Vesta Asteroid Fragments

Part of Hall of Meteorites.

C.6. VESTA hero.jpg
Between the orbits of Mars and Jupiter there is a wide gap.

In the early 1800s, astronomers searching for the “missing” planet in this gap instead discovered smaller objects, which they named asteroids. Today, the known asteroids, including "dwarf planets" Ceres and Vesta, number nearly a million.

Asteroids range from pebble sized to 950 kilometers (590 miles) in diameter. Similar objects were once common throughout the solar system. Most eventually merged into the full-fledged planets, but in the asteroid belt between Jupiter and Mars, Jupiter’s gravitational pull keeps them from combining. The surviving asteroids—and broken pieces that reach Earth as meteorites, such as these samples of Vesta—offer a rare glimpse of the early stages of planet formation.

The Path to Earth

Although the meteorites in this case were long suspected to have come from Vesta, for many years no one could figure out how they got to Earth. Vesta orbits more than twice as far from the Sun as Earth does—and both orbits are nearly circular, so their paths never come close to crossing. How, then, could a piece of Vesta ever reach Earth?

The mystery was solved when scientists discovered a group of small asteroids whose light signatures showed they were once part of Vesta. Some of these "Vestoids" appear to be drifting toward a gap in the asteroid belt.

Diagram of part of Vesta, the Vestoids and the 3:1 resonance gap.
Several Vestoids—small asteroids ejected from Vesta by impacts—appear to be drifting out to a gap in the asteroid belt. Objects in this gap complete exactly three orbits for every one orbit of Jupiter, causing them to pass Jupiter at the same point on every third orbit. This resonance and repeated gravitational tugs from Jupiter eventually pull them into longer, narrower orbits—which can send them toward Earth.

Objects in these gaps are pulled into new orbits by Jupiter's gravity, which could eventually send them flying toward Earth. Similar journeys in the past could account for the rocks from Vesta that have already found their way to Earth.

Illustration of inner solar system showing large belt of asteroids and pointing out three gaps in it.
Asteroids orbit the Sun in a large belt punctuated by distinct gaps. These “Kirkwood gaps” are areas that have been cleared out by Jupiter’s gravitational pull. Two different clusters of asteroids share Jupiter’s orbit.

Volcanism on Vesta

When searching for a meteorite's source, experts can sometimes link a group of related meteorites to a type of asteroid or a region in the asteroid belt. Just one group, the HED meteorites—composed of the howardites, eucrites and diogenites—has been traced back to a specific asteroid, Vesta.

How do we know these meteorites came from Vesta? The composition of an asteroid's surface can be determined by the way it reflects sunlight. Vesta is the only large asteroid whose "light signature" matches the basaltic rock of the HED meteorites; each meteorite type matches a different part of Vesta's surface.

The three types of HED meteorites tell the story of the sometimes violent processes that shaped Vesta. The eucrites are hardened lava that flowed onto Vesta's surface; the diogenites come from rock buried deeper down; and the howardites are a mixture of the other two, created by impact mixing.

A Hubble Space Telescope image of the Vesta asteroid.
Vesta is the second-largest asteroid in the solar system, with a diameter of 525 kilometers (325 miles). Covering most of one side is a giant crater with a central uplift. The huge impact that made this crater knocked off more than enough material to account for all the HED meteorites.
P. Thomas, B. Zellner and NASA


In This Section

C.6.2.1. Millbillillie hero.jpg


C.6.2.2. Kapoeta  Mixed by impacts hero.jpg


Mixed by Impacts

Howardites were created by impacts that crushed and mixed different parts of Vesta and melted enough rock to cement them together. In both Kapoeta and Bholghati, the contrast between different colored materials is visible to the naked eye.

C.6.2.2. Bholghati Mixed by impacts hero.jpg


C.  Johnstown meteorite hero.jpg


Buried by Crystals

Diogenites are made of molten rock that was trapped beneath Vesta's surface. As a result, they cooled much more slowly than the eucrites, so their crystals had more time to grow.

This photo of a diogenite is magnified 40 times—exactly the same amount as the eucrite. The eucrite's smaller crystals indicate that it hardened closer to Vesta's surface.

C. Pasamonte hero.jpg


Surface Lava

Eucrites resemble lava from Hawaiian volcanoes. They formed much the same way, when molten basaltic rock flowed onto Vesta's surface. This lava cooled and hardened so quickly that only very small crystals had time to form.

The rapid cooling on Vesta's surface also prevented iron and magnesium from spreading evenly through the larger pyroxene crystals, causing the shifting colors in the magnified photo at right.

C.6.2.5. Juvinas hero.jpg


C.6.2.6. Ibitra. Look closely hero.jpg


Look Closely

Ibitira contains thousands of bubbles, or vesicles. These bubbles formed when molten lava flowed onto Vesta's surface, where the sudden drop in pressure caused gases dissolved in the lava to form bubbles-just as bubbles form in soda when a bottle is opened.

C.6.2.7.  Shalka hero