By Knicole Colon, PhD
Launched more than a decade ago, the European Space Agency’s Rosetta spacecraft has finally reached its destination. For the first time, humans have maneuvered a spacecraft through the vastness of space to meet up with a comet and, believe it or not, that spacecraft will soon enter in orbit around that comet. Rosetta will then travel along with the comet for over a year and provide us with never-before-seen access to the life of a comet.
This now famous comet is known as Comet 67P/Churyumov-Gerasimernko. Comets are generally named for their discoverers, hence the lengthy surnames. This comet (which we will call 67P for short) is also the 67th periodic comet discovered, and it was discovered in 1969. The periodic part refers to the orbit of the comet. Periodic comets will continue to orbit the Sun as long as they aren’t burned alive (like Comet ISON was in late 2013) or don’t collide with other objects in the Solar System (like Comet Shoemaker-Levy 9 did when it collided with Jupiter in 1994). For those comets that have highly elliptical orbits and survive dangerously close encounters to the Sun, the comet’s proximity to the Sun is what results in the evaporation of cometary material. This effectively creates a temporary atmosphere around the comet, which can form the cometary tails that we all know and love.
Besides having exciting deaths and awesome-looking tails, comets are quite interesting objects since they contain complex organic compounds made up of carbon, hydrogen, oxygen, and nitrogen. It has been hypothesized that the building blocks of life on Earth came from comets that deposited organic molecules and water on Earth. If this is the case, then we need to understand how exactly this happened. Given the high interest in the composition of comets, they have been heavily studied for years. For example, there have been a number of spacecraft that had flybys of different comets in the past. However, this is the first time that a spacecraft will enter in orbit and travel along with a comet for a significant amount of time. We will be able to see firsthand how a frozen comet (that potentially contains original material from the formation of the Solar System) is affected over time by the Sun. On top of that, the Rosetta spacecraft is home to a little lander called Philae which will in fact land on the nucleus of Comet 67P this November. Prior to landing, data from Rosetta will help astronomers determine an optimal and safe landing site for Philae. This may be a bit more difficult than anticipated, given that as Rosetta approached Comet 67P, it discovered that the comet has a double nucleus with very variable terrain (as shown here and here).
Once Philae has landed and secured itself to the comet’s surface with harpoons (necessary due to the extremely low surface gravity, estimated to be about one ten-thousandth of Earth’s surface gravity), it will send back to Earth an incredible amount of information. Philae has ten instruments installed to do this (not to mention the numerous instruments installed on Rosetta). Some of these will take close-up pictures and run tests to determine the chemical composition of the comet’s surface. A drill system will obtain soil samples at different depths and a mass spectrometer will analyze those samples. A radar will be used to determine the internal structure of the comet. Needless to say, these little spacecrafts are going to tell us a great deal about this comet.
Currently, the Rosetta spacecraft is less than 62 miles from the comet’s surface. By mid-September it will be just 19 miles from the surface, and then it will be maneuvered to officially enter orbit around the comet at that time. Philae’s landing on the surface is currently scheduled for November 2014, so keep an eye out for news on that. Just like landing men on the Moon and rovers on Mars, this landing will be one for the record books. Beyond that, stay tuned for when Comet 67P has its closest approach to the Sun in August 2015, with Rosetta in tow.