Abstract
Abstract The most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescales of up to 100–200 Myr, when violent impacts occur between large planetesimals of sizes up to protoplanets. Such events are marked by the production of large amounts of debris, as has been observed in some exceptionally bright and young debris disks (termed extreme debris disks). Here we report five years of Spitzer measurements of such systems around two young solar-type stars: ID8 and P1121. The short-term (weekly to monthly) and long-term (yearly) disk variability is consistent with the aftermaths of large impacts involving large asteroid-sized bodies. We demonstrate that an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometry effects, can produce short-term modulation in the disk light curves. The long-term disk flux variation is related to the collisional evolution within the impact-produced fragments once released into a circumstellar orbit. The time-variable behavior observed in the P1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor condensates as the dominant impact product. Two distinct short-term modulations in the ID8 system suggest two violent impacts at different times and locations. Its long-term variation is consistent with the collisional evolution of two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders. The bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique opportunity to study violent events during the era of terrestrial planet formation.
Highlights
Planet formation is ubiquitous—thousands of exoplanets have been detected through Doppler spectroscopy, transit photometry, microlensing surveys, and direct imaging surveys, with each sensitive to different populations of planets
Disk variability due to the dust produced in the aftermaths of planetesimal impacts in young, luminous debris disks provides a great opportunity to study the violent events during the era of terrestrial planet formation (Meng et al 2015; Wyatt & Jackson 2016)
We focus on the collisional evolution within the impact-produced cloud of dust in Section 5 to qualitatively explain the long-term disk variability
Summary
Planet formation is ubiquitous—thousands of exoplanets have been detected through Doppler spectroscopy, transit photometry, microlensing surveys, and direct imaging surveys, with each sensitive to different populations of planets. The situation is daunting for studying terrestrial planet formation, which extends well past the lifetime of protoplanetary disks and produces exceedingly faint planets requiring currently unobtainable high contrast and spatial resolution for their direct detection. Debris disks around mature stars are excellent tools to search for phases occurring in other planetary systems that are analogous to major events in the evolution of the solar system, such as the formation of terrestrial planets (Kenyon & Bromley 2004, 2006) and the bombardment period in the early solar system (Booth et al 2009; Bottke & Norman 2017). Disk variability due to the dust produced in the aftermaths of planetesimal impacts in young, luminous debris disks provides a great opportunity to study the violent events during the era of terrestrial planet formation (Meng et al 2015; Wyatt & Jackson 2016)
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