For millennia people have wondered about the unpredictable behaviour of Comets, Meteors and Asteroids in the Sky. As far as we know, the German Mathematician and Geographer Peter Apian (Petrus Apianus) was the 1st to postulate, in 1540, that a Cometary Tail always point away from the Sun. In 1619 Kepler suggested that this is because the light of the Sun exerts a Repulsive Force on the particles of the Cometary Tail. Keppler was the first to speculate on this "light pressure."
The depression named Nord-Linger Ries is a large circular depression in Western Bavaria, Germany, located North of the Danube in the now District of Donau-Ries.
The depression is interpreted as a major Meteor Impact Crater formed about 14 million years ago. The original crater rim had an estimated diameter of 24 km (15mi). The present floor of the depression is about 100 to 150m (330 to 490ft) below the eroded remains of the rim. The key evidence was the presence of Coesite, which, in none metamorphosed rocks, can only be formed by the shock pressures associated with meteorite impact.
Another impact crater, the much smaller (3.8km diameter) crater, is located about 42km(26mi) West-Southwest from the centre of Ries. The two craters are believed to have formed nearly simultaneously by the impact of a binary asteroid.
A binary asteroid is a system of two asteroids orbiting their common center of mass or the point around which they both orbit. Recent work suggests that most of them have a significant macro-porosity (a "rubble-pile" interior), and may have formed by disruption of a parent body after an oblique impact or fission.
Recent computer modelling of the Impact Event indicated that the impactors had diameters of about 1.5km (4900ft) (Larger One) and 150m (490ft) (Smaller One). They had a pre-impact separation of some tens of kilometers, and impacted the targeting area at an angle around 30 to 50 degrees from the surface in a West-SouthWest to East-NorthEast direction. The impact velocity is thought to have been about 20km/s (45000mph). The resulting explosion had he power of 1.8 million Hiroshima Bombs, an energy of roughly 2.4x10(x21) Joules.
Ivan Osipo-Vich Yarkov-Sky (24 May 1844-22 January 1902) was a Polish civil engineer working in Russia. By day, he was employed by the Alexand-Rovsk Railway company Moscow-Brest. He was obscure in his own time. In his spare time, he went deeply into the Physical Sciences and searched for a "Grand Theory" of the Physical World. In1888 he described a subtle Thermal Effect that he believed would act on planets and smaller objects orbiting the Sun. Writing in a pamphlet around the year 1900, he noted that the Diurnal Heating of a Rotating Object in Space would cause it to experience a Force that, while tiny, could lead to large long-term effects in the Orbits of Small Bodies, especially meteoroids and asteroids. This effect fell into oblivion. In 1950, longer after his death, his work on the Effects of Thermal Radiation on small objects in the Solar System (Asteroids) was re-discovered and now is so-called Yarkov-Sky Effect in Planetary Astronomy.
The effect is a consequence of the Fact that change in the temperature of an object warmed by radiation (and therefore the intensity of Thermal Radiation from the Object) lags behind changes in the incoming radiation. The surface of the object takes time to become warm when first illuminated; and takes time to cool down when illumination stops.
The Diurnal Effect on a rotating body illuminated by the Sun (e.g. an asteroid or the Earth) is that the surface is warmed by Solar Radiation during the day, and cools at night. Due to the Thermal Properties of the Surface, there is a lag between the absorption of Radiation from the sun, and the Emission of that same Radiation as Heat, so the warmest point on a rotating body occurs around 2 PM site on the surface, or slightly at Noon. This results in a difference between the directions of Absorption and Re-emission of Radiation, which yield a Net Force along the Direction of Motion of the Orbit. If the Object is a pro-grade rotator, the Force is in the direction of motion of the orbit, and causes the Semi-Major Axis of the Orbit to increase steadily; the Object spirals away from the Sun. A retro-grade rotator spirals inward. The Diurnal Effect is the component for Bodies with diameter greater than about 100 m.
The Seasonal Effect is the easiest to understand for the case of a non-rotating orbiting the Sun, for which Each Year consists of exactly One Day. As it travels around its orbit, the "Dusk" Hemisphere which has been heated over a long preceding time period is invariable in the direction of Orbital Motion. The excess of Thermal Radiation in this direction causes a Breaking Force which always causes Spiraling Inward toward the Sun.
In practice, for Rotating Bodies, the Seasonal Effect increases along with the Axial Tilt. It dominates only if the Diurnal Effect is small enough. This may occur because of very rapid Rotation (no time to cool off on the Night Side, hence an almost uniform longitudinal temperature distribution), small size (the whole body is heated throughout) or an Axial Tilt close to 90 degrees.
The Seasonal Effect is more important for smaller Asteroid Fragments (from a few metres up to about 100m), provided their surfaces are not covered by an insulating layer of loose, heterogeneous superficial material, and they do not have exceedingly slow Rotations. Additionally, on very long time-scales over which the Spin Axis of the Body may be repeatedly changed due to collisions (and hence also the direction of the Diurnal Effect changes), the Seasonal Effect will also tend to dominate.
In general, the effect is size dependent, and will affect the semi-major Axis of smaller asteroids, while leaving large asteroids practically unaffected.
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