Scientists at the European Space Agency were delighted this week as the robotic comet lander Philae phoned home, after seven months in hibernation.

Its survival, from what was thought to be an unfortunate touchdown in a shadowed area, could extend the life of the lander well beyond expectations.

Last November, the Rosetta spacecraft, which had made a historic rendezvous with comet 67P, released Philae for the first-ever attempt to land on one of these icy bodies. The attempt succeeded, but not where and when they intended it to land.

Due to the extremely low gravity on the comet (where a human would weigh about as much as the ink in a ballpoint pen), Philae was equipped with grappling gear to prevent itself from bouncing back off the surface.

The grappling gear didn't work, for whatever reason, so the lander bounced, and bounced, and bounced, in high, slow-motion arcs that carried it into the shadow of a cliff - such as that one of its three legs got caught on a rock or a ledge, leaving it tilted at a crazy angle.

Stuck in the shadows

In deep space, shadows are very dark and cold places, where the temperatures can drop to -150ºC. That's bad news for batteries and even worse for solar panels that charge those batteries. So, after 60 hours of taking a few photos and conducting as much science as it could, Philae put itself into hibernation, with only a small chance that it would wake up again when the comet got closer to the sun and the shadow moved back.

Thanks to good planning and a robust design, Philae preserved enough energy in its batteries to protect its instruments from the extreme cold. So, when nature did its part and brought the sun back, Philae was able to phone home and, hopefully, will now resume its scientific investigation.

Philae on comet surface

Data sent back to Earth by Philae, seen in an artist's impression, suggests that the surface of Comet 67P/Churyumov-Gerasimenko is covered in a layer of dust 10 to 20 centimetres thick. Underneath that is a hard surface of ice or ice and dust mixed together. ( ESA/AOES Medialab)

As it turns out, had Philae landed in the sunny spot where it was supposed to, it would have been cooked by now. With no air to spread heat around, temperatures in deep space on a surface in constant sunlight can soar to 150ºC.

So, Philae would have completed its scientific investigation back in November or December when the comet was less active than it is now. By surviving in the shadow for more than half a year, Philae is now waking up when activity on the comet is much higher as it nears the sun for its closest encounter in August.

If it restores itself to full function, we could see some spectacular pictures from the surface, as the ices in the comet vaporize and rise up into space. Perhaps a drill on the belly of the lander will get a direct sample of the comet for analysis. Whatever happens, it will all be a bonus.

In other words, a great benefit could come out of what was thought by many to be a failure.

A history of lucky accidents

Lucky accidents are common in science. In fact, they have been directly responsible for many new discoveries.

In 1929, Alexander Fleming noticed a mould in a culture dish containing staphylococcus bacteria and saw that the area around the mould was clear. He went on to win the Nobel Prize for the discovery of penicillin. 

Radio astronomy was born out of an annoying noise that was regularly interfering with a large radio antenna being developed for transatlantic communications by Bell Labs. Technician Karl Jansky discovered that the stray signals were coming from the Milky Way, and a whole new window on the universe opened up.

By some estimates, at least 30 per cent of scientific discoveries were made by accident, including an unexpected side effect of a drug designed to dilate blood vessels for the treatment of angina, or chest pain. The drug is called Viagra.

But it takes more than luck to appreciate lucky accidents. It takes keen observation and an appreciation for the subject.

As Louis Pasteur said, "Chance favours only the prepared mind."  

The scientists at the European Space Agency are prepared for Philae's wake-up and are looking forward to the encounter with the sun this August. There is much more to come.