Neptune long-lived atmospheric features in 2013–2015 from small (28-cm) to large (10-m) telescopes

•We demonstrate capabilities of amateur astronomers to observe and track large cloud systems in Neptune's atmosphere presenting data from 2013 to 2015.•Two bright discrete features Neptune's South mid-latitudes in 2014 seem to have collided into a single bright feature observed over 2015.•...

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Bibliographic Details
Published in:	Icarus (New York, N.Y. 1962) Vol. 295; no. N/A; pp. 89 - 109
Main Authors:	Hueso, R., de Pater, I., Simon, A., Sánchez-Lavega, A., Delcroix, M., Wong, M.H., Tollefson, J.W., Baranec, C., de Kleer, K., Luszcz-Cook, S.H., Orton, G.S., Hammel, H.B., Gómez-Forrellad, J.M., Ordonez-Etxeberria, I., Sromovsky, L., Fry, P., Colas, F., Rojas, J.F., Pérez-Hoyos, S., Gorczynski, P., Guarro, J., Kivits, W., Miles, P., Millika, D., Nicholas, P., Sussenbach, J., Wesley, A., Sayanagi, K., Ammons, S.M., Gates, E.L., Gavel, D., Victor Garcia, E., Law, N.M., Mendikoa, I., Riddle, R.
Format:	Journal Article
Language:	English
Published:	Goddard Space Flight Center Elsevier Inc 01-10-2017 Elsevier
Subjects:	ASTRONOMY AND ASTROPHYSICS Astrophysics Atmospheres - dynamics Lunar And Planetary Science And Exploration Neptune Neptune - atmosphere Physics Neptune Atmospheres, dynamics Neptune, atmosphere Atmospheres Dynamics Atmosphere
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Summary:	•We demonstrate capabilities of amateur astronomers to observe and track large cloud systems in Neptune's atmosphere presenting data from 2013 to 2015.•Two bright discrete features Neptune's South mid-latitudes in 2014 seem to have collided into a single bright feature observed over 2015.•A bright large feature at planetographic latitude −40° in 2015 was linked to a dark spot observed in Hubble Space Telescope images.•We present zonal wind results from a long-term tracking of several cloud systems in 2013–2015. Since 2013, observations of Neptune with small telescopes (28–50 cm) have resulted in several detections of long-lived bright atmospheric features that have also been observed by large telescopes such as Keck II or Hubble. The combination of both types of images allows the study of the long-term evolution of major cloud systems in the planet. In 2013 and 2014 two bright features were present on the planet at southern mid-latitudes. These may have merged in late 2014, possibly leading to the formation of a single bright feature observed during 2015 at the same latitude. This cloud system was first observed in January 2015 and nearly continuously from July to December 2015 in observations with telescopes in the 2-10-m class and in images from amateur astronomers. These images show the bright spot as a compact feature at −40.1 ± 1.6° planetographic latitude well resolved from a nearby bright zonal band that extended from −42° to −20°. The size of this system depends on wavelength and varies from a longitudinal extension of 8000 ± 900 km and latitudinal extension of 6500 ± 900 km in Keck II images in H and Ks bands to 5100 ± 1400 km in longitude and 4500 ± 1400 km in latitude in HST images in 657 nm. Over July to September 2015 the structure drifted westward in longitude at a rate of 24.48 ± 0.03°/day or −94 ± 3 m/s. This is about 30 m/s slower than the zonal winds measured at the time of the Voyager 2 flyby. Tracking its motion from July to November 2015 suggests a longitudinal oscillation of 16° in amplitude with a 90-day period, typical of dark spots on Neptune and similar to the Great Red Spot oscillation in Jupiter. The limited time covered by high-resolution observations only covers one full oscillation and other interpretations of the changing motions could be possible. HST images in September 2015 show the presence of a dark spot at short wavelengths located in the southern flank (planetographic latitude −47.0°) of the bright compact cloud observed throughout 2015. The drift rate of the bright cloud and dark spot translates to a zonal speed of −87.0 ± 2.0 m/s, which matches the Voyager 2 zonal speeds at the latitude of the dark spot. Identification of a few other features in 2015 enabled the extraction of some limited wind information over this period. This work demonstrates the need of frequently monitoring Neptune to understand its atmospheric dynamics and shows excellent opportunities for professional and amateur collaborations.
Bibliography:	GSFC-E-DAA-TN43919 GSFC GSFC-E-DAA-TN51718 Goddard Space Flight Center AC52-07NA27344 LLNL-JRNL-829489 USDOE National Nuclear Security Administration (NNSA)
ISSN:	0019-1035 1090-2643
DOI:	10.1016/j.icarus.2017.06.009