Hungaria family

The Hungaria family is a group of asteroids in the asteroid belt. The Hungaria asteroids orbit the Sun with a semi-major axis (longest radius of an ellipse) between 1.78 and 2.00 astronomical units (AU). 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 asteroids typically share the following orbital parameters:

The 4:1 resonance Kirkwood gap (at 2.06 AU) marks 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 (at 2.06 AU) and the 2:1 gap (at 3.27 AU).

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 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.

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