Abstract
Transiting giant planets provide a natural opportunity to examine stellar obliquities, which offer clues about the origin and dynamical histories of close-in planets. Hot Jupiters orbiting ...Sun-like stars show a tendency for obliquity alignment, which suggests that obliquities are rarely excited or that tidal realignment is common. However, the stellar obliquity distribution is less clear for giant planets at wider separations where realignment mechanisms are not expected to operate. In this work, we uniformly derive line-of-sight inclinations for 47 cool stars (
T
eff
< 6200 K) harboring transiting hot and warm giant planets by combining rotation periods, stellar radii, and
v
sin
i
measurements. Among the systems that show signs of spin–orbit misalignment in our sample, three are identified as being misaligned here for the first time. Of particular interest are Kepler-1654, one of the longest-period (1047 days; 2.0 au) giant planets in a misaligned system, and Kepler-30, a multiplanet misaligned system. By comparing the reconstructed underlying inclination distributions, we find that the inferred minimum misalignment distributions of hot Jupiters spanning
a
/
R
*
= 3–20 (≈0.01–0.1 au) and warm Jupiters spanning
a
/
R
*
= 20–400 (≈0.1–1.9 au) are in good agreement. With 90% confidence, at least
24
−
10
+
7
%
of warm Jupiters and
14
−
8
+
5
%
of hot Jupiters around cool stars are misaligned by at least 10°. Most stars harboring warm Jupiters are therefore consistent with spin–orbit alignment. The similarity of the hot and warm Jupiter misalignment rates suggests that either the occasional misalignments are primordial and originate in misaligned disks, or the same underlying processes that create misaligned hot Jupiters also lead to misaligned warm Jupiters.
Abstract
Tidal heating on Io due to its finite eccentricity was predicted to drive surface volcanic activity, which was subsequently confirmed by the Voyager spacecraft. Although the volcanic ...activity in Io is more complex, in theory volcanism can be driven by runaway melting in which the tidal heating increases as the mantle thickness decreases. We show that this runaway melting mechanism is generic for a composite planetary body with liquid core and solid mantle, provided that (i) the mantle rigidity,
μ
, is comparable to the central pressure, i.e.,
μ
/(
ρ
gR
P
) ≳ 0.1 for a body with density
ρ
, surface gravitational acceleration
g
, and radius
R
P
; (ii) the surface is not molten; (iii) tides deposit sufficient energy; and (iv) the planet has nonzero eccentricity. We calculate the approximate liquid core radius as a function of
μ
/(
ρ
gR
P
), and find that more than 90% of the core will melt due to this runaway for
μ
/(
ρ
gR
P
) ≳ 1. From all currently confirmed exoplanets, we find that the terrestrial planets in the L 98-59 system are the most promising candidates for sustaining active volcanism. However, uncertainties regarding the quality factors and the details of tidal heating and cooling mechanisms prohibit definitive claims of volcanism on any of these planets. We generate synthetic transmission spectra of these planets assuming Venus-like atmospheric compositions with an additional 5%, 50%, and 98% SO
2
component, which is a tracer of volcanic activity. We find a ≳3
σ
preference for a model with SO
2
with 5–10 transits with JWST for L 98-59bcd.
Abstract
The orientation between a star’s spin axis and a planet’s orbital plane provides valuable information about the system’s formation and dynamical history. For non-transiting planets at wide ...separations, true stellar obliquities are challenging to measure, but lower limits on spin–orbit orientations can be determined from the difference between the inclination of the star’s rotational axis and the companion’s orbital plane (Δ
i
). We present results of a uniform analysis of rotation periods, stellar inclinations, and obliquities of cool stars (SpT ≳ F5) hosting directly imaged planets and brown dwarf companions. As part of this effort, we have acquired new
v
sin
i
*
values for 22 host stars with the high-resolution Tull spectrograph at the Harlan J. Smith telescope. Altogether our sample contains 62 host stars with rotation periods, most of which are newly measured using light curves from the Transiting Exoplanet Survey Satellite. Among these, 53 stars have inclinations determined from projected rotational and equatorial velocities, and 21 stars predominantly hosting brown dwarfs have constraints on Δ
i
. Eleven of these (52
−
11
+
10
% of the sample) are likely misaligned, while the remaining 10 host stars are consistent with spin–orbit alignment. As an ensemble, the minimum obliquity distribution between 10 and 250 au is more consistent with a mixture of isotropic and aligned systems than either extreme scenario alone—pointing to direct cloud collapse, formation within disks bearing primordial alignments and misalignments, or architectures processed by dynamical evolution. This contrasts with stars hosting directly imaged planets, which show a preference for low obliquities. These results reinforce an emerging distinction between the orbits of long-period brown dwarfs and giant planets in terms of their stellar obliquities and orbital eccentricities.
