Extract from The Guardian
Comet 67P/ Churyumov-Gerasimenko, shadowed by the Rosetta spacecraft,
will make its closest approach to the sun at 3.03 am BST on Thursday
morning
Mission scientists have prepared the Rosetta
spacecraft for a cosmic fireworks display as it chaperones the speeding
comet 67P/ Churyumov-Gerasimenko through its closest encounter with the
sun.
Barrelling through space at 120,000 kilometres per hour, the comet and orbiting Rosetta probe will streak past the sun at 3.03am BST on Thursday morning, before heading back out to the deeper reaches of the solar system.
The moment represents a landmark in space exploration as the Rosetta mission becomes the first to shadow a comet as it stirs from its dormant state and starts to spew tonnes of gas and dust, sometimes in the form of spectacular, explosive blasts.
The comet will not exactly graze the sun. It will tear past our home star at a distance of 186 million kilometres, which is farther away than the Earth’s orbit of 150 million kilometres. But even from that far away, the comet will be bathed in ten times more solar energy than it was last year, making its frigid surface billow with gas and dust.
“It’s a huge milestone for the mission,” Andrea Accomazzo, Rosetta’s flight director, told the Guardian. “We are not flying that close to the sun, but for the comet, it’s a massive change.”
Cameras on the spacecraft will take images more rapidly as the comet swings around the sun in the hope of capturing huge blasts that shower material into space. The most dramatic blast yet happened two weeks ago when a violent jet erupted from the comet’s neck for several minutes, sending up a bright plume of debris at ten metres per second. “It was impressive,” said Accomazzo. “We can expect to see more of these fireworks now.”
Rosetta caught up with the 4.5km wide comet in August last year when it was still 500 million kilometres from the sun. As it sped closer, the sun’s radiation warmed ices on the comet, making them sublimate into gases that dislodged dust as they departed. In the past, underground ice has vaporised and punched through the comet’s crust in some regions, leaving the surface pocked with giant sinkholes.
Flying Rosetta around the active comet has been a learning curve in itself. The gases that waft off the comet push the spacecraft around, and its trajectory needs constant adjustment to ensure Rosetta’s instruments are pointing at the comet. Then there is the dust. It blinds Rosetta’s star tracker, which tells the spacecraft how to orient itself to beam data back to Earth. To escape the worst of the dust clouds, Rosetta recently retreated to a safe distance of 300km.
The closest approach to the sun, known as the perihelion, is when the comet receives the most sunlight during its 6.5 year orbit. But the comet will continue to warm for several weeks yet, just as the hottest days of summer follow the longest day of the year.
The comet is already shedding a tonne of dust and 300kg of water vapour and other gases every second. If that amount was lost evenly from the whole surface of the comet, the ground would fall a metre every time it passed the sun. In reality, because of variations in the surface, some regions will lose more than others. The comet is unlikely to shed material more quickly over the next month, but it could erupt with more violent explosions.
“We are hoping for more jets,” said Nicolas Altobelli, deputy project scientist on the Rosetta mission. “They are very spectacular and could be a way to get material from the interior of the comet to analyse.”
Scientists on the team have their eyes on a 500 metre-long crack that runs around part of the comet’s neck. How it got there is unclear. It may be a join from when two hunks of dusty ice joined together to form the strange rubber duck-shaped comet in the first place. Or it may be a stress fracture that deepens when the comet becomes more active.
Accomazzo says the odds of the comet breaking in two along the crack are minimal, but scientists cannot rule out the possibility. Altobelli finds the idea tantalising. “Maybe we will be lucky and the comet will split in half,” he said. “That would be a nightmare for some of my colleagues, but scientifically we’d get to see material from the inside of the comet.”
Such dramatic events aside, researchers are keen to see how the surge in activity resculpts the comet’s surface. When the dust and gas calm down in February next year Rosetta is expected to fly closer in, for the first time revealing the aftermath of a comet’s closest encounter with the sun.
