Yesterday, after ten years of chasing, the European Space Agency’s (ESA) Rosetta spacecraft became the first ever to intercept and go into orbit around a comet. Now scientists can begin the next step in one of the most exciting investigations into how the Solar System formed that we’ve seen so far.
ESA scientists brought Rosetta to within 100km of the comet – a 3km by 5km rock called 67P Churyumov-Gerasimenko – and established a stable orbit by slowing it down with its thrusters. Perhaps surprisingly, while it’s taken ten years to get there, 67P was only discovered 50 years ago, but while not as famous a comet as Halley it’s just as scientifically interesting. Comets are considered to be primitive building blocks of the Solar System, and relics of the formation of the planets, while some even believe that they provided Earth with both water and other key ingredients too which were necessary for igniting the evolution of life.
67P was first discovered in 1969 by Soviet astronomers Ivanovych Churyumov and Svetlana Ivanova Gerasimenko. The hope is that Rosetta will unlock the secrets of this early history – which is why it was named after the Rosetta Stone, the discovery of which in 1799 provided the key to translating Ancient Egyptian hieroglyphs and Demotic script into Ancient Greek (and thus any other language). It was launched from Europe’s spaceport in Kourou, French Guiana, in March 2004, into a long journey of loops around the Sun as it aimed to get onto the same trajectory as 67P.
Rosetta has trekked over 6bn km, passing by Earth three times, Mars once, and soaring past two asteroids, using the gravitational pull of those objects to change velocity and catch up with 67P. The riskiest part of this was when it was put into hibernation mode for 31 months to conserve power as its orbit brought it out to a distance roughly equal to the orbit of Jupiter and then back in again – where it was successfully awakened in January of this year, for the final part of the voyage.
Since May, Rosetta has performed a series of ten rendezvous manoeuvres to gradually fine-tune the spacecraft’s speed and trajectory to match those of the comet, which travels through space at speeds of up to 135,000km/h. Despite the unprecedented complexity of the mission, Rosetta’s smooth arrival was confirmed yesterday morning.
Here’s a video from the ESA showing Rosetta’s near-decade-long journey, and here’s how it’s going to orbit around 67P closer and closer:
The spacecraft now has quite the adventure to come, edging closer to the comet over the next six weeks in two triangular-shaped trajectories, first from a distance of 100km and then at 50km. Depending on the activity of the comet, it will further attempt a near-circular orbit from a distance of 30km, simultaneously scrutinising the comet’s surface for a suitable landing site for its small lander probe – Philae, named after an obelisk that was also used to decipher Egyptian hieroglyphs in the 19th century.
Philae will, sometime in November, detach from the main body of the spacecraft and anchor itself to the surface of the comet with a high-powered harpoon. Meanwhile, Rosetta will spend the next 18 months analysing the comet from every angle, retrieving crucial data enabling scientists to investigate how planets were created. The spacecraft will also accompany the comet around the Sun as it moves back out towards the orbit of Jupiter.
The mission has some similarities with Japan’s 2005 Hayabusa mission, which rendezvoused with and landed on an asteroid named Itokawa. It was meant to scoop up material from the asteroid’s surface, and return it to Earth for study – those samples arrived in 2010, but we know that its capture mechanism malfunctioned. To this day, there is some uncertainty as to whether the capsule managed to successfully collect the asteroid rock fragments.
The Rosetta mission is significantly more complex, too – while both Itokawa and 67P have miniscule gravitational pull, the former’s orbit around the Sun is relatively simple, and Hayabusa simply chased Itokawa closely around the Sun in the same orbit. Rosetta will, by reducing its speed to less than a metre per second, genuinely orbit 67P. As the comet moves towards the Sun and heats up, there are also likely to be gas and dust particles shed off into space to form its tail – and initial photographs sent to us by Rosetta, the clearest ever of a comet, do show some emissions already.
Yesterday, the elated ESA science and mission control experts celebrated the long awaited arrival, jokingly describing it as being similar to arriving at “Scientific Disneyland”. The arrival was streamed live on the ESA’s website, and Rosetta is already sending back incredible high-resolution images of the surface of 67P. So far, it looks a lot rockier and more solid than expected – less like a “dirty snowball”, and more like an asteroid.
Around the internet, there was excitement at the arrival of Rosetta. The hashtag #RosettaAreWeThereYet flooded Twitter, as people from all over the world eagerly awaited the news, like impatient school kids – even the Philae lander’s own Twitter account got involved:
— Philae Lander (@Philae2014) August 6, 2014
But it didn’t stop there – after Rosetta finally reached its destination, even former Star Trek captain William Shatner joined the fun by engaging in playful chitchat, checking on operations with the Nasa and ESA Twitter account.
— NASA (@NASA) August 2, 2014
— ESA (@esa) August 6, 2014
Although we know what the comet looks like from the outside, we don’t know what it looks like from the inside, and that’s what Rosetta and Philae will be uncovering over the next few months – as long as they have enough power from the craft’s huge solar panels, that is, as unlike most probes that venture out past the orbit of Mars, it has no onboard nuclear generator.
As one mission controller explained, Rosetta is going to finally “unlock the treasure chest of our own history”.