Vesta: The Giant Asteroid Visited by Dawn

Vesta at a glance

Vesta orbits in the main asteroid belt. Heinrich Olbers found it on March 29, 1807, at Bremen, according to JPL's Small-Body Database. NASA says it is the second most massive body in the main belt, accounting for almost 9 percent of the total mass of all asteroids.

An astronomical unit (AU) is the average distance from Earth to the Sun, about 149.6 million km (93 million miles). Vesta's surface reflects about 42 percent of the sunlight that reaches it, much more than the dark C-type asteroids that NASA describes as the most common kind.

A small world with layers

Many asteroids are rubble piles, as the guide to what asteroids are explains. Vesta is different. NASA says Vesta has separated into a crust, a mantle and a core, a layering shared with the terrestrial planets. JPL's summary says Vesta is more closely related to the terrestrial planets, including Earth, than to typical asteroids. NASA's Dawn science page says its results suggest "pervasive, perhaps even global melting" early in Vesta's history, and that Vesta is poor in volatiles, the easily vaporized materials such as water.

Gravity measurements from Dawn put the iron core at about 225 km (140 miles) in diameter. A body that melted and sorted its materials by weight, with heavy iron sinking and lighter rock floating up, is called differentiated. Differentiation is the reason Vesta acts more like a small planet than a pile of leftovers. NASA's Ceres page makes the same point, saying internal differentiation is a feature typical of small planets like Ceres and Vesta.

The giant basins

Two large impacts shaped Vesta's surface. Rheasilvia is the younger, about 500 km (310 miles) wide and about 19 km (12 miles) deep. Veneneia is the older, about 400 km (250 miles) wide. In the middle of Rheasilvia rises a central peak 19 to 26 km (12 to 16 miles) high and more than 160 km (100 miles) wide. NASA says it competes with Olympus Mons on Mars for the title of tallest mountain in the Solar System. JPL describes it as more than twice the height of Mount Everest.

The impacts also left what NASA calls planet-encircling trough systems. JPL counts more than 90 chasms, some as large as the Grand Canyon. Young craters show pitted terrain and gullies, which NASA reads as signs of released volatiles and perhaps short-lived water flow. Hydrated material on the surface is described as likely coming from outside Vesta.

The two impacts together threw out about 1 percent of Vesta. NASA says the debris ranged from sand and gravel to boulders and smaller asteroids, which are called Vestoids.

Dawn at Vesta

JPL calls Dawn the first probe to enter orbit around an object in the main belt, and says it is the only spacecraft with the capability to orbit two extraterrestrial destinations. Its ion engines made the double visit possible. JPL notes Dawn spiraled down to an altitude of 210 km (130 miles) above Vesta.

• September 27, 2007: Dawn launches.
• July 2011: Dawn enters orbit around Vesta.
• September 2012: Dawn leaves Vesta, after about 14 months in orbit.
• March 6, 2015: Dawn arrives at Ceres, a dwarf planet in the same belt.
• November 1, 2018: the mission ends.

As of November 11, 2026, the close-up maps and measurements of Vesta that NASA publishes still come from Dawn's visit in 2011 and 2012.

Dawn was an orbiter and did not bring anything home. Rock from Vesta was already on Earth in the form of meteorites, and Dawn's measurements let scientists confirm the link. Sample-return missions to other asteroids are covered in the stories of OSIRIS-REx at Bennu and of the Hayabusa missions.

Meteorites from Vesta

NASA's Dawn page says Dawn confirmed Vesta as the parent body of the howardite, eucrite and diogenite groups of meteorites, shortened to HED. The same page says about 6 percent of all meteorites found on Earth are attributed to the Vesta impacts it describes. JPL states that Vesta is the source of more meteorites on Earth than Mars or the Moon is. Those are two separate NASA statements, so quote each with its source.

How rock from one asteroid reaches Earth is a chain of events: an impact throws debris into space, the pieces drift for a long time, and some happen to cross Earth's path. Meteorites therefore give laboratories a way to study Vesta rock directly, without a spacecraft having to bring a sample back. The classes and names of those rocks are explained in the guide to the types of meteorites.

Common mistakes and myths

Myth: Vesta is the largest asteroid, full stop. NASA's asteroid pages call Vesta the largest asteroid, at about 530 km. Ceres is wider at about 939 km (583 miles) in JPL's database, but it has been a dwarf planet since 2006, per NASA.

Myth: all asteroids are shapeless piles of rubble. Vesta has a crust, mantle and core, according to NASA, and JPL says it is closer kin to the terrestrial planets than to typical asteroids.

Myth: meteorites from one asteroid must be a rarity. NASA attributes about 6 percent of meteorites found on Earth to the Vesta impacts, so rock from this single body makes up a notable share of what lands.

Myth: the giant impacts nearly destroyed Vesta. Vesta is still one body. By NASA's figure, about 1 percent of it was ejected by the two impacts.

Frequently asked questions

How big is Vesta?

NASA lists Vesta at about 530 km (329 miles) across. JPL's database gives 523 km (325 miles). The small gap comes from how the shape is measured.

Who discovered Vesta?

Heinrich Olbers discovered Vesta on March 29, 1807, at Bremen, according to JPL's Small-Body Database.

When did Dawn orbit Vesta?

NASA says Dawn circled Vesta from July 2011 until September 2012. It then continued to Ceres.

What does HED stand for?

HED stands for howardite, eucrite and diogenite, three groups of meteorites. NASA says Vesta appears to be their source, and its Dawn science page says Dawn confirmed Vesta as the parent body.