Class%20presentation.ppt
- 1. Proto-planet hypothesis of Kuiper Proto-planets is the disc containing about one tenth the mass of the sun and it becomes internally unstable and breaks up into smaller concentrations. Within each Proto-planet, the heavier elements tend to settle towards the centre and the lighter particles and gases remain in outer shells. It visualises a slightly flattened and slowly rotating disc-shaped solar nebula bulging out from the equator of the sun. In composition, this cloud is similar to the sun and contains mostly hydrogen and helium with small amounts of heavier elements, but the disc and the sun itself are thought of as being cool.
- 2. Bi-parental origin of the earth • It is was proposed by Chamberlin and Moulton, "as another star approached the sun, tremendous tides were set up on the surface of the sun and these tides or filaments of hot gases were pulled out from the sun. • As the star passed, these arms of gas were given a rotational motion. • After the star was gone, the gaseous matter in these arms condensed into solid material and gradually drew together to form planets,
- 3. Big Bang Theory • The Big Bang theory provides the explanation about at the very beginning of our universe. • According to the theory, our universe jumped into existence as “Singularity" around 13.7 billion years ago. • They are thought to exist at the core of "black holes“. Where Black holes are areas of intense gravitational pressure. • The pressure is thought to be so intense that finite matter is actually squished into infinite density. • These zones of infinite density are called “Singularities“. Our universe is thought to have begun as an infinitesimally small, infinitely hot, infinitely dense, something - a singularity. • After its initial appearance, it apparently inflated, expanded and cooled, going from very-very small and very-very hot to the size and temperature of our current universe. It continues to expand and cool to this day and we are inside of it.
- 4. Big Bang Theory - Evidence for the Theory • First of all, we are reasonably certain that the universe had a beginning. • Second, galaxies appear to be moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953) who discovered this phenomenon in 1929. This observation supports the expansion of the universe and suggests that the universe was once compacted. • Third, if the universe was initially very, very hot as the Big Bang suggests, we should be able to find some remnant of this heat. In 1965, Radio astronomers Arno Penzias and Robert Wilson discovered a 2.725 degree Kelvin (-454.765 degree Fahrenheit, -270.425 degree Celsius) Cosmic Microwave Background radiation (CMB) which spread through the observable universe. • Sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase of their distance from Earth. • Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.
- 5. Cosmic microwave background radiation • In cosmology, cosmic microwave background (CMB) radiation (also CMBR, CBR,MBR, and relic radiation) is thermal radiation filling the observable universe almost uniformly. • With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. • However, a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. • This glow is strongest in the microwave region of the radio spectrum. • Cosmic background radiation is well explained as radiation left over from an early stage in the development of the universe, and its discovery is considered a landmark test of the Big Bang model of the universe.
- 6. • When the universe was young, before the formation of stars and planets, it was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. • As the universe expanded, both the plasma and the radiation filling it grew cooler. • When the universe cooled enough, protons and electrons could form neutral atoms. • These atoms could no longer absorb the thermal radiation, and the universe became transparent. Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch. • The event shortly after of photons starting to travel freely through space rather than constantly scattering with electrons and protons in plasma is referred to as photon decoupling. • The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time (and wavelength is inversely proportional to energy according to Planck's relation).
- 7. Redshift • In physics (especially astrophysics), redshift happens when light seen coming from an object that is moving away, is proportionally increased in wavelength, or shifted to the redden/flush of the spectrum. • Redshifts are attributable to the Doppler effect, familiar in the changes in the apparent pitches of sirens and frequency of the sound waves emitted by speeding vehicles and occurs due to the Doppler effect whenever a light source moves away from an observer. • Cosmological redshift is seen due to the expansion of the universe, and sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase of their distance from Earth.
- 8. • Finally, gravitational redshifts are a relativistic effect observed in electromagnetic radiation moving out of gravitational fields. • Conversely, a decrease in wavelength is called Blueshift and is generally seen when a light-emitting object moves toward an observer or when electromagnetic radiation moves into a gravitational field. • Although observing redshifts and blueshifts have several terrestrial applications (e.g.,Doppler radar and radar guns), redshifts are most famously seen in the spectroscopic observations of astronomical objects.
