Romulus is the outer and larger moon of the

main-belt asteroid The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

87 Sylvia. It follows an almost-circular and close-to-equatorial orbit around the asteroid. In this respect it is similar to the other Sylvian moon Remus. Romulus was discovered in February 2001 from the Keck II telescope by

Michael E. Brown Michael E. Brown (born June 5, 1965) is an American astronomer, who has been professor of planetary astronomy at the California Institute of Technology (Caltech) since 2003. His team has discovered many trans-Neptunian objects (TNOs), including ...

and

Jean-Luc Margot Jean-Luc Margot (born 1969) is a Belgian-born astronomer and a UCLA professor who specializes in planetary sciences. Career Margot has discovered and studied several binary asteroids with radar and optical telescopes. His discoveries include ( ...

. Its full designation is (87) Sylvia I Romulus; before receiving its name, it was known as S/2001 (87) 1. The moon is named after Romulus, the mythological founder of

Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus (legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...

, one of the twins of

Rhea Silvia Rhea (or Rea) Silvia (), also known as Ilia (as well as other names) was the mythical mother of the twins Romulus and Remus, who founded the city of Rome. Her story is told in the first book of ''Ab Urbe Condita Libri'' of Livy and in Cassius D ...

raised by a wolf. 87 Sylvia has a low density, which indicates that it is probably a

rubble pile In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the ...

formed when debris from a collision between its parent body and another asteroid re-accreted gravitationally. Therefore, it is likely that both Romulus and Remus, the second of Sylvia's moons, are smaller rubble piles which accreted in orbit around the main body from debris of the same collision. In this case their albedo and density are expected to be similar to Sylvia's. Romulus's orbit is expected to be quite stable − it lies far inside Sylvia's

Hill sphere The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sph ...

(about 1/50 of Sylvia's

Hill radius The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sp ...

), but also far outside the

synchronous orbit A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. Simplified meanin ...

. From Romulus's surface, Sylvia takes up an angular region 16°×10° across, while Remus's apparent size varies between 0.62° and 0.19° (for comparison, Earth's

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

has an apparent size of about 0.5°).

References

External links

Data on (87) Sylvia from Johnston's archive
(maintained by W. R. Johnston) *
Rubble-Pile Minor Planet Sylvia and Her Twins
' (ESO news release, August 2005) Includes images and artists impressions *

' (SpaceDaily.com, March 2001) Includes a discovery image.

confirming the discovery of S/2001 (87) 1

reporting discovery of S/2004 (87) 1 and naming Romulus and Remus {{Small Solar System bodies Asteroid satellites Discoveries by Michael E. Brown 87 Sylvia

See also

References

External links