Engineering topics

Noll, Keith S.

Publications and source records attributed to Noll, Keith S..

At least 19 records

NASA NTRS2017

2004 TT357: A Potential Contact Binary in the Trans-Neptunian Belt

We report photometric observations of the trans-Neptunian object 2004 TT(sub 357) obtained in 2015 and 2017 using the 4.3 m Lowell's Discovery Channel Telescope. We derive a rotational period of 7.79 +/- 0.01 hr and a peak-to-peak lightcurve amplitude of 0.76 +/- 0.03 mag. 2004 TT(sub 357) displays a large variability that can be explained by a very elongated single object or can be due to a contact/close binary. The most likely scenario is that 2004 TT(sub 357) is a contact binary. If it is in hydrostatic equilibrium, we find that the lightcurve can be explained by a system with a mass ratio q(sub min) = 0.45 +/- 0.05, and a density of p(sub min) = 2 g/cu.cm, or less likely a system with q(sub max) = 0.8 +/- 0.05, and ρ(sub max) = 5 g/cu.cm. Considering a single triaxial ellipsoid in hydrostatic equilibrium, we derive a lower limit to the density of 0.78 g/cu.cm, and an elongation (a/b) of 2.01 assuming an equatorial view. From Hubble Space Telescope data, we report no resolved companion orbiting 2004 TT(sub 357). Despite an expected high fraction of contact binaries in the trans-Neptunian belt, 2001 QG(sub 298) is the unique confirmed contact binary in the trans- Neptunian belt, and 2004 TT(sub 357) is only the second candidate to this class of systems, with 2003 SQ(sub 317).

Thirouin, Audrey↗

NASA NTRS2016

OSSOS. IV. Discovery of a Dwarf Planet Candidate in the 9:2 Resonance with Neptune

We report the discovery and orbit of a new dwarf planet candidate, 2015 RR245, by the Outer Solar System Origins Survey (OSSOS). The orbit of 2015 RR245 is eccentric (e 0.586), with a semimajor axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR245 has g - r 0.59 +/- 0.11 and absolute magnitude Hr 3.6 +/- 0.1; for an assumed albedo of pV 12, the object has a diameter of approximately 670 km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR245 is securely trapped on ten-megayear timescales in the 9:2 mean-motion resonance with Neptune. It is the first trans-Neptunian object (TNO) identied in this resonance. On hundred-megayear timescales, particles in 2015 RR245-like orbits depart and sometimes return to the resonance, indicating that 2015 RR245 likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9:2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk and reinforces the view that distant resonances are heavily populated in the current solar system. This object further motivates detailed modeling of the transient sticking population.

Bannister, Michele T.↗

NASA NTRS2016

Discovery of a Makemakean Moon

We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the Hubble Space Telescope's Wide Field Camera 3 on UTC 2015 April 27 at 7.80 +/- 0.04 mag fainter than Makemake and at a separation of 0farcs57. It likely evaded detection in previous satellite searches due to a nearly edge-on orbital configuration, placing it deep within the glare of Makemake during a substantial fraction of its orbital period. This configuration would place Makemake and its satellite near a mutual event season. Insufficient orbital motion was detected to make a detailed characterization of its orbital properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days and must have a semimajor axis > or approx. = 21,000 km. We find that the properties of Makemake's moon suggest that the majority of the dark material detected in the system by thermal observations may not reside on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform dark surface. This dark moon hypothesis can be directly tested with future James Webb Space Telescope observations. We discuss the implications of this discovery for the spin state, figure, and thermal properties of Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.

Parker, Alex H.↗

NASA NTRS2016

Rotational Properties of the Haumea Family Members and Candidates: Short-Term Variability