- 9. Black Hole • A black hole is a region of space-time where gravity prevents anything, including light, from escaping. • The theory of general relativity predicts that a sufficiently compact mass will deform space-time to form a black hole. • Around a black hole there is a mathematically defined surface called an event-horizon that marks the point of no return.
- 10. • It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. • Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. • After a black hole has formed it can continue to grow by absorbing mass from its surroundings. • By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies.
- 11. Kepler’s laws of planetary motion The first and second laws (Fig.) were published in 1609 and the third law appeared in 1619. The laws may be formulated as follows: • The orbit of each planet is an ellipse with the Sun at one focus; • The orbital radius of a planet sweeps out equal areas in equal intervals of time; • The ratio of the square of a planet’s period (T2) to the cube of the semi-major axis of its orbit (a3) is a constant for all the planets, including the Earth.
- 12. Significance Kepler’s • Kepler’s three laws are purely empirical, derived from accurate observations. In fact they are expressions of more fundamental physical laws. • The elliptical shapes of planetary orbits described by the first law are a consequence of the conservation of energy of a planet orbiting the Sun under the effect of a central attraction that varies as the inverse square of distance. • The second law describing the rate of motion of the planet around its orbit follows directly from the conservation of angular momentum of the planet. • The third law results from the balance between the force of gravitation attracting the planet towards the Sun and the centrifugal force away from the Sun due to its orbital speed.
- 13. Bode’s law • In 1772 the German astronomer Johann Bode devised an empirical formula to express the approximate distances of the planets from the Sun. • A series of numbers is created in the following way: the first number is zero, the second is 0.3, and the rest are obtained by doubling the previous number. This gives the sequence 0, 0.3, 0.6, 1.2, 2.4, 4.8, 9.6, 19.2, 38.4, 76.8, etc. Each number is then augmented by 0.4 to give the sequence: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 38.8, 77.2, etc. This series can be expressed mathematically as follows: dn=0.4, for n=1 and dn=0.4+0.3 x2n-2 for n>2
- 14. • This expression gives the distance dn in astronomical units (AU) of the nth planet from the Sun. It is usually known as Bode’s law but, as the same relationship had been suggested earlier by J. D. Titius of Wittenberg, it is sometimes called Titius–Bode’s law.
- 15. Formation of Moon • For a long period of time, the fundamental question regarding the history of the Moon was of its origin. • Early hypotheses included i) fission from the Earth, ii) capture iii) co-accretion. iv) Today, the giant impact hypothesis is widely accepted by the scientific community
- 16. Fission hypothesis • The idea that the ancient Earth, with an accelerated rotation, expelled (split up) a part of its mass, was proposed by George Darwin (son of the famous biologist Charles Darwin). • It was commonly assumed that the Pacific Ocean represented the scar of this event. • However, today it is known that the oceanic crust that makes up this ocean basin is relatively young, about 200 million years old or less, whereas the Moon is much older. • However, the fact that the Pacific is not the result of lunar creation does not disprove fission theory. • This hypothesis also cannot account for the angular momentum of the Earth-Moon system.
- 17. Lunar capture • This hypothesis states that the Moon was captured, completely formed, by the gravitational field of the Earth. • This is doubtful, since a close encounter with the Earth would have produced either a collision or an alteration of the trajectory of the body in question, so if it had indeed happened, the Moon probably would never return to meet again with the Earth. • For this hypothesis to function, there would have to be a large atmosphere extended around the primitive Earth, which would be able to slow the movement of the Moon before it could escape. • This hypothesis has difficulty in explaining the essentially identical oxygen isotope ratios of the two worlds.
- 18. Co-accretion hypothesis • This hypothesis states that the Earth and the Moon formed together as a double system from the ancient accretion disk of the Solar System. • The problem with this hypothesis is that it does not explain the angular momentum of the Earth-Moon system or why the Moon has a relatively small iron core compared to the Earth (25% of its radius compared to 50% for the Earth)
- 19. Giant impact theory • At present the most widely accepted explanation for the origin of the Moon involves a collision of two proto- planetary bodies during the early accretional period of Solar System evolution. • This "giant impact theory", satisfies the orbital conditions of the Earth and Moon and can account for the relatively small metallic core of the Moon. • Collisions between planetesimals are now recognized to lead to the growth of planetary bodies early in the evolution of the Solar System.
