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NASA NTRS1995

NH3, H2S, and the Radio Brightness Temperature Spectra of the Giant Planets

Recent radio interferometer observations of Neptune enable comparisons of the radio brightness temperature (T(sub B)) spectra of all four giant planets. This comparison reveals evidence for fundamental differences in the compositions of Uranus' and Neptune's upper tropospheres, particularly in their ammonia (NH3) and hydrogen sulfide (H2S) mixing ratios, despite those planets' outward similarities. The tropospheric abundances of these constituents yield information about their deep abundances, and ultimately about the formation of the planets from the presolar nebula (Atreya et al.). Figures 1, 2, 3, and 4 show the T(sub B) spectra of Jupiter, Saturn, Uranus, and Neptune, respectively, from 0.1 to tens of cm wavelength. The data shown are collected from many observers. Data for Jupiter, Saturn, and Uranus are those cataloged by de Pater and Massie (1985), plus the Saturn Very Large Array (VLA) data by Grossman et al. Figure 3, Uranus, shows only data acquired since 1973. Before 1973 Uranus' T(sub B) increased steadily as its pole moved into view, causing significant scatter in those data. Neptune data at greater than 1 cm, all taken at the VLA, are collected from de Pater and Richmond, de Pater et al., and Hofstadter. For a variety of reasons, such as susceptibility to source confusion, single-dish data at those wavelengths are much noisier than the more reliable VLA data and have been ignored. Single-dish data by Griffin and Orton shortward of 0.4 cm are shown, along with the Owens Valley Radio Observatory (interferometer) datum at 0.266 cm by Muhleman and Berge. Spectra of Jupiter, Saturn, and Neptune share certain gross characteristics. In each spectrum, T(sub B) at 1.3 cm is approximately 120-140 K, less than approximately 30 K different from that at 0.1 cm. All three spectra show a break in slope at or near 1.3 cm, with T(sub B) increasing fairly rapidly with wavelength longward of 1.3 cm. Visible and IR spectroscopy show that NH3, whose strong inversion spectrum peaks at appropximately 1.3 cm, is an important tropospheric species at Jupiter and Saturn. Its signature on the Jovian radio spectrum is obvious, causing the prominent "hole" at 1.3 cm. At Saturn it is more subdued but is the source of that spectrum's change in slope at 1.3 cm. Radiative transfer models of Jupiter and Saturn with near-solar deep NH3 abundances agree well with the data (e.g., de Pater).

Spilker, Thomas R.↗

NASA NTRS1991

Herman-Wallis factors in the C2H2nu5 infrared fundamental near 14 microns

The presence of acetylene has been confirmed for some time in the atmospheres of the outer planets Jupiter, Saturn, Neptune, and Saturn's satellite Titan. For these atmospheres, the determination of C2H2 abundances using its strong nu5 fundamental requires laboratory line position and intensity measurements. The 1-m Fourier transform spectrometer at McMath solar telescope of Kitt Peak National Observatory was used to measure C2H2 at an unapodized spectral resolution of 0.0025/cm. Synthetic spectra are generated by convolving a Voigt line shape with an instrument function and varying intensity parameters by means of a nonlinear least squares technique. Intensities of 37 nu5 lines spanning P18 through R20 were measured using 0.123 torr of gas in a 1-cm cell. A Herman-Wallis intensity correction parameter of 1.3(4) x 10 to the -3rd has been derived using a least squares linear fit.