Haumea is one of the most interesting and intriguing trans-Neptunian objects (TNOs). It is a large, bright, fast rotator, and its spectrum indicates nearly pure water ice on the surface. It has at least two satellites and a dynamically related family of more than 10 TNOs with very similar proper orbital parameters and similar surface properties. The Haumean family is the only one currently known in the trans-Neptunian belt. Various models have been proposed, but the formation of the family remains poorly understood. In this work, we have investigated the rotational properties of the family members and unconfirmed family candidates with short-term variability studies, and report the most complete review to date. We present results based on five years of observations and report the short-term variability of five family members, and seven candidates. The mean rotational periods, from Maxwellian fits to the frequency distributions, are 6.27 +/- 1.19 hr for the confirmed family members, 6.44 +/- 1.16 hr for the candidates, and 7.65 +/- 0.54 hr for other TNOs (without relation to the family). According to our study, there is a possibility that Haumea family members rotate faster than other TNOs, however, the sample of family member is still too limited for a secure conclusion. We also highlight the fast rotation of 2002 GH(sub 32). This object has a 0.36 +/- 0.02 mag amplitude lightcurve and a rotational period of about 3.98 hr. Assuming 2002 GH(sub 32) is a triaxial object in hydrostatic equilibrium, we derive a lower limit to the density of 2.56 g cm(exp -3). This density is similar to Haumea's and much more dense than other small TNO densities.

Thirouin, Audrey↗

NASA NTRS2012

JESTR: Jupiter Exploration Science in the Time Regime

Solar system objects are inherently time-varying with changes that occur on timescales ranging from seconds to years. For all planets other than the Earth, temporal coverage of atmospheric phenomena is limited and sparse. Many important atmospheric phenomena, especially those related to atmospheric dynamics, can be studied in only very limited ways with current data. JESTR is a mission concept that would remedy this gap in our exploration of the solar system by ncar-continuous imaging and spectral monitoring of Jupiter over a multi-year mission lifetime.

Noll, Keith S.↗

NASA NTRS2012

Resonant Transneptunian Binaries: Evidence for Slow Migration of Neptune

As Neptune migrated, its mean-motion resonances preceded it into the planetesimal disk. The efficiency of capture into mean motion resonances depends on the smoothness of Neptune's migration and the local population available to be captured. The two strongest resonances, the 3:2 at 39.4 AU and 2:1 at 47.7 AU, straddle the core repository of the physically distinct and binary-rich Cold Classicals, providing a unique opportunity to test the details of Neptune's migration. Smooth migration should result in a measurable difference between the 3:2 and 2:1 resonant object properties, with low inclination 2:1s having a high fraction of red binaries, mirroring that of the Cold Classicals while the 3:2 will would have fewer binaries. Rapid migration would generate a more homogeneous result. Resonant objects observed with HST show a higher rate of binaries in the 2:1 relative to the 3:2, significant at the 2cr level. This suggests slow Neptune migration over a large enough distance that the 2:1 swept through the Cold Classical region. Colors are available for only a fraction of these targets but a prevalence of red objects in outer Resonances has been reported. We report here on ongoing observations with HST in cycle 19 targeting all unobserved Resonants with observations that will measure color and search for binary companions using the WFC3.

Noll, Keith S.↗

NASA NTRS2000

Evidence for a Trapped Radical (OH) on Ariel, Oberon, and Titania from Hubble Space Telescope Ultraviolet Spectra

The moons Ariel, Titania, and Oberon have orbits lying within the magnetosphere of Uranus, exposing them to particle irradiation from trapped Ions. This Is similar to the situation experienced by the jovian moons Europa, Ganymede, and Callisto, as well as the saturnian satellites Enceladus, Tethys, Dione, and Rhea. Identification of SO2 on Europa, Ganymede and Callisto, and O3 on Ganymede, Rhea, and Dione has supported suggestions that chemical modifications occur on icy bodies due to ion bombardment associated with the particles entrained within the magnetospheric fields of Jupiter and Saturn. Similar to the Jovian and saturnian satellites mentioned above, water ice is a major component on the larger uranian satellites", thus one might anticipate chemical modification to he an important process in the uranian system. Laboratory studies or the interaction of ultraviolet (uv) and charged-particle radiation with water ice show that in addition to molecular species, a variety of radicals are also produced. We report here evidence for an uv absorption feature in the spectra of Ariel, Titania, and Oberon that we identify as due, in part, to OH; providing the first evidence of a radical produced and trapped on an icy moon within our solar system.

