4 Vesta

At a glance

Key points

A giant impact basin nearly as wide as Vesta covers its south pole.

• Crust, mantle and iron core like a mini-planet
• Rheasilvia basin is nearly as wide as Vesta
• Some meteorites on Earth came from Vesta

Surface

Rheasilvia, about 500 km wide, spans about 95% of Vesta's mean diameter and overlaps an older basin, Veneneia. Its central peak is among the tallest mountains in the Solar System. Troughs circling the equator, including Divalia Fossa, formed as the impact shock rang through the body.

Exploration

Dawn orbited Vesta from July 2011 to September 2012 before leaving for Ceres, the first spacecraft to orbit two worlds beyond Earth.

A patchwork of light and dark

Vesta has one of the widest ranges of surface brightness of any rocky body. The pale material is basaltic crust; the dark streaks and splotches are thought to be carbon-rich debris from roughly 300 small dark asteroids, 1 to 10 km across, that struck it over the past 3.5 billion years. The Rheasilvia impact itself, less than a billion years ago, removed about one percent of Vesta's mass and launched the fragments that still reach Earth as HED meteorites.

Observing it

Vesta is the brightest asteroid in Earth's sky, because its surface reflects about 42% of incoming light, more than four times as much as Ceres. In a telescope it shows no disc: it looks like a star that shifts against the background from night to night. In October 2026 it reaches opposition in Cetus at about magnitude 6.4, just below naked-eye visibility for most people but easy in binoculars. At the most favourable oppositions it approaches magnitude 5.

What we still don't know

How Vesta survived intact while most protoplanets of its kind were destroyed or absorbed. A 2025 reanalysis of Dawn's tracking data found its interior less strongly layered than earlier models assumed, pointing to a smaller iron core. The authors offer two explanations, both still debated: Vesta never fully separated into layers, or it reassembled from the debris of a larger, layered body.

Missions

1. 2007–2018

   Dawn

   NASACompleted

   Orbited Vesta (2011–2012) then Ceres (2015–2018) with ion propulsion.

Related entries

• Main asteroid beltRocky debris between Mars and Jupiter
• CeresDwarf planet · largest body in the asteroid belt

Sources

1. Park et al. 2025, A small core in Vesta, Nature Astronomy (opens in a new tab)
2. JPL Small-Body Database: 4 Vesta (opens in a new tab)
3. NASA Science: 4 Vesta (opens in a new tab)
4. NASA JPL: Horizons ephemeris system (opens in a new tab)

Last reviewed 10 Oct 2026 against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.