HED meteorite
HED stands for howardite, eucrite, diogenite. This acronym defines a specific clan of achondrite meteorites that make up about 5% of all falls to Earth. These rocks account for roughly 60% of all known achondrites. Scientists broadly divide the group into three primary categories: Howardites, Eucrites, and Diogenites. Several subgroups exist within both the eucrite and diogenite families. The diversity suggests complex geological histories rather than simple formation events.
All members of this meteorite family trace their roots to the crust of asteroid Vesta. No matter their final composition on Earth, they share a common birthplace in space. Differences in chemical makeup result from ejection at different moments during Vesta's geologic history. Radioisotope ratios confirm these crystallization ages fall between 4.43 billion years and 4.55 billion years. These dates place the formation of the parent body near the dawn of our solar system. The rocks are differentiated, meaning they formed through igneous processes similar to those creating magmatic rocks on Earth.
Extensive igneous processing shaped the internal structure of the HED parent body before any debris ever left its surface. This process created textures and mineral compositions that closely resemble terrestrial igneous rocks. The differentiation occurred deep within the crust of the asteroid itself. Radioisotope dating provides the timeline for when these molten materials cooled into solid rock. Scientists analyze these ratios to determine the precise age of each sample. The data confirms that the parent body underwent significant melting and cooling cycles early in solar system history.
A massive impact event on the southern hemisphere of Vesta ejected debris into space less than 1 billion years ago. An enormous crater now covers much of this southern region and serves as the primary candidate for the site of this collision. The amount of rock excavated from this single hole exceeds the total volume required to account for all known V-type asteroids. Some debris traveled outward as small asteroids with diameters of roughly one kilometer or less. Other fragments formed the distinct Vesta family while others scattered further across the main belt.
Gravitational perturbations by Jupiter moved some of the far-flung asteroid debris toward unstable regions of the solar system. These objects eventually settled into the 3:1 Kirkwood gap, an area where orbits become highly unpredictable. Asteroids entering this zone get ejected into very different paths over a timescale of about 100 million years. Some bodies were perturbed into near-Earth orbits, creating small V-type asteroids like 3551 Verenia. Others such as 3908 Nyx and 4055 Magellan followed similar trajectories toward our planet. Smaller impacts on these near-Earth objects later dislodged rock-sized meteorites that struck Earth.
Most HED meteorites spent between 6 million and 73 million years traveling through space before impacting Earth. Cosmic ray exposure measurements provide the data for this duration estimate. Scientists believe these rocks arose from several distinct impact events rather than a single explosion. The long transit time allowed cosmic rays to penetrate the surface layers of the falling stones. This radiation history helps researchers distinguish between samples originating from different parent fragments. The variation in exposure ages reflects the complex journey from the asteroid belt to terrestrial soil.
Continue Browsing
Common questions
What does the acronym HED stand for in meteorite classification?
HED stands for howardite, eucrite, and diogenite. This acronym defines a specific clan of achondrite meteorites that make up about 5% of all falls to Earth.
Where did HED meteorites originate before reaching Earth?
All members of this meteorite family trace their roots to the crust of asteroid Vesta. No matter their final composition on Earth, they share a common birthplace in space.
When were HED meteorites formed according to radioisotope dating?
Radioisotope ratios confirm these crystallization ages fall between 4.43 billion years and 4.55 billion years. These dates place the formation of the parent body near the dawn of our solar system.
How long do most HED meteorites travel through space before impacting Earth?
Most HED meteorites spent between 6 million and 73 million years traveling through space before impacting Earth. Cosmic ray exposure measurements provide the data for this duration estimate.
Why are there differences in chemical makeup among HED meteorites?
Differences in chemical makeup result from ejection at different moments during Vesta's geologic history. Scientists believe these rocks arose from several distinct impact events rather than a single explosion.