Maguire, William C.↗

NASA NTRS1993

Remote sounding of tropospheric minor constituents

The etalon interferometer, or Fabry-Perot interferometer (FPI), with its high throughput and high spectral resolution was widely used in the remote-sensing measurements of the earth's atmospheric composition, winds, and temperatures. The most recent satellite instruments include the Fabry-Perot interferometer flown on the Dynamics Explorer-2 (DE-2) and the High Resolution Doppler Imager (HRDI) to be flown on the Upper Atmosphere Research Satellite (UARS). These instruments measure the Doppler line profiles of the emission and absorption of certain atmospheric species (such as atomic oxygen) in the visible spectral region. The successful space flight of DE-FPI and the test and delivery of UARS-HRDI demonstrated the extremely high spectral resolution and ruggedness of the etalon system for the remote sensing of earth and planetary atmospheres. Recently, an innovative FPI focal plane detection technique called the Circle-to-Line Interferometer Optical (CLIO) system was invented at the Space Physics Research Laboratory (SPRL). The CLIO simplifies the FPI focal plane detection process by converting the circular rings or fringes into a linear pattern similar to that produced by a conventional spectrometer, while retaining the throughput advantage of the etalon interferometer. CLIO makes the use of linear array detectors more practical and efficient with FPI, the combination of FPI and CLIO represents a very promising new technique for the remote sensing of the lower atmospheres of Earth, Mars, Venus, Neptune, and other planets. The Multiorder Etalon Spectrometer (MOES), as a combination of the rugged etalon and the CLIO, compares very favorably to other spaceborne optical instruments in terms of performance versus complexity. The feasibility of an advanced etalon spectrometer for the remote sensing of tropospheric trace species, particularly carbon monoxide (CO), nitrous oxide (N2O), and methane (CH4) was discussed. The etalon atmospheric spectroscopy techniques are described, instrument design and related technical issues are discussed. The primary objective is to establish the concept of atmospheric spectroscopy with the CLIO and etalon system and its applications for the measurements of tropospheric trace species analyze system requirements and performance, determine the feasibility of components and subsystem implementation with available technology, and develop inversion algorithm for retrieval simulation and data analysis.

Drayson, S. Roland↗

NASA NTRS1995

Robotic Planetary Science Missions Enabled with Small NTR Engine/Stage Technologies

The high specific impulse (Isp) and engine thrust-to-weight ratio of liquid hydrogen (LH2)-cooled nuclear thermal rocket (NTR) engines makes them ideal for upper stage applications to difficult robotic planetary science missions. A small 15 thousand pound force (klbf) NTR engine using a uranium-zirconium-niobium 'ternary carbide' fuel (Isp approximately 960 seconds at approximately 3025K) developed in the Commonwealth of Independent States (CIS) is examined and its use on an expendable injection stage is shown to provide major increases in payload delivered to the outer planets (Saturn, Uranus, Neptune and Pluto). Using a single 'Titan IV-class' launch vehicle, with a lift capability to low Earth orbit (LEO) of approximately 20 metric tons (t), an expendable NTR upper stage can inject two Pluto 'Fast Flyby' spacecraft (PFF/SC) plus support equipment-combined mass of approximately 508 kg--on high energy, '6.5-9.2 year' direct trajectory missions to Pluto. A conventional chemical propulsion mission would use a liquid oxygen (LOX)/LH2 'Centaur' upper stage and two solid rocket 'kick motors' to inject a single PFF/SC on the same Titan IV launch vehicle. For follow on Pluto missions, the NTR injection stage would utilize a Jupiter 'gravity assist' (JGA) maneuver to launch a LOX/liquid methane (CH4) capture stage (Isp approximately 375 seconds) and a Pluto 'orbiter' spacecraft weighing between approximately 167-312 kg. With chemical propulsion, a Pluto orbiter mission is not a viable option because c inadequate delivered mass. Using a 'standardized' NTR injection stage and the same single Titan IV launch scenario, 'direct flight' (no gravity assist) orbiter missions to Saturn, Uranus and Neptune are also enabled with transit times of 2.3, 6.6, and 12.6 years, respectively. Injected mass includes a storable, nitrogen tetroxide/monomethyl hydrazine (N2O4/MMH) capture stage (Isp approximately 330 seconds) and orbiter payloads 340 to 820% larger than that achievable using a LOX/LH2-fueled injection stage. The paper discusses NTR technology and mission characteristics, shows NTR stage and payload accommodations within the 26.2 m long Titan IV payload fairing, and discusses NTR stage performance as a function of assumed cryogenic tank technology.

Borowski, Stanley K.↗

NASA NTRS2001

Quasar Host Galaxies/Neptune Rotation/Galaxy Building Blocks/Hubble Deep Field/Saturn Storm

Computerized animations simulate a quasar erupting in the core of a normal spiral galaxy, the collision of two interacting galaxies, and the evolution of the universe. Hubble Space Telescope (HST) images show six quasars' host galaxies (including spirals, ellipticals, and colliding galaxies) and six clumps of galaxies approximately 11 billion light years away. A false color time lapse movie of Neptune displays the planet's 16-hour rotation, and the evolution of a storm on Saturn is seen though a video of the planet's rotation. A zoom sequence starts with a ground-based image of the constellation Ursa major and ends with the Hubble Deep Field through progressively narrower and deeper views.

