Jupiter formed as a pebble pile around the N₂ ice line

Abstract

Context. The region around the H 2 O ice line, due to its higher surface density, seems to be the ideal location to form planets. The core of Jupiter, as well as the cores of close in gas giants are thus thought to form in this region of the disk. Actually constraining the formation location of individual planets has proven to be difficult, however. Aims. We aim to use the Nitrogen abundance in Jupiter, which is around 4 times solar, in combination with Juno constraints on the total mass of heavy elements in Jupiter, to narrow down its formation scenario. Methods. Different pathways of enrichment of Jupiter's atmosphere, such as the accretion of enriched gas, pebbles or planetesimals are considered and their implications for the oxygen abundance of Jupiter is discussed. Results. The super solar Nitrogen abundance in Jupiter necessitates the accretion of extra N 2 from the proto-solar nebula. The only location of the disk that this can happen is outside, or just inside the N 2 ice line. These constraints favor a pebble accretion origin of Jupiter, both from the composition as well as from a planet formation perspective. We predict that Jupiter's oxygen abundance is between 3.6 and 4.5 times solar.

Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

“…Because HR 8799e is the innermost planet of the HR 8799 system, this could indicate that all HR 8799 planets formed outside of the CO iceline. Similar formation distances, relative to the icelines, have been theorized for Jupiter in the Solar System (Öberg & Wordsworth 2019;Bosman et al 2019). Using sophisticated gas-grain chemical modeling for the protoplanetary disk we find that the planet could also have formed more closely to the star, but outside the CO 2 iceline.…”

“…Finally, we note that the nitrogen content may be a better way of constraining a planets formation location in the disk (Öberg & Wordsworth 2019;Bosman et al 2019), where a large N-content corresponds to a formation in the outer parts of the disk. However, this would require to study planets cooler than HR 8799e, for which most of its accreted nitrogen is in the form of N 2 , and therefore invisible due to the low N 2 opacity.…”

Tracing the Formation History of Giant Planets in Protoplanetary Disks with Carbon, Oxygen, Nitrogen, and Sulfur

“…Nevertheless, the behavior of the S/N ratio as a tracer of the enrichment from planetesimal accretion shown in Figure 6 depends only on the fact that, while the bulk of N in disks is in gaseous form as N 2 (see Figure 3 and Section 2.5, as well as Eistrup et al (2016Eistrup et al ( , 2018, Bosman et al (2019), and Öberg & Wordsworth (2019)), the bulk of S is instead trapped in refractory solids (see Figure 3 and Section 2.5, as well as Lodders (2010), Palme et al (2014), and Kama et al (2019)). Consequently, even if the slope of the S/N curve as a function of planetary migration will depend on the NH 3 -N 2 and the S refractory-volatile partitionings, the direct proportionality between S/N ratio, planetary migration and enrichment in high-Z elements due to planetesimal accretion will not.…”

“…The higher the fraction of N that remains in gaseous form as N 2 , the steeper the slopes of the curves of the N-based elemental ratios. Recent work (Bosman et al 2019) argued that the 1:1 NH 3 :N 2 ratio adopted by astrochemical models of protoplanetary disks (Eistrup et al 2016(Eistrup et al , 2018 should be considered as an upper limit, and based on observational data, realistic partitioning should include significantly less ammonia.…”

“…Since the early work of Öberg et al (2011), several studies have been devoted to understanding the link between the abundances of the two most abundant high-Z elements, carbon (C) and oxygen (O), and the planetary formation process; for more recent discussions, see, e.g., Madhusudhan et al (2016), Mordasini et al (2016), Booth & Ilee (2019), Cridland et al (2019), and references therein. Recently, a few studies have taken a first look at nitrogen (N), as well (Bosman et al 2019;Öberg & Wordsworth 2019). However, the implications of formation regions extending as far from the star as ALMA reveals, as well as those of accreting large amounts of high-Z material across many of the compositional regions inside disks, remain poorly understood.…”