The first Indian planetary mission to moon, Chandrayaan-1, launched on 22nd October, 2008, with a suite of Indian and International payloads on board, collected very significant data over its mission duration of close to one year. This mission was a huge success. Here we present some of the achievements of Chandrayaan -1.
1) Discovery of hydroxyl (-OH ) and water molecule in sunlit lunar surface region around the poles
The data from the Moon Mineralogy Mapper onboard Chandrayaan-1 has indicated the presence of hydroxyl and water molecules on the lunar surface. Further, Mini-Synthetic Aperture Radar (Mini-SAR) instrument of Chandrayaan-1 has indicated existence of sub surface water-ice deposits in the base of the craters of permanent sun shadow region. A mass spectrometer based experiment on the Indian Moon Impact Probe (MIP) of Chandrayaan-1 also indicated presence of water molecules in the lunar exosphere. During its 25-minute descent, the impact probe's Chandra's Altitudinal Composition (CHACE) recorded direct evidence of water in 650 mass spectra gathered in the thin atmosphere above the Moon's surface (Probably the first time in history a direct evidence of water on moon).
Liquid water cannot persist at the Moon's surface, and water vapor is decomposed by sunlight, with hydrogen quickly lost to outer space. Water, and the chemically related hydroxyl group (-OH), can also exist in forms chemically bound as hydrates and hydroxides to lunar minerals rather than as free water.
Where did water comes
According to European Space Agency (ESA) scientists, the lunar regolith (a loose collection of irregular dust grains making up the Moon’s surface) absorbs hydrogen nuclei from solar winds. An interaction between the hydrogen nuclei and oxygen present in the dust grains are expected to produce hydroxyl (HO−) and water (H2O).
2) exposure of large anorthositic blocks confirming the global lunar magma hypothesis
There are different theories regarding to the origin of Moon one of the most dominant theory is giant impact hypothesis. Giant-impact hypothesis suggests a Mars-sized body called Theia impacted Earth, creating a large debris ring around Earth, which then accreted to form the Moon. This collision also resulted in the 23.5° tilted axis of the earth, thus causing the seasons. Due to this collision a large amount of energy was liberated in the formation of the Moon and it is predicted that as a result a large portion of the Moon was once completely molten, forming a lunar magma ocean. Evidence for the magma ocean hypothesis comes from the highly anorthositic (A kind of rock , Lunar anorthosites constitute the light-colored areas of the Moon's) compositions of the crust in the lunar highlands, as well as the existence of rocks with a high concentration of the geochemical component referred to as KREEP (an acronym built from the letters K (the atomic symbol for potassium), REE (Rare Earth Elements) and P (for phosphorus), is a geochemical component of some lunar impact breccia and basaltic rocks)
3) signature of sub surface ice layers in permanently shadowed regions near the lunar north pole
Chandrayaans Mini-SAR experiment indicated possible large deposits of water-ice in the northern lunar craters. The Moon has no atmosphere; any substance on the lunar surface is exposed directly to vacuum. For water ice, this means it will rapidly sublime directly into water vapor and escape into space, as the Moon's low gravity cannot hold gas for any appreciable time. Over the course of a lunar day (~29 Earth days), all regions of the Moon are exposed to sunlight, and the temperature on the Moon in direct sunlight reaches about 395 K (395 Kelvin, which is equal to about 250 degrees above zero F). So any ice exposed to sunlight for even a short time would be lost. The only possible way for ice to exist on the Moon would be in a permanently shadowed area.
Within the craters of the pole the temperatures would never rise above about 100 K (280 degrees below zero F). Any water ice at the bottom of the crater could probably exist for billions of years at these temperatures.
NASA's Mini-SAR instrument, which flew aboard India's Chandrayaan-1 spacecraft, found more than 40 small craters with water ice. The craters range in size from 1 to 9 miles (2 to 15 km) in diameter. Although the total amount of ice depends on its thickness in each crater, its estimated there could be at least 600 million metric tons of water ice. The red circles denote fresh craters; the green circle mark anomalous craters
4) evidence for a new refractory rock type
Material that has a relatively high equilibrium condensation temperature is called refractory. Moon Mineralogy Mapper has discovered new rock types which are very small. What is surprising is that their combination is uncommon.
5) mapping of reflected lunar neutral atoms and identification of mini-magnetosphere
The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Chandrayaan-1 spacecraft has resulted in a comprehensive data set about interaction of solar wind with the lunar surface. A large fraction of up to 20% of solar wind hitting the lunar surface is reflected as energetic neutral atoms back to space. This is contrary to the classical assumption that the lunar surface is a perfect absorber.
The lunar surface is directly exposed to solar wind plasma due to the Moon's lack of a magnetosphere or a dense atmosphere. This results in intense space weathering of the regolith regolith (is a layer of loose, heterogeneous superficial material covering solid rock) covered surface. When solar wind hits the surface a fraction of it is reflected as protons and as neutral hydrogen atoms. Although it lacks a global magnetic field, the Moon possesses regions of local magnetization, referred as magnetic anomalies, with magnetic field strengths of up to 100 nT at the surface.