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NASA NTRS2008

Update on the Ares V to Support Heavy Lift for U.S. Space Exploration Policy

The focus of design efforts in the near future will be on the primary Lunar mission. We are currently just beginning to integrate the design functions from the various centers for this mission. We appreciate all thoughts and ideas for different ways to use the Ares V platform. The Ares V can support an order of magnitude more science instrumentation for outer planetary exploration missions. It can also reach outer planets such as Neptune and other high energy insertion destinations. Current Ares V Point-of-Departure (51.00.48) exceeds Saturn mass capability by approx.40%. Ares V Lunar Capabilities Concept Review analysis focused on meeting lunar requirements and developing margin. Ares V is sensitive to Loiter, Attitude, Power, and Altitude requirements in addition to payload performance. LCCR-approved 51.00.48 POD 5.5-segment steel case booster/6 engine core) Ares V can meet current Human Lunar Return requirements with approx.6 mT of Margin. LCCR-approved 51.00.47 option maintained (5 segment HTPB composite case booster/6 engine core) can meet HLR requirement with more than 9 mT Margin. Ares V team is actively reaching out to external organizations during this early concept phase to ensure that the Ares V vehicle can be leveraged for national security, scientific and commercial development needs.

Creech, Steve↗

NASA NTRS2019

Ablators for Human and Robotic Exploration of the Moon, Mars and Beyond

When Apollo was designed to carry astronauts safely back from the Moon, at return speeds exceeding 11 km/s, it required development of a new lightweight ablative material to protect the capsule and crew from the intense heat of entry. Soon after the Apollo program, successful Mars Viking Lander missions employed a different and much lighter ablator in more benign entry conditions. On the other hand, the Pioneer-Venus and Galileo Probe missions that followed required yet another ablative system, to manage the extreme heating at those destinations, which was like flying a ballistic missile nose tip into a thermonuclear explosion. NASA had to invent a new heat-shield concept based on the rocket nozzle and ballistic missile ablative materials. In the mid 1990's, as the Science focus returned to Mars, advances in manufacturing, testing and materials technology led to innovative lightweight ablators that enabled comet and asteroid sample return missions and facilitated large lander missions such as MSL and Mars 2020. NASA's current plans for robotic and human exploration of the Moon, Mars and beyond introduce different constraints and new expectations for ablators. Human missions to Moon and Mars, sample return missions from Mars, and exploration of Uranus and Neptune, the two planets we are yet to explore, will require ablators that can withstand extreme environments, with verifiable robustness, and with raw materials and manufacturing approaches that are sustainable in the longer term. This talk will review the history of ablators as well as current ablative TPS development that addresses the requirements for future missions to Moon, Mars and beyond.

Mars and Beyond↗

NASA NTRS1994

NH(sub 3), H(sub 2)S, and the Radio Brightness Temperature Spectra of the Giant Planets

Recent radio interferometer observations of Neptune enable comparisons of the radio brightness temperature (T(sub b)) spectra of all four giant planets. The data shown are collected from many observers. Spectra of Jupiter, Saturn, and Neptune share certain gross characteristics. Ammonia is known to be an important tropospheric constituent at Jupiter and Saturn. Its signature on the Jovian spectrum is obvious, while at Saturn it is a bit more subdued. Uranus' T(sub b) spectrum does not fit the same pattern. One possible cause for the apparent ammonia depletion has been offered. That is that a superabundance of H(sub 2)S could react out most of the NH(sub 3). The presence of the H(sub 2)S was postulated as there is no direct observational evidence of H(sub 2)S, which has not yet been detected at any of the giant planets. It is merely the most likely candidate to deplete NH(sub 3).Some researchers suggest a significant H(sub 2)S superabundance at Neptune also. Some researchers suggest that this H(sub 2)S may be the major source of cm opacity in Neptune's upper troposphere, rather than the NH(sub 3) that had been suggested earlier.

