Rosetta spacecraft prepares for celestial rendezvous with comet

AFTER a decade-long trek through the solar system, the Rosetta spacecraft will today land on the surface of a comet.

IN what promises to be a nail-biting event worthy of a Hollywood script, rocket scientists will today attempt the challenging task of trying to land a probe on the surface of a comet.

After a decade long trek through the solar system, the European Space Agency’s spacecraft Rosetta made a historic rendezvous with a comet known as 67P/Churyumov-Gerasimenko in August. The craft is now in orbit just 10km above the comet’s surface. If all goes well, a small probe called Philae will descend from the mother ship and become the first craft to ever survive a landing on a comet.

Made of ancient ice, dust and other materials, comets are objects of scientific curiosity because they have survived virtually intact from the earliest days of the solar system, more than 4.6 billion years ago. Because comets carry water and organic molecules, scientists also hope that the Rosetta mission will provide insights into whether comets could have brought water to Earth and possibly kick-started life here.

“We already have a wealth of data about the comet, but the lander will tell us more about its surface material, such as the composition, strength and hardness,” said Gerhard Schwehm, a former mission manager for Rosetta and currently a consultant to the mission. “We can’t learn that from 10km away.”

INTERACTIVE: Rosetta’s comet rendezvous

The Philae probe, which is the size of a small fridge and weighs about 100kg, will have a ringside seat to a slowly unfolding celestial display. As 67P flies closer to the sun, vast amounts of its icy material will be blasted off its surface and form the comet’s characteristic halo and twin tails.

Later today, a thruster burn will push Rosetta further away until it is about 14 miles from the comet. This is the first tense moment: if the thruster burn goes awry, Rosetta won’t be in the right place to release the lander so that it lands at the desired area of the comet.

According to the plan, Philae will separate from the mother ship at 10:03am Central European Time (8pm AEDT).

The time cited is when an event in space can be known or confirmed on the ground. The actual event would have occurred 28 minutes and 20 seconds earlier, since that is how long it takes for the signal to reach Earth.

Q&A with Dr Matt Taylor, project scientist on the European Space Agency’s Rosetta mission.

Q: Is 67P rotating and will the Philae lander have to account for this during descent and touch down?

A: Yes, it is rotating at a rate of 12.4 hours. We are taking this into account in the descent.

Q: Why is it named after the Rosetta Stone?

A: We consider comets as relics of the early solar system and by studying them we will learn more about the constituents of that system, unlocking those secrets. The Rosetta stone was key to unlocking the secrets of the Egyptian hieroglyphs and ancient Egypt, so we thought it was appropriate and cool to use that name.

Q: How long will the mission take?

A: The mission was launched in 2004. It has taken 10 years to get to the comet and will last until the end of 2015. It may last longer, that depends on how much fuel the orbiter has.

Q: Are there instruments that might shine some light towards the theory that life could possibly originate from comets crashing on planets?

A: The orbiter has instruments that will be investigating whether comets have the building blocks of proteins on them.

Q: Do you want to share some of the obstacles you have encountered and how you overcame them?

A: The mission was planned a long time ago and launched in 2004. Even that was a challenge as it was originally planned to go to a different comet, and to be launched in 2003. However, a launcher issue meant we had to change targets. The next challenge was to get the spacecraft out to the orbit of the comet. You cannot do that directly, you are limited by how much mass you can put in orbit, so we had to go on a long journey, using the gravity of Mars and Earth as slingshots to get us out to the comet. We got so far out that we had to put the spacecraft in sleep mode as it was too far from the sun to have enough power. It came back this year, and we have now rendezvoused with a comet. We will land and then spend over a year with the comet. This in itself is difficult as comets constantly change and evolve and get more active as they get closer to the sun!

Q: How exactly is it going to land?

A: The landing is a challenge too, gravity is much less than on a planet. It is a 100,000th that of Earth’s at the surface. So the lander weighs 100kg on Earth and only 1g on the comet. That is why when we land, we have to fire harpoons into the surface, and screw ourselves in, to stop us bouncing off back into space!

Q: I heard that the harpoons that will help with the landing will also be able to provide data on how hard the comet is. How much of the science will be done by the cameras onboard versus other instruments? How many different kinds of instruments are there on the lander?

A: The Lander has 10 instruments on board. There are two camera systems, Civa and Rolis, one does the panoramas, the other looks at the surface. We also have spectrometers, plasma measurements, measurements of the nucleus surface strength and makeup (as you alluded to with the harpoons).

Compiled by Sarah Marshall

The Wall Street Journal