Neptune-mass Planet Research Articles

ExELS: an exoplanet legacy science proposal for the ESA Euclid mission - II. Hot exoplanets and sub-stellar systems

The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the frequency of cold exoplanets down to Earth mass from host separations of ~1 AU out to the free-floating regime by detecting microlensing events in Galactic Bulge. We show that ExELS can also detect large numbers of hot, transiting exoplanets in the same population. The combined microlensing+transit survey would allow the first self-consistent estimate of the relative frequencies of hot and cold sub-stellar companions, reducing biases in comparing "near-field" radial velocity and transiting exoplanets with "far-field" microlensing exoplanets. The age of the Bulge and its spread in metallicity further allows ExELS to better constrain both the variation of companion frequency with metallicity and statistically explore the strength of star-planet tides. We conservatively estimate that ExELS will detect ~4100 sub-stellar objects, with sensitivity typically reaching down to Neptune-mass planets. Of these, ~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be expected in VIS if the cadence can be increased to match the 20-minute H-band cadence. The separation of planets from brown dwarfs via Doppler boosting or ellipsoidal variability will be possible in a handful of cases. Radial velocity confirmation should be possible in some cases, using 30-metre-class telescopes. We expect secondary eclipses, and reflection and emission from planets to be detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500 planetary-radius companions will be characterised with two-colour photometry and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission from) a large sample of hot Jupiters in the H-band can be explored statistically.

PHOTO-DYNAMICAL ANALYSIS OF THREE KEPLER OBJECTS OF INTEREST WITH SIGNIFICANT TRANSIT TIMING VARIATIONS

KOI-227, KOI-319 and KOI-884 are identified here as (at least) two planet systems. For KOI-319 and KOI-884, the observed Transit Timing Variations (TTVs) of the inner transiting planet are used to detect an outer non-transiting planet. The outer planet in KOI-884 is 2.6 Jupiter masses and has the orbital period just narrow of the 3:1 resonance with the inner planet (orbital period ratio 2.93). The distribution of parameters inferred from KOI-319.01's TTVs is bimodal with either a 1.6 Neptune-mass (M_N) planet wide of the 5:3 resonance (period 80.1 d) or a 1 Saturn-mass planet wide of the 7:3 resonance (period 109.2 d). The radial velocity measurements can be used in this case to determine which of these parameter modes is correct. KOI-227.01's TTVs with large 10 hour amplitude can be obtained for planetary-mass companions in various major resonances. Based on the Bayesian evidence, the current TTV data favor the outer 2:1 resonance with a companion mass 1.5 M_N, but this solution implies a very large density of KOI-227.01. The inner and outer 3:2 resonance solutions with sub-Neptune-mass companions are physically more plausible, but will need to be verified.

Is it possible to detect planets around young active G and K dwarfs?

Theoretical predictions suggest that the distribution of planets in very young stars could be very different to that typically observed in Gyr old systems that are the current focus of radial velocity surveys. However, the detection of planets around young stars is hampered by the increased stellar activity associated with young stars, the signatures of which can bias the detection of planets. In this paper we place realistic limitations on the possibilities for detecting planets around young active G and K dwarfs. The models of stellar activity based on tomographic imaging of the G dwarf HD 141943 and the K1 dwarf AB Dor and also include contributions from plage and many small random starspots. Our results show that the increased stellar activity levels present on young Solar-type stars strongly impacts the detection of Earth-mass and Jupiter mass planets and that the degree of activity jitter is directly correlated with stellar \vsinis. We also show that for G and K dwarfs, the distribution of activity in individual stars is more important than the differences in induced radial velocities as a function of spectral type. We conclude that Jupiter mass planets can be detected close-in around fast-rotating young active stars, Neptune-mass planets around moderate rotators and that Super-Earths are only detectable around very slowly rotating stars. The effects of an increase in stellar activity jitter by observing younger stars can be compensated for by extending the observational base-line to at least 100 epochs.