Roush, Ted L.↗

NASA NTRS1998

HD 98800: A Unique Stellar System of Post-T Tauri Stars

HD 98800 is a system of four stars, and it has a large infrared excess that is thought to be due to a dust disk within the system. In this paper we present new astrometric observations made with Hipparcos, as well as photometry from Hubble Space Telescope WFPC2 images. Combining these observations and reanalyzing previous work allow us to estimate the age and masses of the stars in the system. Uncertainty in these ages and masses results from uncertainty in the temperatures of the stars and any reddening they may have. We find that HD 98800 is most probably about 10 Myr old, although it may be as young as 5 Myr or as old as 20 Myr old. The stars in HD 98800 appear to have metallicities that are about solar. An age of 10 Myr means that HD 98800 is a member of the post T Tauri class of objects, and we argue that the stars in HD 98800 can help us understand why post T Tauris have been so elusive, HD 98800 may have formed in the Centaurus star-forming region, but it is extraordinary in being so young and yet so far from where it was born.

Soderblom, David R.↗

NASA NTRS1994

The Spectrum of Titan near 3.4 Micron: Comparison of Spectral Features to Organic Molecules

In August 1993 we observed the spectrum of Titan from 2.9 to 4.1 micrometers at a resolving power of R=500-1000 (dw approx. 2-4 per cm). The spectrum shows, as expected, a strong absorption throughout this region from three strong bands Of CH4. However, comparison of the spectrum to simple radiative transfer models and to the spectrum of Jupiter reveal some interesting differences. A broad emission feature that we attribute to CH4 is centered at 3.3 micrometers. At 3.45 micrometers we see a distinct narrow absorption feature that is present in both the Jupiter and laboratory spectrum, but only when other features, absent in the Titan spectrum, are also present. In our attempt to understand the origin of this spectral feature we have compared the spectrum to CH4 and other organic molecules. Interesting similarities appear between the aliphatic hydrocarbons (CH2 and CH3 groups) seen in laboratory organics and the Titan spectrum, but only if we assume that the shorter wavelength feature (CH3) is masked by the broad CH4 emission. A second problem with the explanation is that like column abundance of organic haze (Toon et al. 1991) is insufficient to provide the required number of molecules to create a spectral feature with tau approx. 1. Laboratory organics produced through a variety of processes have been compared to the Titan spectrum and the results arc presented.

Pendleton, Yvonne↗

NASA NTRS1993

3- to 13-micron spectra of Io

The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obtain 3- to 13-micron spectra of Io on June 14-16, 1991. The extinction correction and its error for each standard star (Alpha Boo, Alpha Lyr, and Mu UMa) were found individually by performing an unweighted linear fit of instrumental magnitude as a function of airmass. The model results indicate two significant trends: (1) modest differences between the two hemispheres at lower background temperatures and (2) a tendency to higher temperatures, smaller areas, and less power from the warm component at higher background temperatures with an increased contrast between the two hemispheres. The increased flux from 8 to 13 microns is due primarily to a greater area on the Loki (trailing) hemisphere for the warm component, although temperature also plays a role.

Noll, Keith S.↗

NASA NTRS1993

Titan - 1.5 micron photometry and spectrophotometry and a search for variability

The first photometric measurements of Titan in the mid-IR free of possible contamination from long-wavelength filter leaks are reported. A low-resolution spectrum covering the last unobserved gap in Titan's near-IR spectrum from 3.1 to 5.1 micron is shown. A series of photometric measurements is reported that may lay the foundation for long-term searches for variations in the albedos. Low-resolution spectra of Ganymede, Callisto, and Europa are also reported along with marginal detections of Neptune at 4.8 micron and two 4.8 micron observations of Uranus.

Noll, Keith S.↗

NASA NTRS1992

Search for sulfur (H2S) on Jupiter at millimeter wavelengths

Jupiter was observed at two wavelengths near 1.4 mm in an attempt to detect gaseous hydrogen sulfide (H2S) or place new upper limits on its abundance on Jupiter's atmosphere. Although no H2S was detected, the first brightness temperature observations of Jupiter at 1.4 mm are reported with a spectral resolution of approximately 1 GHz using Mars as a calibration standard. The methodology and results of a laboratory experiment in which H2S absorption at 1.4 mm was measured in a simulated Jovian atmosphere. The results of laboratory measurements are applied to a radiative transfer model which is used to interpret the observations of Jupiter.

