Comets have long both fascinated and terrified human philosophers. Ancient oracle bones from China record attempts to divine the meaning of comet sightings. In the pre-modern western world, comets were considered bad omens, foretelling the deaths of kings or other important figures.
Despite the superstition surrounding comets, many early thinkers made accurate claims about these icy bodies. For example, 18th century German philosopher Emmanuel Kant believed (correctly) that comets were bodies composed of a volatile material (such as ice) that was melted and sent streaming behind the comet by the heat of the sun.
Although remote observations have provided strong evidence that comets are composed largely of water, until this month we had never made observations from the surface of a comet.
The Rosetta Mission, launched by the European Space Agency in 2004, changed that this month when it landed a probe on the surface of a comet called 67P/Churyumov–Gerasimenko.
Let’s take a look at some comet mysteries that scientists hope will be resolved by the data transmitted by the Rosetta probe and its lander Philae.
Organic Molecules: Complex organic molecules have been detected by past comet missions. The Philae lander and the Rosetta orbiter contain mass spectrometers, which will be used to measure and quantify these complex molecules.
Some scientists theorize that complex organic molecules, which are the building blocks of nucleic acids and amino acids, may have delivered to Earth by comets, setting the stage for the formation of life.
Composition: It is widely believed that the composition of a comet is representative of the composition of the nascent solar system. Some of the questions scientists would like to answer using the instruments on the Rosetta orbiter and its lander (called Philae) revolve around the contributions of comets to the current composition of the earth. The compound scientists are most interested in finding is water (in the form of ice). It has long been theorized that the earth’s oceans owe their existence, at least in part, to water delivered when comets collided with the earth. Although previous space missions have measured the composition of the outgassing materials found in a comets tail, the Rosetta mission is the first to return data from the actual surface body of a comet.
Activity: Although the Philae lander is currently disabled due to a lack of sunlight, the Rosetta orbiter will still be able to make some observations of changes that occur on and around the comet as it approaches the heat of the sun. As frozen gases within the comet are warmed, they will sublimate and be expelled from the body of the comet, forming a “tail” of gas, or coma, behind the comet. By studying activity on the comet, scientists will learn more about its composition and structure.
To learn more about the Rosetta mission, take a look at this useful FAQ published by the ESA.
UPDATE: This article describes some of the results that have very recently been announced. It also provides a good visual look at the Philae lander.