A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b

GJ 436b is a warm--approximately 800 kelvin--exoplanet that periodically eclipses its low-mass (half the mass of the Sun) host star, and is one of the few Neptune-mass planets that is amenable to detailed characterization. Previous observations have indicated that its atmosphere has a ratio of methane to carbon monoxide that is 10(5) times smaller than predicted by models for hydrogen-dominated atmospheres at these temperatures. A recent study proposed that this unusual chemistry could be explained if the planet's atmosphere is significantly enhanced in elements heavier than hydrogen and helium. Here we report observations of GJ 436b's atmosphere obtained during transit. The data indicate that the planet's transmission spectrum is featureless, ruling out cloud-free, hydrogen-dominated atmosphere models with an extremely high significance of 48σ. The measured spectrum is consistent with either a layer of high cloud located at a pressure level of approximately one millibar or with a relatively hydrogen-poor (three per cent hydrogen and helium mass fraction) atmospheric composition.

Cloudy with a chance of dustballs

The flat and featureless transmission spectra of two intermediate-sized extrasolar planets, observed during the planets' passage across their host stars, shed light on the properties of their atmospheres. See Letters p.66 & p.69 Two papers in this issue of Nature report Hubble Space Telescope observations of two separate sub-Jupiter-sized extrasolar planets. Heather Knutson et al. observed four transits of the Neptune-mass planet GJ 436b and Laura Kreidberg et al. observed 15 transits of the smaller 'super-Earth' GJ 1214b. The transmission spectra of starlight passing through the atmospheres of these planets should give a good indication of the nature of their respective atmospheres, and for both planets the spectra obtained from Hubble's Wide Field Camera 3 are virtually featureless. Knutson et al. argue that their data are consistent with either a high cloud deck at pressures of 0.1–10 mbar or a hydrogen-poor atmosphere on GJ 436b. Kreidberg et al. conclude that their near-infrared spectra are consistent with the presence of high-altitude clouds that obscure the lower layers of GJ 1214b.

Terrestrial planets in high-mass disks without gas giants

Fil: de Elia, Gonzalo Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Astrofisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronomicas y Geofisicas. Instituto de Astrofisica la Plata; Argentina

Planetary Companions to Three Evolved Intermediate-Mass Stars: HD 2952, HD 120084, and ω Serpentis

Abstract We report on the detections of planetary companions orbiting around three evolved intermediate-mass stars based on precise radial velocity measurements at Okayama Astrophysical Observatory. HD 2952 (K0III, 2.5 $M_{\odot}$) and $\omega$ Ser (G8III, 2.2 $M_{\odot}$) host a relatively low-mass planet with minimum masses of $m_2$ sin$i =$ 1.6 $M_{\rm J}$ and 1.7 $M_{\rm J}$ in nearly circular orbits with periods of $P =$ 312 and 277 d, respectively. HD 120084 (G7 III, 2.4 $M_{\odot}$) hosts an eccentric planet with $m_2$ sin$i =$ 4.5 $M_{\rm J}$ in an orbit with $P =$ 2082 d and an eccentricity of $e =$ 0.66. The planet has one of the largest eccentricities among those ever discovered around evolved intermediate-mass stars, almost all of which have an eccentricity smaller than 0.4. We also show that the radial-velocity variations of stellar oscillations for G giants can be averaged out below a level of a few m s$^{-1}$, at least on a timescale of a week by high-cadence observations. This enables us to detect a super-Earth and a Neptune-mass planet in short-period orbits even around such giant stars.

GAP OPENING BY EXTREMELY LOW-MASS PLANETS IN A VISCOUS DISK

By numerically integrating the compressible Navier-Stokes equations in two dimensions, we calculate the criterion for gap formation by a very low mass (q ~10^{-4}) protoplanet on a fixed orbit in a thin viscous disk. In contrast with some previously proposed gap-opening criteria, we find that a planet can open a gap even if the Hill radius is smaller than the disk scale height. Moreover, in the low-viscosity limit, we find no minimum mass necessary to open a gap for a planet held on a fixed orbit. In particular, a Neptune-mass planet will open a gap in a minimum mass solar nebula with suitably low viscosity (\alpha <10^{-4}). We find that the mass threshold scales as the square root of viscosity in the low mass regime. This is because the gap width for critical planet masses in this regime is a fixed multiple of the scale height, not of the Hill radius of the planet.

