12 research outputs found
Hiding in the Shadows: Searching for Planets in Pre--transitional and Transitional Disks
Transitional and pre--transitional disks can be explained by a number of
mechanisms. This work aims to find a single observationally detectable marker
that would imply a planetary origin for the gap and, therefore, indirectly
indicate the presence of a young planet. N-body simulations were conducted to
investigate the effect of an embedded planet of one Jupiter mass on the
production of instantaneous collisional dust derived from a background
planetesimal disk. Our new model allows us to predict the dust distribution and
resulting observable markers with greater accuracy than previous work.
Dynamical influences from a planet on a circular orbit are shown to enhance
dust production in the disk interior and exterior to the planet orbit while
removing planetesimals from the the orbit itself creating a clearly defined
gap. In the case of an eccentric planet the gap opened by the planet is not as
clear as the circular case but there is a detectable asymmetry in the dust
disk.Comment: Accepted to ApJL 25th September 2013. 4 figures, 1 tabl
Hiding in the Shadows II: Collisional Dust as Exoplanet Markers
Observations of the youngest planets (1-10 Myr for a transitional disk)
will increase the accuracy of our planet formation models. Unfortunately,
observations of such planets are challenging and time-consuming to undertake
even in ideal circumstances. Therefore, we propose the determination of a set
of markers that can pre-select promising exoplanet-hosting candidate disks. To
this end, N-body simulations were conducted to investigate the effect of an
embedded Jupiter mass planet on the dynamics of the surrounding planetesimal
disk and the resulting creation of second generation collisional dust. We use a
new collision model that allows fragmentation and erosion of planetesimals, and
dust-sized fragments are simulated in a post process step including
non-gravitational forces due to stellar radiation and a gaseous protoplanetary
disk. Synthetic images from our numerical simulations show a bright double ring
at 850 m for a low eccentricity planet, whereas a high eccentricity planet
would produce a characteristic inner ring with asymmetries in the disk. In the
presence of first generation primordial dust these markers would be difficult
to detect far from the orbit of the embedded planet, but would be detectable
inside a gap of planetary origin in a transitional disk.Comment: Accepted for publication in Ap
Modelling the seasonal cycle of Uranusās colour and magnitude, and comparison with Neptune
We present a quantitative analysis of the seasonal record of Uranusās disc-averaged colour and photometric magnitude in StrƶmgrenĀ bĀ andĀ yĀ filters (centred at 467 and 551ānm, respectively), recorded at the Lowell Observatory from 1950 to 2016, and supplemented withĀ HST/WFC3 observations from 2016 to 2022. We find that the seasonal variations of magnitude can be explained by the lower abundance of methane at polar latitudes combined with a time-dependent increase of the reflectivity of the aerosol particles in layer near the methane condensation level at 1 ā 2ābar. This increase in reflectivity is consistent with the addition of conservatively scattering particles to this layer, for which the modelled background haze particles are strongly absorbing at both blue and red wavelengths. We suggest that this additional component may come from a higher proportion of methane ice particles. We suggest that the increase in reflectivity of Uranus in both filters between the equinoxes in 1966 and 2007, noted by previous authors, might be related to Uranusās distance from the Sun and the production rate of dark photochemical haze products. Finally, we find that although the visible colour of Uranus is less blue than Neptune, due to the increased aerosol thickness on Uranus, and this difference is greatest at Uranusās solstices, it is much less significant than is commonly believed due to a long-standing misperception of Neptuneās ātrueā colour. We describe how filter-imaging observations, such as those from Voyager-2/ISS andĀ HST/WFC3, should be processed to yield accurate true colour representations
Latitudinal variations in methane abundance, aerosol opacity and aerosol scattering efficiency in Neptune's atmosphere determined from VLT/MUSE
Spectral observations of Neptune made in 2019 with the MUSE instrument at the Very Large Telescope in Chile have been analysed to determine the spatial variation of aerosol scattering properties and methane abundance in Neptuneās atmosphere. The darkening of the South Polar Wave (SPW) at ā¼ 60ā¦S, and dark spots such as the Voyager 2 Great Dark Spot is concluded to be due to a spectrally-dependent darkening (Ī» < 650nm) of particles in a deep aerosol layer at ā¼ 5 bar and presumed to be composed of a mixture of
~ 650 nm, with bright zones latitudinally separated by ā¼ 25ā¦ . This feature, similar to the spectral characteristics of a discrete deep bright spot DBS-2019 found in our data, is found to be consistent with a brightening of the particles in the same ā¼5-bar aerosol layer at Ī» > 650 nm. We find the properties of an overlying methane/haze aerosol layer at ā¼ 2 bar are, to first-order, invariant with latitude, while variations in the opacity of an upper tropospheric haze layer reproduce the observed reflectivity at methane-absorbing wavelengths, with higher abundances found at the equator and also in a narrow āzoneā at 80ā¦S. Finally, we find the mean abundance of methane below its condensation level to be 6-7% at the equator reducing to ā¼3% south of ā¼25ā¦S, although the absolute abundances are model dependent
