After a general description of the Nasa New Horizons Mission in a previous article that described its main objectives and the region of the Solar System where the spacecraft is currently operating, it can be useful to understand its payload more in detail and explain some of its current scientific results.The New Horizons payload is highly power efficient because of the little power available, and it represents a degree of miniaturization that is unprecedented in planetary exploration. It consists of seven instruments: three optical instruments, two plasma instruments, a dust sensor and a radio science receiver/radiometer.
If considering the imaging activities of the mission, it could be of great interest to examine LORRI and Ralph, the two instruments that are mapping and characterizing Pluto and Charon from a geological and chemical point of view.
In these last six months the largest part of images arriving from New Horizons have been captured by LORRI(LOng Range Reconassance Imager), a panchromatic high resolution imager, consisting of a telescope with an 8.2-inch (20.8 centimeter) aperture. LORRI could be simply described as a digital camera with a large telephoto telescope, but fortified to operate in the hostile termal conditions near Pluto.
LORRI has no colour filters so and it can be defined as the “Eagles Eyes” of New Horizons, thanks to its high resolution (up to 50m at the closest approach).
But the main “eye” of the spacecraft is certainly the instrument called Ralph, a visible and infrared imager/spectrometer that is equipped with MVIC(Multispectral Visible Imaging Camera) and an advanced infrared compositional spectrometer called LEISA(Linear Etalon Imaging Spectral Array). A spectrometer is an instrument that can measure the intensity of the light in specific portion of the electromagnetic spectrum and it is often used to identify materials. This is possible because each chemical element is characterized by its own spectral fingerprint that can be analyzed together with the spectrometer measurements, for example to detect the surface composition of Pluto and its moons.
Ralph has been specifically designed to study the surface geology and morphology, thanks to its four filters that can map in blue(400-550nm), red(540-700nm), Near InfraRed(780-975nm) and narrow band methane(860-910nm). But it can also work together with other instruments to obtain more information about the composition and temperature of both Pluto and Charon.
Looking for example at the following image, what comes out is the cooperation between LORRI and Ralph when they can observe and analyze the same area.
Pluto image on the left side have been obtained firstly by combining four different captures of LORRI when the spacecraft was at a distance of 450,000 km from the surface. Then the color data from the Ralph filters are used to detect differences in the composition and texture of Pluto’s surface and what comes out is an enhanced global view of the dwarf planet. The image on the right is a magnified view from the global scene that has been taken by LORRI with a distance of 48,000 km. This LORRI mosaic(another way to define a composite image) has been then combined with the Ralph color images taken from a distance of 34,000 km, with a resolution of 650m per pixel.
But Ralph can provide valuable scientific information even without the integrated activity with LORRI. This can be achieved with various mathematical or data processing techniques as it will be described for the next image from New Horizons.
This overall view of Pluto has been defined as “psychedelic” even by the members of New zHorizons team, as it is surely far from a real color representation of the scene. Such a weird color composition is the result of an image processing technique called Principal Component Analysis(PCA), a statistical algorithm for data analysis that is also used for machine learning applications. Multispectral data bands from the one scene are often highly correlated but the PCA algorithm can produce uncorrelated output bands that are linear combinations of the original spectral bands. After PCA processing, composite images are more colorful because data are now uncorrelated and their variance has been maximized. In the case of Pluto image the PCA puts in evidence a more detailed geology composition that was hard to detect with the original data.
These few images are a little part of New Horizons activity together with the important scientific results obtained so far For example a widespread presence of water ice has been recently detected on Pluto’s surface with spectrometric analysis, and 3-D topographic maps of Pluto have been created thanks to the imaging instruments. It is possible to know in detail about New Horizons discoveries by visiting the New Horizons official web page that is constantly updated. However new relevant results or images will be described and properly commented on this blog when they will come out.