MASS-RADIUS RELATIONSHIPS FOR VERY LOW MASS GASEOUS PLANETS

Recently, the Kepler spacecraft has detected a sizable aggregate of objects, characterized by giant-planet-like radii and modest levels of stellar irradiation. With the exception of a handful of objects, the physical nature, and specifically the average densities, of these bodies remain unknown. Here, we propose that the detected giant planet radii may partially belong to planets somewhat less massive than Uranus and Neptune. Accordingly, in this work, we seek to identify a physically sound upper limit to planetary radii at low masses and moderate equilibrium temperatures. As a guiding example, we analyze the interior structure of the Neptune-mass planet Kepler-30d and show that it is acutely deficient in heavy elements, especially compared with its solar system counterparts. Subsequently, we perform numerical simulations of planetary thermal evolution and in agreement with previous studies, show that generally, 10 - 20 Earth mass, multi-billion year old planets, composed of high density cores and extended H/He envelopes can have radii that firmly reside in the giant planet range. We subject our results to stability criteria based on extreme ultraviolet radiation, as well as Roche-lobe overflow driven mass-loss and construct mass-radius relationships for the considered objects. We conclude by discussing observational avenues that may be used to confirm or repudiate the existence of putative low mass, gas-dominated planets.

A HOT URANUS ORBITING THE SUPER METAL-RICH STAR HD 77338 AND THE METALLICITY-MASS CONNECTION

We announce the discovery of a low-mass planet orbiting the super metal-rich K0V star HD77338 as part of our on-going Calan-Hertfordshire Extrasolar Planet Search. The best fit planet solution has an orbital period of 5.7361\pm0.0015 days and with a radial velocity semi-amplitude of only 5.96\pm1.74 m/s, we find a minimum mass of 15.9+4.7-5.3 Me. The best fit eccentricity from this solution is 0.09+0.25-0.09, and we find agreement for this data set using a Bayesian analysis and a periodogram analysis. We measure a metallicity for the star of +0.35\pm0.06 dex, whereas another recent work (Trevisan et al. 2011) finds +0.47\pm0.05 dex. Thus HD77338b is one of the most metal-rich planet host stars known and the most metal-rich star hosting a sub-Neptune mass planet. We searched for a transit signature of HD77338b but none was detected. We also highlight an emerging trend where metallicity and mass seem to correlate at very low masses, a discovery that would be in agreement with the core accretion model of planet formation. The trend appears to show that for Neptune-mass planets and below, higher masses are preferred when the host star is more metal-rich. Also a lower boundary is apparent in the super metal-rich regime where there are no very low-mass planets yet discovered in comparison to the sub-solar metallicity regime. A Monte Carlo analysis shows that this, low-mass planet desert, is statistically significant with the current sample of 36 planets at around the 4.5\sigma\ level. In addition, results from Kepler strengthen the claim for this paucity of the lowest-mass planets in super metal-rich systems. Finally, this discovery adds to the growing population of low-mass planets around low-mass and metal-rich stars and shows that very low-mass planets can now be discovered with a relatively small number of data points using stable instrumentation.

Planetary evaporation by UV and X-ray radiation: basic hydrodynamics

We consider the evaporation of close in planets by the star's intrinsic EUV and X-ray radiation. We calculate evaporation rates by solving the hydrodynamical problem for planetary evaporation including heating from both X-ray and EUV radiation. We show that most close-in planets (a<0.1 AU) are evaporating hydrodynamically, with the evaporation occurring in two distinct regimes: X-ray driven, in which the X-ray heated flow contains a sonic point, and EUV driven, in which the X-ray region is entirely sub-sonic. The mass-loss rates scale as L_X/a^2 for X-ray driven evaporation, and as Phi_*^{1/2}/a for EUV driven evaporation at early times, with mass-loss rates of order 10e10-10e14 g/s. No exact scaling exists for the mass-loss rate with planet mass and planet radius, however, in general evaporation proceeds more rapidly for planets with lower densities and higher masses. Furthermore, we find that in general the transition from X-ray driven to EUV driven evaporation occurs at lower X-ray luminosities for planets closer to their parent stars and for planets with lower densities. Coupling our evaporation models to the evolution of the high energy radiation - which falls with time - we are able to follow the evolution of evaporating planets. We find that most planets start off evaporating in the X-ray driven regime, but switch to EUV driven once the X-ray luminosity falls below a critical value. The evolution models suggest that while `hot Jupiters' are evaporating, they are not evaporating at a rate sufficient to remove the entire gaseous envelope on Gyr time-scales. However, we do find that close in Neptune mass planets are more susceptible to complete evaporation of their envelopes. Thus we conclude that planetary evaporation is more important for lower mass planets, particularly those in the `hot Neptune'/`super Earth' regime.

