Amphitrite (planet)

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Amphitrite is a hypothetical ninth planet of the early solar system that is said to have collided with one of them during the migration of Uranus and Neptune . Its existence is assumed based on more recent models for the development of the protoplanetary disk .

This hypothesis can also be used to explain characteristics of the outer gas planets ( rotational anomaly of Uranus ; heat balance of Neptune ) as well as the origin and orbit properties of the unusual Neptune moon Triton , which have not yet been satisfactorily deduced.

The hypothesis

Formation of Amphitrites

Nice model / orbit simulation of the outer planets and the planetesimal belt: a) early configuration before Jupiter and Saturn get into 2: 1 resonance; b) Scattering of the planetesimals after the orbit exchange of Neptune (dark blue) and Uranus (light blue); c) final orbits.

Due to the mass distribution in the protoplanetary disk, the two outer gas planets Neptune and Uranus must have formed much closer to the sun than they are currently, in the Nice model at around 11.5 and 14.2 astronomical units (AU). A belt of planetesimals with a total mass of 35 earth masses was connected to them in the area between 15 and 30 AU . Under these conditions, a rocky planet with a mass of about two earth masses may have formed here at approx. 18 AU , for which the name Amphitrite is suggested.

Offense amphitrites

In the Nice model, the original orbits of Uranus and Neptune were destabilized when Jupiter and Saturn got into 2: 1 resonance . Uranus and Neptune are then said to have migrated outward - reinforced by the decreasing friction in the thinning planetary disk - until they reached their current orbits at 19.2 and 30.1 about four billion years ago due to the gravity of the two inner gas planets AE were fixed. During their migration, one of them is said to have collided with Amphitrite and absorbed him. Amphitrite's moon Triton is said to have been captured by Neptune.

Triton

This hypothesis is supported by Triton's unusual properties. It orbits Neptune in a retrograde way , ie against its direction of rotation at a distance of just over 14 Neptune radii (354,759 km) in a strongly inclined orbit. This must originally have been very eccentric with a periapsis of only seven Neptune radii. Triton is not only extraordinarily large, its composition also identifies it as a Kuiper Belt Object (KBO). It cannot therefore originate with Neptune, but must have been captured by him. The following variants were discussed:

  • A direct capture of Tritons as a single object is unlikely, as this would have required orbital parameters that would have to be closely coordinated with Neptune due to the large mass of Tritons, the high orbital speeds before capture and its narrow orbit afterwards. In addition, Triton's kinetic energy would have had to be reduced from a multiple to its current value, for which only a larger impact would be considered in this scenario . However, the difference between the energy input required for deceleration and that leading to the complete destruction of the moon is so small and the orbit adjustments with the impactor have to be so precise that this scenario is extremely unlikely.
  • A trapping Tritons of a binary KBO analogous to Pluto - Charon system, absorbing at the Tritons partners either Neptune or was thrown by him from the solar system, Tritons would plausibility deceleration because the kinetic energy had been taken by his partner. For statistical reasons , however, this scenario is unlikely: Since the smaller partner is almost always captured by a binary system , Triton should have been tied to a more massive KBO. However, in the development of the planetary disk there have been fewer than 100 KBO with greater mass than Triton, of which in turn very few could have been bound in binary objects. In addition, this hypothesis is also unrealistic with regard to the kinetic conditions , since the approach speeds of Neptune in relation to the orbital speed of the objects of the binary system were too high for Triton to be captured.

On the other hand, it is kinetically plausible that Triton was captured as a single object in a wide orbit (d ~ 1 million km). According to this hypothesis, this would have happened through Amphitrite, whose orbit was in the area of ​​the planetesimal ring at that time, to which Triton must originally have belonged.

There are two possible scenarios for Triton's transition from Amphitrite to Neptune:

Collision variants

According to the Nice model, Neptune emerged closer to the sun than Uranus, but overtook it during its migration and was the first to reach the assumed orbit Amphitrites. As Triton also most of his after a collision of his planet Neptune Amphitrite with kinetic energy would have lost his remaining in would gravitational field Neptune plausible. In this scenario, the energy input through the collision would explain Neptune's unusually high energy radiation, which is 2.7 times the amount of energy received from solar radiation .

Uranus . An alternative scenario describes a tearing of the bond between Amphitrite and his moon Triton by Neptune, his capture Tritons and the subsequent collision of Amphitrite with Uranus . The cause of its rotational anomaly ( axis of rotation in the ecliptic ) is assumed to be a collision with an object with approximately twice the earth's mass. According to the Nice model, Uranus reached the assumed orbit Amphitrites in the course of its migration only after passing through Neptune, but stayed there longer. Since cosmic collisions are extremely rare, missing Amphitrite due to the rapidly migrating Neptune and instead the collision with Uranus are quite possible.

Naming

The Oceanid Amphitrite on a Corinthian illustration (approx. 575-550 BC)

Amphitrite (Ἀμφιτρίτη) is an oceanid or nereid of Greek mythology , ruler of the seas and wife of Poseidon (Roman Neptune). She is the mother of the sea god Triton .

See also

Individual evidence

  1. ^ A b Gomes / Levison / Tsiganis / Morbidelli: Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets . In: Nature 435, p. 466, 2005
  2. ↑ Tsiganis / Gomes / Morbidelli / Levinson: Origin of the orbital architecture of the giant planets of the Solar System . In: Nature 435, p. 459, 2005 (PDF; 1.4 MB)
  3. ^ Desch, Steve: Mass Distribution and Planet Formation in the Solar Nebula . In: The Astrophysical Journal , 671, pp. 878–893, 2007 (PDF; 282 kB)
  4. ↑ a b c Desch / Porter: Amphitrite: A Twist on Triton's Capture Paper for the 41st Lunar and Planetary Science Conference (2010) (PDF; 209 kB)
  5. ↑ McKinnon / Lunine / Band Field, 1995: Neptune and Triton , University of Arizona, p 807
  6. ↑ a b Agnor / Hamilton: Neptune's capture of its moon Triton in a binary-planet gravitational encounter . In: Nature 441, pp. 192-194, 2006
  7. ↑ Vokrouhlický / Nesvorny / Levison: Irregular Satellite Captions by Exchange Reactions . In: The Astronomical Journal 136, pp. 1463–1476, 2008 (PDF; 5.5 MB)
  8. ^ Goldreich / Lithwick / Sari: Formation of Kuiper-belt binaries by dynamical friction and three-body encounters . In: Nature 420, p. 643, 2002
  9. ↑ Pearl / Conrath: The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data . In: Journal of Geophysical Research Supplement 96, pp. 18.921-18.930, 1991
  10. ^ Wayne / Slattery / Benz / Cameron: Giant impacts on a primitive Uranus . In: Icarus 99-1, p. 167, 1992

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