- 20. • A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that :planets form out of cosmic dust grains that collide and stick to form larger and larger bodies. When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, enormously aiding further growth into moon-sized protoplanets. • It is generally believed that about 3.8 billion years ago, after a period known as the Late Heavy Bombardment, most of the planetesimals within the Solar System had either been ejected from the Solar System entirely, into distant eccentric orbits, or had collided with larger objects due to the regular gravitational bump from the Jovian planets (particularly Jupiter and Neptune)
- 21. LUNAR Landscape • The lunar landscape is characterized by impact craters, their ejecta, a few volcanoes, hills, lava flows and depressions filled by magma.
- 22. Lunar topography • The moon contains a ~70-km thick basaltic crust that differentiated from a denser, underlying mantle at least 4.4 billion years ago. • The crustal rocks returned by the Apollo Mission range in age from 4.3 to 3.1 billion years old. In contrast, the oldest rocks on earth are rarely more than 3 billion years old. • The lunar crust is easily discernible into two primary types of terrains: the older highlands, which comprise about 83% of the lunar surface (light regions in image), and the younger lunar maria, which comprise the remaining 17% (dark regions). • The heavily cratered highlands are covered with a layer of regolith, a mixture of fine dust and fragmented debris generated by meteorite impacts. Beneath the regolith, two crustal rocks types dominate the highlands.
- 23. The highlands • The most distinctive aspect of the Moon is the contrast between its bright and dark zones. • Lighter surfaces are the lunar highlands and the darker plains are called maria (singular mare, from the Latin for sea). • The highlands are anorthositic in composition, whereas the maria are basaltic. • The maria often coincide with the "lowlands," but it is important to note that the lowlands (such as within the South Pole-Aitken basin) are not always covered by maria. • The highlands are older than the visible maria.
- 24. The lunar maria • The lunar maria (singular: mare) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. • They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. • The lunar maria are large flows of basaltic lava, that correspond to low- albedo surfaces, covering nearly one third of the near-side. Only a few percent of the far-side has been affected by mare volcanism. • They are less reflective than the "highlands" as a result of their iron-rich compositions, and hence appear dark to the naked eye. • The ages of the mare basalts have been determined both by direct radiometric dating and by the technique of crater counting. • The oldest radiometric ages are about 4.2 Ga, whereas the youngest ages determined from crater counting are about 1 Ga (1 Ga = 1 billion years). • Most of the mare formed between about 3 and 3.5 Ga. The maria are clearly younger than the surrounding highlands given their lower density of impact craters.
- 25. Rille • Rille (German for 'groove/ channel') is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length. Based on observations from the Apollo mission, it is generally believed that this rille was formed by volcanic processes. lunar dome • A lunar dome is a type of shield volcano that is found on the surface of the Earth's Moon. They are typically formed by highly viscous, possibly silica-rich lava, erupting from localized vents followed by relatively slow cooling. Lunar domes are wide, rounded, circular features with a gentle slope rising in elevation a few hundred meters to the mid-point. They are typically 8-12 km in diameter, but can be up to 20 km across.