A SECOND GIANT PLANET IN 3:2 MEAN-MOTION RESONANCE IN THE HD 204313 SYSTEM

We present 8 years of high-precision radial velocity (RV) data for HD 204313 from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a Neptune-mass planet at 0.2 AU. Using our own data in combination with the published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian (M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the planets are in a 3:2 mean motion resonance, which would potentially affect their stability. We perform a detailed stability analysis, and verify the planets must be in resonance.

THE GJ 436 SYSTEM: DIRECTLY DETERMINED ASTROPHYSICAL PARAMETERS OF AN M DWARF AND IMPLICATIONS FOR THE TRANSITING HOT NEPTUNE

The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6-day orbit. We present results of our interferometric measurements to directly determine the stellar diameter ($R_{\star} = 0.455 \pm 0.018 R_{\odot}$) and effective temperature ($T_{\rm EFF} = 3416 \pm 54$ K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436's stellar mass ($M_{\star} = 0.507^{+ 0.071}_{- 0.062} M_{\odot}$) and density ($\rho_* = 5.37^{+ 0.30}_{- 0.27} \rho_\odot$), planetary radius ($R_{p} = 0.369^{+ 0.015}_{- 0.015} R_{Jupiter}$), planetary mass ($M_{p} = 0.078^{+ 0.007}_{- 0.008} M_{Jupiter}$), implying a mean planetary density of $\rho_{p} = 1.55^{+ 0.12}_{- 0.10} \rho_{Jupiter}$. These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ 436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with {\it Spitzer} monitoring observations.

Red Optical Planet Survey: a new search for habitable earths in the southern sky

We present the first results from our Red Optical Planet Survey (ROPS) to search for low mass planets orbiting late type dwarfs (M5.5V - M9V) in their habitable zones (HZ). Our observations, with the red arm of the MIKE spectrograph (0.5 - 0.9 microns) at the 6.5 m Magellan Clay telescope at Las Campanas Observatory indicate that >= 92 per cent of the flux lies beyond 0.7 microns. We use a novel approach that is essentially a hybrid of the simultaneous iodine and ThAr methods for determining precision radial velocities. We apply least squares deconvolution to obtain a single high S/N ratio stellar line for each spectrum and cross correlate against the simultaneously observed telluric line profile, which we derive in the same way. Utilising the 0.62 - 0.90 micron region, we have achieved an r.m.s. precision of 10 m/s for an M5.5V spectral type star with spectral S/N ~160 on 5 minute timescales. By M8V spectral type, a precision of ~30 m/s at S/N = 25 is suggested, although more observations are needed. An assessment of our errors and scatter in the radial velocity points hints at the presence of stellar radial velocity variations. Of our sample of 7 stars, 2 show radial velocity signals at 6-sigma and 10-sigma of the cross correlation uncertainties. If the signals are planetary in origin, our findings are consistent with estimates of Neptune mass planets that predict a frequency of 13 - 27 per cent for early M dwarfs.Our current analysis indicates the we can achieve a sensitivity that is equivalent to the amplitude induced by a 6 M_Earth planet orbiting in the habitable zone. Based on simulations, we estimate that <10 M_Earth habitable zone planets will be detected in a new stellar mass regime, with <=20 epochs of observations.

Orbital migration induced by anisotropic evaporation

Short period planets are subject to intense energetic irradiations from their stars. It has been shown that this can lead to significant atmospheric mass-loss and create smaller mass planets. Here, we analyse whether the evaporation mechanism can affect the orbit of planets. The orbital evolution of a planet undergoing evaporation is derived analytically in a very general way. Analytical results are then compared with the period distribution of two classes of inner exoplanets: Jupiter-mass planets and Neptune-mass planets. These two populations have a very distinct period distribution, with a probability lower than 10^-4 that they were derived from the same parent distribution. We show that mass ejection can generate significant migration with an increase of orbital period that matches very well the difference of distribution of the two populations. This would happen if the evaporation emanates from above the hottest region of planet surface. Thus, migration induced by evaporation is an important mechanism that cannot be neglected.

