4 Vesta - Wikipedia
METEORITE BOMBARDMENT AND DATING OF PLANETARY SURFACES. G. Neukum. Importance of the Determination of Age in the study of the. Physical . Ph.D. in Geophysics through Astrophysics and Planetary Sciences Department; Spring M.S. in . Issues in Crater Studies and the Dating of Planetary Surfaces, 1, #, , . Mars: Implications for the Late-Heavy Bombardment and Isochron Ejected Lithologies at Barringer Meteorite Crater (AKA Meteor Crater). Dating by measurement of impact crater frequencies developed in the past years primarily on the basis of the data from the missions to the Moon and Mars.
Colors of the two hemispheres are not to scale, [g] and the equatorial region is not shown. South pole of Vesta, showing the extent of Rheasilvia crater.
Terraforming - Wikipedia
Prior to the arrival of the Dawn spacecraftsome Vestan surface features had already been resolved using the Hubble Space Telescope and ground-based telescopes e. The Rheasilvia crater is younger and overlies the Veneneia crater.
Spectroscopic analyses of the Hubble images have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into the mantleas indicated by spectral signatures of olivine. It is km across and predates Rheasilvia green at bottom.
Several old, degraded craters rival Rheasilvia and Veneneia in size, though none are quite so large. Their official names from largest to smallest west to east are Marcia, Calpurnia, and Minucia. Marcia is the youngest and cross-cuts Calpurnia. Minucia is the oldest. A second series, inclined to the equator, is found further north. These troughs are thought to be large-scale graben resulting from the impacts that created Rheasilvia and Veneneia craters, respectively.
The troughs may be graben that formed after another asteroid collided with Vesta, a process that can happen only in a body that, like Vesta, is differentiated. The presence of olivine within the Rheasilvia region would also be consistent with excavation of mantle material. However, olivine has only been detected in localized regions of the northern hemisphere, not within Rheasilvia. Features associated with volatiles[ edit ] Pitted terrain has been observed in four craters on Vesta: Marcia, Cornelia, Numisia and Licinia.
Along with the pitted terrain, curvilinear gullies are found in Marcia and Cornelia craters. The curvilinear gullies end in lobate deposits, which are sometimes covered by pitted terrain, and are proposed to form by the transient flow of liquid water after buried deposits of ice were melted by the heat of the impacts. Carbonaceous chondrites are comparatively rich in mineralogically bound OH.
From the first appearance of calcium—aluminium-rich inclusions the first solid matter in the Solar Systemforming about 4. The deeper layers of the crust crystallize to form plutonic rocks, whereas older basalts are metamorphosed due to the pressure of newer surface layers. Slow cooling of the interior Vesta is the only known intact asteroid that has been resurfaced in this manner.
Because of this, some scientists refer to Vesta as a protoplanet. Composition of the Vestan crust by depth  Basaltic lava flowsa source of non-cumulate eucrites. Plutonic rocks consisting of pyroxenepigeonite and plagioclasethe source of cumulate eucrites. Plutonic rocks rich in orthopyroxene with large grain sizes, the source of diogenites. Vesta could have been classified as a dwarf planet if it had retained a spherical shape, and it has other qualities that lead to the thought it could be a protoplanet.
The only thing that knocked it out of the category of a dwarf planet was the formation of two large impact basins at its southern pole.
Regolith[ edit ] Vesta's surface is covered by regolith distinct from that found on the Moon or asteroids such as Itokawa.
This is because space weathering acts differently. A Meteorite is a piece of rock from outer space that strikes the surface of the Earth. A Meteoroid is a meteorite before it hits the surface of the Earth. Meteors are glowing fragments of rock matter from outside the Earth's atmosphere that burn and glow upon entering the Earth's atmosphere.
They are more commonly known as shooting stars. Some meteors, particularly larger ones, may survive passage through the atmosphere to become meteorites, but most are small objects that burn up completely in the atmosphere. They are not, in reality, shooting stars. Meteor Showers - During certain times of the year, the Earth's orbit passes through a belt of high concentration of cosmic dust and other particles, and many meteors are observed.
The Perseid Shower, results from passage through one of these belts every year in mid-August, and Leonid shower occurs in mid-November. Throughout history there have been reports of stones falling from the sky, but the scientific community did not recognize the extraterrestrial origin of meteorites until the s.
Within recent history meteorites have even hit humans- - a small meteorite crashed through the roof of a garage in Illinois - A 5kg meteorite fell through the roof of a house in Alabama. In Antarctica they are easily seen on the snow covered surface or embedded in ice.
The fall of meteorites to the Earth's surface is part of the continuing process of accretion of the Earth from the dust and rock of space. When these rock fragments come close enough to the Earth to be attracted by its gravity they may fall to the Earth to become part of it. As we will see the evolution of life on the Earth has likely been affected by collisions with these space objects, and collisions could affect the Earth in the future as well.
