TOI-2498 b: a hot bloated super-Neptune within the Neptune desert
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Neptune Polar Orbiter with Probes
The giant planets of the outer solar system divide into two distinct classes: the gas giants Jupiter and Saturn, which consist mainly of hydrogen and helium; and the ice giants Uranus and Neptune, which are believed to contain significant amounts of the heavier elements oxygen, nitrogen, and carbon and sulfur. Detailed comparisons of the internal structures and compositions of the gas giants with those of the ice giants will yield valuable insights into the processes that formed the solar system and, perhaps, other planetary systems. By 2012, Galileo, Cassini and possibly a Jupiter Orbiter mission with microwave radiometers, Juno, in the New Frontiers program, will have yielded significant information on the chemical and physical properties of Jupiter and Saturn. A Neptune Orbiter with Probes (NOP) mission would deliver the corresponding key data for an ice giant planet. Such a mission would ideally study the deep Neptune atmosphere to pressures approaching and possibly exceeding 1000 bars, as well as the rings, Triton, Nereid, and Neptune s other icy satellites. A potential source of power would be nuclear electric propulsion (NEP). Such an ambitious mission requires that a number of technical issues be investigated, however, including: (1) atmospheric entry probe thermal protection system (TPS) design, (2) probe structural design including seals, windows, penetrations and pressure vessel, (3) digital, RF subsystem, and overall communication link design for long term operation in the very extreme environment of Neptune's deep atmosphere, (4) trajectory design allowing probe release on a trajectory to impact Neptune while allowing the spacecraft to achieve a polar orbit of Neptune, (5) and finally the suite of science instruments enabled by the probe technology to explore the depths of the Neptune atmosphere. Another driving factor in the design of the Orbiter and Probes is the necessity to maintain a fully operational flight system during the lengthy transit time from launch through Neptune encounter, and throughout the mission. Following our response to the recent NASA Research Announcement (NRA) for Space Science Vision Missions for mission studies by NASA for implementation in the 2013 or later time frame, our team has been selected to explore the feasibility of such a Neptune mission.
Bienstock, Bernard↗
Voyager: Neptune Encounter Highlights
Voyager encounter data are presented in computer animation (CA) and real (R) animation. The highlights include a view of 2 full rotations of Neptune. It shows spacecraft trajectory 'diving' over Neptune and intercepting Triton's orbit, depicting radiation and occulation zones. Also shown are a renegade orbit of Triton and Voyager's encounter with Neptune's Magnetopause. A model of the spacecraft's complex maneuvers during close encounters of Neptune and Triton is presented. A view from Earth of Neptune's occulation experiment is is shown as well as a recreation of Voyager's final pass. There is detail of Voyager's Image Compensation technique which produces Voyager images. Eighteen images were produced on June 22 - 23, 1989, from 57 million miles away. A 68 day sequence which provides a stroboscopic view - colorization approximates what is seen by the human eye. Real time images recorded live from Voyager on 8/24/89 are presented. Photoclinometry produced the topography of Triton. Three images are used to create a sequence of Neptune's rings. The globe of Neptune and 2 views of the south pole are shown as well as Neptune rotating. The rotation of a scooter is frozen in images showing differential motion. There is a view of rotation of the Great Dark Spot about its own axis. Photoclinometry provides a 3-dimensional perspective using a color mosaic of Triton images. The globe is used to indicate the orientation of Neptune's crescent. The east and west plumes on Triton are shown.
