As the dusts settles (quite literally) around the landing of the Philae probe, scientists have confirmed that craft didn’t touch down just once – it actually bouncedon the surface of the comet twice.

But what’s happening here? Since when did spacecraft bounce?

Well, it’s all down to the comet's gravity. 67P/Churyumov-Gerasimenko may be an icy mass the size of a mountain, but gravity is an incredibly weak force (you overcome it every time you get out of bed in the morning) and it only really becomes noticeable with huge, planetary masses.

The comet's gravity is actually several hundred thousand times weaker than that on Earth and, to make matters worse, the uneven shape of the comet means that even this force varies over its surface.

Its gravity is so weak that scientists working on the Philae lander had to take account of the fact that even the slightest movement on the craft – say, adjusting a camera to look left or right – could be enough to lift it off the surface.

An artist's impression of the lander. It looks sturdy, but it essentially weighs just grams thanks to the low gravity. (Getty Images)

To compensate for this they put thrusters on the top of the craft to push it into the surface (unlike the Curiosity rover which had thrusters on the bottom to stop it from slamming into Mars) as well as pair of harpoons and three ice screws to secure it in place once it was near enough.

Unfortunately, this is where things went wrong: the thrusters and harpoons failed for unknown reasons and consequently Philae rebounded.

Not hard (the craft was only travelling at a leisurely one metre per second) but enough to keep it airborne for several hours -imagine the lander barely moving as it floats hundreds of metres above the surface, attached by only a thin thread of gravity.

Thankfully, however, Philae has now definitely landed, although there’s still some concern about its long term prospects without harpoons to secure it in place.

In pictures: European Space Agency's Rosetta mission Show all 22 1 /22 In pictures: European Space Agency's Rosetta mission In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Image of Comet 67P/CG taken by the Philae lander from a distance of approximately 3km from the surface In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Rosetta's lander Philae took this parting shot of its mothership shortly after separation In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Parting shot of the Philae lander after separation, captured by one of Rosetta's cameras In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission A technician celebrates after the successful landing of the Philae lander, in the control room at the ESA headquarters in Darmstadt Reuters In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Scientists celebrate at a mission observation centre in Toulouse, southern France as they receive information that Philae has landed on the Churyumov-Gerasimenko comet AP In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Astronomer Klim Ivanovych Churyumov, who discovered the comet 67P/ Churyumov-Gerasimenko in 1969, reacts after the successful landing of the Philae lander on the comet Reuters In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission A model demonstrates how the landing device Philae, of the space probe Rosetta, stands on the comet 67P/Churyumov-Gerasimenko at the press center of the satellite control center of the European Space Agency in Darmstadt, Germany EPA In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission An artist impression of Rosetta's lander Philae on the surface of comet Getty Images In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Picture taken on October 28 by the navigation camera on Rosetta shows the boulder-strewn neck region of comet 67/P Churyumov-Gerasimenko. It was captured from a distance of 9.7 km from the center of the comet Getty Images In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Picture taken on October 24 shows a raised plateau on the larger lobe of the comet Getty Images In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission The probe is supposed to fly to a comet and put down a small laboratory on the top of it In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission A scientist from the European Space Agency with an airworthy copy of space probe 'Rosetta' in the control center in Darmstadt, Germany In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Maneuvers designed for the actual space probe are simulated with the replica. 'Rosetta' will be woken up from an energy saving hibernation after 957 days In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission A European Space Agency employee sits in the control room for the Rosetta mission in Darmstadt, Germany In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Scientists at the European Space Agency are expecting their comet-chasing probe Rosetta to wake from almost three years of hibernation In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Europe's Rosetta probe on a NASA mission In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission NASA is participating in the European Space Agency's Rosetta mission, whose goal is to observe one such space-bound icy dirt ball from up close for months on end In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission An impression of the Philae lander In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission ESA probe Rosetta with Mars in the background. The three-tonne probe blasted off aboard an an Ariane V rocket from Kourou, French Guiana in 2004 In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov–Gerasimenko, the spacecraft measures 32 m across including the solar arrays, while the comet nucleus is thought to be about 4 km wide In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission The spacecraft, festooned with 25 instruments between its lander and orbiter (including three from NASA), is programmed to 'wake up' from hibernation In pictures: European Space Agency's Rosetta mission European Space Agency's Rosetta mission An Ariane V carrying the three-tonne probe Rosetta blasting off from Kourou, beginning a decade-long quest to hunt a comet in the depths of the Solar System and shadow it around the Sun in a bid to tease out secrets of how life began on Earth