Inner mean-motion resonances with eccentric planets: a possible origin for exozodiacal dust clouds

Abstract

High levels of dust have been detected in the immediate vicinity of many stars, both young and old. A promising scenario to explain the presence of this short-lived dust is that these analogues to the zodiacal cloud (or exozodis) are refilled in situ through cometary activity and sublimation. As the reservoir of comets is not expected to be replenished, the presence of these exozodis in old systems has yet to be adequately explained. It was recently suggested that meanmotion resonances with exterior planets on moderately eccentric (e p 0.1) orbits could scatter planetesimals on to cometary orbits with delays of the order of several 100 Myr. Theoretically, this mechanism is also expected to sustain continuous production of active comets once it has started, potentially over Gyr time-scales. We aim here to investigate the ability of this mechanism to generate scattering on to cometary orbits compatible with the production of an exozodi on long time-scales. We combine analytical predictions and complementary numerical N-body simulations to study its characteristics. We show, using order of magnitude estimates, that via this mechanism, low-mass discs comparable to the Kuiper belt could sustain comet scattering at rates compatible with the presence of the exozodis which are detected around Solar-type stars, and on Gyr time-scales. We also find that the levels of dust detected around Vega could be sustained via our proposed mechanism if an eccentric Jupiter-like planet were present exterior to the system's cold debris disc.

The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey

“…The correlation between our HZ dust detections and cold dust suggests that the origin of bright HZ dust is somehow connected to the presence of dust or mi-nor bodies further away from the star, e.g., through inward transport of dust due to PR drag (Wyatt 2005) or through dust delivery by comets (Nesvorný et al 2010;Faramaz et al 2017;Sezestre et al 2019). It is, however, noteworthy that there are several detections of HZ dust in systems that do not have a detected cold debris disk despite sensitive searches.…”

“…The amount of dust that reaches the HZ may then be used to constrain the presence of planets between the outer reservoir and the HZ that prevent a fraction of the dust from migrating (Moro-Martín & Malhotra 2003;Bonsor et al 2018). Alternatively, the dust may be produced by comets sublimating or otherwise disintegrating when they reach the HZ from further out in the system (Nesvorný et al 2010;Faramaz et al 2017;Marino et al 2017;Sezestre et al 2019), which is thought to be the main source of zodiacal dust in the Solar system (Nesvorný et al 2010;Shannon et al 2015;Poppe et al 2019). Thus, observations of HZ dust have the potential to put constraints on the cometary activity in the system, providing insights into the dynamics of the outer regions (Bonsor et al 2012(Bonsor et al , 2014Faramaz et al 2017;Marino et al 2017) and the environmental conditions of potential rocky planets (cometary bombardment, delivery of water; Kral et al 2018).…”

Exocomets: A spectroscopic survey

“…In some cases, the stars hosting exocomets are associated with a debris disc. We note, however, that scattering of exocomets by eccentric planets can take place in planetary systems with low luminous, nondetectable debris discs with flux levels comparable to the Kuiper belt (Faramaz et al 2017).…”

Exozodiacal clouds: hot and warm dust around main sequence stars

“…Another mechanism to deliver comets into the inner regions of a planetary system was recently proposed by Faramaz et al [87]. The mechanism involves a planet on a moderately eccentric orbit (e p 0.1), located exterior to a planetesimal belt.…”

“…In other cases Downloaded by [University of Liege] at 05:23 25 October 2017 Figure 17. Comet production rate calculated via a numerical simulation of a Kuiper Belt analogue with a 0.75-Jupiter-mass planet located at 75 au, showing that the production of comets can be sustained for Gyr-time scales [87].…”