Rock Vapor Research Articles

Revisiting the Iconic Spitzer Phase Curve of 55 Cancri e: Hotter Dayside, Cooler Nightside, and Smaller Phase Offset

Thermal phase curves of short-period exoplanets provide the best constraints on the atmospheric dynamics and heat transport in their atmospheres. The published Spitzer Space Telescope phase curve of 55 Cancri e, an ultra-short-period super-Earth, exhibits a large phase offset suggesting significant eastward heat recirculation, unexpected on such a hot planet. We present our rereduction and analysis of these iconic observations using the open source and modular Spitzer Phase Curve Analysis pipeline. In particular, we attempt to reproduce the published analysis using the same instrument detrending scheme as the original authors. We retrieve the dayside temperature ( K), nightside temperature ( K at 2σ), and longitudinal offset of the planet's hot spot, and quantify how they depend on the reduction and detrending. Our reanalysis suggests that 55 Cancri e has a negligible hot spot offset of degrees east. The small phase offset and cool nightside are consistent with the poor heat transport expected on ultra-short-period planets. The high dayside 4.5 μm brightness temperature is qualitatively consistent with SiO emission from an inverted rock vapor atmosphere.

K2 and Spitzer phase curves of the rocky ultra-short-period planet K2-141 b hint at a tenuous rock vapor atmosphere

K2-141 b is a transiting, small (1.5 R⊕) ultra-short-period (USP) planet discovered by the Kepler space telescope orbiting a K-dwarf host star every 6.7 h. The planet's high surface temperature of more than 2000 K makes it an excellent target for thermal emission observations. Here we present 65 h of continuous photometric observations of K2-141 b collected with Spitzer's Infrared Array Camera (IRAC) Channel 2 at 4.5 μm spanning ten full orbits of the planet. We measured an infrared eclipse depth of ${f_{{{\rm{p}} \mathord{\left/ {\vphantom {{\rm{p}} {{{\rm{f}}_{\rm{*}}}}}} \right. \kern-\nulldelimiterspace} {{{\rm{f}}_{\rm{*}}}}}}} = 142.9_{ - 39.0}^{38.5}$ ppm and a peak to trough amplitude variation of $A = 120.6_{ - 43.0}^{42.3}$ ppm. The best fit model to the Spitzer data shows no significant thermal hotspot offset, in contrast to the previously observed offset for the well-studied USP planet 55 Cnc e. We also jointly analyzed the new Spitzer observations with the photometry collected by Kepler during two separate K2 campaigns. We modeled the planetary emission with a range of toy models that include a reflective and a thermal contribution. With a two-temperature model, we measured a dayside temperature of ${T_{{\rm{p,d}}}} = 2049_{ - 359}^{362}$ K and a night-side temperature that is consistent with zero (Tp,n < 1712 K at 2σ). Models with a steep dayside temperature gradient provide a better fit to the data than a uniform dayside temperature (ΔBIC = 22.2). We also found evidence for a nonzero geometric albedo ${A_{\rm{g}}} = 0.282_{ - 0.078}^{0.070}$. We also compared the data to a physically motivated, pseudo-2D rock vapor model and a 1D turbulent boundary layer model. Both models fit the data well. Notably, we found that the optical eclipse depth can be explained by thermal emission from a hot inversion layer, rather than reflected light. A thermal inversion may also be responsible for the deep optical eclipse observed for another USP, Kepler-10 b. Finally, we significantly improved the ephemerides for K2-141 b and c, which will facilitate further follow-up observations of this interesting system with state-of-the-art observatories such as James Webb Space Telescope.