hydrogen sulfide spectra opacity troposphere giant↗

NASA NTRS1998

Voyager Outreach Compilation

This NASA JPL (Jet Propulsion Laboratory) video presents a collection of the best videos that have been published of the Voyager mission. Computer animation/simulations comprise the largest portion of the video and include outer planetary magnetic fields, outer planetary lunar surfaces, and the Voyager spacecraft trajectory. Voyager visited the four outer planets: Jupiter, Saturn, Uranus, and Neptune. The video contains some live shots of Jupiter (actual), the Earth's moon (from orbit), Saturn (actual), Neptune (actual) and Uranus (actual), but is mainly comprised of computer animations of these planets and their moons. Some of the individual short videos that are compiled are entitled: The Solar System; Voyage to the Outer Planets; A Tour of the Solar System; and the Neptune Encounter. Computerized simulations of Viewing Neptune from Triton, Diving over Neptune to Meet Triton, and Catching Triton in its Retrograde Orbit are included. Several animations of Neptune's atmosphere, rotation and weather features as well as significant discussion of the planet's natural satellites are also presented.

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NASA NTRS1972

Cometary Nuclei: Models

Arguments for the existence of some kind of icy-conglomerate cometary nucleus are put forward, and the role of clathrates in the condensation of comets from the solar nebula is discussed. The division of cosmic materials into three types is described, and it is suggested that whereas Jupiter, and to a large extent Saturn, condensed directly from gas and the terrestrial planets and asteroids collected from planetesimals of earthy material, the comets were formed as snow balls in the vicinity of Uranus and Neptune, with these two planets themselves representing accumulations of comets. The evidence for the existence of a comet belt beyond Neptune is considered, and it is concluded that at 50 AU from the sun the mass of such a belt cannot be more than that of the Earth. Finally, some of the problems associated with the mission to periodic Comet d'Arrest are discussed, in particular those concerned with the detectability of the nucleus and the hazards of a close encounter.

Whipple, F. L.↗

NASA NTRS1989

A quiescent magnetosphere for Neptune

It is argued that, if Neptune has a large magnetic moment, a weak supply of plasma for its magnetosphere, and a magnetic moment that is in near alignment with the planetary spin axis, the Neptunian magnetosphere is almost completely quiescent except for a region near the magnetopause. There are two magnetic power sources: the flowing, magnetized solar wind, and the kinetic energy of planetery spin. It is predicted that Neptune has a magnetic moment of at least 1 G-RN to the 3rd, the sum of ionospheric and Triton injections of plasma into Neptune's magnetosphere is less than 1 kg/sec, and Neptune's dipole is aligned with the spin axis and located close to the center of the planet. The criterion for Neptune to be a quiescent magnetosphere is defined by the expenditure of less than 10 to the 9th Watts from all power sources.

Dessler, A. J.↗

NASA NTRS1974

The source of Neptune's internal heat and the value of Neptune's tidal dissipation factor

The suggestion is made that Neptune's observed internal heating is the action of tidal torques between Triton and Neptune in despinning the planet and causing the orbital decay of Triton's orbit. These result from the frictional dissipation of tides within Neptune. It is shown that the considered process implies a value of the tidal dissipation factor of approximately 170. The results of the investigation do not change the conclusion which follows from the lack of internal heating for Uranus that the interiors of Uranus and Neptune differ significantly.

Trafton, L.↗

NASA NTRS1984

Oblatenesses of Uranus and Neptune

The oblateness of a planet is closely related to its rotation rate and internal mass distribution, and is therefore an important indicator of gross planetary structure. Analysis of Stratoscope II images of Uranus yields epsilon = 0.022 + or - 0.001, and stellar occultation observations yield epsilon = 0.024 + or - 0.003. Because of the current pole on aspect of Uranus, it is unlikely that a significantly more accurate value can be determined by stellar occultations before Voyager 2 encounters Uranus in January, 1986. Neptune's oblateness has been determined from stellar occultation observations made in 1968 and 1983. The 1968 observations yield an oblateness of 0.021 + or - 0.004. A recent determination of Neptune's oblateness using both the 1968 and 1983 observations is consistent with this value. Space Telescope observations of several stellar occultations by Neptune could provide a significantly more accurate determination of the oblateness before the Voyager 2 encounter in 1990.

