of a piece of paper resting on your hand – so the engine must run continuously for weeks, months or even years to generate significant thrust.
This is what Dawn has been doing for the past few years, as it neared its encounter with the dwarf planet. When it was close enough, the gravity of the planet grabbed the small vehicle, which will now allow it to slowly spiral inwards to a tighter and tighter orbit over the next few months.
As the spacecraft and planet are moving rather sedately compared to each other, about 100mph (160km/h) difference in speed (39,000mph or 63,000km/h in total), there was little opportunity for anything to go wrong with the capture.
‘It’s always possible for something to go wrong, it’s a complex probe in the depths of space, always possible for a glitch or anomaly to occur. However, it is pretty straightforward,’ said Dr Rayman.
As the spacecraft entered orbit on the ‘dark’ side of the planet – with the other side illuminated by the sun – it won’t be taking any new images for a few weeks, until around 10 April, except for maybe a few of the dwarf planet in darkness.
By 10 April, scientists at Nasa in California are expecting Dawn to return images 9.6 times better than anything possible than Hubble.
Four days later, the spacecraft will return images that are 14 times better as it makes its closest approach to the dwarf planet so far – a distance of just 14,000 miles (22,000km).
The most impressive images, though, will begin to be returned in December of this year – when Dawn begins its scientific orbit around the planet.
It will be at an altitude of just 225 miles (360km) above the surface – below the orbital height of the International Space Station around Earth – allowing it to get high resolution images of the surface.
The primary science mission for the spacecraft will last until June 2016 – by which the team expects to have achieved all of its scientific goals -and it is unlikely the spacecraft will be extended beyond that date, as it will probably start running out of fuel by then.
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