Source record↗
HATS-7b: A HOT SUPER NEPTUNE TRANSITING A QUIET K DWARF STAR
We report the discovery by the HATSouth network of HATS-7b, a transiting Super-Neptune with a mass of 0.120 ± 0.012 M{sub J}, a radius of 0.563{sub −0.034}{sup +0.046} R{sub J}, and an orbital period of 3.1853 days. The host star is a moderately bright (V=13.340 ± 0.010 mag, K{sub S}=10.976 ± 0.026 mag) K dwarf star with a mass of 0.849 ± 0.027 M{sub ⊙}, a radius of 0.815{sub −0.035}{sup +0.049} R{sub ⊙}, and a metallicity of [Fe/H] =+0.250 ± 0.080. The star is photometrically quiet to within the precision of the HATSouth measurements, has low RV jitter, and shows no evidence for chromospheric activity in its spectrum. HATS-7b is the second smallest radius planet discovered by a wide-field ground-based transit survey, and one of only a handful of Neptune-size planets with mass and radius determined to 10% precision. Theoretical modeling of HATS-7b yields a hydrogen–helium fraction of 18 ± 4% (rock-iron core and H{sub 2}–He envelope), or 9 ± 4% (ice core and H{sub 2}–He envelope), i.e., it has a composition broadly similar to that of Uranus and Neptune, and very different from that of Saturn, which has 75% of its mass in H{sub 2}–He. Based on a sample of transiting exoplanets with accurately (<20%) determined parameters, we establish approximate power-law relations for the envelopes of the mass–density distribution of exoplanets. HATS-7b, which, together with the recently discovered HATS-8b, is one of the first two transiting super-Neptunes discovered in the Southern sky, is a prime target for additional follow-up observations with Southern hemisphere facilities to characterize the atmospheres of Super-Neptunes (which we define as objects with mass greater than that of Neptune, and smaller than halfway between that of Neptune and Saturn, i.e., 0.054 M{sub J}<M{sub p}<0.18 M{sub J}).
79 ASTRONOMY AND ASTROPHYSICS↗
Reaction between Hydrogen and Ferrous/Ferric Oxides at High Pressures and High Temperatures—Implications for Sub-Neptunes and Super-Earths
Abstract Sub-Neptune exoplanets may have thick hydrogen envelopes and therefore develop a high-pressure interface between hydrogen and the underlying silicates/metals. Some sub-Neptunes may convert to super-Earths via massive gas loss. If hydrogen chemically reacts with oxides and metals at high pressures and temperatures ( P − T ), it could impact the structure and composition of the cores and atmospheres of sub-Neptunes and super-Earths. While H 2 gas is a strong reducing agent at low pressures, the behavior of hydrogen is unknown at the P − T expected for sub-Neptunes’ interiors, where hydrogen is a dense supercritical fluid. Here we report experimental results of reactions between ferrous/ferric oxides and hydrogen at 20–40 GPa and 1000–4000 K utilizing the pulsed laser-heated diamond-anvil cell combined with synchrotron X-ray diffraction. Under these conditions, hydrogen spontaneously strips iron off the oxides, forming Fe-H alloys and releasing oxygen to the hydrogen medium. In a planetary context where this reaction may occur, the Fe-H alloy may sink to the metallic part of the core, while released oxygen may stabilize as water in the silicate layer, providing a mechanism to ingas hydrogen to the deep interiors of sub-Neptunes. Water produced from the redox reaction can also partition to the atmosphere of sub-Neptunes, which has important implications for understanding the composition of their atmospheres. In addition, super-Earths converted from sub-Neptunes may contain a large amount of hydrogen and water in their interiors (at least a few wt% H 2 O). This is distinct from smaller rocky planets, which were formed relatively dry (likely a few hundredths wt% H 2 O).
58 GEOSCIENCES↗
Results from observations of the 15 June 1983 occultation by the Neptune system
Observations of eight Neptune occultations from six sites in the southwestern Pacific on June 15, 1983. The data were used to search for evidence of rings around Neptune down to a distance of 0.03 Neptune radii from the planetary surface, but the results were negative. An astrometric analysis of the timings yielded solution for the equatorial radius a(0) of Neptune at 1 microbar pressure and the oblatness e at this level. The results are: a(0) = 25,295 + or - 50 km; e = 0.022 + or - 0.004, from which a value for a(1) (equatorial radius at 1 bar pressure) of 24,830 + or - 100 km; and a rotation period of P = 15 h (+3, -2 h) is derived. These results are based on a recent determination of Neptune's pole position and mass quadruple moment, and are consistent with the hypothesis that Neptune and Uranus have homologous mass distributions, although the constraint on interior structure is a weak one. If the probable uncertainty of the pole position is taken into account, error bars on e and derived quantities should be increased by about 50 percent. The present determinations of Neptune atmospheric temperatures at 1 microbar are consistent with earlier results and when combined with all previous data give an average value of 156 + or - 10 K. There is only slight evidence for any latitude dependence in the temperatures. Profiles with a high signal-to-noise ratio suggest the possible presence of an absorbing layer at altitudes higher than the 1-microbar level.
