Asteroids

The different groups of asteroids (Atens,Amors,Apollos,Trojans,TNOs) are one one of the best studied celestial bodies at the ADG in Vienna. Different research work has been done to explain the stability properties of these objects and to investigate their collision possibilities.
 

The Asteroid Belts

On distinguishes four different asteroidal belts in our solar system. There are :

  • the NEAs the Near Earth Asteroids (1)
  • the Mainbelt between Mars and Jupiter (2)
  • the Trojanbelt in the 1:1 resonance with Jupiter (3)
  • the Kuiperbelt outside the neptunian orbit (4)

In the diagram above, you can see the different gaps an groups in the asteroid distribution of the main belt.Their reason are the resonances : If the orbital movement of an asteroid and an major planet shows an integer relation (i.e. if Jupiter performs 1 revolution, a trojan asteroids performs also 1 revolution -


this is the 1:1 resonance), then this can result in a stabilisation or perturbation of the asteroidal orbit. You can see the so called Kirkwood gaps, i.e. at the 3:1 or the 5:2 resonance.
The picture on the right shows the Kuiperbelt, which surrounds our solarsystem.

    


Danger for Earth ?


During earth history, our planet was often target for objects from space. Everyday, about 6 t. of material go down on earth. But really big objects hitting the earth are a rather uncommon event. On the diagramm you can see the probability of an impact as a function of the amount of destructive power. Objects with an explosive force as the Hiroshima bomb hit the earth, statisticaly spoken, every year. Catastrophes like the event the killed the dinosaurs happen statistically seen every Billion years.


The Barringer crater in the desert of Arizona is the remanent of an object with about 300000 tons. It is one mile wide an 570 feet deep.The right pictures compares its size with the city of New York

The "mysterious" event at Tugunska in Sibira whas the effect of a huge meteor impact, which exploded before it hit the earth, the effects of the shockwave are visible in the picture

A Tsunami - a giant flood wave - is an event, which is caused by an impact in the ozean. But it can also be caused by earthquakes under the sea.

65 million years ago, a giant meteor hit the northern part of the mexican peninsula Yucatan. This has caused the dying of the dinosaurs. On satellite photos one can see the crater with an diameter of 200 km !
   


Collision with Atens ?

The NEAs, the Near Earth Asteroids kann be divided in 3 different groups :
  • the ATENS, with an semimajor axis smaller than that of earth
  • the APOLLOS, with an semimajor axis bigger than that of earth
  • the AMORS, witch do not cross the earth orbits and stay inside the orbit of mars

In a work of R.Dvorak and E.Pilat-Lohinger, the Aten encounters with earth and venus had been examined. For this calculations 4 different modells were used. A 9 body system (the whole solar system), one with 8, one with 6 bodies and one just with sun, earth,mars and jupiter.The result of some test caculation showed, that the 6 body system (Solarsystem without mercury, uranus, neptune and pluto) gives the best results.

On the 3 pcitures on the right you can see, that the encounters of the ATENS with earth and venus correlates with jumps in inclination and semimajor axis. This special asteroid (2062 ATEN) later develops to an APOLLO. The table below shows the different encounters with earth .The Earth encounter with the asteroid 34955, which happens 5000 years ago, could be observerd by the ancient cultures, because the object was bright enough to be seen. The second table shows, that their is a bigger probability for the ATENS to hit the venus, than the earth.

   
  
  

The Apollos

An other work should research the "mixing" between Atens and Apollos. Therfore, the orbital elements of 24 Atens and 54 Apollos, were calculated numerically. The pictures on the left show the values of eccentricity and inclination before and after the integration over 500000 years (squares - Apollos, circles - Atens). One can see, that 3 Apollos became Atens, and 5 Atens became Apollos.
In the table below, one can see the collision probability of the different groups of asteroids. It shows, that the collision with an Aten is much more probable than with an Apollo. The big objects (Aten I) have a smaller collision probability then the small objects (Aten II).


   
  


What are the trojans ?

This work should explain the role of the trojan asteroids with positive Liapunovexponents, which mean that they show a chaotic behaviour. Such asteroids are know as "asteroids in stable chaotic motion". The table below shows the very short Liapunovtimes (the smaller, the more chaotic) of these trojans.

For the numerical integration of this objects the calculation of orbital elemenst during 100 million years, 11 intervalls were chosen, in which the evolution of the elements was observed for 1 million years. The r.m.s of the semimajor axis, the inclination and the eccentricity was calculated. These values were compared with the "proper elements". The pictures below (left) show the evolution of e and i for 4 asteroids (upper picture : L4 - Phoinix and 1991 HN, lower picture : L5 - Mentor and Achates). One can see the different behaviour which correspondends with the different Liapunov times.

The last two pictures show the correlation between rms(e) an ep (eccentricity) for Mentor. This connection holds also for the other parameters, but not for ip (inclination) and rms(i), which can be seen on the lower picture.