- 26. Wrinkle ridges • Wrinkle ridges are features created by compressive tectonic forces within the maria, when the basaltic lava first cooled and contracted. These features represent buckling of the surface and form long ridges across parts of the maria. Some of these ridges may outline buried craters or other features beneath the maria. They frequently outline ring structures buried within the mare, follow circular patterns outlining the mare, or intersect protruding peaks. A prime example of such an outlined feature is the crater Letronne. Graben • Grabens are tectonic features that form under extension stresses. Structurally, they are composed of two normal faults, with a down-dropped block between them. Most grabens are found within the lunar maria near the edges of large impact basins. •
- 27. Impact craters • Impact crater is the most notable geological process on the Moon. The craters are formed when a solid body, such as an asteroid or comet, collides with the surface at a high velocity (mean impact velocities for the Moon are about 17 km per second). The kinetic energy of the impact creates a compression shock wave that radiates away from the point of entry. This is succeeded by a rarefaction wave, which is responsible for propelling most of the ejecta out of the crater. Finally there is a hydrodynamic rebound of the floor that can create a central peak. • • The most recent impacts are distinguished by well-defined features, including a sharp-edged rim. Small craters tend to form a bowl shape, while larger impacts can have a central peak with flat floors. Larger craters generally display slumping features along the inner walls that can form terraces and ledges. •
- 28. Regolith or Lunar Soil • The surface of the Moon has been subject to billions of years of collisions with both small and large asteroid and comet • Over time, these impact processes have broken up and crushed the surface materials, forming a fine grained layer termed "regolith". • The thickness of the regolith varies between 2 meters beneath the younger maria, to up to 20 meters beneath the oldest surfaces of the lunar highlands. • The regolith is predominantly composed of materials found in the region, but also contains traces of materials ejected by distant impact craters. • The term "mega-regolith" is often used to describe the heavily fractured bedrock directly beneath the near-surface regolith layer.
- 29. Regolith or Lunar Soil • The regolith contains rocks, fragments of minerals from the original bedrock, and glassy particles formed during the impacts. • In most of the lunar regolith, half of the particles are made of mineral fragments fused by the glassy particles. • The chemical composition of the regolith varies according to its location; the regolith in the highlands is rich in aluminum and silica, just as the rocks in those regions. • The regolith in the maria is rich in iron and magnesium and is silica-poor, as the basaltic rocks from which it is formed. • The lunar regolith is very important because it also stores information about the history of the Sun. • The atoms that compose the solar wind – mostly helium, neon, carbon and nitrogen – hit the lunar surface and insert themselves into the mineral grains. • Upon analyzing the composition of the regolith, particularly its isotopic composition, it is possible to determine if the activity of the Sun has changed with time.
- 30. Lunar lava tubes • Lunar lava tubes form a potentially important location for constructing a future lunar base, • Which may be used for local exploration and development, or as a human outpost to serve exploration beyond the Moon. • A lunar lava cave potential has long been suggested and discussed in literature and thesis. • Any undamaged lava tube on the moon could serve as a shelter from the severe environment of the lunar surface, with its frequent meteorite impacts, high-energy ultraviolet radiation and energetic particles, and extreme diurnal temperature variations.
- 32. Internal structure of Moon • The current model of the interior of the Moon was derived using seismometers left behind during the manned Apollo program missions, as well as investigations of the Moon's gravity field and rotation. • The crust of the Moon is on average about 50 km thick (though this is uncertain by about ±15 km, ). • It is widely believed that the far-side crust is on average thicker than the near side by about 15 km. • Seismology has constrained the thickness of the crust only near the Apollo 12 and 14 landing sites. • While the initial Apollo-era analyses suggested a crustal thickness of about 60 km at this site, • Recent re-analyses of this data set suggest a thinner value, somewhere between about 30 and 45 km.
- 34. Core • In 2010 reanalysis of the old Apollo seismic data on the deep moonquakes using modern processing methods confirmed that the Moon has an iron rich core with the radius of 330 ± 20 km. • The same reanalysis established that the solid inner core made of pure iron has the radius of 240 ± 10 km. • The core is surrounded by the partially (10 to 30%) melted layer of the lower mantle with the radius of 480 ± 20 km (thickness ~150 km). • These results imply that 40% of the core by volume has solidified. The density of the liquid outer core is about 5 g/cm3 and it can contain as much 6% sulfur by weight. The temperature in the core is probably about 1600– 1700 C.
- 35. Lunar Magnetic field • Compared to that of Earth, the Moon has only a very weak external magnetic field. • Other major differences are that the Moon does not possess a dipolar magnetic field like the Earth does (as would be generated by a geodynamo in its core), • the magnetizations that are present are almost entirely crustal in origin. • One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. The small size of the lunar core, however, is a potential obstacle to this theory. • Alternatively, it is possible that on airless bodies such as the Moon, transient magnetic fields could be generated during impact processes. In support of this, it has been noted that the largest crustal magnetizations appear to be located near the antipodes of the largest impact basins.