4 VESTA - HOWARDITE I EUCRITE I DIOGENITE

Howardite | Eucrite | Diogenite

Welcome to the fascinating world of the HED meteorites! If you’ve ever gazed up at the night sky and wondered about the mysteries of the asteroid belt, you’re not alone. Among these celestial treasures that fall to Earth are meteorites from some of the largest asteroids in the asteroid belt. Particularly those widely thought to originate from the second largest differentiated asteroid Vesta. Click here to read about why some researchers are not convinced the HED clan of meteorites are from Vesta or the Vestoids. The meteorites from Vesta and the Vestoids (more on that later) are collectively part of the HED Clan of achondrite meteorites. The HED clan includes three distinct types: Howardite, Eucrite, and Diogenite. Each of these tell a unique story about the formation processes and impact events associated with Vesta and the Vestoids (V-type asteroids). They also help us better understand our solar system as a whole and the processes that shaped it.

Vesta was discovered in 1807 by the German astronomer Heinrich Wilhelm Olbers. It originally had the number 4 in its name to indicate that it was the fourth asteroid to be discovered. When it was first found, Heinrich and other astronomers thought Vesta was a planet like Mars and the Earth. At that time astronomers were still learning how to distinguish between planets and large asteroids. Since then, astronomers became better at determining the difference between a large asteroid and a planet. Now that so many other asteroids have been discovered, most people simply refer to it as Vesta and have stopped using the number 4 when referring to it.

Eucrites are primarily composed of basaltic minerals such as calcium-rich feldspar, and pyroxene. They are thought to be remnants of lava flows on Vesta's surface or hypabyssal near-surface intrusive magmas. Their composition reveals a lot about the geological history of Vesta's surface and upper crust, and the conditions that existed on the asteroid billions of years ago. Studying eucrites can help us understand not just Vesta, but also the early conditions of our own planet.

Eucrites are often what are known as impact breccia, with varying sized fragmented clasts embedded within a finer grained matrix. However, not all eucrites are breccia. Some are unbrecciated, and likely look a lot like they did while still part of Vesta's crust. The rarest of the eucrites are not only unbrecciated but also unequilibrated. These eucrites are the most primitive of the HED meteorites and represent material that has not changed much from when it first crystallized into a rock from the hot magma on or just below the Vestan surface. 

 

Eucrites available for collectors and institutions

Diogenites, which unlike the eucrites have little or no feldspar, are primarily composed of low-Ca pyroxene. Diogenites will sometimes have significant amounts of olivine, but this is less common. Like eucrites, diogenites can be either impact breccias or unbrecciated. Diogenites represent a deeper region of the crust of Vesta. These meteorites are less common than the eucrites, and provide a glimpse into the more primitive materials that formed the building blocks of our solar system. They are an interesting example of the complex internal processes that lead to the formation of these larger differentiated asteroids, planets and moons.

Diogenites available for collectors and institutions

Howardites are a mix of both eucrites and diogenites, making them a fascinating combination of materials. They are primarily composed of basaltic rock and provide insights into the volcanic activity that once occurred on Vesta. When you hold a Howardite, you’re holding a piece of history that showcases the dynamic processes that shaped this ancient celestial body. If an HED has more than 10 vol% of either eucrite or diogenite it is considered a howardite. For example, if an HED meteorite has a composition of 70% eucrite and 30% diogenite it will be considered a howardite. Conversely, if it has 70% diogenite and 30% eucrite it will also be considered a howardite. If an HED meteorite has 91% eucrite (or more) and 9% (or less) diogenite, it remains a eucrite. The reverse is also true, so that if an HED meteorite has 91% diogenite (or more) and 9% (or less) of eucrite it remains a diogenite. In a very real sense, the howardite meteorites are not a completely different type of HED meteorite. They are simply a mix of the only two distinct types of meteorites from Vesta. And what a beautiful mix they are!

Whether you’re a budding astronomer, a meteorite collector, a geology enthusiast, or simply curious about the cosmos, learning about these meteorites can be an exciting journey. Each piece is a tangible connection to our Solar System, and hopefully sparking curiosity and wonder about our place in it. So, if you ever come across a Howardite, Eucrite, or Diogenite, take a moment to appreciate the incredible story it carries from the depths of space to your hands.

We invite everyone to embrace the adventure of learning about meteorites and to let your curiosity guide you through the cosmos. The Solar System is vast and full of mysteries waiting to be uncovered, and every meteorite is a stepping stone on that journey.

HED Achondrite meteorites available for collectors and institutions