How the Rosetta Mission Works

Comets light up our night sky and inspire wonder in children and adults alike.  Their burning up in the atmosphere creates a light-show for everyone to admire.  Today, scientists know that the lightshow we see whenever comets hit our atmosphere is actually the result of the intense heat generated by hitting dense air at high speed. The outer layers of the comet then combust and burn away. Some scientists postulate that organic molecules may have reached earth in its formative period by hitching a ride onto comets. Little is known about comet formation; however, scientists believe that most of today’s comets formed around the time that the gas giants of our solar system, Jupiter and Saturn, were beginning to condense from the disk of gas that surrounded our sun.  Since we know so little about comets and their age, a team at the European Space Agency (ESA) in collaboration with the National Aeronautics and Space Administration (NASA) designed a mission that would land a spacecraft on a comet to study its composition and test for organic matter.  This mission was named “Rosetta” and recently succeeded.

Goals and Areas of Investigation

Rosetta has just completed its ten year mission of catching the comet “67P/Churyumov-Gerasimenko” (C-G).  It became the first spacecraft to land on a comet and also the first spacecraft to observe this specific comet from such a short range.  Rosetta will closely study how the Sun’s heat transforms the comet, changing the block of rock and ice. Aside from observing changes in the comet, another primary goal of the Rosetta mission will be to document the typical makeup of the comet and investigate the possibility of organic compounds underneath the comet’s surface.

One of the main objectives of the Rosetta mission is to develop a better understanding of the “nucleus” of a comet, or its dense inner core.  In order to realize this aim, Rosetta will be carrying radar and microwave equipment that will attempt to “see” deep into the comet without directly drilling through it.  Additional thermal and spectroscoping imaging will investigate the levels of noble gases in the core of the comet.

The possibility of finding organic molecules on C-G excites proponents of the theory that life on earth originated from building blocks brought in from outer space on comets that burnt up in the earth’s atmosphere.  Rosetta’s Philae lander will test for the potential presence of nucleotides, similar to those that make up DNA and RNA, and amino acids, which are the molecules that make up proteins. Additionally, the lander will carry out an experiment to determine the “handedness” of molecules, identifying if left-handed or right-handed (Left-handed and right handed merely refer to the way atoms arrange themselves around an asymmetric carbon) isomers are more common on the comet.  Life on Earth, due to what appears to be a strange fluke, uses only left-handed isomers. Many theories circulate about why this is true, the most well supported says that this bias might be the result of light shining on these molecules in space.  Light waves behave similarly to corkscrews, meaning they can twist in either of two directions. Light circularly polarized one way can preferentially destroy molecules with one kind of handedness, while light circularly polarized the other way might suppress the other handedness.

If the comet also contains a majority of left-handed organic molecules, this discovery could give credence to those scientists who believe that life originated from the organic matter brought to earth by comets.

Behind the Name

The Rosetta mission is named after the famous Rosetta Stone, used by historians and archeologists to decipher Egyptian hieroglyphics.  Scientists hope Rosetta, similar to its namesake, will illuminate the language of the universe and improve understanding of Earth’s origins as well as those of comets.

Early Results

Since Rosetta has reached its target comet, it has already begun to take readings of levels of various compounds on and inside the comet.  Most notably, Rosetta has first started to measure H2O levels on C-G.  Why H2O?  The answer lies in Earth’s oceans.  The origin of the Earth’s oceans has yet to be determined.  The sheer amount of water on Earth suggests that the planet was bombarded by comets and asteroids that delivered water when they collided with its surface and early atmosphere.   In order to determine where the water came from, Rosetta will analyze at the proportion of deuterium – a hydrogen isotope –  in relation to normal hydrogen.  Preliminary results show that the D/H ratio is two or three times greater than in Earth’s oceans.

“This surprising finding could indicate a diverse origin for the Jupiter-family comets (The family that C-G is in) – perhaps they formed over a wider range of distances in the young Solar System than we previously thought,” claims Dr. Kathrin Altwegg, principal investigator on the Rosetta mission.  Moreover, previous comets from this family have contained varying Deuterium/Hydrogen (D/H) levels, with only one comet ever showing D/H levels similar to those of the earth’s oceans.  These findings suggest that asteroids, not comets, were the primary contributors to the formation of our planet’s massive oceans. 


As Rosetta follows C-G into the inner solar system and observes how the comet changes as it approaches the sun, it will continue to deliver valuable data back to scientists in Germany.  Even though its journey is far from over, it has already has a massive impact.  The launch of the mission was one of the most ambitious in history for the ESA, requiring years to plan and build. Already, that effort has paid off due to meaningful results that have allowed us to more fully understand our origins and the origins of elements from the natural world. Furthermore, the landing of Philae on C-G demonstrates the feasibility of comet mining in the future by demonstrating that it is feasible to land on fast moving comets with landing probes. 

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