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.
Highlights
The past decade was prolific in terms of detecting gas, mostly CO, C, and O, around main sequence stars, changing the paradigm of evolved planetary systems that were thought to be devoid of gas after 10 Myr
A single 30 km radius planetesimal would release around 10−14 M⊕ Myr−1 – much lower than what can be detected with missions targeting specific Kuiper belt objects (KBOs; e.g., Lisse et al 2021)
Our model leads to a gas wind with a 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 an atomic wind of ∼10−11 M⊕, as summarized in Table 1
Summary
The past decade was prolific in terms of detecting gas, mostly CO, C, and O, around main sequence stars, changing the paradigm of evolved planetary systems that were thought to be devoid of gas after 10 Myr. Most bright exoplanetesimal belts show the presence of gas, as demonstrated recently with ALMA (Moór et al 2017), and it could be that all these belts have gas at some level, even if undetectable with current instruments These belts, similar to our Kuiper belt (KB), are made of large bodies colliding with one another and creating dust that can be observed around extrasolar stars through its emission in the infrared above that of the star, which can be resolved at high resolution (showing e.g., gaps and asymmetries that may be related to the presence of planets). We can explain the gas in these previously considered hybrid disks as entirely secondary because CO released from planetesimals becomes shielded by the carbon produced when it photo-dissociates (and by CO itself through self-shielding), which can accumulate to large amounts (Kral et al 2019; Marino et al 2020)
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