The Hungaria group is a dynamical group of asteroids in the asteroid belt. The Hungaria asteroids orbitthe Sun with a semi-major axis between 1.78 and 2.00 astronomical units. They are the innermost dense concentration of asteroids in the Solar System—the near-Earth asteroids are much more sparse—and derive their name from their largest member 434 Hungaria. The Hungaria group includes the Hungaria family, a collisional asteroid family which dominates its population.
Description
The Hungaria asteroids typically share the following orbital parameters:
The 4:1 resonance Kirkwood gapmarks the outer boundary of the Hungaria family, while interactions with Mars determine the inner boundary. For comparison the majority of asteroids are in core region of the asteroid belt, which lies between the 4:1 gap and the 2:1 gap. Most Hungarias are E-type asteroids, which means they have extremely bright enstatitesurfaces and albedos typically above 0.30. Despite their high albedos, none can be seen with binoculars because they are far too small: the largest is only about 11 km in size. They are, however, the smallest asteroids that can regularly be glimpsed with amateur telescopes. 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 perturbed 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's orbital plane where that planet exerts much smaller forces. 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 are still in the process of being ejected from the Solar System due to Mars's influence. Long-term changes in the orbit of Mars are believed to be a critical factor in the current removal of Hungaria asteroids. At the highest eccentricities, similar to the extreme values observed today or even slightly greater, Mars will perturb Hungaria asteroids and force them into ever more eccentric and unstable orbits when their ascending node is close in longitude to Mars's aphelion. This ultimately leads over millions of years to the formation of the short-lived Amor asteroids and Earth-crossers.
