Rosetta: Rendezvous with Comet 67P/Churyumov-Gerasimenko (“67P / CG”)

On Wednesday 6th of August 2014 and after a mammoth 10-year journey across the Solar System, the European Space Agency space probe Rosetta will rendezvous with a comet called “67P / Churyumov-Gerasimenko” (67P/CG) – a tiny icy worldlet just 4-5 kilometre long orbiting the Sun in an elliptical orbit and currently several hundred million kilometres distance from Earth.

By Wednesday 6th August, Rosetta will have settled into a 25-kilometer orbit around 67P/CG. In November 2014, a small automated Lander called Philae attached to Rosetta will be sent down to the surface. Both spacecraft will continue to travel with the comet for the next 16 months as it circles and approached the Sun (closest approach on August 13th 2015); scrutinizing its composition and behaviour as the Sun’s heat transforms the tiny frozen world into a hive of volatile activity that temporarily swells it into a gaseous entity many millions of kilometres in size.

By analysing the comet with a suite of 22 instruments, Rosetta and Philae will conduct a comprehensive analysis of the material makeup of the comet that will provide important new information regarding the origin of Earth, Earth’s oceans and life itself.

Overview and Objectives of the Rosetta Mission
Rosetta is a European Space Agency (ESA) mission to orbit and land on comet 67P /Churyumov-Gerasimenko (“67P/CG”) as it circles the Sun. The primary mission lasts from August 6th 2014 to December 31st 2015.

It is a mission made up of a main Rosetta space probe orbiter and a smaller lander attached to Rosetta named Philae. Rosetta will settle into orbit on August 6th 2014 and continue to orbit the comet over the next 16 months. In November 2014 Philae will land on the comet’s surface. Both will travel with the comet as it orbits the Sun and reaches closest approach to the Sun on August 13th 2015.

Comets are made up of icy volatile materials like water and carbon dioxide, as well as dust and other materials. So as 67P/CG approaches its closest point to the Sun in its orbit (called perihelion), its volatile materials will heat up and sublimate, forming a vast spherical gaseous coma and perhaps a tail, both of which will be more rarefied than the air we breathe and reach for millions of kilometres into space. Since 67P/CG does not approach the Sun too closely (as some other comets do), it is not likely to become as chaotic a ‘volatile cauldron’ as those which travel much closer to the Sun.

While Philae will measure the composition of, and activity on the comet directly from the surface; Rosetta, orbiting at a distance of just 25km, will also measure the volatile materials emanating from the comet into its immediate space vicinity, and indeed will be able to see how the comet changes and reacts to the Sun’s heat and solar wind as they move closer to the Sun in August 2015.

The data gleaned from the comet will reveal its internal makeup and composition, including any organic materials present, to the atomic and molecular levels; providing significant new insight into the origin of the Solar System, the origin of Earth and its oceans and the origin of life.

Journey to Comet 67P/Churyumov-Gerasimenko
Because no current rocket (including the powerful ESA Arianne-5 rocket upon which Rosetta was launched) has the capability to send such a large 3-Tonne spacecraft directly to a comet such as 67P/Churyumov-Gerasimenko, Rosetta was ‘bounced around the inner Solar System like a cosmic billiard ball’, during its ten-year trek to Comet 67P/Churyumov-Gerasimenko.

Since its launch in 2004 from Kourou in French Guiana, Rosetta has criss-crossed the inner Solar System four times, has travelled over 6 billion kilometres, including availing of three gravity-assist flybys of Earth (2005, 2007 and 2009) and one of Mars (2007); and is finally due to arrive at comet 67P/CG – just 4 to 5 kilometres in length – at a distance of several hundred million kilometres from Earth.

Hibernation and Wakeup
Rosetta’s 10 year deep-space odyssey comprised lengthy periods of inactivity, punctuated by relatively short spells of intense activity when encountering Earth, Mars, and several asteroids. Ensuring that the spacecraft survived the hazards of travelling through deep space for more than ten years has been one of the major challenges of the Rosetta mission, and has been hugely successful to date.

To that end, Rosetta was placed in hibernation between June 8th 2011 and January 20th 2014 in order to limit consumption of power and fuel. During that lengthy hibernation, the spacecraft rotated once each minute while facing the Sun for solar power; with the only electrical systems kept running being the radio receivers and command decoders. On January 20th 2014, a “wake-up” command was sent to Rosetta. ESA scientists were hugely relieved that the dormant spacecraft received the command and awoke from its hibernation in excellent health and ready to take on all challenges ahead of it.