Latitudinal Variations in Methane Abundance, Aerosol Opacity and Aerosol Scattering Efficiency in Neptune's Atmosphere Determined From VLT/MUSE
Spectral observations of Neptune made in 2019 with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) in Chile have been analyzed to determine the spatial variation of aerosol scattering properties and methane abundance in Neptune's atmosphere. The darkening of the South Polar Wave at ā¼60Ā°S, and dark spots such as the Voyager 2 Great Dark Spot is concluded to be due to a spectrally dependent darkening (Ī» 650 nm. We find the properties of an overlying methane/haze aerosol layer at ā¼2 bar are, to first-order, invariant with latitude, while variations in the opacity of an upper tropospheric haze layer reproduce the observed reflectivity at methane-absorbing wavelengths, with higher abundances found at the equator and also in a narrow āzoneā at 80Ā°S. Finally, we find the mean abundance of methane below its condensation level to be 6%ā7% at the equator reducing to ā¼3% south of ā¼25Ā°S, although the absolute abundances are model dependent.We are grateful to the United Kingdom Science and Technology Facilities Council for funding this research (Irwin: ST/S000461/1, Teanby: ST/R000980/1). Glenn Orton was supported by funding to the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). Leigh Fletcher and Mike Roman were supported by a European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation programme, grant agreement no. 723890) at the University of Leicester. Santiago PĆ©rez-Hoyos and Agustin SĆ”nchez-Lavega are supported by the Spanish project PID2019-109467GB-I00 (MINECO/FEDER, UE), Elkartek21/87 KK-2021/00061 and Grupos Gobierno Vasco IT-1742-22
Modelling the seasonal cycle of Uranusās colour and magnitude, and comparison with Neptune
We present a quantitative analysis of the seasonal record of Uranusās disc-averaged colour and photometric magnitude in Strƶmgren b and y filters (centred at 467 and 551ānm, respectively), recorded at the Lowell Observatory from 1950 to 2016, and supplemented with HST/WFC3 observations from 2016 to 2022. We find that the seasonal variations of magnitude can be explained by the lower abundance of methane at polar latitudes combined with a time-dependent increase of the reflectivity of the aerosol particles in layer near the methane condensation level at 1 ā 2ābar. This increase in reflectivity is consistent with the addition of conservatively scattering particles to this layer, for which the modelled background haze particles are strongly absorbing at both blue and red wavelengths. We suggest that this additional component may come from a higher proportion of methane ice particles. We suggest that the increase in reflectivity of Uranus in both filters between the equinoxes in 1966 and 2007, noted by previous authors, might be related to Uranusās distance from the Sun and the production rate of dark photochemical haze products. Finally, we find that although the visible colour of Uranus is less blue than Neptune, due to the increased aerosol thickness on Uranus, and this difference is greatest at Uranusās solstices, it is much less significant than is commonly believed due to a long-standing misperception of Neptuneās ātrueā colour. We describe how filter-imaging observations, such as those from Voyager-2/ISS and HST/WFC3, should be processed to yield accurate true colour representations
The temporal brightening of Uranusā northern polar hood from HST/WFC3 & HST/STIS observations
Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus' north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023, https://doi.org/10.1038/s41550-023-02047-0) (IRW23), consisting of a deep haze layer based at ā¼5 bar, a 1ā2 bar haze layer, and an extended haze rising up from the 1ā2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (STIS) (HST/STIS) observations (Sromovsky et al., 2014, 2019, https://doi.org/10.1016/j.icarus.2014.05.016, https://doi.org/10.1016/j.icarus.2018.06.026) revealing a reduction in cloud-top CH4 volume mixing ratio (VMR) (i.e., above the deep ā¼5 bar haze) by an average of 0.0019 Ā± 0.0003 between 40ā80ā¦N (ā¼10% average reduction) from 2012 to 2015. A combination of latitudinal retrievals on the HST/WFC3 and HST/STIS data sets, again employing the IRW23 model, reveal a temporal thickening of the 1ā2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase in integrated opacity of 1.09 Ā± 0.08 (ā¼33% increase) at 0.8 Āµm north of ā¼45Ā°N, concurrent with a decrease in the imaginary refractive index spectrum of the 1ā2 bar haze layer north of ā¼40Ā°N and longwards of ā¼0.7 Āµm. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 Ā± 0.1 (58% increase) north of 45Ā°N between 2012 and 2015, and from the aforementioned decrease in CH4 VMR. Our results are consistent with the slowing of a stratospheric meridional circulation, exhibiting subsidence at the poles