Vesta

The second-largest asteroid in the solar system is a puzzler. Most studies say it has the same layers as a planet, but that it’s not massive enough to pull itself into a fully rounded shape like a planet. But one study found that it’s not layered at all.

Vesta accounts for almost a tenth of all the mass in the asteroid belt. Its average diameter is about 325 miles. But it’s flattened and a bit stretched out.

The surface of Vesta is covered with volcanic rock. Combined with other observations, that suggests that Vesta is layered, with a distinct core, mantle, and crust. If so, then it formed very early in solar-system history, allowing it to incorporate a lot of radioactive material. Heat from radioactive decay partially melted it, allowing heavier materials to sink to the center and lighter ones to float to the surface.

But a study last year contradicted that. Using delicate measurements of Vesta’s gravity field, scientists determined that the asteroid isn’t fully layered. It might have started to develop layers, but never got hot enough to finish the job. Or it might have formed from debris blasted off a larger body by a giant impact – creating a massive space rock that’s all jumbled up.

Vesta lines up opposite the Sun in our sky tonight. It’s brightest for the year, and it’s in view all night. Even so, you need binoculars to spot it. It’s not far below the bright planet Saturn, which is low in the east at nightfall.

Script by Damond Benningfield