Imaging properties of SARA allow mapping of this reflection process at small spatial scales. Above strong magnetic anomalies on the surface, energetic neutral atom images show a pronounced reduction in energetic neutral atom flux resulting from the formation of a partial void of the solar wind, a mini magnetosphere, above these regions. The extent of such mini-magnetospheres depends strongly on solar wind conditions. Several mini-magnetospheres were identified so far in chandrayaans data, mostly located on the lunar farside. Although SARA observations were made during on average very quite solar wind conditions between February 2010 and August 2010, scientists imaged the same mini-magnetospheres under different conditions indicating the stability of the phenomenon but also the limiting conditions where solar wind presses the mini-magnetosphere down to the surface. Magnetic anomalies often correlate with surface albedo anomalies. Shielding of the surface from solar wind is a possible reason for such albedo changes. Mini-magnetospheres provide a way to shield the surface from the solar wind. However that this shielding is only partially and strongly particle energy dependent.
6) possible signature of water molecule in lunar exosphere
[exosphere is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the density is too low for them to behave as a gas by colliding with each other]
Instrument onboard Chandrayaan-1 that asserted presence of water in sunlit lunar exosphere was Chandra’s Altitudinal Composition Explorer (CHACE). CHACE is a quadrupole mass spectrometer, a payload of the Moon Impact Probe (MIP). CHACE has detected presence of H2O (mass number 18) in the lunar atmosphere along with some other masses. The mass spectra taken by CHACE suggest that the exosphere is dominated by the H2O and CO2 molecules
7) preserved lava tube that may provide site for future human habitation.
The Terrain Mapping Camera (TMC) – having high spatial resolution (5m) and three dimensional viewing capabilities. This had the best orbital sensor parameters ever flown to the Moon before this mission. The TMC captured the lunar surface features with an unprecedented clarity.
A buried uncollapsed and near horizontal Lava tube detected using TMC nadir image in Oceanus Procellarum area on Moon. The lava tube detected by TMC has been analyzed thoroughly in terms of morphometry, topography, surface composition and surface ages of the surrounding regions using sensors onboard Chandryaan-1. A Digital Elevation Model was generated to view the feature in three dimensional perspectives which has helped in estimating the dimensions of the tube which is about 1.7 kms long and approx. 120 meter in diameter. Compared to the most terrestrial lava tubes, this tube is larger. This may be due to the less gravity and absence of atmospheric pressure on the Moon. This lava tube lies between two rilles (collapsed portion of a larger original lava tube) indicating that the roof of this section of the tube has remained intact over the years.
Such a lava tube could be a potential site for future human habitability on the Moon and could be used for future manned missions aimed at scientific explorations, providing a safe environment from hazardous radiations, Galactic cosmic rays, meteoritic impacts, extreme temperatures, etc. This tube could as well be used as a transit out-posts enroute to other planetary bodies. The settlement would be protected from radiation, micro-meteor impacts, dust and extreme temperature changes by the lava structure that provides a natural environmental control with a nearly constant temperature of minus 20 degrees Celsius (-4 degrees Fahrenheit), unlike that of the lunar surface showing extreme variation, maximum of 130 degrees Celsius (266 degrees Fahrenheit) to a minimum of minus 180 degrees Celsius (-292 degrees Fahrenheit) in its diurnal (day-night) cycle. Dimensions of a lava tube have been demonstrated for the first time on any planetary body. Past detections have mostly identified the ‘sky-light’ holes believed to open into lava tubes or identifying candidate tube in 2 dimensions without dimensional estimations of individual tube.
8) radiation dose en-route and around the moon
Chandrayaan – 1s RADOME (Radiation Dose Monitor Experiment) from the Bulgarian Academy of Sciences used to map the radiation environment around the Moon.
The RADOM is a very small (~10 x 5 x 2 cm3 ) and low-weight (~100 gm) instrument . It consists of a single 0.3 mm thick Si-PIN semiconductor detector with 2 cm2 area; one low noise hybrid charge-sensitive preamplifier (A225F from Amptek Inc.); a fast 12 bit ADC; 2 microcontrollers and buffer memory. Pulse height analysis technique is applied for determination of the energy deposited during individual particle interaction. The measurement of energy deposited by individual particles can then be used to infer the absorbed dose in the silicon detector. The unit is managed by microcontrollers through specially developed firmware. RS232 interface facilitates transmission of data stored in the buffer memory to the Chandrayaan-1 telemetry.
RADOM was the first scientific payload to be switched on after the launch of the Chandrayaan-1. RADOM observations beginning within two hours after the launch of the Chandrayaan-1 and continuing till the end of the mission demonstrated that it could successfully characterize different radiation fields in the Earth and Moon environments. Signature and intensity of proton and electron radiation belts, solar energetic particles as well as galactic cosmic rays were well recognized and measured. Effect of solar modulation of galactic cosmic rays could also be discerned in the data.
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