Hungaria family

The Hungaria asteroids are a group of asteroids in the main belt that orbit the Sun between 1.78 and 2.00 AU. The asteroids typically have a low eccentricity (below 0.18) and an inclination of 16 to 34 degrees. [ [http://www.easysky.de/eng/screenshots/index.htm EasySky - Screenshots ] ] They have an orbital period of approximately 2.5 years. They have a resonance with Jupiter of 9:2 and with Mars of 3:2. They are named after the largest member, 434 Hungaria, and are the innermost dense concentration of asteroids, lying somewhat inwards of the "core" of the main belt that lies beyond the 4:1 Kirkwood gap.

Most Hungarias are E-type asteroids, which means they have extremely bright enstatite surfaces and albedos typically above 0.30. Despite their high albedos, none can be seen with binoculars because they are far too small: the largest (434 Hungaria) is only about 20 km in size. They are, however, the smallest asteroids that can regularly be glimpsed with amateur telescopes [ [http://www.socastrosci.org/2006%20papers/Warner_AsteroidLightcurves.pdf Asteroid lightcurves] ] .

The origin of the Hungaria group of asteroids is well known. At the 4:1 orbital resonance with Jupiter that lies at semi-major axes of 2.06 AU, any orbiting body is sufficiently strongly peturbed to be forced into an extremely eccentric and unstable orbit, creating the innermost Kirkwood gap. Interior to this 4:1 resonance, asteroids in low inclination orbits are, unlike those outside the 4:1 Kirkwood gap, strongly influenced by the gravitational field of "Mars". Here, instead of Jupiter's influence, perturbations by Mars have, over the lifetime of the Solar System, thrown out all asteroids interior to the 4:1 Kirkwood gap except for those far enough from Mars' orbital plane where that planet exerts much smaller forces.cite journal
author=Spratt, Christopher E.
title=The Hungaria group of minor planets
journal=Royal Astronomical Society of Canada, Journal (ISSN 0035-872X)
year=1990
date=April 1990
volume=84
issue=2
pages=123–131
url=http://adsabs.harvard.edu/abs/1990JRASC..84..123S ]

This has left a situation where the only remaining concentration of asteroids inward of the 4:1 resonance lies at high inclination orbits, although they have fairly low eccentricities. However, even at the present time in Solar System history some Hungaria asteroids cross the orbit of Mars and in the process of still being ejected from the solar system due to Mars' influence (unlike asteroids in the "core" of the Main Belt, where Jupiter's influence predominates).

Long-term changes in the orbit of Mars are believed to be a critical factor in the removal of Hungaria asteroids. At the highest eccentricities, similar to the extreme values observed today or even slightly greater, Mars will perturbe Hungaria asteroids and force them into ever more eccentric and unstable orbits when their ascending node is close in longitude to Mars' aphelion [ [http://main.chemistry.unina.it/~alvitagl/solex/MarsDist.html Distance of Mars from Earth] ] . This ultimately leads over millions of years to the formation of the short-lived Amor asteroids and Earth-crossers.

ee also

* E-type asteroid
* Aubrite
* (144898) 2004 VD17
* 64 Angelina
* 3103 Eger
* 44 Nysa
* 55 Pandora
* 2867 Šteins

References