August 2014 Rendezvous with Comet 67P/Churyumov-Gerasimenko
Since its reawakening in January, Rosetta has been steadily approaching the comet. For the past 90 days or so, it has been moving at only about 2 metres per second with respect to the comet. As you read this, the space probe is imaging the comet, allowing ESA scientists and engineers to determine the comet’s size, shape and orientation and rotation; allowing for Rosetta to complete its orbital insertion, which takes place on Wednesday August 6th 2014.

Using its approximately 1.7 Tonnes of propellant, the space probe’s propellant system and 24 thrusters recently manoeuvred the probe into an orbit just ahead of the comet, with the final orbit about the comet to be established on August 6th.

Rosetta will then start its science program, using eleven different instruments to photograph and map the comet to great precision, determine its internal structure and monitor any gas and dust emanating from the surface.

November Landing on Comet 67P/Churyumov-Gerasimenko
Once the comet has been mapped, five potential landing sites will be identified. Once ESA scientists have determined the best one, they will plan for a November landing. At that time Rosetta will move to within 1 kilometre of the comet, and release the lander Philae, which will set gently down on the comet at walking pace.

Once secure on the surface, it will anchor itself to the comet (because the comet’s gravity is too small to securely hold the lander on the surface) and proceed to conduct a series of sophisticated experiments, including drilling into the comet’s surface and placing surface materials into the body of the lander where their makeup can be determined to atomic and molecular levels.

Journey towards and away from the Sun
Comet 67P/CG is known as a Jupiter-class comet, meaning that its orbit is affected by the strong gravity of the giant planet Jupiter. Indeed Jupiter changed the orbit of 67P/CG in 1959, so that now the comet travels on an elliptical orbit that brings it to within 185 million kilometres of the Sun at closest approach (perihelion) and out to over 850 million kilometres at its furthest (aphelion).

Over the next 16 months and during the next perihelion on August 13th 2015, both Rosetta and Philae will monitor, image and measure all that happens on and around the comet as it draws nearer to the Sun. As already indicated, because 67P/CG will not travel too close to the Sun, so it is not expected to become as chaotic as comets which venture much closer to the Sun. Nevertheless, there will be plenty of activity, and as of June 2014, Rosetta has already begun to see small quantities of water emanating from the comet, and such activity will but increase greatly over the next year or so, providing both probes with an unprecedented opportunity to examine the makeup, composition and interaction of the comet as it orbits about the Sun.

Rosetta and Philae: Science Objectives and Instruments
Rosetta and Philae are charges with carrying out the following tasks:
• Detailed imaging and mapping of the comet
• Determination of the internal structure of the comet
• Determination of the material makeup, including elemental, isotopic and molecular details, of the comet’s volatile materials, dust and other materials and any organic materials expected to be present in the comet
• Image, monitor and measure the release of all materials, volatile or otherwise, from the comet as it reaches its closest point to the Sun in August 2015; and observe how these materials interact with the Sun’s solar wind and magnetic field

So how will Rosetta and Philae do all of that? The Rosetta orbiter contains no less than 11 scientific instruments including cameras for imaging the comet, a thermal camera to determine its material makeup, a type of radar know as radio-sounding that can penetrate the comet and determine its interior makeup, a mass-spectrometer and dust analyser to analyse materials emanating from the comet and plasma and magnetic field analysers for monitoring the interaction of the comet’s materials with the Sun’s solar wind and magnetic field.

Philae’s science package of 10 instruments is arguably more sophisticated; and includes an Alpha Proton X-Ray Spectrometer (as on the Mars Rovers) to determine the elemental makeup of the surface, a drill to drill into the surface and place samples into its body where a suite of instruments will determine the molecular makeup of the materials, including organic materials, and even determine the isotopic nature of the elements (critical for determining whether comets were the primeval source of all of Earth’s water). Radio-sounding and acoustic instruments will measure the internal structure of the comet, while high resolution cameras will image its surface.

Both the orbiter and the lander will conduct a suite of hard-science experiments typical of modern analytical laboratories. The instruments on board both Rosetta and Philae are more sophisticated than those on the Mars Exploration Rovers Spirit and Opportunity, and on a par with most of the instruments on the Mars Science Laboratory Curiosity; constituting one of the most sophisticated space science missions ever conducted.

