Solar System Analogs Research Articles

Formation of Ares Vallis (Mars) by effusions of low-viscosity lava within multiple regions of chaotic terrain

Ares Vallis is one of the largest outflow channels on Mars, extending northward >1500 km from the highlands of Margaritifer Terra into the Chryse impact basin. This outflow system developed primarily during the Hesperian and Amazonian as a result of voluminous effusions from the subsurface that took place within Iani Chaos, Aram Chaos, Margaritifer Chaos, and Hydaspis Chaos. Though Ares Vallis is widely interpreted as a product of catastrophic outbursts from aquifers, its basic attributes do not appear to support aqueous origins of any kind: aquifer outburst mechanisms lack meaningful solar system analogs, clear examples of fluvial or diluvial sedimentary deposits are apparently absent at Ares Vallis, and there is no mineralogical evidence along component channels and within terminal basins for extensive aqueous alteration or for deposition of thick evaporite units. Instead, as is the case at hundreds of ancient channels of the inner solar system, the nature of Ares Vallis is aligned with dry volcanic origins. Such origins are broadly consistent with the system's relatively pristine mineralogy, the widespread mantling of component channels by lava flows, and the apparent presence of voluminous mare-style flood lavas within terminal basins. With assumed lava viscosities of 1 Pa s and temperatures of 1350 °C, discharge rates of ~97 × 106 m3/s are estimated at Ares Vallis for 100-m-deep flows along channel reaches with widths of 25 km and slopes of only 0.2°. Mechanical and thermal incision are respectively estimated to be ~12.2 m/day and 2.3 m/day for 100-m-deep flows on these slopes. Formation of the main Ares Vallis channel and associated regions of chaos is likely to have required a minimum effused lava volume of ~1.8 × 106 km3, and still greater lava volumes would have been necessary to form associated channel reaches including those located south of Margaritifer Chaos.

Fly-by encounters between two planetary systems I: Solar system analogues

ABSTRACTStars formed in clusters can encounter other stars at close distances. In typical open clusters in the Solar neighbourhood containing hundreds or thousands of member stars, 10–20 per cent of Solar-mass member stars are expected to encounter another star at distances closer than 100 au. These close encounters strongly perturb the planetary systems, directly causing ejection of planets or their capture by the intruding star, as well as exciting the orbits. Using extensive N-body simulations, we study such fly-by encounters between two Solar system analogues, each with four giant planets from Jupiter to Neptune. We quantify the rates of loss and capture immediately after the encounter, e.g. the Neptune analogue is lost in one in four encounters within 100 au, and captured by the flying-by star in 1 in 12 encounters. We then perform long-term (up to 1 Gyr) simulations investigating the ensuing post-encounter evolution. We show that large numbers of planets are removed from systems due to planet–planet interactions and that captured planets further enhance the system instability. While encounters can initially leave a planetary system containing more planets by inserting additional ones, the long-term instability causes a net reduction in planet number. A captured planet ends up on a retrograde orbit in half of the runs in which it survives for 1Gyr; also, a planet bound to its original host star but flipped during the encounter may survive. Thus, encounters between planetary systems are a channel to create counter-rotating planets, This would happen in around 1 per cent of systems, and such planets are potentially detectable through astrometry or direct imaging.

The formation of solar-system analogs in young star clusters

The solar system was once rich in the short-lived radionuclide (SLR) 26Al but poor in 60Fe. Several models have been proposed to explain these anomalous abundances in SLRs, but none has been set within a self-consistent framework of the evolution of the solar system and its birth environment. The anomalous abundance in 26Al may have originated from the accreted material in the wind of a massive ≳20 M⊙ Wolf-Rayet star, but the star could also have been a member of the parental star-cluster instead of an interloper or an older generation that enriched the proto-solar nebula. The protoplanetary disk at that time was already truncated around the Kuiper-cliff (at 45 au) by encounters with other cluster members before it was enriched by the wind of the nearby Wolf-Rayet star. The supernova explosion of a nearby star, possibly but not necessarily the exploding Wolf-Rayet star, heated the disk to ≳1500 K, melting small dust grains and causing the encapsulation and preservation of 26Al in vitreous droplets. This supernova, and possibly several others, caused a further abrasion of the disk and led to its observed tilt of 5.6 ± 1.2° with respect to the equatorial plane of the Sun. The abundance of 60Fe originates from a supernova shell, but its preservation results from a subsequent supernova. At least two supernovae are needed (one to deliver 60Fe and one to preserve it in the disk) to explain the observed characteristics of the solar system. The most probable birth cluster therefore has N = 2500 ± 300 stars and a radius of rvir = 0.75 ± 0.25 pc. We conclude that systems equivalent to our solar system form in the Milky Way Galaxy at a rate of about 30 Myr−1, in which case approximately 36 000 solar-system analogs roam the Milky Way.

