87 Sylvia

87 Sylvia was a very big asteroid, about tied for seventh place among the largest ones we know. It belonged to a group called the Cybele group, which is located beyond the main belt of asteroids. 87 Sylvia was special because it was the first asteroid found to have more than one moon. It is also the parent body of something called the Sylvia family.

Discovery and naming

Sylvia was discovered by N. R. Pogson on May 16, 1866, from Madras (Chennai), India. The name was chosen to honor Rhea Silvia, the mother of Romulus and Remus.

Physical characteristics

Sylvia is a very dark asteroid, and scientists believe it has a simple makeup inside. Because it has moons, scientists could measure its mass, density, and how its mass is spread out. Sylvia's density is low, about 1.4 times the density of water, which means it has a lot of empty space. Models suggest it was made up of about 35% rock, 13% ice, and 52% empty space. Today, it has a layer on the outside without water, and inside, there is ice mixed with rock up to about 46 kilometers from the center, and then rock with empty spaces beyond that.

Sylvia spins quickly, completing a full turn every 5.2 hours. This quick spin gives it a speed of about 65 meters per second at the equator. The shape of Sylvia is flattened and stretched out, but we do not have clear pictures of its surface to see any specific features.

Satellite system

87 Sylvia has two small moons orbiting around it. These moons are named Romulus and Remus, after the famous children from mythology.

Romulus, the first moon, was found on February 18, 2001, using a big telescope called the Keck II. Remus, the second moon, was found three years later on August 9, 2004, by scientists in California and France.