Evaporation from the Lunar Magma Ocean Was Not the Mechanism for Fractionation of the Moon’s Moderately Volatile Elements

Abstract The cause of chemical depletion and isotopic fractionation of moderately volatile elements (MVEs) in the Moon is a long-standing problem. Here we examine MVE isotopic fractionation during Moon formation using potassium as a primary example. We show that the degree of isotopic fractionation due to evaporation of the lunar magma ocean (LMO) depended critically on the vapor pressure above the LMO. Based on our analysis of evaporation and escape of the resulting rock-vapor atmosphere, LMO evaporation alone could not have caused the observed MVE isotopic compositions. The combination of exposure of the liquid of the LMO to the surface for on the order of 102–103 yr, near-equilibrium evaporation at the melt surface, and hydrodynamic escape facilitated by proximity of the Earth leads to no resolvable isotope or elemental fractionation. This study provides a basis for the simplifying assumption that rock vapor immediately above a magma ocean will be in thermodynamic equilibrium with the melt at the surface of the planetary body even where hydrodynamic escape is operative.

Near-equilibrium isotope fractionation during planetesimal evaporation

Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations.Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order <1 m that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (≥0.1% M⊕) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~700 km yield a steady-state far-field vapor pressure of 10−8 bar and a vapor pressure at the surface of 10−4 bar, corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas.We model the Si and Mg isotopic composition of bulk Earth as a consequence of accretion of planetesimals that evaporated subject to the conditions described above. The results show that the best fit to bulk Earth is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of H2 on timescales of 104 to 105 years.

Thermal radiation from impact plumes

AbstractPlumes produced by the impacts of asteroids and comets consist of rock vapor and heated air. They emit visible light, ultraviolet, and infrared radiation, which can greatly affect the environment. We have carried out numerical simulations of the impacts of stony and cometary bodies with a diameter of 0.3, 1, and 3 km, which enter the atmosphere at various angles, using a hydrodynamic model supplemented by radiation transfer. We assumed that the cosmic object has no strength, and deforms, fragments, and vaporizes in the atmosphere. After the impact on the ground, the formation of craters and plumes was simulated, taking the internal friction of destroyed rocks and the trail formed in the atmosphere into account. The equation of radiative transfer, added to the equations of gas dynamics, was used in the approximation of radiative heat conduction or, if the Rosseland optical depth of a radiating volume of gas and vapor was less than unity, in the volume‐emission approximation. We used temperature and density distributions obtained in these simulations to calculate radiation fluxes on the Earth's surface by integrating the equation of radiative transfer along rays passing through a luminous region. We used tables of the equation of state of dunite and quartz (for stony impactors and a target) and air, as well as tables of absorption coefficients of air, vapor of ordinary chondrite, and vapor of cometary material. We have calculated the radiation impulse on the ground and the impact radiation efficiency (a ratio of thermal radiation energy incident on the ground to the kinetic energy of a body), which ranges from ~0.5% to ~9%, depending on the impactor size and the angle of entry into the atmosphere. Direct thermal radiation from fireballs and impact plumes, poses a great danger to people, animals, plants, and economic objects. After the impacts of asteroids at a speed of 20 km s−1 at an angle of 45°, a fire can occur at a distance of 250 km if the asteroid has a diameter of 0.3 km, and at a distance of 2000 km if the diameter is 3 km.

OVERCOMING THE METER BARRIER AND THE FORMATION OF SYSTEMS WITH TIGHTLY PACKED INNER PLANETS (STIPs)

We present a solution to the long outstanding meter barrier problem in planet formation theory. As solids spiral inward due to aerodynamic drag, they will enter disk regions that are characterized by high temperatures, densities, and pressures. High partial pressures of rock vapor can suppress solid evaporation, and promote collisions between partially molten solids, allowing rapid growth. This process should be ubiquitous in planet-forming disks, which may be evidenced by the abundant class of Systems with Tightly-packed Inner Planets (STIPs) discovered by the NASA Kepler mission.

Recently discovered 3.42-3.23 Ga impact layers, Barberton Belt, South Africa: 3.8 Ga detrital zircons, Archean impact history, and tectonic implications

