Rosetta: chasing a time-capsule bigger than Mt. Fuji

“Comets can be thought of as the deep frozen leftovers from the formation of the solar system,” said Dr Matt Taylor from the European Space Agency, opening his public lecture yesterday titled ‘The Rosetta Story: A comet, an amazing spacecraft and their journey around the Sun’, part of the Sixth Alfven Conference hosted by UCL.

Studying these “potato-shaped”’ (his words, not mine) left-overs might provide scientists with answers about how water and the building blocks of life were delivered to Earth. Rosetta is a mission that aims to do it in a way never tried before, by getting up close and personal with a comet.

“When the Sun formed 4.5 billion years ago, material blasted out, creating planets, moons and smaller bodies including comets, which are pristine time-capsules from the birth of our solar system,” Dr Taylor added.

“Scientists know that the water originally on Earth evaporated, only to be replaced later. This new water provided the environment necessary for life and they think comets might have played a part.”

So what is already known about comets and where does Rosetta fit in?

Comets have been part of our culture since 500 BC when, along with eclipses, they were considered bad omens, foretelling destruction, war, royal downfall and death – possibly proving true for Harold Godwinson in 1066 and later for Mark Twain, who was born and died in the same years that Halley’s Comet flew by Earth.

Scientists have since studied comets from ground-based telescopes and satellites, but only fleetingly and from more than 100 km away. Giotto, ESA’s first interplanetary space probe, carried 10 instruments – including one led by UCL – first to comet Halley in 1986 and six years later to the weaker comet Grigg-Skjellerup, to study how comets interact with the solar wind.

From this, we know that they have a nucleus of dust and ice about 1–10 km across, from which ice sublimates forming a coma that might be as big as 1,000km wide and tails which may be millions of km long.

Two tails stream from the coma – one of gas and plasma, and the other of dust – it’s the coma and these tails that we see blazing when comets pass by Earth.

Rosetta will first catch up with a comet called 67-P/Churyumov-Gerasimenko (C-G for those in the know) in August this year, before escorting it at a slow, walking pace of 1 m/s sometimes at distances below 10km depending on comet activity, throughout this and next year.

In that time, it will take detailed physical and chemical measurements of the comet and deploy a laboratory called Philae to land on its surface on which it will, and I quote Dr Taylor, “see, touch, scratch and sniff” to learn about the comet.

All this will be happening as C-G hurtles on its orbit towards the Sun, during which its surface will change with increasing temperatures, causing material to evaporate.

This will provide scientists, including those working on Rosetta at UCL, with additional information about its composition and how it changes in orbit – possibly unearthing clues to our origins.

Rosetta was launched in 2004 and has since travelled around the Sun five times, picking up energy from Earth and Mars to line it up with its final destination: C-G.

For the coldest, loneliest leg of the mission, as Rosetta travelled out towards the orbit of Jupiter, the spacecraft was put into deep-space hibernation. The ‘Wake up, Rosetta!’ campaign followed Rosetta’s progress in contacting Earth – an event Dr Taylor described as extremely tense and nail-biting in the ESA control room on 20 January 2014.

Since successfully waking up, it is now closely catching up with C-G and, in the next few weeks, scientists expect Rosetta to arrive at the comet, with Philae’s deployment to the surface following in November.

Next year will see Rosetta ride alongside C-G as it passes through its closest approach of the Sun in mid-August 2015, with the nominal end of the mission in December 2015.

Dr Taylor concluded that the next challenge will be finding a suitable position from which to track C-G and defining the criteria for finding a safe landing site on the surface of the comet.

For updates on Rosetta, follow @ESA_Rosetta and #RosettaAreWeThereYet, or the Rosetta blog.