Hubbard, W. B.↗
The Voyager 2 mission to Neptune
Voyager 2 and its twin, Voyager 1, were launched in 1977. Both spacecraft investigated Jupiter's and Saturn's systems. Voyager 2 continued on to fly past Utranus in 1986 and Neptune in 1989, while Voyager 1 headed out of the solar system. The mission at Neptune presented many engineering and scientific challenges. Neptune is about 30 Astronomical Units (AU) from the sun and earth, resulting in extremely low lights levels (nearly 1000 times lower than at earth) and in communication distances of nearly 4.5 billion kilometers. To compensate for the long communication distances, several new techniques were developed. As at Uranus, an onboard backup computer compressed the imaging data. In addition, the data return was further improved by electronically arraying and expanding several receiving antennas. As a result, the data rates from Neptune were about the same as they were from Saturn, even though the distance was three times greater. Several changes were made in the onboard software to optimize Voyager's operations at the very low light levels at Neptune. Finally, to obtain the maximum information from the Neptune encounter, a trajectory was selected which passed within just 5000 kilometers of Neptune's atmosphere, but which also posed several possible environmental hazards.
Haynes, Norman R.↗
Ohmic Dissipation in Mini-Neptunes
In the presence of a magnetic field and weakly ionizing winds, ohmic dissipation is expected to take place in the envelopes of Jovian and lower-mass planets alike. While the process has been investigated on the former, there have been no studies done on mini-Neptunes so far. From structure and thermal evolution models, we determine that the required energy deposition for halting the contraction of mini-Neptunes increases with planetary mass and envelope fraction. Scaled to the insolation power, the ohmic heating needed is small: ∼10{sup −5} orders of magnitude lower than for exo-Jupiters ∼10{sup −2}. Conversely, from solving the magnetic induction equation, we find that ohmic energy is dissipated more readily for lower-mass planets and those with larger envelope fractions. Combining these two trends, we find that ohmic dissipation in hot mini-Neptunes is strong enough to inflate their radii (∼10{sup 15} W for T{sub eq}=1400 K). The implication is that the radii of hot mini-Neptunes may be attributed in part to ohmic heating. Thus, there is a trade-off between ohmic dissipation and H/He content for hot mini-Neptunes, adding a new degeneracy for the interpretation of the composition of such planets. In addition, ohmic dissipation would make mini-Neptunes more vulnerable to atmospheric evaporation.
79 ASTRONOMY AND ASTROPHYSICS↗
Occultation by a possible third satellite of Neptune
The 24 May 1981 close approach of Neptune to an uncataloged star was photoelectrically monitored from two observatories separated by 6 kilometers parallel to the occultation track. An 8.1-second drop in signal, recorded simultaneously at both sites, is interpreted as resulting from the passage of a third satellite of Neptune in front of the star. From the duration of the event, the derived minimum diameter for an object sharing Neptune's motion is 180 kilometers. If the object was in Neptune's equatorial plane and there are no significant errors in the prediction ephemeris, the object was located at a distance of 3 Neptune radii from Neptune's center.