The Barberton greenstone belt (BGB) includes eight known layers containing spherical particles (spherules) that condensed from rock vapor clouds formed by the impact of large meteorites or asteroids 3.47–3.23 Ga. Previous studies have inferred that the spherules represent bolides at least 20–70 km across. Spherule beds S1–S4 have been previously characterized in detail: we provide here the first detailed analysis of more recently discovered beds S5–S8. All eight beds are composed of the same basic compositional and textural spherule types, including nearly pure silica spherules representing nonaluminous melt precursors, nearly pure phyllosilicate spherules representing mostly mafic and ultramafic liquids, and compositionally mixed spherules. Evidence of spherule amalgamation and surface corrosion within the rock vapor clouds is developed in some beds. Bed S6, which occurs within a thick sequence of ultramafic volcanic rocks, is overlain by a tsunami layer containing zircons as old as 3811 ± 7 Ma, suggesting deep, possibly impact-related crustal uplift and erosion in distant areas. The formation of at least 8 major impact layers representing bolides 20–70 km in diameter over an interval of ∼240 m.y. suggests impact rates greatly exceeding those of later geologic time, and provides direct evidence that terrestrial bombardment by large bolides did not end abruptly at 3.8 Ga, but waned gradually until 3.0 Ga or even later. The coincidence of at least four large impact layers and the initiation of BGB deformation at 3.26–3.23 Ga suggests that an impact cluster at this time may have disrupted a long-lived earlier geodynamic system and triggered the development of a contrasting, more modern plate tectonic regime.

A pressure measurement method for high‐temperature rock vapor plumes using atomic line broadening

Knowledge of pressure conditions is essential in understanding phase changes and chemical reactions. Although several methods have been proposed for the measurement of pressure in impact‐induced vapor plumes, they are somewhat unreliable. In this study, we developed a pressure measurement method for vapor clouds based on spectral line broadening. Under the nearest neighbor approximation, it is possible to analytically express the full width at half maximum as a function of the perturber number density. On the basis of these relations and spectroscopic constants of atomic emission lines of Fe I at 381.58 nm and Ca I at 646.26 nm, quadratic Stark broadening is the dominant broadening mechanism if the degree of ionization exceeds 1%. Resonance broadening and van der Waals broadening should be considered if the degree of ionization is less than 1%. Taking into account the appropriate broadening mechanisms, it is possible to accurately measure the pressure in vapor clouds. We conducted laser ablation experiments using the proposed pressure measurement method in combination with the Boltzmann plot method for temperature. The obtained pressures and temperatures are consistent with an adiabatic expansion. This strongly suggests that the proposed method can measure pressure of vapor clouds accurately. Because thermodynamic quantities can be determined when both pressure and temperature are known, the proposed method enables a complete thermodynamic description of vapor clouds, thereby serving as a powerful tool in investigating the thermodynamic and chemical properties of impact‐ and laser‐induced vapor clouds.

Atmospheric loss and supply by an impact-induced vapor cloud: Its dependence on atmospheric pressure on a planet

Hypervelocity impact would vaporize the impactor and part of planetary surface and create a rock vapor cloud. Results from previous studies suggest that the energetic impact would have a role to blow off and cause a large-scale loss of the planetary atmosphere through expansion of the vapor cloud. Impact also has been considered as a material source. Numerous, repeated impact events during the heavy bombardment period could greatly affect the amount of volatiles and the atmospheric pressure on the planetary surface in either way. To discuss the evolution of the atmospheric pressure by impacts, we carried out hydro-calculations with a two-dimensional hydrodynamic code and investigated the dependence of the loss and supply of the atmosphere on the atmospheric pressure. We integrated both effects by impacts over impactor size distribution and assessed the evolution of the atmospheric pressure on early Mars. Using this approach, we found that the numerous impacts likely increase the atmosphere monotonically or control the atmospheric pressure to some value, rather than causing the monotonic decrease as the previous study suggested.

Evidence for Water at Meridiani

The Mars Exploration Rover Opportunity has examined sedimentary structures in the Burns formation at Meridiani Planum. The materials in this formation reflect, in part, subaqueous deposition of reworked, sulfate-rich, clastic sediments that likely formed in a playa-interdune setting. The chemistry and mineralogy of the sedimentary rocks record an origin by evaporation of sulfate- and chloride-rich brines mixed with a fine, altered, basaltic mud or dust component, prior to reworking. Cementation and postdepositional reactions to form hematite-rich concretions and crystal-mold porosity reflect diagenesis in a groundwater-saturated subsurface. More recent dehydration events are evidenced by polygonal textures in rocks within craters and exposed on the plains. The timing of formation of fracture fillings that cut across bedding is not well constrained and may be early postdiagenetic or later. The fracture fillings may have formed by solutions remobilized along zones of weakness. Alteration rinds may reflect more recent interactions between rock and atmospheric water vapor.

