After a ten-year-long journey, the Rosetta spacecraft has now traveled to within 145 miles of the comet 67P/Churyumov-Gerasimenko, which was not the first choice of comets for the spacecraft to eventually encounter. The Rosetta spacecraft has journeyed approximately 4 billion miles to get a closer look at the comet and for the Philae probe aboard the Rosetta to eventually to land upon it and take samples to learn more about it and other comets. The Rosetta spacecraft has taken some of the most dramatic images ever taken of a comet, though the comet 46P/Wirtanenit was actually the first choice of the project’s European Space Agency (ESA) scientists.
Right now, the Rosetta spacecraft is closer to the comet 67P/Churyumov-Gerasimenko than the international Space Station (ISS) is to Earth. That proximity is enabling the Rosetta spacecraft to send back amazing shots of the comet, which, like comets, in general, somewhat resembles a “dirty snowball.”
Comets are composed of water in the form of ice, dust, frozen carbon dioxide and ammonia. The darkness of the surface of the comet 67P/Churyumov-Gerasimenko has led some scientists to guess it has an organic or carbon coating or that the body of the comet might be largely carbon-based. If this is proven by the samples that the Philae probe that is connected to the Rosetta spacecraft will take when it lands upon the comet, it will help to bolster the theory that comets might have brought the necessary building blocks of life to Earth when they crashed into the planet billions of years ago.
The “tails” often associated with comets are formed when the materials that compose comets heat up as the comets approach closer to the sun and get heated up. Sometimes, more than one tail forms. The tails give comets one of the most distinctive shapes of space objects, making them easily recognizable to most people who see them.
As comets go, 67P/Churyumov-Gerasimenko was discovered relatively recently, on Sept. 20, 1969. Klim Churyumov discovered the comet when he was doing a survey of comets.
Part of the reason that 67P/Churyumov-Gerasimenko was chosen by Rosetta’s mission planners as a target is one of sheer economics. They wanted to find a comet which was near the ecliptic plane that the planets orbit on for the Rosetta space craft to land on. Locating such a comet would make the costs and mission length less than the case would be with other comets.
Also, the scientists wanted the Rosetta space craft’s Philae probe to land upon an active comet, one that was already also written about and well-known. The third factor was that the comet had to be approaching the inner solar system during the same time of the Rosetta space craft launch.
The first choice of the scientists was not 67P/Churyumov-Gerasimenko but was comet 46P/Wirtanen. The scientists decided upon 67P/Churyumov-Gerasimenko, instead, only because an unavoidable launch delay caused them to miss the opportunity to land on comet 46P/Wirtanen.
Already, the scientists behind the mission have learned that the comet 67P/Churyumov-Gerasimenko’s nucleus is less dense than water. This means that the body of the comet might be porous.
The Philae probe will land on 67P/Churyumov-Gerasimenko carrying nine instruments with which to analyze the comet and take photographic images. One of the instruments is called CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission). It is a type of radar that the ESA scientiests will use to get an idea about the underlying structure of the comet.
The Rosetta spacecraft and the comet 67P/Churyumov-Gerasimenko are now about 252 million miles (405 million kilometers) from Earth. The Rosetta spacecraft and the Philae probe will study the comet for a year.
By late August, five potential landing sites will be chosen and the main landing site will be selected by mid-September. As of now, the Philae probe is expected to land on the comet on November 11, 2014.
There are three U.S. NASA scientific instruments aboard the Rosetta spacecraft.They are the Ion and Electron Sensor (IES); Alice, which is an ultraviolet spectrometer; and, the Microwave Instrument for the Rosetta Orbiter, or MIRO.
Though the Roseeta spacecraft project is primarily an ESA mission, NASA and EU member countries have also contributed to the mission. NASA is involved in seven of the 21 Rosetta mission’s instrument collaborations. Also, NASA and its Deep Space Network are working together with the ESA’s Ground Station Network to aid in the navigation and tracking of the spacecraft.
The Rosetta spacecraft and the Philae probe will spend a year analyzing the comet 67P/Churyumov-Gerasimenko and taking samples of not only the surface material, but also core and gas samples. The nucleus of the comet will be studied, as will its interior. The shape of the comet roughly resembles that of a dumbbell. Finding a satisfactory landing place might be difficult, as the surface is strewn with boulders the size of houses.
It is expected that during the year-long Rosetta spacecraft mission, we will learn more about comets than we have in the past half-century. The comet 67P/Churyumov-Gerasimenko was not the first choice of comets that the ESA scientists wanted to study, but the knowledge being gained from the mission is already rewriting our understanding of comets.
Written By Douglas Cobb