Hidden Planets: Implications from ‘Oumuamua and DSHARP. (arXiv:1909.06387v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rice_M/0/1/0/all/0/1">Malena Rice</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laughlin_G/0/1/0/all/0/1">Gregory Laughlin</a>
The discovery of ‘Oumuamua (1I/2017 U1), the first interstellar interloper,
suggests an abundance of free-floating small bodies whose ejection into
galactic space cannot be explained by the current population of confirmed
exoplanets. Shortly after ‘Oumuamua’s discovery, observational results from the
DSHARP survey illustrated the near-ubiquity of ring/gap substructures within
protoplanetary disks, strongly suggesting the existence of a vast population of
as-yet undetected wide-separation planets that are capable of efficiently
ejecting debris from their environments. These planets have $a gtrsim 5$ au
and masses of order Neptune’s or larger, and they may accompany $sim$50% of
newly formed stars (Zhang et al. 2018). We combine the DSHARP results with
statistical constraints from current time-domain surveys to quantify the
population of detectable icy planetesimals ejected by disk-embedded giant
planets through gravity assists. Assessment of the expected statistical
distribution of interstellar objects is critical to accurately plan for and
interpret future detections. We show that the number density of interstellar
objects implied by ‘Oumuamua is consistent with ‘Oumuamua itself having
originated as an icy planetesimal ejected from a DSHARP-type system via gravity
assists, with the caveat that ‘Oumuamua’s lack of observed outgassing remains
in strong tension with a cometary origin. Under this interpretation,
‘Oumuamua’s detection points towards a large number of long-period giant
planets in extrasolar systems, supporting the hypothesis that the observed gaps
in protoplanetary disks are carved by planets. In the case that ‘Oumuamua is an
ejected cometary planetesimal, we conclude that LSST should detect up to a few
interstellar objects per year of ‘Oumuamua’s size or larger and over 100
yr$^{-1}$ for objects with $r > 1,{rm m}$.
The discovery of ‘Oumuamua (1I/2017 U1), the first interstellar interloper,
suggests an abundance of free-floating small bodies whose ejection into
galactic space cannot be explained by the current population of confirmed
exoplanets. Shortly after ‘Oumuamua’s discovery, observational results from the
DSHARP survey illustrated the near-ubiquity of ring/gap substructures within
protoplanetary disks, strongly suggesting the existence of a vast population of
as-yet undetected wide-separation planets that are capable of efficiently
ejecting debris from their environments. These planets have $a gtrsim 5$ au
and masses of order Neptune’s or larger, and they may accompany $sim$50% of
newly formed stars (Zhang et al. 2018). We combine the DSHARP results with
statistical constraints from current time-domain surveys to quantify the
population of detectable icy planetesimals ejected by disk-embedded giant
planets through gravity assists. Assessment of the expected statistical
distribution of interstellar objects is critical to accurately plan for and
interpret future detections. We show that the number density of interstellar
objects implied by ‘Oumuamua is consistent with ‘Oumuamua itself having
originated as an icy planetesimal ejected from a DSHARP-type system via gravity
assists, with the caveat that ‘Oumuamua’s lack of observed outgassing remains
in strong tension with a cometary origin. Under this interpretation,
‘Oumuamua’s detection points towards a large number of long-period giant
planets in extrasolar systems, supporting the hypothesis that the observed gaps
in protoplanetary disks are carved by planets. In the case that ‘Oumuamua is an
ejected cometary planetesimal, we conclude that LSST should detect up to a few
interstellar objects per year of ‘Oumuamua’s size or larger and over 100
yr$^{-1}$ for objects with $r > 1,{rm m}$.
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