Reitsema, H. J.↗
Observational constraints on the atmospheres of Uranus and Neptune from new measurements near 10 micron
Uranus was detected at 10.3, 11.6 and 12.5 micrometers approximately 1 micrometer spectral bandpasses, with respective brightness temperatures of 74.0 + 0.9 or -1.1, 67.6 + 0.5 or -0.7, and 65.5 + 0.6 or -0.7 K and the first detection of Neptune at 10.3 micrometers with a brightness temperature of 77.5 + 0.7 or -0.9 K. We also detected Neptune at 11.36 micrometers with 2% spectral resolution at 81.0 + 0.8 or -0.9 K. The 10 micrometers continuous of both Uranus and Neptune may in part be due to reflected solar radiation as well as thermal emission. If all of the observed flux is reflected light, then the maximum geometric albedo of Uranus is 0.115 + or - 0.020, and that of Neptune is 0.229 + or - 0.043. In the context of previous observations in this region, the maximum stratospheric C2H6 mixing ratio is found to be 3 x 10 to the -8 power for Uranus and 3 x 10 to the -6 power for Neptune. A value for the maximum mixing ratio in the stratosphere of Neptune on the order of 1 - 0.004 appears to be consistent with the available data.
Orton, G. S.↗
Observational constraints on the atmospheres of Uranus and Neptune from new measurements near 10 micrometers
Uranus was detected at 10.3, 11.6 and 12.5 micrometers approximately 1 micrometer spectral bandpasses, with respective brightness temperatures of 74.0 + 0.9 or -1.1, 67.6 + 0.5 or -0.7, and 65.5 + 0.6 or -0.7 K and the first detection of Neptune at 10.3 micrometers with a brightness temperature of 77.5 + 0.7 or -0.9 K. We also detected Neptune at 11.36 micrometers with 2 percent spectral resolution at 81.0 + 0.8 or -0.9 K. The 10 micrometers continuous of both Uranus and Neptune may in part be due to reflected solar radiation as well as thermal emission. If all of the observed flux is reflected light, then the maximum geometric albedo of Uranus is 0.115 + or - 0.020, and that of Neptune is 0.229 + or - 0.043. In the context of previous observations in this region, the maximum stratospheric C2H6 mixing ratio is found to be 3 x 10 to the -8 power for Uranus and 3 x 10 to the -6 power for Neptune. A value for the maximum mixing ratio in the stratosphere of Neptune on the order of 1 - 0.004 appears to be consistent with the available data. Previously announced in STAR as N83-29155
Tokunaga, A. T.↗
Physical Properties of Neptune and Triton Inferred from the Orbit of Triton
The orbital motion of Triton was redetermined from photographic data spanning the interval 1899-1981. The resulting ephemeris should provide Triton positions with respect to Neptune with an accuracy of plus or minus 500 km through the end of the century. The following physical results follow from the orbit solution. The inverse mass of Neptune + Triton is solar mass over (c sub N + m sub T) = 19490 plus or minus 40. No acceleration of the mean motion nor orbital eccentricity were detected, thus constraining the tidal dissipation factors of Neptune and Triton to O sub N less than or equal to 650 and QT less than or equal to 10,000. Tidal heating of Triton is presently insignificant. The gravitational harmonic J sub 2 of Neptune is 0.0043 plus or minus 0.0003 if Triton is as massive as m sub T/ M sub N = 0.00128, and if Neptune's spin is prograde with P approximately 18(h), or J sub 2 = 0.0037 plus or minus 0.0002 if Triton is much less massive. Triton undergoes extreme climatic variations due to the combined motion of it's orbit plane and Neptune's orbital motion. Approximately 10% of Triton's surface is presently hidden from diurnal insolation, which may provide a powerful cold trap for atmospheric voltatiles.
