Remus is the inner and smaller 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 Sylvia (minor planet designation: 87 Sylvia) is the one of the largest asteroids (approximately tied for 7th place, to within measurement uncertainties). It is the parent body of the Sylvia family and member of Cybele group located beyond the m ...

. It follows an almost-circular and close-to-equatorial orbit around the parent asteroid. In this respect it is similar to the other Sylvian moon

Romulus Romulus () was the legendary foundation of Rome, founder and King of Rome, first king of Ancient Rome, Rome. Various traditions attribute the establishment of many of Rome's oldest legal, political, religious, and social institutions to Romulus ...

. Remus was discovered several years after Romulus on images taken starting on August 9, 2004, and announced on August 10, 2005. It was discovered by

Franck Marchis Franck Marchis (born April 6, 1973 in Caen, France), astronomer and planetary scientist, is best known for his discovery and characterization of multiple asteroids, his study of Io volcanism and imaging of exoplanets, planets around other stars ...

UC Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...

, and Pascal Descamps, Daniel Hestroffer, and Jérôme Berthier of the Observatoire de Paris, France, using the Yepun telescope of the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

(ESO) in

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. Marchis, the project leader, was waiting for the completion of the image acquisition programme before starting to process the data. Just as he was set to go on vacation in March 2005, Descamps sent him a brief note entitled "87 Sylvia est triple ?" pointing out that he could see two moonlets on several images of Sylvia. The entire team then focused quickly on analysis of the data, wrote a paper, submitted an abstract to the August meeting in Rio de Janeiro and submitted a naming proposal to the IAU. Its full designation is (87) Sylvia II Remus; before receiving its name, it was known as S/2004 (87) 1. The moon is named after Remus, twin of 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 children 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 ...

asteroid formed when debris from a collision between its parent body and another asteroid re-accreted gravitationally. Thus it is likely that both Remus and Romulus 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. Remus'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 sp ...

(about 1/100 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 Remus's surface, Sylvia appears huge, taking up an angular region roughly 30°×18° across, while Romulus's apparent size varies between 1.6° and 0.5° across.

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External links

Data on (87) Sylvia from Johnston's archive
(maintained by W. R. Johnston) *

'' (ESO news release, August 2005) Includes images and artists impressions

reporting discovery of S/2004 (87) 1 and naming Romulus and Remus {{Small Solar System bodies Asteroid satellites 87 Sylvia 20040809

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