In ancient days, people thought that comets could foretell the future. Today, we think they can tell us about the past. While the planets and moons in our solar system have undergone a great many changes since they were formed, comets may well contain pristine records of our solar system’s early days, and maybe even our galaxy’s early days. They may also provide insights into the origin of life on Earth and perhaps on other worlds.
NASA’s Planetary Science Goals
NASA has identified a number of key goals for planetary science, including the following:
- Learn how the sun's family of planets and minor bodies originated.
- Determine how the solar system evolved to its current diverse state, including the origin and evolution of Earth's biosphere.
- Determine whether there is or ever has been life elsewhere in the solar system.
To meet these goals, NASA intends to investigate the physical, chemical, and isotopic characteristics of Kuiper Belt objects and comets, and attempt to answer the following questions: (a) What are comets made of? (b) What do their physical state and chemical composition tell us about how and where they were formed? (c) Are comets a significant source of Earth's oceans and its early organic inventory?
How the Rosetta Mission Serves These Goals
The International Rosetta mission contributes directly to NASA's planetary science goals by providing a comprehensive investigation of a comet's physical characteristics, composition, and behavior as it journeys toward the sun. These studies will help us learn in great detail what comets are made of, how they work, and how they change as they travel from the deep cold of space beyond the asteroid belt to the warmth between the orbits of Earth and Mars.
By mission's end, Rosetta will have studied several comets, including the comet P/2005 JQ5 (Catalina), one of 70 objects being tracked as possible candidates for colliding with Earth. In 2005, however, scientists gave it only a 1 in 300,000 chance of striking Earth on June 11, 2085.
In 2004, Rosetta trained its instruments on comet T7/Linear. In 2005, it studied comet Tempel-1 as part of the Deep Impact experiment. In 2014, it will accompany comet 67P/Churyumov-Gerasimenko (comet C-G) on its transit into our inner solar system, observing it at very close range for several months.
Rosetta also used MIRO to study Venus in 2004, and used several instruments to study Mars during the flyby of that planet, which provided vital information about its upper atmosphere. Scientists and engineers can use that new information to plan future Mars missions. Rosetta has also studied Earth’s magnetosphere during the flybys of our planet. In addition, Rosetta will also take measurements of two asteroids, Steins and Lutetia, that it will pass along the way to comet C-G.
Will comets lose their wonder as we subject them to our instruments? That’s not likely. The scientific secrets comets contain are sure to be more fascinating than the myths invented by ancient storytellers.
Rosetta’s Science Goals
The prime scientific goal of this mission is to seek the origin of comets. Did they form within our solar system or outside of it, in interstellar space? To find these answers, Rosetta scientists are using the scientific instruments onboard to learn as much as they can about comet C-G. They will:
- Create a portrait of the comet’s nucleus - its shape and dynamic properties.
- Take a complete inventory of the comet’s chemical, mineralogical, and isotopic composition.
- Detail the comet’s physical properties and show how its volatiles and refractories interact
- Show how the coma emerges from the surface of the nucleus, and develops different layers of activity as it grows in the solar wind.
- Explain the comet’s origin - where it was formed, the relationship of its materials to those found in interstellar space, and whether or not it witnessed in the formation of our solar system.
- Create portraits of two asteroids - their shape, composition, and dynamic properties.
The comet’s chemistry
We want to know more about the chemicals inside comet C-G. Rosetta will detect and catalog them. It will also observe C-G’s chemical reactions as it approaches the Sun, where it will encounter more heat and ultraviolet light, as well as intense solar wind.
Just as forensic detectives inspect footprints and ashes, Rosetta scientists will inspect the chemicals, ions and isotopes inside of C-G, as well as their number and distribution. This evidence will tell us much about how and where C-G formed.
Scientists will look for various noble, or inert, gases, such as helium, neon, argon, krypton, xenon, and radon. Noble gases do not interact chemically with other elements and are easily eliminated from icy bodies at low temperatures. We know the temperatures at which these boil away, so if any of them are present in comet C-G, scientists can estimate how warm the comet might have been in the past.
Scientists will also look for chemicals produced by reactions near the Sun. This will help them differentiate between chemicals formed during C-G’s recent visits to the inner solar system and those formed during the eons it spent in the dark and icy nether regions far from the Sun. This chemical analysis of C-G can help us learn more about how ancient comets may have contributed to our atmosphere, our oceans, and even our lives.
The comet’s mechanics
Rosetta will also give us our best look yet at the structure and workings of a comet. We'll see whether comet C-G is a solid body of rock and ice with large gas pockets, a loose pile of rubble and snow, or something else entirely. And we hope that Rosetta will be able to show us, step-by-step, how the comet "machine" works as it transforms a small, quiet, asteroid-like object into an enormous, glowing, jet-spouting display!
Why we need to know more
Comets may not only teach us more about our origins on Earth. They could also show us how to find life elsewhere in the universe. In addition, we may someday need to divert or destroy a comet that’s headed toward Earth. The more we know about a comet’s structure and operation, the better chance we will have to greet it and send it elsewhere. Rosetta is our next step forward in achieving these goals.