A W Harris↗
Tidal interaction: A possible explanation for geysers and other fluid phenomena in the Neptune-Triton system
Discovery of geyser-like plumes on the surface of Triton was a highlight of Voyager 2's passage through the Neptune planetary system. Remarkable as these observations were, they were not entirely without precedent. Considering the confirmed predictions for the 1979 Voyager Jovian passage, it was logical to consider other solar system bodies beside Io where tidal effects could be a significant factor in surface processes. It was our intuition that the Neptune-Triton gravitational bond acting at high inclination to the Neptune equator and the fact that Neptune was a fluid body was significant oblateness would produce tidal and mechanical forces that could be transformed into thermal energy vented on Triton's surface. Prior to the Voyager flyby, others have noted that capture and evolution of Triton's orbit from extreme eccentricity to near circular state today would have resulted in significant tidal heating, but these analysts disregard current day forces. Our calculations indicate that the time varying forces between Neptune-Triton fall midway between those exerted in the Earth-Moon and Jupiter-Io systems, and considering the low level of other energy inputs, this source of internal energy should not be ignored when seeking an explanation for surface activity. In each planet-satellite case, residual or steady-state eccentricity causes time-varying stresses on internal satellite strata. In the case of Jupiter the residual eccentricity is due largely to Galilean satellite interactions, particularly Io-Europa, but in the case of Neptune-Triton, it is the effect of Triton's inclined orbit about an oblate primary.
Kelly, W. D.↗
Mapping the stability region of the 3:2 Neptune-Pluto resonance
Pluto and Charon are most likely the remnants of a large number of objects that existed in the Uranus-Neptune region at early epochs of the solar system. Numerical integrations have shown that, in general, such objects were ejected from the planetary region on timescales of approximately 10(exp 7) years after Neptune and Uranus reached their current masses. It is thought that the Pluto-Charon system survived to current times without being dynamically removed in this way because it is trapped in a set of secular and mean motion resonances with Neptune. The best-known Pluto-Neptune orbit coupling is the 3:2 mean motion resonance discovered almost 30 years ago by C. Cohen and E. Hubbard. These workers showed that the resonance angle, delta is equivalent to 3(lambda(sub P)) - 2(lambda(sub N)) - omega-bar(sub P) where omega-bar(sub P) is the longitude of perihelion of the Pluto-Charon system, and lambda(sub N) and lambda(sub P) are the mean longitude of Neptune and Pluto-Charon respectively, librates about 180 deg with an amplitude, A(sub delta), of 76 deg. A numerical simulation project to map out the stability region of the 3:2 resonance is reported. The results of these simulations are important to understanding whether Pluto's long-term heliocentric stability requires only the 3:2 resonance, or whether it instead requires one or more of the other Pluto-Neptune resonances. Our study also has another important application. By investigating stability timescales as a function of orbital elements, we gain insight into the fraction of orbital phase space which the stable 3:2 resonance occupies. This fraction is directly related to the probability that the Pluto-Charon system (and possibly other small bodies) could have been captured into this resonance.
Levison, H. F.↗
An Analysis of Neptune's Stratospheric Haze Using High-Phase-Angle Voyager Images
We have inverted high-phase-angle Voyager images of Neptune to determine the atmospheric extinction coefficient as a function of altitude and the scattering phase function at a reference altitude. Comparisons between theoretical model and observations help separate the contributions from molecular Rayleigh and aerosol scattering and help determine the variation of the aerosol size, concentration, and scattering properties with altitude. Further comparisons between models and data allow us to place constraints on the location and composition of the hazes, the concentration and downward flux of certain condensible hydrocarbon gases, the eddy diffusion coefficient in the lower stratosphere, and the thermal profile in parts of Neptune's stratosphere. We find that a distinct stratospheric haze layer exists near 12(sub -1, sup +1) mbar in Neptune's lower stratosphere, most probably due to condensed ethane. The derived stratospheric haze production rate of 1.0(sub -0.3, sup +0.2) x 10(exp -15) g cm(exp -2) sec(exp -1) is substantially lower than photochemical model predictions. Evidence for hazes at higher altitudes also exists. Unlike the situation on Uranus, large particles (0.08-0.11 microns) may be present at high altitudes on Neptune (e.g., near 0.5 mbar), well above the region in which we expect the major hydrocarbon species to condense. Near 28 mbar, the mean particle size is about 0.13(sub -0.02, sup +0.02) microns with a concentration of 5(sub -3, sup +3) particles cm(exp -3). The cumulative haze extinction optical depth above 15 mbar in the clear filter is approx. 3 x 10(exp -3), and much of this extinction is due to scattering rather than absorption; thus, if our limb-scan sites are typical, the hazes cannot account for the stratospheric temperature inversion on Neptune and may not contribute significantly to atmospheric heating. We compare the imaging results with the results from other observations, including those of the Voyager Photopolarimeter Subsystem, and discuss differences between Neptune and Uranus.