Global models of planetary system formation in radiatively-inefficient protoplanetary discs

We present the results of N-body simulations of planetary system formation in radiatively-inefficient disc models, where positive corotation torques may counter the rapid inward migration of low-mass planets driven by Lindblad torques. The aim of this work is to examine the nature of planetary systems that arise from oligarchic growth in such discs. We adapt the commonly used Mercury-6 symplectic integrator by including simple prescriptions for planetary migration (types I and II), planetary atmospheres that enhance the probability of planetesimal accretion by protoplanets, gas accretion on to forming planetary cores, and gas disc dispersal. We perform a suite of simulations for a variety of disc models with power-law surface density and temperature profiles, with a focus on models in which unsaturated corotation torques can drive outward migration of protoplanets. In some models, we account for the quenching of corotation torques which arises when planetary orbits become eccentric. Approximately half of our simulations lead to the successful formation of gas giant planets with a broad range of masses and semimajor-axes. Giant planetary masses range from being approximately equal to that of Saturn up to approximately twice that of Jupiter. The semimajor-axes of these range from being ∼0.2 au up to ∼75 au, with disc models that drive stronger outward migration favouring the formation of longer period giant planets. Out of a total of 20 giant planets being formed in our simulation suite, we obtain three systems that contain two giants. No super-Earth or Neptune-mass planets were present in the final stages of our simulations, in contrast to the large abundance of such objects being discovered in observation surveys. This result arises because of rapid inward migration suffered by massive planetary cores that form early in the disc lifetime (for which the corotation torques saturate), combined with gas accretion on to massive cores which leads them to become gas giants. Numerous low-mass planets are formed and survive in the simulations, with masses ranging from a few tenths of an Earth mass up to ∼3 Earth masses. Simulations in which the quenching of corotation torques for planets on modestly eccentric orbits was included failed to produce any giant planets, apparently because Lindblad torques induce rapid inward migration of planetary cores in these systems. We conclude that convergent migration induced by corotation torques operating during planetary formation can enhance the growth rate of planetary cores, but these often migrate into the central star because corotation torques saturate. Outward migration of planetary cores of modest mass can lead to the formation of gas giant planets at large distances from the central star, similar to those observed recently through direct imaging surveys. The excitation of planetary eccentricities through planet–planet scattering during oligarchic growth may quench the effects of corotation torques, however, such that inward migration is driven by Lindblad torques.

KEPLER-18b, c, AND d: A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHT CURVE VALIDATION, WARM-SPITZER PHOTOMETRY, AND RADIAL VELOCITY MEASUREMENTS

We report the detection of three transiting planets around a Sunlike star, which we designate Kepler-18. The transit signals were detected in photometric data from the Kepler satellite, and were confirmed to arise from planets using a combination of large transit-timing variations, radial-velocity variations, Warm-Spitzer observations, and statistical analysis of false-positive probabilities. The Kepler-18 star has a mass of 0.97M_sun, radius 1.1R_sun, effective temperature 5345K, and iron abundance [Fe/H]= +0.19. The planets have orbital periods of approximately 3.5, 7.6 and 14.9 days. The innermost planet "b" is a "super-Earth" with mass 6.9 \pm 3.4M_earth, radius 2.00 \pm 0.10R_earth, and mean density 4.9 \pm 2.4 g cm^-3. The two outer planets "c" and "d" are both low-density Neptune-mass planets. Kepler-18c has a mass of 17.3 \pm 1.9M_earth, radius 5.49 \pm 0.26R_earth, and mean density 0.59 \pm 0.07 g cm^-3, while Kepler-18d has a mass of 16.4 \pm 1.4M_earth, radius 6.98 \pm 0.33R_earth, and mean density 0.27 \pm 0.03 g cm^-3. Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance, leading to large and readily detected transit timing variations.