Composition and Classification of Meteorites Meteorites can be classified generally into three types: Stones - Stony meteorites resemble rocks found on and within the Earth. They are the most common type of meteorite, although because they resemble Earth rocks they are not commonly recognized as meteorites unless someone actually witnesses their fall.
Stony meteorites are composed mainly of the minerals olivine, and pyroxene. Some have a composition that is roughly equivalent to the Earth's mantle. Two types are recognized: Chondrites - Chondrites are the most common type of stony meteorite. They are made of olivine, pyroxene, and iron - nickel alloys that are magnetic. They are composed of small round spheres, called chondrules, made of the minerals olivine and pyroxene.
They appear to have formed by rapid melting followed by rapid cooling early in the history of the solar system. Most chondrites have radiometric age dates of about 4. Achondrites - Achondrites are composed of the same minerals as chondrites, but lack the chondrules. They appear to have been heated, melted, and recrystallized so that the chondrules are no longer present.
Most resemble igneous rocks found on the Earth. Irons - Iron meteorites are composed of alloys of iron and nickel. They are easily recognized because they have a much higher density than normal crustal rocks. Thus, most meteorites found by the general populace are iron meteorites. This pattern results from slow cooling of a once hot solid material. Most research suggest that such slow cooling occurred in the core of much larger body that has since been fragmented.
Iron meteorites give us a clue to the composition of the Earth's core. Stony Irons - Stony iron meteorites consist of a mixture of stony silicate material and iron.
Some show the silicates embedded in a matrix of iron-nickel alloy. Others occur as a breccia, where fragments of stony and iron material have been cemented together by either heat or chemical reactions. Origin of Meteorites Most meteorites appear to be fragments of larger bodies called parent bodies. These could have been small planets or large asteroids that were part of the original solar system.
There are several possibilities as to where these parent bodies, or their fragments, originated. It consists of a swarm of aboutobjects called asteroids.
CHAPTER 5: PLANETARY GEOLOGY: Manual of Remote Sensing
Asteroids are small rocky bodies with irregular shapes that have a cratered surface. About 4, of these asteroids have been officially classified and their orbital paths are known.
Once they are so classified they are given a name. The asteroids are either remnants of a planet that formed in the region between Mars and Jupiter but was later broken up by a collision with another planetary body, or are fragments that failed to accrete into a planet.
The latter possibility is more likely because the total mass of the asteroids is not even equal to our moon. It does appear that some of the asteroids are large enough to have undergone internal differentiation. Differentiation is a process that forms layering in a planetary body i. If these larger asteroids did in fact undergo differentiation, then this could explain the origin of the different types of meteorites.
Because of the shapes of the asteroids it also appears that some of them have undergone fragmentation resulting from collisions with other asteroids. Such collisions could have caused the larger bodies to be broken up into the smaller objects we observe as meteorites.
The Asteroids as Parent Bodies of Meteorites Much evidence suggests that the asteroids could be the parent bodies of meteorites. The larger ones could have differentiated into a core, mantle, and crust. Fragmentation of these large bodies would then have done two things: First the fragments would explain the various types of meteorites found on Earth - the stones representing the mantle and crust of the original parent body, the irons representing the cores, and the stony irons the boundary between the core and mantle of the parent bodies.
Second, the collisions that caused the fragmentation could send the fragments into Earth-crossing orbits. Some of the asteroids have orbits that bring them close to Earth. These are called Amor objects. Some have orbital paths that cross the orbital path of the Earth. These are called Earth-crossing asteroids or Apollo objects. About NEOs with diameters between 1 and 8 km are known, but this is only a fraction of the total number.
Many NEOs will eventually collide with the Earth. These objects have unstable orbits because they are under the gravitational influence of both the Earth and Mars. The source of these objects is likely the asteroid belt. These orbits are not circular like those of the planets and are not necessarily within the same plane as the planets. Most comets have elliptical orbits which send them to the far outer reaches of the solar system and back toward a closer approach to the sun. As a comet approaches the sun, solar radiation generates gases from evaporation of the comet's surface.
These gases are pushed away from the comet and glow in the sun light, thus giving the comet its tail. While the outer surface of comets appear to composed of icy material like water and carbon dioxide solids, they likely contain a more rocky nucleus. Because of their eccentric orbits, many comets eventually cross the orbit of the Earth.
Many meteor showers may be caused by the Earth crossing an orbit of a fragmented comet. The collision of a cometary fragment is thought to have occurred in the Tunguska region of Siberia in The blast was about the size of a 15 megaton nuclear bomb.
It knocked down trees in an area about square miles, but did not leave a crater.