Comets and Origins
Comets are tiny icy worlds usually only single kilometres in diameter. They are remnants of formation of the Solar System 4.6 billion years ago. As the Sun formed, countless trillions of tonnes of volatile materials such as water, carbon dioxide, ammonia and methane, as well as organic materials to the complexity of nucleic acids and amino acids that make up DNA ad proteins in life as we know it, were synthesized in the proto-planetary disk surrounding the Sun.

As the planets like Earth and Mars formed, the lighter elements and synthesized volatile materials moved further out from the Sun, contributing to the formation of the gas giant planets Jupiter, Saturn, Uranus and Neptune; but with the left over volatiles forming a vast swarm of perhaps a trillion comets, most of which reside in the Oort Cloud far out in the Solar System between 0.1 and 1 Light Year distance (one-hundred-billion to one-thousand-billion kilometres out – by comparison Pluto resides at approximately six-billion kilometres from the Sun.)

What is so crucial about comets is that they retain a record of the actual synthesis of both volatile materials such as water and carbon dioxide, and of organic molecules to the complexity of genetic nucleotides and amino acids known to be important to life as we know it, in the region of the Sun before the Earth itself had formed.

Hence “67P CG” represents one of a vast family of objects that are potentially older than the Earth, retaining a pristine record of complex chemistry occurring about the Sun relevant to the formation of life on Earth before and when the Earth was taking form. For this reason, comets are seen as very important in our search for the origin of the Solar System, of Earth and its oceans and of life itself.

Rosetta Mission – Relevance and Value to Science & Society
Given that we still have very little idea as to how life originated, studying such primeval evidence as retained in comets constitutes one of the most important endeavours in science. The Rosetta mission is arguably as important as the Mars exploration programme in search of evidence of origins on Mars, and perhaps The Hubble Space Telescope and the CERN Large Hadron Collider, both of which are currently revolutionising our understanding of the nature, origin and fate of the Universe itself.

Among the questions regarding the origin of life we must answer are:
• What is the origin of Earth oceans? In particular, is the water making up our oceans indigenous to our planet, or did it arrive from a mass bombardment of comets, asteroids and meteorites known to have occurred billions of years ago?
• Where did the basic organic materials for life originate – from organic synthesis on our planet, or from organic materials within comets and meteorites manufactured in the vicinity of the Sun before and during Earth formation?

The Rosetta mission may go some way toward answering both of these fundamental questions, among others.

And so we can see why this mission is named Rosetta. As with the Rosetta stone which allowed modern society to decipher the hieroglyphics of ancient Egypt – the Rosetta mission to 67P/CG may provide the cipher to enable us to better read the cosmic book of life – to see better the connection between the origin of life on Earth and its connection to the origin of the Solar System; and to link the origin of life on Earth to a deeper insight into the cosmic abundance of life.

This opportunity has been afforded to us through the technological and scientific endeavour of our ancestors and current generation of scientists alike, and we have taken that opportunity. To not do so would be a dereliction of duty to ourselves, to society, to our place in the great unfolding human story and to future generations who will need the insights we glean from this mission to make new and ever more enlightened decisions and undertake new endeavours to better understand who we are, where we have come from and what our cosmic fate can be.

I recommend that you follow the Rosetta mission over the next 16 months or so via the following links. In the Documents section of this blog (see Menu at top of Blog) you will also find a downloadable PDF document titled “TPS_ESA_Rosetta” containing this blog in a more bullet-point format, as well as containing greater detail on both the Rosetta Orbiter and Philae Lander and their science instruments, as well as a set of images including source URSs to hi-res versions, and required credits should you use any of the images.

Web (ESA):

Rosetta on Twitter:

Rosetta on Facebook:

Rosetta Blog:

Rosetta on Youtube:


1. Rosetta Space-probe and Philae Comet Lander:


Caption: In November 12014, Rosetta (upper) will set the Philae lander (lower) onto the surface of comet 67P / Churyumov-Gerasimenko as it closely approaches and then circles the Sun

Hi-Res Source:

Credit: ESA–J. Huart

2. Illustration of the size of comet 67P/ Churyumov-Gerasimenko

Caption: Illustration showing the relative size of comet 67P / Churyumov-Gerasimenko to well known features on Earth. Though huge on a human scale, comet “67P” is a small celestial body and possesses only a very weak gravity.

Hi Res Source:

Credit: ESA

3. Comet images on August 1st 2014 67P / Churyumov-Gerasimenko


Caption: On 1st of August, Rosetta took this image of comet 67P / Churyumov-Gerasimenko, revealing it to be a double lobed, peanut shaped object.

Hi-Res Source:

Credit: ESA