AN INDEPENDENT ANALYSIS OF KEPLER-4b THROUGH KEPLER-8b

We present two independent, homogeneous, global analyses of the transit light curves, radial velocities and spectroscopy of Kepler-4b through Kepler-8b, with numerous differences over the previous methods. These include: 1) improved decorrelated parameter fitting set, 2) new limb darkening coefficients, 3) time-stamps modified to BJD for consistency with RV, 4) two different methods for compensating for the integration-time of Kepler LC-data, 5) best-fit secondary-eclipse depths and excluded upper limits, 6) fitted mid-transit times, durations, depths and baseline fluxes for individual transits. We make several new determinations: 1) We detect a secondary eclipse for Kepler-7b of depth (47+/-14)ppm and significance 3.5-sigma. We conclude reflected light is a more plausible origin than thermal emission and determine a geometric albedo of Ag=(0.38+/-0.12). 2) An eccentric-orbit model for the Neptune-mass planet Kepler-4b is marginally detected to 2-sigma confidence with e=(0.25+/-0.12). If confirmed, this would place Kepler-4b in a similar category as GJ436b and HAT-P-11b as an eccentric, Neptune-mass planet. 3) We find marginal (2-sigma) evidence for Kepler-5b's secondary eclipse of depth (26+/-17)ppm. The most plausible explanation is reflected light caused by a planet with Ag=(0.15+/-0.10). 4) A 2.6-sigma peak in Kepler-6b TTV periodogram is detected and is not easily explained as an aliased frequency. We find that a resonant/non-resonant perturber, Trojan or exomoon all provide inadequate explanations and the most likely source is stellar rotation. 5) We find different impact parameters relative to the discovery papers in most cases, but generally self-consistent. 6) We constrain the presence of resonant planets, exomoons and Trojans using transit timing.

THE NASA-UC ETA-EARTH PROGRAM. III. A SUPER-EARTH ORBITING HD 97658 AND A NEPTUNE-MASS PLANET ORBITING Gl 785

We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and Gl 785. These planets were detected by Keplerian modelling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass Msini = 8.2 +/- 1.2 M_Earth, orbital period P = 9.494 +/- 0.005 d, and an orbit that is consistent with circular. Gl 785 b is a Neptune-mass planet with Msini = 21.6 +/- 2.0 M_Earth, P = 74.39 +/- 0.12 d, and orbital eccentricity 0.30 +/- 0.09. Photometric observations with the T12 0.8 m automatic photometric telescope at Fairborn Observatory show that HD 97658 is photometrically constant at the radial velocity period to 0.09 mmag, supporting the existence of the planet.

Collisional evolution of irregular satellite swarms: detectable dust around Solar system and extrasolar planets

Since the 1980's it has been becoming increasingly clear that the Solar System's irregular satellites are collisionally evolved. We derive a general model for the collisional evolution of an irregular satellite swarm and apply it to the Solar System and extrasolar planets. Our model reproduces the Solar System's complement of observed irregulars well, and suggests that the competition between grain-grain collisions and Poynting-Robertson (PR) drag helps set the fate of the dust. Because swarm collision rates decrease over time the main dust sink can change with time, and may help unravel the accretion history of synchronously rotating regular satellites that show brightness asymmetries. Some level of dust must be present on AU scales around the Solar System's giant planets, which we predict may be at detectable levels. We also predict whether dust produced by extrasolar circumplanetary swarms can be detected. The coronagraphic instruments on JWST will have the ability to detect the dust generated by these swarms, which are most detectable around planets that orbit at tens of AU from the youngest stars. Because the collisional decay of swarms is relatively insensitive to planet mass, swarms can be much brighter than their host planets and allow discovery of Neptune-mass planets that would otherwise remain invisible. This dust may have already been detected. The observations of the planet Fomalhaut b can be explained as scattered light from dust produced by the collisional decay of an irregular satellite swarm around a 10 Earth-mass planet. Such a swarm comprises about 5 Lunar masses worth of irregular satellites. Finally, we consider what happens if Fomalhaut b passes through Fomalhaut's main debris ring, which allows the circumplanetary swarm to be replenished through collisions with ring planetesimals. (abridged)