French, R. G.↗

NASA NTRS1985

The internal structures and the relative rotation rates of Uranus and Neptune

An analysis of the difference between the interior structures of Uranus and Neptune is presented, based on models which fit the observed mass, radius, and gravitational moments for the assumed rotation periods of these planets. If Uranus and Neptune are assumed to be as similar in internal structure as they are in mass and radius, the rotation period for Neptune must be shorter than that for Uranus. It is suggested that the true rotation period is given by Neptune's oblateness, while the photometric period corresponds to the motion of Rossby waves in the upper atmosphere.

Podolak, M.↗

NASA NTRS1991

Satellite sweeping of energetic particles at Neptune

The calculation of the absorption rate of charged particles by planetary satellites introduced by Paonessa and Cheng (1987) is generalized to include an arbitrary offset of the dipole center from the planet center, appropriate for Neptune. The absorption rates calculated for particles of fixed L shell, energy, and pitch angle reflect the features of the complicated geometry of the dipole and the moons. This absorption probability is found to be insignificant compared with that of the rings at L shells to which both sets of absorbers map. However, at larger radii the sweeping rate is controlled by the moons, and the corresponding absorption features provide a starting point for understanding the Voyager energetic particle observations.

Paranicas, C. P.↗

NASA NTRS1989

Predictions of lightning activity at Neptune

Spacecraft observations of the seven innermost planets suggest that lightning is present on all planets with dense atmospheres. Thus lightning may be expected to occur on Neptune as well. Based on the level of lightning activity observed on Jupiter and on the assumption that the lightning energy dissipation rate is a constant fraction of the dissipation rate of the convective energy, the lightning rate on Neptune is estimated to be 1/19 that observed on Jupiter. It is predicted that approximately 60 events should be recorded by the Voyager imager during its search of the nightside of Neptune.

Borucki, W. J.↗

NASA NTRS2013

The Cosmic Shoreline

Volatile escape is the classic existential problem of planetary atmospheres. The problem has gained new currency now that we can study the cumulative effects of escape from extrasolar planets. Escape itself is likely to be a rapid process, relatively unlikely to be caught in the act, but the cumulative effects of escape in particular, the distinction between planets with and without atmospheres should show up in the statistics of the new planets. The new planets make a moving target. It can be difficult to keep up, and every day the paper boy brings more. Of course most of these will be giant planets loosely resembling Saturn or Neptune albeit hotter and nearer their stars, as big hot fast-orbiting exoplanets are the least exceedingly difficult to discover. But they are still planets, all in all, and although twenty years ago experts could prove on general principles that they did not exist, we have come round rather quickly, and they should be welcome now at LPSC. Here we will discuss the empirical division between planets with and without atmospheres. For most exoplanets the question of whether a planet has or has not an atmosphere is a fuzzy inference based on the planet's bulk density. A probably safe presumption is that a low density planet is one with abundant volatiles, in the general mold of Saturn or Neptune. On the other hand a high density low mass planet could be volatile-poor, in the general mold of Earth or Mercury. We will focus on planets, mostly seen in transit, for which both radius and mass are measured, as these are the planets with measured densities. More could be said: a lot of subtle recent work has been devoted to determining the composition of planets from equations of state or directly observing atmospheres in transit, but we will not go there. What interests us here is that, from the first, the transiting extrasolar planets appear to have fit into a pattern already seen in our own Solar System, as shown in Fig. 1. We first noticed this in 2004 when there were just two transiting exoplanets to consider. The trend was well-defined by late 2007. Figure 1 shows how matters stood in Dec 2012 with approx.240 exoplanets. The figure shows that the boundary between planets with and without active volatiles - the cosmic shoreline, as it were - is both well-defined and follows a power law.

Zahnle, Kevin J.↗

NASA NTRS1984

Variability of Neptune

Earth based observers of Neptune found that the planet varies in brightness at various wavelengths in ways that suggest that changes occur in the planet's atmosphere on several different time-scales. Global inhomogeneities in high altitude haze distribution that are stable for several days permit measurements of the planet's rotation period (about 18 hours), but this stability sometimes breaks down, obscuring the diurnal lightcurve. In addition, there is an apparent long term variability of the brightness of Neptune in anticorrelation with the cycle of solar activity. This slow variability of low amplitude may be punctuated by outbursts of high altitude condensation of particles in the atmosphere, whose decay time is several months.

Dale P Cruikshank↗