32 research outputs found
Excitation of Planetary Obliquities Through Planet-Disk Interactions
The tilt of a planet's spin axis off its orbital axis ("obliquity") is a
basic physical characteristic that plays a central role in determining the
planet's global circulation and energy redistribution. Moreover, recent studies
have also highlighted the importance of obliquities in sculpting not only the
physical features of exoplanets but also their orbital architectures. It is
therefore of key importance to identify and characterize the dominant processes
of excitation of non-zero axial tilts. Here we highlight a simple mechanism
that operates early on and is likely fundamental for many extrasolar planets
and perhaps even Solar System planets. While planets are still forming in the
protoplanetary disk, the gravitational potential of the disk induces nodal
recession of the orbits. The frequency of this recession decreases as the disk
dissipates, and when it crosses the frequency of a planet's spin axis
precession, large planetary obliquities may be excited through capture into a
secular spin-orbit resonance. We study the conditions for encountering this
resonance and calculate the resulting obliquity excitation over a wide range of
parameter space. Planets with semi-major axes in the range are the most readily affected, but
large- planets can also be impacted. We present a case study of Uranus and
Neptune and show that this mechanism likely cannot help explain their high
obliquities. While it could have played a role if finely tuned and envisioned
to operate in isolation, large-scale obliquity excitation was likely inhibited
by gravitational planet-planet perturbations.Comment: 12 pages, 8 figures, accepted to Ap
Can Cold Jupiters Sculpt the Edge-of-the-Multis?
Compact systems of multiple close-in super-Earths/sub-Neptunes ("compact
multis") are a ubiquitous outcome of planet formation. It was recently
discovered that the outer edges of compact multis are located at smaller
orbital periods than expected from geometric and detection biases alone,
suggesting some truncation or transition in the outer architectures. Here we
test whether this "edge-of-the-multis" might be explained in any part by
distant giant planets in the outer regions ( AU) of the systems. We
investigate the dynamical stability of observed compact multis in the presence
of hypothetical giant () perturbing planets. We
identify what parameters would be required for hypothetical perturbing planets
if they were responsible for dynamically sculpting the outer edges of compact
multis. "Edge-sculpting" perturbers are generally in the range
days for the average compact multi, with most between days.
Given the relatively close separation, we explore the detectability of the
hypothetical edge-sculpting perturbing planets, finding that they would be
readily detectable in transit and radial velocity data. We compare to
observational constraints and find it unlikely that dynamical sculpting from
distant giant planets contributes significantly to the edge-of-the-multis.
However, this conclusion could be strengthened in future work by a more
thorough analysis of the detection yields of the perturbing planets.Comment: 15 pages, 5 figures, accepted for publication in Ap