Ilmarë (moon)

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(174567) Varda I (Ilmarë)
Provisional or systematic name S / 2009 (174567) 1
Central body (174567) Varda
Properties of the orbit
Major semi-axis 4809 ± 39 km
Periapsis 4705 km
Apoapsis 4912 km
eccentricity 0.0215 ± 0.0080
Orbit inclination 21.2 °
Orbital time 5.75058 ± 0.00015 d
Mean orbital velocity 0.060 km / s
Physical Properties
Albedo 0.102 ± 0.024
Apparent brightness 22.0 likes
Medium diameter km
surface 334,000 km 2
Medium density g / cm 3
discovery
Explorer

Keith S. Noll et al. a.

Date of discovery April 26, 2009
Remarks Smaller component of a double asteroid system.

Ilmarë is a moon of the trans-Neptunian object Varda in the Kuiper belt , which is classified as a "hot" Cubewano or an extended Scattered Disk Object (DO) in terms of orbital dynamics . At 326 km, the companion has about half the diameter of the mother asteroid . Since both celestial bodies revolve around the common center of gravity , the system can also be understood as a double asteroid system.

Discovery and naming

Ilmarë was discovered by a team of astronomers led by Keith S. Noll ( GSFC ) on images from the Hubble Space Telescope on April 26, 2009. The discovery was announced in 2011; the companion was given the provisional designation S / 2009 (174567) 1 .

On January 16, 2014 the moon was officially named by the International Astronomical Union (IAU) after Ilmarë, "the heavenly maiden" or "heavenly beauty", a maid of the star queen Varda Elentári from J. R. R. Tolkien's Silmarillion ; she is considered the most powerful of the female Maiar .

After her discovery, Varda could be dated back to 1980 on photos; therefore, Varda's orbit is now relatively well known. In August 2020 there were a total of 259 astrometric observations over a period of 38 years. The last observation so far was made in July 2018 at the Purple Mountain Observatory . (As of August 6, 2020)

Track properties

Ilmarë orbits the common barycentre in an elliptical orbit at an average distance of 4809 km to the planetoid (13.4 Varda or 29.5 Ilmarë radii) and needs 5 days 18 hours 0.8 minutes, which is 19891.5 orbits in a Varda year (around 313.18 earth years). The orbit eccentricity is 0.22, the orbit is inclined 21.2 ° to the plane of the planetoid .

In this binary system, a month accordingly lasts 23.35 Varda days.

size

The diameter of Ilmarë is currently estimated at 326 km, based on an estimated reflectivity of 9%, analogous to the mother planetoid. Based on this diameter, the total surface area is around 334,000 km 2 . The discovery of the moon does not seem to have any significant influence on the determination of the size of the mother planetoid, which, according to current estimates, is 716.6 km in size. This means that Ilmarë should have 45.5% the diameter of Varda. The system mass was determined to be 2.664 ± 0.064  ·  10 20 . The apparent magnitude of Ilmarë is 22.0  m .

So far, mass, density and composition are only known for the entire system. According to the current state of knowledge, Ilmarë is the second largest asteroid moon in the solar system after Vanth . The next larger is Haumeas Hiʻiaka with 320 km, which is classified as a dwarf planet moon. The next larger "pure" asteroid moons are Salacias Actaea with 290 km and Xiangliu with 270-300 km. Since Varda is classified as a "highly probable" dwarf planet candidate, it can be assumed that Ilmarë will also receive the status of a dwarf planet moon in the foreseeable future. The proportions of Ilmarë and Varda come very close to the proportions of the Pluto - Charon system.

Provisions of the diameter for Ilmarë
year Dimensions km source
2014 361.0 +42.0−38.0 Vilenius et al. a.
2014 <188.0 Thirouin et al. a.
2015 326.0 +38.0−34.0 Grundy et al. a.
The most precise determination is marked in bold .

The surfaces of Varda and Ilmarë appear reddish in the visible spectrum and near infrared. The spectrum shows no absorption lines from water ice, but from methanol ice . Overall, Ilmarë seems to be a little redder than the mother asteroid.

See also

Individual evidence

  1. ↑ a b W. Grundy: TNBs with known P, a, and e . Lowell Observatory . Retrieved March 25, 2019.
  2. ↑ v ≈ π * a / period (1 + sqrt (1-e²))
  3. ↑ a b c W. Grundy: Varda and Ilmarë (174567 2003 MW12) . Lowell Observatory . Retrieved March 25, 2019.
  4. ↑ a b W. Grundy: Orbit Status of Known Binary TNOs . Lowell Observatory . Retrieved March 25, 2019.
  5. ↑ a b c W. Grundy u. a .: The mutual orbit, mass, and density of the large transneptunian binary system Varda and Ilmarë (PDF) . In: Icarus . 257, May 4, 2015, pp. 130-138. arxiv : 1505.00510 . bibcode : 2015Icar..257..130G . doi : 10.1016 / j.icarus.2015.04.036 .
  6. ↑ MPC : MPEC 2010-S44: Distant Minor Planets (2010 OCT.11.0 TT) . IAU . September 25, 2010. Accessed March 4, 2019.
  7. ^ Marc W. Buie : Orbit Fit and Astrometric record for 174567 . SwRI (Space Science Department). Retrieved March 4, 2019.
  8. ^ Wm. R. Johnston: Asteroids with Satellites - (174567) Varda and IImare . Johnston's Archives. January 31, 2015. Accessed March 25, 2019.
  9. ↑ JPL : 174567 Varda (2003 MW12) . CalTech . Retrieved August 6, 2020.
  10. ^ IAU : (174567) Varda = 2003 MW12 . MPC . Retrieved August 6, 2020.
  11. ↑ Mike Brown: How many dwarf planets are there in the outer solar system?
  12. ↑ E. Vilenius et al. a .: “TNOs are cool”: A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations (PDF) . In: Astronomy and Astrophysics . 564, No. A35, March 25, 2014, p. 18. arxiv : 1403.6309 . doi : 10.1051 / 0004-6361 / 201322416 .
  13. ↑ A. Thirouin et al. a .: Rotational properties of the binary and non-binary populations in the trans-Neptunian belt . In: Astronomy and Astrophysics . 569, September 8, 2014, p. A3. arxiv : 1407.1214 . bibcode : 2014A & A ... 569A ... 3T . doi : 10.1051 / 0004-6361 / 201423567 .