NASA has contributed three instruments to Rosetta - ALICE, MIRO, and IES - plus a significant portion of the electronics package for another instrument, ROSINA. ALICE , MIRO, and IES will provide information about the dynamics of comet C-G: how it develops its coma and tails, and how its chemicals interact with each other, and with radiation and the solar wind.
ALICE will map the comet’s nucleus for pockets of both dust and ice. MIRO and ROSINA will examine the vicinity for signs of water coming off the nucleus. MIRO will do it remotely, and ROSINA will do it by waiting for particles to actually hit the detectors. IES will look for examples of direct interaction between the solar wind and the nucleus.
ALICE may also help scientists learn more about the origin of the comet and what its interstellar material can tell us about the origin of our solar system. While ALICE and MIRO detect uncharged atoms and molecules, IES will detect their charged counterparts - ions - as well as electrons.
ALICE is an ultraviolet spectrometer, and MIRO is the Microwave Instrument for the Rosetta Orbiter. Both are remote-sensing instruments that will be used to explore the comet's physical characteristics, including how its structure and composition change over time as it travels toward the Sun. ALICE and MIRO can detect invisible electromagnetic waves (ultraviolet and microwave ranges) associated with objects far away, just as people can see visible light from stars light years away. En route to comet C-G in 2005, ALICE and MIRO explored comet Tempel-1 from about 46 million miles away, participating in NASA’s Deep Impact experiment. ALICE will also be the first ultraviolet spectrometer to study a comet at close range. ALICE can detect a wide range of molecules and atoms, but will leave the charged particles (ions and electrons) to IES.
MIRO is the first microwave instrument to fly in space and explore celestial bodies. As both spectrometer and radiometer, it can detect temperature as it identifies chemicals. Perhaps most important, MIRO can see and measure its target molecules even when ALICE and other instruments are blinded by dust. The microwaves that MIRO detects can penetrate dusty environments that block the visible and ultraviolet ranges of light.
IES (Ion and Electron Sensor) detects the presence and energy of ions and electrons in the comet and asteroid environments. It is an in situ (in place) instrument, meaning that it must directly contact ions and electrons to measure them, just as we must directly contact perfume molecules to identify their scent. For this reason, IES had no role in the Deep Impact experiment because it took place 46 million miles from Rosetta. ALICE and MIRO, being remote-sensing instruments, were able to observe Deep Impact. During the Earth and Mars flybys, however, IES collected data on both ion and electron masses and energies in those planets' magnetospheres, and it will be "in situ" for the asteroid flybys as well.
The scientific missions for these instruments, and others on Rosetta, sometimes overlap. For example, ALICE and MIRO, and some other instruments will observe some of the same chemicals. Studying the same things with different instruments and at different wavelengths of light can lead to two outcomes: corroboration, when all the instruments agree on what they see, or conflict, when they disagree. Both outcomes are useful to scientists. Corroboration enables scientists to accept their results with greater confidence than if they used only one instrument. If conflicts arise, however, they must find the reason. And that can lead to the discovery of new science.