Compositional grading in an 3.24 Ga impact-produced spherule bed, Barberton greenstone belt, South Africa: A key to impact plume evolution

Compositional grading of spherules in the ~3.24 Ga spherule bed S3, Barberton greenstone belt, South Africa, provides constraints on the evolution of the impact-generated rock vapor plume within which the spherules formed. Two fall-deposited sections of S3, 40 km apart, are both about 30 cm thick and composed almost entirely of spherules. These spherules are diverse in size, composition and texture. Although they have been chemically altered, primary textures and some mineralogy is preserved. Both sections show a similar compositional grading, which includes five stratigraphic zones, each composed of a distinctive assemblage of spherule types. Petrographic and geochemical data suggest that this stratigraphic layering is the same in both sections. This regionally consistent grading suggests large-scale compositional and thermal layering in the impact plume. REE data indicate that the basal part of S3 in these sections contains the most refractory material and that the upper part contains the most basaltic components. Overall, the beds show a temporal evolution consistent with the condensation sequence predicted for a fractionation-modified mixing of chondritic and basaltic materials.

Spherule beds 3.47-3.24 billion years old in the Barberton Greenstone Belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution.

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approximately 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.

Flash heating on the early Earth.

It has been suggested that very large impact events (approximately 500 km diameter impactors) sterilized the surface of the young Earth by producing enough rock vapor to boil the oceans. Here, we consider surface heating due to smaller impactors, and demonstrate that surface temperatures conductive to organic synthesis resulted. In particular, we focus on the synthesis of thermal peptides. Previously, laboratory experiments have demonstrated that dry heating a mixture of amino acids containing excess Asp, Glu, or Lys to temperatures approximately 170 degrees C for approximately 2 hours yields polypeptides. It has been argued that such temperature conditions would not have been available on the early Earth. Here we demonstrate, by analogy with the K/T impact, that the requisite temperatures are achieved on sand surfaces during the atmospheric reentry of fine ejecta particles produced by impacts of bolides approximately 10-20 km in diameter, assuming approximately 1-100 PAL CO2. Impactors of this size struck the Earth with a frequency of approximately 1 per 10(4)-10(5) y at 4.2 Ga. Smaller bolides produced negligible global surface heating, whereas bolides > 30 km in diameter yielded solid surface temperatures > 1000 K, high enough to pyrolyze amino acids and other organic compounds. Thus, peptide formation would have occurred globally for a relatively narrow range of bolide sizes.

Refugia from asteroid impacts on early Mars and the early Earth

Impacts of asteroids and comets posed a major hazard to the continuous existence of early life on Mars, as on Earth. The chief danger was presented by globally distributed ejecta, including transient thick rock vapor atmospheres. On Earth, much of the thermal radiation is absorbed by boiling the oceans. Any surviving life is either in deep water or well below the surface. Global thermal excursions are buffered by the heat capacity of the oceans. But when impacts are large enough to vaporize the oceans (&gt;l028 J), thermal buffering serves only to prolong the disaster for thousands of years, while the oceans rain out. Without oceans, thermal buffering does not occur on Mars. Relatively small impacts (1026 J) frequently heat the surface everywhere to the melting point. However, owing to the low Martian escape velocity, the most energetic ejecta (including the rock vapor) more easily escape to space, while massive quantities of less energetic ejecta are globally distributed. Survival in deep subsurface environments is more likely on Mars because (1) Mars' lower background heat flow and lower gravity allow deeper colonies, and (2) the thermal heat pulse from a major impact is briefer. Only thermophile organisms could have survived impacts of asteroids large enough to leave heat or boil the entire terrestrial ocean. Studies of terrestrial microorganisms indicate that the last common ancestor may have been thermophile and the survivor of such a catastrophe. This organism should be distinguished from the first common ancestor. An additional refugium is ejection of rock to space by impacts and thier return to a habitable planet.