Moses, Julianne I.↗
Neptune's Eccentricity and the Nature of the Kuiper Belt
The small eccentricity of Neptune may be a direct consequence of apsidal wave interaction with the trans-Neptune population of debris called the Kuiper belt. The Kuiper belt is subject to resonant perturbations from Neptune, so that the transport of angular momentum by density waves can result in orbital evolution of Neptune as well as changes in the structure of the Kuiper belt. In particular, for a belt eroded out to the vicinity of Neptune's 2:1 resonance at about 48 astronomical units, Neptune's eccentricity can damp to its current value over the age of the solar system if the belt contains slightly more than an earth mass of material out to about 75 astronomical units.
Ward, William R.↗
Aerocapture Guidance Performance for the Neptune Orbiter
A performance evaluation of the Hybrid Predictor corrector Aerocapture Scheme (HYPAS) guidance algorithm for aerocapture at Neptune is presented in this paper for a Mission to Neptune and the Neptune moon Triton'. This mission has several challenges not experienced in previous aerocapture guidance assessments. These challengers are a very high Neptune arrival speed, atmospheric exit into a high energy orbit about Neptune, and a very high ballistic coefficient that results in a low altitude acceleration capability when combined with the aeroshell LD. The evaluation includes a definition of the entry corridor, a comparison to the theoretical optimum performance, and guidance responses to variations in atmospheric density, aerodynamic coefficients and flight path angle for various vehicle configurations (ballistic numbers). The benefits of utilizing angle-of-attack modulation in addition to bank angle modulation to improve flight performance is also discussed. The results show that despite large sensitivities in apoapsis targeting, the algorithm performs within the allocated AV budget for the Neptune mission bank angle only modulation. The addition of angle-of-attack modulation with as little as 5 degrees of amplitude significantly improves the scatter in final orbit apoapsis. Although the angle-of-attack modulation complicates the vehicle design, the performance enhancement reduces aerocapture risk and reduces the propellant consumption needed to reach the high energy target orbit for a conventional propulsion system.
Masciarelli, James P.↗
SPITZER SPACE TELESCOPE MID-IR LIGHT CURVES OF NEPTUNE
We have used the Spitzer Space Telescope in 2016 February to obtain high cadence, high signal-to-noise, 17 hr duration light curves of Neptune at 3.6 and 4.5 μ m. The light curve duration was chosen to correspond to the rotation period of Neptune. Both light curves are slowly varying with time, with full amplitudes of 1.1 mag at 3.6 μ m and 0.6 mag at 4.5 μ m. We have also extracted sparsely sampled 18 hr light curves of Neptune at W1 (3.4 μ m) and W2 (4.6 μ m) from the Wide-feld Infrared Survey Explorer ( WISE )/ NEOWISE archive at six epochs in 2010–2015. These light curves all show similar shapes and amplitudes compared to the Spitzer light curves but with considerable variation from epoch to epoch. These amplitudes are much larger than those observed with Kepler / K 2 in the visible (amplitude ∼0.02 mag) or at 845 nm with the Hubble Space Telescope ( HST ) in 2015 and at 763 nm in 2016 (amplitude ∼0.2 mag). We interpret the Spitzer and WISE light curves as arising entirely from reflected solar photons, from higher levels in Neptune’s atmosphere than for K 2. Methane gas is the dominant opacity source in Neptune’s atmosphere, and methane absorption bands are present in the HST 763 and 845 nm, WISE W1, and Spitzer 3.6 μ m filters.
79 ASTRONOMY AND ASTROPHYSICS↗