Joiner, Joanna↗

NASA NTRS1991

The spectrum of Saturn from 1990 to 2230/cm - Abundances of AsH3, CH3D, CO, GeH4, NH3, and PH3

An analysis is presented of the abundances and vertical distributions of all known absorbers in the 5-micron spectrum of Saturn, in view of previously unpublished observations, synthetic spectra of each atmospheric constituent, and an atmospheric model for synthesizing Saturn's spectrum in order to make comparisons with observations. The model used encompasses the abundances of all gaseous absorbers, their vertical distributions, clouds, and the thermal and reflected solar components of planetary flux. A coherent understanding is in this way obtained of both the many variables affecting Saturn's 5-micron spectrum and the similarities between Jupiter and Saturn.

Noll, Keith S.↗

NASA NTRS1990

The strange gases of Jupiter and Saturn

The various gases found in the atmospheres of Jupiter and Saturn are discussed. A history of scientific investigation of these planets is outlined and results of these discoveries are considered. The molecular species found in these two planets are classified into several groups. The first group consists of H2, He, CH4, NH3, and H2O while the second group contains gases formed as the chemical byproducts of solar radiation, including simple hydrocarbons such as C2H2 and C2H6 and charged particles such as H3(+). The last group contains compounds which are chemically unstable in parts of Jupiter's atmosphere that have been probed and include Ge and As; two elements usually found in minerals on earth. An investigation of origin of these elements which are currently part of the upper reaches of the atmosphere of Jupiter and Saturn has led to discoveries about much deeper and hotter parts of atmospheres that can never be observed directly. A number of hypotheses are presented to account for the presence of various unexpected compounds, such as carbon monoxide.

Noll, Keith S.↗

NASA NTRS1990

The abundance of AsH3 in Jupiter

Both ground-based and airborne observations of the AsH3 Q-branch at 2126/cm, in conjunction with newly-analyzed laboratory comparison spectra at AsH3, are employed in the derivation of a new estimate of Jovian As abundance. The mole fraction on AsH3 in the Jovian atmosphere is 0.22 + or - 0.11 ppb; this is merely 0.5 times the solar abundance, and a factor-of-9 less than the mole fraction found in Saturn, duplicating the pattern noted in the relative abundance of P in these two planets and furnishing a useful constraint for models of heavy element incorporation in the outer planets' gaseous envelopes.

Noll, Keith S.↗

NASA NTRS1989

Arsine in Saturn and Jupiter

New spectra of Saturn and Jupiter are reported that show a prominent, heretofore unidentified absorption near 2126/cm. The observation is interpreted as unambiguous evidence for the presence of arsine, AsH3. The abundance of AsH3 appears to be almost a factor of two higher in Saturn than in Jupiter. The observed enrichments are consistent with the core instability model for the formation of giant planets. Models of arsenic chemistry that predict strong depletions of AsH3 at temperatures below 370 K are not consistent with the observations, suggesting that vertical convection or perhaps some other mechanism inhibits depletion. Arsenic is the first new element identified in a planetary atmosphere since germanium was found in Jupiter a decade ago.

Noll, Keith S.↗

NASA NTRS1988

Evidence for interstellar H2O in the Orion molecular cloud

A search for interstellar gas phase H2O in the infrared spectrum of the BN object in Orion is reported. There is absorption (S/N = 2-4) at the position of the nu3 1(01)-2(02) line of H2O at 3801.42/cm, the strongest expected H2O line. Statistical analysis of the spectrum provides corroborating evidence for other H2O lines. With an assumed H2O excitation temperature of 150 K, N(H2O) of 2.3 x 10 to the 17th/sq cm or less toward the BN object is derived. The H2O column density implies abundance ratios of (H2O)/(CO) = 0.01-0.08 or less and (HDO)/(H2O) = 0.8-3.0 x 10 to the -3rd or more. The gas-to-ice ratio is (H2O gas)/(H2O ice) = 0.06 with an estimated uncertainty of a factor of 5.

Knacke, R. F.↗

NASA NTRS1988

Evidence for germane in Saturn

Observations in Saturn have prompted the development of an 0.4 + or - 0.2 ppb mole fraction for germane (GeH4) on the basis of the P- and R-branch lines' spectra. The presence of germane in Saturn implies a disequilibrium of the upper atmosphere by rapid vertical convection. It is suggested that future, more realistic radiative transfer models that include the effects of scattering within a cloud layer will probably only reduce the mole fraction presently derived for germane, by increasing the effective path length in a given atmospheric layer.

Noll, Keith S.↗