The small Philae lander that became the first to touch down on a comet in November last year fell silent in July and has not called home since. Stuck at an angle, with one leg in the air, the ground beneath its remaining feet is slowly disappearing.
Barrelling through space at 120,000 kilometres per hour, the comet and orbiting Rosetta probe will streak past the sun at 3.03am BST on Thursday morning, before heading back out to the deeper reaches of the solar system.
The moment represents a landmark in space exploration as the Rosetta mission becomes the first to shadow a comet as it stirs from its dormant state and starts to spew tonnes of gas and dust, sometimes in the form of spectacular, explosive blasts.
The comet will not exactly graze the sun. It will tear past our home star at a distance of 186 million kilometres, which is farther away than the Earth’s orbit of 150 million kilometres. But even from that far away, the comet will be bathed in ten times more solar energy than it was last year, making its frigid surface billow with gas and dust.
“It’s a huge milestone for the mission,” Andrea Accomazzo, Rosetta’s flight director, told the Guardian. “We are not flying that close to the sun, but for the comet, it’s a massive change.”
Cameras on the spacecraft will take images more rapidly as the comet swings around the sun in the hope of capturing huge blasts that shower material into space. The most dramatic blast yet happened two weeks ago when a violent jet erupted from the comet’s neck for several minutes, sending up a bright plume of debris at ten metres per second. “It was impressive,” said Accomazzo. “We can expect to see more of these fireworks now.”
Rosetta caught up with the 4.5km wide comet in August last year when it was still 500 million kilometres from the sun. As it sped closer, the sun’s radiation warmed ices on the comet, making them sublimate into gases that dislodged dust as they departed. In the past, underground ice has vaporised and punched through the comet’s crust in some regions, leaving the surface pocked with giant sinkholes.
Flying Rosetta around the active comet has been a learning curve in itself. The gases that waft off the comet push the spacecraft around, and its trajectory needs constant adjustment to ensure Rosetta’s instruments are pointing at the comet. Then there is the dust. It blinds Rosetta’s star tracker, which tells the spacecraft how to orient itself to beam data back to Earth. To escape the worst of the dust clouds, Rosetta recently retreated to a safe distance of 300km.
The closest approach to the sun, known as the perihelion, is when the comet receives the most sunlight during its 6.5 year orbit. But the comet will continue to warm for several weeks yet, just as the hottest days of summer follow the longest day of the year.
The comet is already shedding a tonne of dust and 300kg of water vapour and other gases every second. If that amount was lost evenly from the whole surface of the comet, the ground would fall a metre every time it passed the sun. In reality, because of variations in the surface, some regions will lose more than others. The comet is unlikely to shed material more quickly over the next month, but it could erupt with more violent explosions.
“We are hoping for more jets,” said Nicolas Altobelli, deputy project scientist on the Rosetta mission. “They are very spectacular and could be a way to get material from the interior of the comet to analyse.”
Scientists on the team have their eyes on a 500 metre-long crack that runs around part of the comet’s neck. How it got there is unclear. It may be a join from when two hunks of dusty ice joined together to form the strange rubber duck-shaped comet in the first place. Or it may be a stress fracture that deepens when the comet becomes more active.
Accomazzo says the odds of the comet breaking in two along the crack are minimal, but scientists cannot rule out the possibility. Altobelli finds the idea tantalising. “Maybe we will be lucky and the comet will split in half,” he said. “That would be a nightmare for some of my colleagues, but scientifically we’d get to see material from the inside of the comet.”
Such dramatic events aside, researchers are keen to see how the surge in activity resculpts the comet’s surface. When the dust and gas calm down in February next year Rosetta is expected to fly closer in, for the first time revealing the aftermath of a comet’s closest encounter with the sun.
The small Philae lander that became the first to touch down on a comet in November last year fell silent in July and has not called home since. Stuck at an angle, with one leg in the air, the ground beneath its remaining feet is slowly disappearing.
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