Confirmed: Vesta, the second largest of the asteroids, is a runt planet.

Observations by NASA’s Dawn spacecraft show that Vesta formed within the first few million years of the solar system, that its surface is in places as bright as snow and in others as dark as coal, and that it contains an iron core that may have even briefly generated a magnetic field — all very planetlike features.

Both Vesta and Ceres, the largest asteroid and the Dawn’s next destination, are also heavy enough that gravity has made them round.

“The Dawn team finds itself calling these things planets all the time,” Christopher T. Russell, the mission’s principal investigator, said in an interview.

In the current parlance of astronomers, however, Vesta and Ceres, like Pluto, are dwarf planets, not planets. The definition of planet, set by the International Astronomical Union in 2006, not only takes into account size and appearance, but also requires that a planet be the gravitational bully in its orbit. While Vesta and Ceres are round, they have not vacuumed up or pushed away thousands of other rocks in similar orbits.