On July 14, 2015, the NEW HORIZONS probe flew over and sent pictures of the Pluto planet and its satellite Charon, revealing information about their geology, their surface and atmosphere.
A composite of enhanced color images of Pluto (lower right) and Charon (upper left), taken by NASA’s New Horizons spacecraft on July 14, 2015
Credits: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Pictures of mountains show that geological activity is important. Areas of carbon monoxide ice, methane, nitrogen were detected. The Pluto's atmosphere consists mainly of nitrogen. However, Pluto’s small mass allows hundreds of tons of atmospheric nitrogen to escape into space each hour. So, scientists are trying to answer a new question: where does all the nitrogen come from ?
New Horizons is equipped with seven scientific instruments: three optical instruments, including the ALICE spectrograph, two plasma detectors, solar wind sensor and a radiometer. The probe was launched January 19, 2006, from Florida and went July 14 closer to the dwarf planet.
The spectrograph ALICE works in the ultraviolet (500.1800 Å) and is equipped with a HORIBA Jobin Yvon diffraction grating. Alice is a light spectrograph (4.5 kilograms) of low power (4.4 watts) developed by SWRI (Southwest Research institute) for the study of the atmosphere: determination of atomic and molecular compounds and their relative abundances.
The key optical component of the ALICE instrument is the toroidal holographic replica diffraction grating manufactured byHORIBA Jobin Yvon in 2005. The development of this grating batch was the result of a fruitful collaboration between the Southwest Research Institute (SWRI – USA), and HORIBA Jobin Yvon’s team.
The ALICE diffraction grating, with a groove density of 1600 gr/mm, made on a metallic material substrate to minimize the weight, was optimized to work in a Rowland Circle type imaging spectrograph. Thanks to the holographic recording and space-qualified (TRL 9) replication process, the ALICE grating exhibited low stray light and no ghost. The grating active area is 35 mm in the dispersion direction by 20 mm in the spatial dimension. The spectrograph uses the first diffraction order through the full spectral bandpass 70 nm – 205 nm. The spectral resolution was measured between 0.98 and 1.25 nm with a spectral resolving power of 55-200.
The Alice spectrometer is the evolution of the one used in Rosetta, from the European Space Agency, which is flying around the 67P/Churyumov-Gerasimenko comet.
After 10 years of life, with more than 9 years of operation in a space environment during the NEW HORIZONS journey, the ALICE holographic replica grating has kept its initial high performance and continues to bring to the scientific community extraordinary discoveries.