Authors: David C. Slater, S. Alan Stern, John Scherrer, Webster Cash, James C. Green, & Erik Wilkinson
Status: 1995. In SPIE Proceedings EUV, X-ray, and Gamma-Ray instrumentation for Astronomy VI, Oswald H. W. Siegmund, John V. Vallerga, Eds., Proc. 2518, pp. 211-222.
Abstract: We report on the status of modifications to an existing extreme ultraviolet (EUV) telescope/spectrograph sounding rocket payload for planetary observations in the 800 - 1200 A wavelength band. The instrument is composed of an existing Wolter Type II grazing incidence telescope, a newly built 0.4-m normal incidence Rowland Circle spectrograph, and an open-structure resistive-anode microchannel plate detector. The modified payload has successfully completed three NASA sounding rocket flights within 1994-1995. Future flights are anticipated for additional studies of planetary and cometary atmospheres and intersteller absorption. A detailed description of the payload, along with the performance characteristics of the integrated instrument are presented. In addition, some preliminary flight results from the above three missions are also presented.
Title: Collisional Timescales in the Kuiper Disk and Their Implications
Author: Alan Stern
Status: From the Astronomical Journal, 1995.
Abstract: We explore the rate of collisions among bodies in the
present-day Kuiper Disk as a function the total mass and population
size structure of the disk. We find that collisional evolution is an
important evolutionary process in the Disk as a whole, and indeed, that
it is likely the dominant evolutionary process beyond ~42 AU,
where dynamical instability timescales exceed the age of the solar
system. Two key findings we report from this modelling work are: (i)
That unless the disk's population structure is sharply truncated for
radii smaller than ~1-2 km, collisions between comets and smaller
debris are occuring so frequently in the disk, and with high enough
velocities, that the small body (i.e., km-class object) population in
the disk has probably developed into a collisional cascade, thereby
implying that the Kuiper Disk comets may not all be primordial, and
(ii) that the rate of collisions of smaller bodies with larger
100
Title: The 825-1110 Å EUV Spectrum of Venus
Authors: Alan Stern, David C. Slater, G. Randall Gladstone,
Erik Wilkenson, Webster C. Cash, James C. Green, Donald M. Hunten, &
Tobias C. Owen
Status: To Appear in Icarus .
Abstract: On 15 August 1994 we launched the EUVS sounding rocket
payload to observe an ~300 Å region of Venus's EUV airglow
spectrum. The EUVS telescope/spectrograph obtained good data at five
times higher spectral resolution than previously available. We present
these data and compare our results to those obtained by the Galileo UVS
and Venera 11/12 UV spectrophotometers. We tentatively identify several
new spectral emissions, including both singly ionized nitrogen and
molecular nitrogen in Venus's spectrum, for the first time; we also
discuss the on-going debate over the `Ar' features in Venus's
emission spectrum.
Authors: S. Alan Stern, Laurence Trafton, & Brian Flynn
Status: To Appear in Icarus .
Abstract: Using the Hubble Space Telescope (HST) we have
obtained useful spectra of Triton at a resolution of 2 Å, from
1900-3278 Å, at five rotational phases in 1992 and 1993. We
present these data and analyze them to evaluate the rotational
variability of Triton's mid-ultraviolet reflectance spectrum, albedo,
and color slope. The main characteristics of Triton's UV reflectance
spectrum include: (i) the detection of a rotationally-independent
cessation in Triton's well-known, red albedo slope near 2750 Å
(ii) the apparent presence of either a blue albedo upturn or a broad,
solid-state aborption feature with ~6% depth at this transition
wavelength; (iii) the detection of one or additional, broad,
presumably solid state absorption features between 2000 and 2100
Å which may be related to photochemical byproducts of atmospheric
chemistry lying on Triton's surface; and (iv) no evidence for
atmospheric emissions at this spectral resolution. Regarding the
atmosphere, we have analyzed the lack of spectral features due to OH,
NO, and CO molecules in the HST spectra, in order to provide new
constraints on the bulk mixing ratios of these species in Triton's
atmosphere. The derived mixing ratio upper limits are M_OH < 3X10^-6,
M_NO < 8X10^-5, and M_CO < 1.5X10^-2. These constraints constitute the
first-ever data on OH and NO abundance in Triton's atmosphere, and a
confirmation that the CO abundance is lower than the initial
Voyager-UVS upper limit. Returning to Triton's surface, we have found
that the main characteristics of Triton's UV rotational lightcurve
derived from these five observations spread in rotational phase
include: (i) a monotonically increasing lightcurve amplitude down to
wavelengths as short as 2400 Å (ii) strong structural
similarities in the UV and visible lightcurves down to 2400 Å
(iii) a sharply reduced lightcurve amplitude below 2250 Å and
(iv) no indication that the 2750 Å surface absorption feature
depth is correlated with rotational phase. These results are
interpreted in the text.
Last Updated: 1996 December 4