A molecular wind blows out of the Kuiper belt

Abstract

Context. In this Letter we aim to explore whether gas is also expected in the Kuiper belt (KB) in our Solar System. Aims. To quantify the gas release in our Solar System, we use models for gas release that have been applied to extrasolar planetary systems as well as a physical model that accounts for gas released due to the progressive internal warming of large planetesimals. Methods. We find that only bodies larger than about 4 km can still contain CO ice after 4.6 Gyr of evolution. This finding may provide a clue as to why Jupiter-family comets, thought to originate in the KB, are deficient in CO compared to Oort cloud comets. We predict that gas is still currently being produced in the KB at a rate of 2 × 10−8 M⊕ Myr−1 for CO and that this rate was orders of magnitude higher when the Sun was younger. Once released, the gas is quickly pushed out by the solar wind. Therefore, we predict a gas wind in our Solar System starting at the KB location and extending far beyond with regards to the heliosphere, with a current total CO mass of ∼2 × 10−12 M⊕ (i.e., 20 times the CO quantity that was lost by the Hale-Bopp comet during its 1997 passage) and CO density in the belt of 3 × 10−7 cm−3. We also predict the existence of a slightly more massive atomic gas wind made of carbon and oxygen (neutral and ionized), with a mass of ∼10−11 M⊕. Results. We predict that gas is currently present in our Solar System beyond the KB and that, although it cannot be detected with current instrumentation, it could be observed in the future with an in situ mission using an instrument similar to Alice on New Horizons but with larger detectors. Our model of gas release due to slow heating may also work for exoplanetary systems and provide the first real physical mechanism for the gas observations. Lastly, our model shows that the amount of gas in the young Solar System should have been orders of magnitude greater and that it may have played an important role in, for example, planetary atmosphere formation.

A Predicted Dearth of Majority Hypervolatile Ices in Oort Cloud Comets

“…Neither was any marked increase in hypervolatile emission seen from the recently split comets 73P/SW3 (Dello Russo et al 2007) nor from 17P/Holmes (Dello Russo et al 2008), again showing from direct observational studies that the cores/ interiors of Jupiter-family comets do not contain any large amount of pure hypervolatile ices "hidden down deep." 27 Instead the low but finite level of hypervolatile ices seen in cometary comae is thought to be due to their inclusion as minority impurities in bulk majority water ice and CO 2 ice phases (Jewitt 2009;Lisse+21;Davidsson+21), and it is from these phases that it can be released via thermal, sputtering, or collisional processes (Kral et al 2021 and references therein).…”

“…One can also see that mesostable ices like CO 2 , while easily removed from the surface, can remain stably at depth inside a KBO for more than the age of the solar system. 26 Another thermal loss timescale on the order of 4 Gyr has also recently been published by Kral et al (2021), but this model utilized an aphysical thermal diffusivity = 10 −10 m 2 s −2 , which is more than 2 orders of magnitude lower than that of the most insulating solid material currently known, aerogel, and more than 3 orders of magnitude lower than the parameter values used by Davidsson+21, Prialnik+21, and Steckloff+21 in their models. Scaling the 4 Gyr timescale by a factor of 1/300 to correct for the thermal diffusivity error, the Kral et al timescales become consistent with the 10-20 Myr timescales for loss of all pure CO/N2/CH4-like ices.…”

Planetesimal/Debris discs

“…Once this gas is released from planetesimals it is expected to spread forming an accretion disc , unless radiation pressure or stellar winds are strong enough to blow out the gas (Youngblood et al, 2021;Kral et al, 2021). How massive such a gaseous circumstellar disc can be depends on the rate at which gas is being released and the rate at which gas is lost via accretion onto the central star or inner bodies.…”

Upper Limits on the Escape of Volatiles from (486958) Arrokoth Using New Horizons Alice Ultraviolet Spectrograph Observations

“…The stellar appulse data were reduced and analyzed in a similar way to the solar appulse data, but found to be less constraining on escape rates; the upper limits they provide on Q i and N i are also listed in Table 1. The timing of volatile loss from primitive bodies is an active area of research, in our own solar system (e.g., Kral et al 2021;Lisse et al 2021;Steckloff et al 2021) and beyond (e.g., Moór et al 2017).…”