ALICE (spectrograph)

ALICE (spectrograph)
Name	ALICE (spectrograph)
Mission	Rosetta
Operator	European Space Agency
Launched	2004
Type	Ultraviolet imaging spectrograph
Wavelength	Extreme ultraviolet to far ultraviolet
Detector	Microchannel plate
Spectral resolution	Moderate
Mass	~4 kg
Power	~4.4 W
Principal investigator	Alan Stern

ALICE (spectrograph) is an ultraviolet imaging spectrograph flown on the Rosetta mission that studied Comet 67P/Churyumov–Gerasimenko. Built and led by a United States instrument team in cooperation with the European Space Agency, the instrument provided far-ultraviolet and extreme-ultraviolet spectroscopy of cometary coma and nucleus, contributing to compositional, photochemical, and surface studies during the Rosetta escort phase.

Overview

ALICE was developed under leadership associated with the Southwest Research Institute and the Smithsonian Astrophysical Observatory and was part of the Rosetta payload alongside instruments such as VIRTIS, MIRO, OSIRIS, and COSIMA. It observed emissions from hydrogen, oxygen, carbon, and noble gases in the coma of 67P/Churyumov–Gerasimenko, complementing measurements by MAVEN at Mars, New Horizons in the Kuiper Belt, and Hubble Space Telescope ultraviolet observations. The instrument team included investigators linked to Johns Hopkins University Applied Physics Laboratory, NASA Goddard Space Flight Center, and the Jet Propulsion Laboratory, integrating heritage from the Alice instrument on the New Horizons Pluto flyby and technology used on missions like Europa Clipper and Cassini–Huygens.

Design and Instrumentation

ALICE utilized an off-axis telescope feeding a Rowland-circle spectrograph with a concave holographic grating and a microchannel plate detector coated for solar-blind sensitivity. The optical train emphasized stray light suppression similar to designs on instruments developed at Ball Aerospace, Lockheed Martin, and Northrop Grumman. Electronics and data handling leveraged heritage from instruments supported by the National Aeronautics and Space Administration and the European Space Agency, with thermal control strategies informed by lessons from Rosetta partner spacecraft such as Mars Express and Venus Express. The detector assembly included a sealed tube, a charge-coupled device alternative approach, and photon-counting capability analogous to systems developed at the Space Telescope Science Institute and Harvard–Smithsonian Center for Astrophysics.

Capabilities and Performance

ALICE covered extreme-ultraviolet to far-ultraviolet wavelengths, enabling detection of Lyman-alpha and Lyman-beta transitions as well as atomic oxygen and carbon lines used to infer water, carbon dioxide, and CO abundances. Spectral resolution supported discrimination of coma emission features observed in campaigns coordinated with the European Southern Observatory, Keck Observatory, and the Very Large Telescope. Sensitivity and field of view permitted studies of both near-nucleus regions and extended coma, with performance validated against calibration targets including stars cataloged by the Hipparcos mission and standards used by the International Ultraviolet Explorer and the Far Ultraviolet Spectroscopic Explorer teams.

Science Objectives and Key Discoveries

Primary goals included quantifying coma composition, mapping spatial distributions of volatile species, and studying interactions between cometary emissions and the solar wind. ALICE data revealed unexpectedly low molecular oxygen relative to expectations based on interstellar chemistry debated by researchers from Caltech, Princeton University, and the University of Cambridge. Observations of water photodissociation products linked to in situ mass spectra from ROSINA and co-analysis with MIRO microwave measurements refined estimates of production rates employed by planetary scientists at the Max Planck Institute for Solar System Research and the Institute of Astrophysics of Andalusia. ALICE also detected signatures informing studies of surface ice, refractory organics, and argon abundances compared with noble-gas constraints explored by teams at the University of Bern and the University of Michigan.

Operational History

ALICE was integrated into the Rosetta orbiter managed by the European Space Agency and supported through cruise, Earth and Mars gravity assists, and the long hibernation period, with instrument operations coordinated by mission control centers in Darmstadt and across partner institutions in the United States. Science operations intensified during the rendezvous, escort, and perihelion phases, with coordinated campaigns that involved ground facilities like the Atacama Large Millimeter/submillimeter Array and space observatories including Chandra X-ray Observatory and Spitzer Space Telescope. Instrument commanding and anomaly resolution referenced operational practices from missions like Galileo, Ulysses, and Pioneer.

Data Processing and Calibration

Raw photon-event lists from the microchannel plate were processed to generate calibrated spectra, using flat-field maps, wavelength solutions, and sensitivity curves developed by the ALICE team in conjunction with standards from the Hubble Space Telescope calibration pipeline. Cross-calibration employed datasets from VIRTIS, OSIRIS, and ROSINA and incorporated radiometric corrections consistent with methods used by the International Astronomical Union working groups and the Planetary Data System. Archive products were delivered to ESA archives and NASA repositories, enabling secondary analyses by researchers affiliated with institutions such as MIT, Columbia University, and the University of California system.

Collaborations and Mission Context

ALICE operations and science were embedded within the international Rosetta consortium that included the European Space Agency, NASA, the Russian Space Research Institute, and research groups from France, Germany, Italy, Spain, Sweden, and the United Kingdom. Collaborative science exploited synergies with instruments from the Italian National Institute for Astrophysics, the French National Centre for Scientific Research, and the Max Planck Society, fostering interdisciplinary studies spanning astrochemistry, planetary geology, and heliophysics. Results from ALICE informed broader comparative studies involving data from missions such as Stardust, Deep Impact, and Rosetta’s own Philae lander experiments, and have been incorporated into discussions at conferences hosted by the American Astronomical Society and the European Geosciences Union.

Category:Ultraviolet spectrographs Category:Rosetta mission instruments Category:Spacecraft instruments