Romulus, formal designation 87 Sylvia I, is the outer and larger moon of the
main-belt asteroid
The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...
87 Sylvia
87 Sylvia is 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 main asteroid belt (see minor-planet ...
. 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.
Discovery and naming
Romulus was discovered in February 2001 from the
Keck II telescope by
Michael E. Brown and
Jean-Luc Margot
Jean-Luc Margot (born 1969) is a Belgian-born astronomer and a UCLA professor with expertise in planetary sciences and SETI.
Career
Margot has discovered and studied several binary asteroids with radar and optical telescopes. His discoveries ...
. Its formal designation is (87) Sylvia I; before receiving its name, it was known as S/2001 (87) 1.
The moon is named after
Romulus
Romulus (, ) was the legendary founder and first king of Rome. Various traditions attribute the establishment of many of Rome's oldest legal, political, religious, and social institutions to Romulus and his contemporaries. Although many of th ...
, the mythological founder of
Rome
Rome (Italian language, Italian and , ) is the capital city and most populated (municipality) of Italy. It is also the administrative centre of the Lazio Regions of Italy, region and of the Metropolitan City of Rome. A special named with 2, ...
, 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.Livy I.4.2 This event was portrayed numerous times in Roman art. Her story is told in the ...
raised by a wolf.
Characteristics
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 consists of numerous pieces of debris that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the various chunks that make 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 is a common model for the calculation of a Sphere of influence (astrodynamics), gravitational sphere of influence. It is the most commonly used model to calculate the spatial extent of gravitational influence of an astronomical ...
(about 1/50 of Sylvia's
Hill radius
A hill is a landform that extends above the surrounding terrain. It often has a distinct summit, and is usually applied to peaks which are above elevation compared to the relative landmass, though not as prominent as mountains. Hills fall unde ...
), 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 meani ...
.
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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
has an apparent size of about 0.5°).
See also
*
Remus (moon)
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
Astronomical objects discovered in 2001