The Rosetta spacecraft is due to wake up on the morning of January 20 after a 30-month hibernation in deep space. For the past ten years, the 3-tonne spacecraft has been on a one-way trip to a 4km-wide comet. When it arrives, it will set about performing a manoeuvre that has never been done before: landing on a comet’s surface.
The spacecraft has already achieved some success on its long journey through the solar system. It has passed by two asteroids, Steins in 2008 and Lutetia in 2010, and tried out some of its instruments on them.
Because Rosetta’s journey is so protracted, preserving energy has been of utmost importance, which is why it was put into hibernation in June 2011. The journey has taken so long because the spacecraft needed to be “gravity-assisted” by many planets in order to reach the necessary velocity to match the comet’s orbit.
When it wakes up, Rosetta is expected to take a few hours to establish contact with Earth, 673 million km away. The scientists involved will wait with bated breath. Dan Andrews, part of a team at the Open University who built one of Rosetta’s on-board instruments, said, “If there isn’t sufficient power Rosetta will go back to sleep and try again later. The wake-up process is driven by software commands already on the spacecraft. It will wake itself up autonomously and spend some time warming up and orienting its antenna towards Earth to ‘phone home’.” If multiple attempts fail to wake Rosetta, it could mean the end of the mission.
Rosetta should reach comet 67P/Churyumov-Gerasimenko in May 2014, at which point it will decelerate to match the speed of the comet. In August 2014 Rosetta will enter orbit around the comet to scout 67P’s surface in search of a landing spot. Then, in November 2014, Rosetta’s on-board lander, Philae, will be ejected from the orbiting spacecraft onto the surface of the comet. There are a lot of things that need to come together perfectly for this to go smoothly, but space endeavours are designed to charter unknown territories and Rosetta will be doing just that.
If Rosetta manages this successfully, it will make history as the first spacecraft to land on the surface of a comet. Success is by no means assured, as scientists have no idea what to expect when Rosetta arrives at the comet. Will the comet’s surface be icy, soft, hard, or rocky? This affects what kind of landing the spacecraft can expect, and whether it will sink into the comet or bounce off. Another problem is that comet 67P is small and has a weak gravitational field, which will make holding the spacecraft on its surface challenging, even after a successful landing.
At a cost of €1 billion (US$ 1.36 billion) it is important we get some value for our money with this mission. To ensure we do, Rosetta was designed to help answer some of the most basic questions about Earth and our solar system, such as where water and life originated, even if the landing doesn’t work out as well as we hope it will.
Comets are thought to have delivered some of the chemicals needed for life, including water to Earth, and possibly other planets. This is why comet ISON, which sadly did not survive its close encounter with the Sun, had created excitement among scientists. If it had survived, it would have been the closest scientists could get to a comet with modern instruments.
Comet ISON’s demise means Rosetta is more important than ever. Without measuring the composition of comets, we won’t fully understand the origin of our planet. Comet 67P is thought to have preserved the very earliest ingredients of the solar system, acting as a small, deep-freeze time capsule. The hope is it will now reveal its long-held secrets to Rosetta.
Andrews said, “It will be the first time a spacecraft will approach a comet and actually stay with it for a prolonged period of time, studying the processes whereby a comet ‘switches on’ as it approaches the Sun.”
Once on the comet’s surface, the Philae lander will deploy instruments to measure different forms of the elements hydrogen, carbon, nitrogen, and oxygen in the comet ice. This will allow scientists to understand the composition of the water and organic components that were collected by the comet 4.6 billion years ago, at the very start of the Solar System.
All this depends on whether Rosetta wakes up on Monday. If it does, like the 2,000-year old stone it has been named after, it will reveal a world that has long fascinated humanity.
Natalie Starkey receives funding from the Science and Technology Facilities Council. She is affiliated with The Open University.