Observational Cosmology Journal Club May 14, 2018; Ryohei Nakatani 1. Haze heats Pluto s atmosphere yet explains its cold temperature Xi Zhang, Darrell F. Strobel & Hiroshi Imanaka; Nature, 551, 352, (2017) (doi:10.1038/nature24465) 2. The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation Ortiz et al.; Nature, 550, 219, (2017) (doi:10.1038/nature24051) 3. Discovery and Physical Characterization of a Large Scattered Disk Object at 92 au Gerdes et al.; ApJL, 839, L15, (2017) (doi:10.3847/2041-8213/aa64d8)
1. Haze heats Pluto s atmosphere yet explains its cold temperature Ø Pluto 1930: Discovered as the 9th planet a = 40 au, T = 248 years R = 0.19 R E (Moon: 0.27 R E ) M = 0.0021 M E (Moon: 0.012 M E ) 2006 Jan.: New Horizons was launched. 2006 Aug.: Classified as a dwarf planet by IAU 2015: New Horizons captured the FIRST close-up images Pluto image captured by New Horizons in 2015 http://pluto.jhuapl.edu/multimedia/science-photos/image.php?page=1&gallery_id=2&image_id=472 Pluto before New Horizons (Hubble 2002-2003) http://astronomyor.blogspot.jp New Horizons spacecraft http://pluto.jhuapl.edu/mission/spacecraft/index.php#systems-and-components
New Horizons revealed many layers of haze in Pluto s atmosphere. (haze = ; Dunst; brume) ~ 100 km 400 nm 975 nm (panchromatic) image of Pluto s surface https://www.nasa.gov/image-feature/haze-layers-above-pluto According to haze-formation and -transport models, the haze particles extend to ~ 1000km; the sizes are ~10 nm 1 µm, depending on the altitude. (Cheng, A. F. et al., Icarus 290, 112, 2017)
New Horizons found that the temperature of Pluto s atmosphere is much lower than that predicted by theoretical studies! Theoretically predicted T distribution (Zhu et al., Icarus, 228, 301, 2014) Actually observed T distribution by New Horizons (Gladstone et al, Science, 351, 1280, 2016) Water vapor cooling could explain the low temperature, but water needs to oversaturate by many orders of magnitude, which is implausible. This paper models Pluto s atmosphere under the effects of haze heating/cooling.
< Model assumptions > Hydrostatic atmosphere ( gas + particles. They are in thermal equilibrium ) Haze profiles of the model spherical symmetric Modeling T distribution with solving heat-transfer until the system reaches steady state. Imaginary part of refractive index Including radiative heating and cooling due to relevant gas components (N 2, CH 4, CO, C 2 H 2, HCN, ) Including radiative heating and cooling due to hazes. Solar ultraviolet and visible lights heat hazes, and hazes cool the system through IR emission. (These profiles are constructed on the basis of haze formation models and observational data obtained by New Horizons.)
Solar flux received by the atmosphere Imaginary part of the haze refractive indices (attenuation) from various sources Gray: total gas heating/cooling Red: radiative equilibrium case, using k in the previous slide Others: Heating/cooling of various haze components, based on the observed temperature profile. Hazes on Pluto have substantial solar heating and infrared cooling rates, compared to the gas components!
Predicted spectra from Pluto s atmosphere, Pluto should appear several orders of magnitude brighter than its surface blackbody spectrum would imply, at wavelengths shorter than 25 µm The colored spectra are based on several models of haze-mediated cooling (as in the previous Figure) Haze contribution would be seen by JWST in the future. (No other current telescope can observe it.) Dots: Detection limits of James Webb Space Telescope
2. The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation 30 AU https://en.wikipedia.org/wiki/haumea http://www.knowledgesuttra.com/blog/dwarf-planet-haumea-fastest-spinning-solar-system/ Haumea (center) and its two moons, Hi iaka (above) & Namaka (below) a = 43 au e = 0.197 i = 28 deg. M = 0.00066 M E This study aims to characterize Haumea.
Earth Haumea Distant star (URAT1 533-182543) Haumea makes a shadow onto the Earth surface during the star occultation. The stellar occultation were simultaneously observed on Jan 21st, 2017, at the observatories. Limits of shadow path The light curve of the occultation was obtained at the ten observatories (green + blue).
Normalized flux from the star plus Haumea VS time obtained at the ten observatories Assuming the shape of the projected shadow is a ellipse, we can infer the shape of Haumea with the occultation durations. 1704 4 km Blue: square-well fit Determines the times of star disappearance and reappearance. 1138 26 km
2287 km In addition to the main occultation, there are brief dimmings before and after the main event. 541km = narrow (~ 70 km), dense ring around Haumea that absorbs 50% of incoming stellar flux Position angles of minor axes of the ellipses are almost equal. It suggests that the ring orbits in Haumea s equatorial plane.
3. Discovery and Physical Characterization of a Large Scattered Disk Object at 92 au With using visible and infrared data collected during Dark Energy Survey (DES) 2014 2016, a trans-neptunian object was detected.
Follow-up study with ALMA Stacked image: 224, 226, 240, 242 GHz Beam size = 0. 30 0. 25 The central source = (0.33 0. 05) (0.25 0. 03) point source Deriving albedo P V and radius D Lower albedo a mixed ice-rock composition The size with this composition sufficiently strong self-gravity to shape the object spherical a candidate dwarf planet The object is named 2014 UZ 224 and is also nicknamed ``DeeDee (meaning Distant- Dwarf).