(21) Lutetia
(21) Lutetia is a large asteroid, about 121 × 101 × 75 km, in the main belt. ESA's Rosetta flew 3,170 km from it on 10 July 2010, on its way to comet 67P, and the pull it felt from Lutetia gave the asteroid's mass.
Key facts
Science
Physical
- Mean radius
- 49 km · 1% of Earth's radius
- Mass
- 1.70 × 10¹⁸ kg · 0.0000232 Moon masses
- Density
- 3,450 kg/m³ · 3.4× water
- Computed from mass and radius
- Rotation period
- 8.17 hours
Orbital
- Semi-major axis
- 2.43 AU
- From catalogued orbital elements (MPC)
- Eccentricity
- 0.1648
- From catalogued orbital elements (MPC)
- Inclination
- 3.06 °
- From catalogued orbital elements (MPC)
- Orbital period
- 3.80 years
- From catalogued orbital elements (MPC)
- Perihelion
- 2.03 AU
- Computed from the orbital elements
- Aphelion
- 2.84 AU
- Computed from the orbital elements
- Mean orbital velocity
- 19.1 km/s
- Computed from the orbital elements
Discovery
- Discovered
- November 15, 1852
- Discoverer
- Hermann Goldschmidt (Paris)
Composition
- Make-up
- Its spectrum places it in the M class of Tholen's taxonomy and the Xk class of Bus's (JPL Small-Body Database). Rosetta's pictures show a complex geology: the north-polar region is covered by a thick layer of regolith that has flowed in major landslides, and the surface is ancient. Its mass, measured from the Doppler shift its gravity imposed on Rosetta's radio signal, and its volume give one of the highest densities measured for an asteroid (Pätzold et al. 2011) — so Lutetia is most likely a primordial planetesimal, unlike the smaller asteroids visited before it, which are probably shattered fragments or rubble piles (Sierks et al. 2011).
Radiation & temperature
- Insolation
- 0.169 S⊕ · 17% of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
- Geometric albedo
- 0.19
- Geometric albedo 0.19 ± 0.01 (Sierks et al. 2011).
- Equilibrium temperature
- 169 K (-104 °C)
- Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate
Discovery & history
- Discovered
- November 15, 1852
- By
- Hermann Goldschmidt (Paris)
- Name
- Named after Lutetia, the Latin name of Paris, where it was found.
Hermann Goldschmidt found it at Paris on 15 November 1852. On 10 July 2010 Rosetta passed it 3,170 km away (3,168 km in the mission's archive) and imaged the northern side that was lit. The Doppler shift its gravity imposed on Rosetta's radio signal measured its mass, and with the volume from the pictures gave one of the highest densities measured for an asteroid.
Passed 3,170 km away (3,168 km in the mission's archive); the pull of Lutetia's gravity on its radio signal gave the mass, and a density of 3.4 g/cm³, one of the highest measured for an asteroid.
Images
Images from open archives · credit shown per image