Basic Feature Guide

The following guide is designed to accompany Asteroid Mappers.

There are many, many different types of features on planetary surfaces such as Vesta. Below are some example features that you may come across in your explorations:

Example images from Vesta

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Light Albedo Feature

Bright albedo feature (Ejecta)

Bright albedo feature

When craters are formed, the impact scatters about the crater a blanket of bright material. Called an ejecta deposit, it is made of pulverized material. This ejecta appears very bright when first formed, but slowly fades as it ages due to interactions with micrometeorites and the radiation of space. When you see craters with bright ejecta and bright rays, you are seeing some of the youngest features. Studying young craters is an important part of asteroid science, but to do that, we need to know where they are!

Dark Albedo Feature

Dark albedo feature (Ejecta)

Dark albedo feature

Dark features can come from either volcanic eruptions, or more commonly through special, impact craters.

Sometimes an impact event that forms a crater punches through the top, light-colored layer and excavates a darker layer from underneath. When this happens, the dark colored material gets thrown into the air and falls to the  surface to form a crater ejecta. This material appears dark in contrast to the surrounding surface, so we mark it as a dark albedo feature.




Boulders are strewn across the surface of Vesta, but they are highly non-uniform. Sometimes we find them at the bottom of craters, sometimes on crater walls. Other times strewn around the rims of large craters. We may even find evidence of rolling boulders.

And yet, there are many craters that don’t seem to have any boulders in or near them whatsoever. Help us figure out where they are by marking them with the Mark Boulder tool. Look carefully, as they may be very small!

Concentric Craters

Concentric craters

Concentric crater

Sometimes craters look like there is one crater nested just inside a slightly larger crater. This is not a freak accident, where one crater impacted just inside another one (though that does occur, but very very rarely). Scientists think these craters form when the region impacted consists of two layers of very different material; a weak rubble (or regolith) layer on top of a harder rock layer. The weak layer is more easily ejected by the impact than the hard layer, forming a slightly larger crater in the regolith than in the rock below. These craters allow us to understand the depth of different layers of material in different regions of the moon.

Crater Chains

Discrete crater chains

Discrete crater chain

One of the most intriguing types of feature is the crater chain. These streaks of craters can be formed through three types of events: a broken object hitting the asteroid or material scattered during a “primary” impact event.

Sometimes, when a large crater is formed, the impact can hurl large blocks of material (ejecta) that land in a row. This forms chains of craters that we call “secondary craters” (since they formed as a result of the main, primary crater). If you see a bunch of craters in a row, the most common explanation is that they formed from these secondary impacts.

Ropy crater chains

Ropy crater chain

In some, much rarer cases, crater chains can also form when a string of broken up asteroid or comet pieces hits. Gravitational disruptions and impacts between objects can sometimes break up comets and asteroids. These broken up pieces may continue along the same orbital path, but spread out as they travel. When these strings of rock or ice hit an object they can form crater chains.

Odd Shaped Feature

What to do if you see something that looks weirdly shaped and you don’t know what it is? Or, you know what it is but we don’t have a specific selection option for it, say, an elliptical crater. Use this classification.

Odd Albedo Feature

If you see a feature that doesn’t seem to have any three-dimensionality to it but is rather a bright or dark splotch, select this option. We never know what we might find!


We may not have a pull-down item for something that you see. You may not know at all what you see other than it’s weird – you can’t tell if it’s light or dark, there’s a topography difference, or anything else. Use this option if all else fails.

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