704 Interamnia is a large F-type asteroid. With a mean diameter of around 330 kilometres, it is the fifth-largest asteroid, after Ceres, Vesta, Pallas and Hygiea. Its mean distance from the Sun is 3.067 (AU). It was discovered on 2 October 1910 by Vincenzo Cerulli, and named after the Latin name for Teramo, Italy, where Cerulli worked. Its mass is probably between fifth and tenth highest in the asteroid belt, with a mass estimated to be 1.2% of the mass of the entire asteroid belt.[6] Observations by the Very Large Telescope's SPHERE imager in 2017–2019, combined with occultation results, indicate that the shape of Interamnia may be consistent with hydrostatic equilibrium for a body of its density with a rotational period of 7.6 hours. (Its current period is 8.7 hours.) This suggests that Interamnia may have formed as an equilibrium body, and that impacts changed its rotational period after it fully solidified.[4]

704 Interamnia

Discovery
Discovered by	Vincenzo Cerulli
Discovery date	2 October 1910
Designations
MPC designation	(704) Interamnia
Pronunciation	/ɪntərˈæmniə/[1]
Named after	Teramo
Alternative designations	1910 KU; 1952 MW
Minor planet category	Main belt
Adjectives	Interamnian /ɪntərˈæmniən/[1]
Orbital characteristics[2]
Epoch July 01, 2021 (JD 2459396.5, heliocentric)
Uncertainty parameter 0
Observation arc	110.8 yr
Aphelion	3.53 AU (528 Gm)
Perihelion	2.58 AU (386 Gm)
Semi-major axis	3.056 AU (457.2 Gm)
Eccentricity	0.155
Orbital period (sidereal)	5.34 yr (1951 d)
Average orbital speed	16.92 km/s[citation needed]
Mean anomaly	248°
Mean motion	0° 11m 4.2s / day
Inclination	17.31°
Longitude of ascending node	280.3°
Argument of perihelion	94.8°
Physical characteristics
Dimensions	c/a = 0.86±0.03[3] 362 × 348 × 310 ± 8 km[4]
Mean diameter	332±5 km[3] 332±6 km (volume equivalent)[4]
Mass	(35±5)×1018 kg[3] (38±13)×1018 kg[4]
Mean density	1.84±0.28 g/cm3[3] 2.0±0.7 g/cm3[4]
Synodic rotation period	8.71 h[4]
Pole ecliptic latitude	62±5°
Pole ecliptic longitude	87±5°
Geometric albedo	0.067[3] 0.078±0.014 geometric (0.645±0.014 BV, 0.259±0.021 UB)[2]
Spectral type	F/B[2]
Apparent magnitude	9.9 to 13.0[5]
Absolute magnitude (H)	6.38[2]

Characteristics

Although Interamnia is the largest asteroid after the "big four", it is a very little-studied body. It is easily the largest of the F-type asteroids, but until 2017-2019 there existed very few details of its internal composition or shape, and no light curve analysis has yet been done to determine the ecliptic coordinates of Interamnia's poles (and hence its axial tilt). Studies by the Very Large Telescope give an average diameter of about 332 km and found an ellipsoidal shape for Interamnia, similar to 4 Vesta; the resulting density calculation (1.98 ± 0.68 g·cm⁻³) is not precise enough to definitely infer Interamnia's composition, but the presence of hydrated materials at the surface and its overall spectral similarities to Ceres suggest that it is likely an icy body. The absence of an affiliated asteroid family implies that Interamnia has not suffered a giant impact within the past 3 billion years,[7] in contrast to 4 Vesta and 10 Hygeia.[8][9]

Its very dark surface and relatively large distance from the Sun means Interamnia can never be seen with 10x50 binoculars. At most oppositions its magnitude is around +11.0, which is less than the minimum brightness of Vesta, Ceres or Pallas. Even at a perihelic opposition its magnitude is only +9.9,[5] which is over four magnitudes lower than Vesta.

Its orbit is slightly more eccentric than that of Hygiea (15% versus 12%) but differs from Hygiea's in its much greater inclination and slightly shorter period. Another difference is that Interamnia's perihelion is located on the opposite side from the perihelia of the "big four", so that Interamnia at perihelion is actually closer to the Sun than Ceres and Pallas are at the same longitude. It is unlikely to collide with Pallas because their nodes are located too far apart, whilst although its nodes are located on the opposite side from those of Ceres, it is generally clear of Ceres when both cross the same orbital plane and a collision is again unlikely.^{[original research?]}

Surface

There are no deep basins visible in the VLT images. Any large craters must have flat floors, consistent with an icy C/F-type composition.[10]

Mass

In 2001, Michalak estimated Interamnia to have a mass of (7±2)×10¹⁹ kg. Michalak's estimate depends on the masses of 19 Fortuna, 29 Amphitrite, and 16 Psyche; thus this mass was obtained assuming an incomplete dynamical model.[11]

In 2011, Baer calculated Interamnia had a mass of (3.9±0.2)×10¹⁹ kg.[12]

Goffin's 2014 astrometric reanalysis gives an even lower mass of (2.7±0.1)×10¹⁹ kg.[13]

In 2019, Hanuš et al. consolidated 21 selected prior mass estimates, dating from 1992 to 2017, with a metastatistical result of (3.8±1.3)×10¹⁹ kg (that is, (2.5 to 5.1)×10¹⁹ kg to within 1 sigma uncertainty.[4]

• 
  VLT-SPHERE image of Interamnia
• 
  Animation of 704 Interamnia's orbit 2000-2020
    Sun ·   Earth ·   Mars ·   Jupiter ·   704 Interamnia
• 
  The Transiting Exoplanet Survey Satellite (TESS) observed 704 Interamnia passing close to a target star, TIC 14802783, on 18/01/19.

See also

• List of Solar System objects by size

References

External links

• Animation of Asteroid Interamnia taken on 1 & 2 April 2003
• Interamnia Occultations Observed before 2003
• Occultation of GSC 23450183 by 704 Interamnia on 17 December 1996
• Occultation of HIP36189 by 704 Interamnia on 23 March 2003
• (704) Interamnia: A transition object between a dwarf planet and a typical irregular-shaped minor body
• 704 Interamnia at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 704 Interamnia at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

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