Abstract
We present the direct-imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2
M
⊙
member of the 24 ± 3 Myr
β
Pic moving group. AF Lep was observed as part of our ongoing ...high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in
L
′
with the vector vortex coronagraph reveal a point source, AF Lep b, at ≈340 mas, which exhibits orbital motion at the 6
σ
level over the course of 13 months. A joint orbit fit yields precise constraints on the planet’s dynamical mass of
3.2
−
0.6
+
0.7
M
Jup
, semimajor axis of
8.4
−
1.3
+
1.1
au, and eccentricity of
0.24
−
0.15
+
0.27
. AF Lep hosts a debris disk located at ∼50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (
i
*
=
54
−
9
+
11
°
) and orbital inclination (
i
o
=
50
−
12
+
9
°
) are in good agreement, which is consistent with the system having spin–orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.
Abstract
The large-scale structure of the solar system has been shaped by a transient dynamical instability that may have been triggered by the interaction of the giants planets with a massive ...primordial disk of icy debris. In this work, we investigate the conditions under which this primordial disk could have coalesced into planets using analytic and numerical calculations. In particular, we perform numerical simulations of the solar system’s early dynamical evolution that account for the viscous stirring and collisional damping within the disk. We demonstrate that if collisional damping would have been sufficient to maintain a temperate velocity dispersion, Earth-mass trans-Neptunian planets could have emerged within a timescale of 10 Myr. Therefore, our results favor a scenario wherein the dynamical instability of the outer solar system began immediately upon the dissipation of the gaseous nebula to avoid the overproduction of Earth-mass planets in the outer solar system.
The large scale structure of the Solar System has been shaped by a transient dynamical instability that may have been triggered by the interaction of the giants planets with a massive primordial disk ...of icy debris. In this work, we investigate the conditions under which this primordial disk could have coalesced into planets using analytic and numerical calculations. In particular, we perform numerical simulations of the Solar System's early dynamical evolution that account for the viscous stirring and collisional damping within the disk. We demonstrate that if collisional damping would have been sufficient to maintain a temperate velocity dispersion, Earth mass trans-Neptunian planets could have emerged within a timescale of 10 Myr. Therefore, our results favor a scenario wherein the dynamical instability of the outer Solar System began immediately upon the dissipation of the gaseous nebula to avoid the overproduction of Earth mass planets in the outer Solar System.
Transiting giant planets provide a natural opportunity to examine stellar obliquities, which offer clues about the origin and dynamical histories of close-in planets. Hot Jupiters orbiting Sun-like ...stars show a tendency for obliquity alignment, which suggests that obliquities are rarely excited or that tidal realignment is common. However, the stellar obliquity distribution is less clear for giant planets at wider separations where realignment mechanisms are not expected to operate. In this work, we uniformly derive line-of-sight inclinations for 47 cool stars (\(T_\mathrm{eff}\) \(<\) 6200 K) harboring transiting hot and warm giant planets by combining rotation periods, stellar radii, and \(v \sin i\) measurements. Among the systems that show signs of spin-orbit misalignment in our sample, three are identified as being misaligned here for the first time. Of particular interest are Kepler-1654, one of the longest-period (1047 d; 2.0 AU) giant planets in a misaligned system, and Kepler-30, a multi-planet misaligned system. By comparing the reconstructed underlying inclination distributions, we find that the inferred minimum misalignment distributions of hot Jupiters spanning \(a/R_{*}\) = 3-20 (\(\approx\) 0.01-0.1 AU) and warm Jupiters spanning \(a/R_{*}\) = 20-400 (\(\approx\) 0.1-1.9 AU) are in good agreement. With 90\(\%\) confidence, at least 24\(^{+9}_{-7}\%\) of warm Jupiters and 14\(^{+7}_{-5}\%\) of hot Jupiters around cool stars are misaligned by at least 10\(^\circ\). Most stars harboring warm Jupiters are therefore consistent with spin-orbit alignment. The similarity of hot and warm Jupiter misalignment rates suggests that either the occasional misalignments are primordial and originate in misaligned disks, or the same underlying processes that create misaligned hot Jupiters also lead to misaligned warm Jupiters.
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