The carbon budget in the outer solar nebula

Area of Science:

• Planetary Science
• Astrochemistry
• Solar System Formation

Background:

• Pluto and Charon's internal structures suggest a higher silicate mass fraction compared to giant planet satellites.
• This compositional difference implies distinct formation pathways, with Pluto/Charon likely forming directly from the solar nebula.

Purpose of the Study:

• To determine the composition of the outer solar nebula, focusing on the form of carbon.
• To understand the implications of different carbon forms on the formation of Pluto, Charon, and giant planet satellites.

Main Methods:

• Detailed modeling of Pluto and Charon's internal structures.
• Cosmic abundance calculations.
• Analysis of giant planet atmospheric compositions.
• Review of laboratory studies and spacecraft observations.

Main Results:

• The Pluto/Charon system has a mean silicate mass fraction of approximately 0.7, significantly higher than giant planet satellites.
• The majority of carbon in the outer solar nebula was likely gaseous carbon monoxide (CO).
• Condensed materials accounted for 10-20% of outer solar nebula carbon, with organic material being the dominant solid form.

Conclusions:

• Pluto and Charon formed directly from the solar nebula, while giant planet satellites formed from circumplanetary nebulae.
• Carbon monoxide was the primary carbon species in the outer solar nebula, with organic materials as the main condensed form.
• Methane and CO ices were minor components in Pluto/Charon, and clathrates played a limited role in carbon sequestration.