The Origin of the Moon and the Single Impact Hypothesis V

Previous papers in this series have described the smooth particle hydrodynamics (SPH) method, which has been employed to explore the possibility that a major planetary collision may have been responsible for the formation of the Moon. In those simulations the SPH code used particles of equal mass and fixed smoothing lengths; I have found that the results obtained were reliable regarding what happens to the interiors of the colliding planets. Because the particles placed into the surrounding space were isolated rather than overlapping, however, that part of the calculation was unreliable. Ten additional cases have been run with 5000 particles in the Protoearth and 5000 in the Impactor, with variable smoothing lengths. Three of the cases had Protoearth/Impactor mass ratios of 5:5, 6:4, and 7:3. The other cases had a mass ratio of 8:2 and a variety of angular momenta. All cases had zero velocity at infinity. In every case the product of the collision became surrounded by evaporated particles of rock vapor, forming an extended atmosphere; however, relatively little mass extended beyond the Roche lobe. If the Moon formed from a rock disk in orbit around the Earth, then some other mechanism would be needed to transport angular momentum and mass outward in the equatorial plane, so that rock condensates from the hot atmosphere would be precipitated beyond the Roche limit, thus providing material for collection into the Moon. Most of this atmospheric material was originally in the Impactor and was mixed with terrestrial rock before evaporation. Recent calculations by R. M. Canup and L. W. Esposito (1996, Icarus119, 427–446) have shown that it is very difficult to form the Moon from a gaseous disk largely confined to within the Roche lobe. On the other hand, higher-angular-momentum collisions can leave a quite massive body in orbit about the Earth, and this could form much or essentially all of the Moon. These questions remain challenging and require further investigations.

Physical conditions on early earth: Implications for the origin of life

The history of the earth can be divided into the earlier part of the accretion, the later part of accretion and core formation, and the remaining history. The early part of accretion is irrelevant to the origin of life because of the extreme conditions associated with the late stages of accretion. The impact of several lunar to Mars-sized objects appears inevitable. These large impacts surrounded the earth with rock vapor tens to hundreds of kilometers thick. Although the solid surface was quickly reestablished any ocean or atmosphere existing before the last very large impact was either buried or lost. The iron core of the earth formed during accretion and released enough gravitational energy to melt the interior of the earth. Moderate sized impacting bodies formed local pockets of impact melt. Following the last very large impact the earth (and the moon) were near their present sizes and the energy flux from impacts was sufficiently less than the present solar heat flux. A cool surface with oceans and an atmosphere then could persist. The internal tectonics and degassing mechanisms of the earth were different than during the rest of earth history. In particular, the eruption of total ly melted rock to the surface was a much more efficient means of heat loss than plate movements and the return of the frozen material to the interior may have efficiently cooled the interior. Once the last pockets of very hot material in the mantle erupted and were used up, plate tectonics became the dominate mode of heat transfer from the earth 's interior. The interior temperature at the s tar t of plate tectonics need not have been particularly high as cold total ly frozen material acted to cool the mantle during the early epic of total melting and volcanism. Mare-sized impacts were infrequent during the period of heavy bombardment and mare formulation on the moon that the surface geology of the earth was probably dominated by internal processes rather than cratering. In particular, the resurfacing of the earth was probably comparable to that of present-day active volcanic regions where life is abundant in spite of frequent disasters. The mare-forming imparts on the earth would have produced heavy casualities in any life that existed, but the worst effects were local and not a danger to life globally. Conversely, impacts were sufficiently infrequent that meteoritic iron, shocked or melted rocks, and shock-induced atmospheric gasses were not dependable material for the sustenance of early life. The origin of an atmosphere and an ocean following the last major impact was probably rapid, but quantitative observations exist only for radiogenic rare gasses and not for CO 2 and H20. As at present, competing processes tended to degas volatiles and to return them to the earth 's interior. Volcanic activity and metamorphism released gasses and lower temperature alteration particularly at mid-oceanic ridges returned volatiles into the interior. Although the