Chandrayaan-1 was India’s first unmanned lunar probe. It was launched by the Indian Space Research Organization (ISRO) in 22nd October 2008, and operated until August 2009. Chandrayaan-1 is aimed at chemical, mineralogical and photo-geologic mapping of the moon in visible, near infrared, low energy and high energy X-rays with high spatial resolution.
Specifically, the objectives will be to carry out high-resolution three-dimensional mapping of topographic features along with the simultaneous mapping of distribution of minerals such as Si, Al, Mg, Ca, Ilmenites (FeTiO3, which may retain 3He) and elemental chemical species including radioactive nuclides. This mapping could unravel the mysteries about the origin and evolution of the planetary system in general and moon-earth system in particular.
Looming at about 384,400 km from the Earth, the Moon is the brightest object in the night sky and only second in brightness to that of the Sun. It has a diameter of 3,476 km and a mass of 7.35x1022 kg with a mean density of only 3.35 g/cc as compared to 5.52 g/cc of that of Earth. It has no atmosphere and degassing from the surface produces only trace gases. The gravitational force on the Moon is only 1/6th of that of Earth, and is not able to retain its atmosphere. The Moon does not have a substantial core of molten iron like Earth and hence has no magnetic field. The Moon undergoes extremes in temperature. It is scorching heat at 110º C during the day and freezing cold at .180º C during night.
The Moon.s surface is generally dry, dusty and rocky. The rocky crust is about 60 km thick on the near side that faces the Earth and about 107 km on the far side. Moon.s terrain is divided into two sharply contrasting areas. The rugged and very ancient mountainous .Highlands regions and smooth younger lowland, Maria regions. While Earth.s mountain ranges are formed by movements and coming closer of crust sections pushing against each other (known as plate tectonics), the lunar highlands did not result from an active uplifting process due to crustal dynamics. But its surface has been periodically bombarded with different sizes of meteorites and asteroids. During the initial period of lunar evolution, such giant meteor impacts resulted in the creation of flatlands or lunar basins. The regions not affected by these giant impacts are the lunar highlands.
Ancient observers thought that the round and dark areas on the face of the Moon are seas, which they called Maria (Latin word for seas). Maria are not seas at all but relatively flat areas produced by massive flow of lava from earlier period of lunar volcanism. Maria comprises 16 percent of the Moon.s surface and has huge impact basins. They are concentrated in the near side of the Moon. Associated with the Lunar Maria are gravity anomalies called mascons (mass concentrations). A spacecraft would accelerate as it nears the Maria region and decelerate as it moves away due to such gravitational anomalies.
The Moon is covered with a gently rolling layer of powdery soil and rock fragments called the regolith, which is made of debris created by the meteor impacts forming the craters. Such craters are the remains of collisions between an asteroid, comet or meteorite and the Moon. The size, mass, speed and angle of the falling object determine the size, shape and complexity of resulting craters. Surface of the Moon is scarred with millions of impact craters and the record has been retained on Moon,s surface.
One striking difference between the lunar surface material and that of Earth concerns the most common kinds of rocks. On the Earth the most common rocks are sedimentary because of atmospheric and water erosion of the surface. On the Moon there is no atmosphere and little or no water, and the most common kind of rock is igneous (.fire-formed-rocks.). According to studies, the lunar surface material has the following geological characteristics:
Analysis of lunar rock samples indicate that
The abundance of radioactive elements in rock samples can be used to determine the age of the rocks in a process called radioactive dating. Using such techniques on lunar samples brought back by the Apollo missions, it has been found that the oldest material from the surface of the Moon is almost as old as we believe the Solar system to be that is 5 billion years. Thus the material brought back from the Moon by Apollo missions provides a window on the very early history of our Solar system that would be difficult to find on the Earth, which is geologically active and has consequently obliterated its early geological features.
Seismic S waves apparently do not traverse the region below the zone of Moonquakes, suggesting that this material has very low shear strength, possibly containing some liquid.
Origin of Moon
The origin of the Moon is still not clearly understood and there have been speculations about its origin how it was formed and how it acquired its present orbit around the Earth. Studies using the chemical, mineralogical, isotopic and chronological data led to postulation of five major theories on the origin of the Moon:
The Fission Theory:
At some time in the distant past, the Moon had separated from the Earth Perhaps the Earth was not as round then as it is today and that imbalance caused it to split in two.
The Capture Theory:
The Moon was formed somewhere in the solar system and was later captured by the gravitational field of the Earth.
The Co-accretion Theory:
The Earth and Moon may have been formed at the same time from solar nebula by co-accretion.
The Colliding Planetesimal Theory:
Moon condensed from the debris of the interaction of Earth-orbiting and Sun-orbiting planetesimals (very large chunks of rocks like asteroids) early in the history of the solar system.
The Giant Impact Theory:
A planetesimal of Mars size had impact with the Earth, early in its history, ejecting large volume of matter from the evolving Earth, which aggregated and formed the Moon.
Apart from the scientific interest, the Moon could have economic benefits to mankind. This includes exploitation of the resource potential of the Moon including habitation of the Moon to reap the benefits on a continuous basis. The Moon has abundant resources of oxygen, hydrogen and other solar wind gases trapped in its regolith. Understanding the availability of such resources from the perspective of mineralogy, lithology and regional geology is a prerequisite for efficient human presence on the Moon. Early studies of the lunar regolith showed that there is a relative abundance of Helium-3 (3He) isotope on the Moon compared to that of Earth. 3He can be used as a fusion element and is thus considered as one of the important fuels for power generation in the future. Since 3He has high diffusivity, it normally gets lost from lunar grains. However, the mineral Ilmenite (FeTiO3) is abundant on the Moon and has high retentivity for 3He. The distribution of 3He associated with Fe and Ti can be determined by geochemical mapping since it would have the same distribution as (Fe + Ti). Over the four billion-year history of the Moon, several hundred million tonnes of 3He have impacted the surface of the Moon from the solar wind. The analyses of Apollo and Luna samples showed that over 1 million tonnes of 3He still remain embedded in the surface of the Moon. Even a small fraction of this could provide the world.s electricity for centuries to come. A large number of studies are being carried out to determine the technical feasibility of having a human outpost on the Moon.
The twenty-first century will mark a significant milestone in the history of human development: the colonization of the Moon! The Moon being the nearest neighbor of Earth and with 1/6 th of the Earth’s gravity offers a unique outpost for planetary exploration. The conditions may be adapted to generate lunar self-sustaining bases for such endeavors. Moon’s far side would provide an excellent site for establishing an astronomical observatory because of the absence of atmosphere and the absence of Earth’s reflected radiation on the far side of Moon.