Constraints on the nature of the effusive volcanic eruptions that incised Ravi Vallis, Mars

Ravi Vallis is a Martian outflow channel that is widely interpreted as a product of one or more catastrophic outbursts of groundwater from adjacent Aromatum Chaos. However, solar system analogs are unknown for formation of large channels by outbursts from aquifers, and the Ravi Vallis region lacks the obvious sedimentological and mineralogical signatures expected of aqueous origins. Instead, the basic nature of this channel system is consistent with volcanic origins involving voluminous effusions of low-viscosity lavas. On bedrock slopes of only 0.2°, 50-m-deep lava flows with viscosities of 1 Pa s are predicted to have been characterized by discharge rates of ∼3 × 107 m3/s for 25-km-wide flows, with associated mechanical incision rates of ∼4 m/day and thermal incision rates of ∼2 m/day. Formation of Aromatum Chaos and the preserved 215-km-long extent of Ravi Vallis is conservatively estimated on the basis of thermal considerations to have required eruption of a minimum of ∼64,000 km3 of lava, but greater volumes would have been necessary to form the original (unknown) length of this channel system. A volcanic origin for Ravi Vallis is consistent with development of all Martian outflow channels by igneous processes, and with the broader premise that early development of immense volcanic channel systems is typical of all large rocky bodies.

The Disk Substructures at High Angular Resolution Project (DSHARP). VII. The Planet–Disk Interactions Interpretation

Abstract The Disk Substructures at High Angular Resolution Project (DSHARP) provides a large sample of protoplanetary disks with substructures that could be induced by young forming planets. To explore the properties of planets that may be responsible for these substructures, we systematically carry out a grid of 2D hydrodynamical simulations, including both gas and dust components. We present the resulting gas structures, including the relationship between the planet mass, as well as (1) the gaseous gap depth/width and (2) the sub/super-Keplerian motion across the gap. We then compute dust continuum intensity maps at the frequency of the DSHARP observations. We provide the relationship between the planet mass, as well as (1) the depth/width of the gaps at millimeter intensity maps, (2) the gap edge ellipticity and asymmetry, and (3) the position of secondary gaps induced by the planet. With these relationships, we lay out the procedure to constrain the planet mass using gap properties, and study the potential planets in the DSHARP disks. We highlight the excellent agreement between observations and simulations for AS 209 and the detectability of the young solar system analog. Finally, under the assumption that the detected gaps are induced by young planets, we characterize the young planet population in the planet mass–semimajor axis diagram. We find that the occurrence rate for >5 M J planets beyond 5–10 au is consistent with direct imaging constraints. Disk substructures allow us to probe a wide-orbit planet population (Neptune to Jupiter mass planets beyond 10 au) that is not accessible to other planet searching techniques.

A Catalog of Spectra, Albedos, and Colors of Solar System Bodies for Exoplanet Comparison.

We present a catalog of spectra and geometric albedos, representative of the different types of solar system bodies, from 0.45 to 2.5 μm. We analyzed published calibrated, uncalibrated spectra, and albedos for solar system objects and derived a set of reference spectra and reference albedos for 19 objects that are representative of the diversity of bodies in our solar system. We also identified previously published data that appear contaminated. Our catalog provides a baseline for comparison of exoplanet observations to 19 bodies in our own solar system, which can assist in the prioritization of exoplanets for time intensive follow-up with next-generation extremely large telescopes and space-based direct observation missions. Using high- and low-resolution spectra of these solar system objects, we also derive colors for these bodies and explore how a color-color diagram could be used to initially distinguish between rocky, icy, and gaseous exoplanets. We explore how the colors of solar system analog bodies would change when orbiting different host stars. This catalog of solar system reference spectra and albedos is available for download through the Carl Sagan Institute.

Formation of Solar system analogues – II. Post-gas-phase growthand water accretion in extended discs via N-body simulations

This work is the second part of a project that attempts to analyze the formation of Solar system analogues (SSAs) from the gaseous to the post-gas phase, in a self-consistently way. In the first paper (PI) we presented our model of planet formation during the gaseous phase which provided us with embryo distributions, planetesimal surface density, eccentricity and inclination profiles of SSAs, considering different planetesimal sizes and type I migration rates at the time the gas dissipates. In this second work we focus on the late accretion stage of SSAs using the results obtained in PI as initial conditions to carry out N-body simulations. One of our interests is to analyze the formation of rocky planets and their final water contents within the habitable zone. Our results show that the formation of potentially habitable planets (PHPs) seems to be a common process in this kind of scenarios. However, the efficiency in forming PHPs is directly related to the size of the planetesimals. The smaller the planetesimals, the greater the efficiency in forming PHPs. We also analyze the sensitivity of our results to scenarios with type I migration rates and gap-opening giants, finding that both phenomena act in a similar way. These effects seem to favor the formation of PHPs for small planetesimal scenarios and to be detrimental for scenarios formed from big planetesimals. Finally, another interesting result is that the formation of water-rich PHPs seems to be more common than the formation of dry PHPs.

Exploring the realm of scaled solar system analogues with HARPS

Context. The assessment of the frequency of planetary systems reproducing the solar system’s architecture is still an open problem in exoplanetary science. Detailed study of multiplicity and architecture is generally hampered by limitations in quality, temporal extension and observing strategy, causing difficulties in detecting low-mass inner planets in the presence of outer giant planets. Aims. We present the results of high-cadence and high-precision HARPS observations on 20 solar-type stars known to host a single long-period giant planet in order to search for additional inner companions and estimate the occurence rate fp of scaled solar system analogues – in other words, systems featuring lower-mass inner planets in the presence of long-period giant planets. Methods. We carried out combined fits of our HARPS data with literature radial velocities using differential evolution MCMC to refine the literature orbital solutions and search for additional inner planets. We then derived the survey detection limits to provide preliminary estimates of fp. Results. We generally find better constrained orbital parameters for the known planets than those found in the literature; significant updates can be especially appreciated on half of the selected planetary systems. While no additional inner planet is detected, we find evidence for previously unreported long-period massive companions in systems HD 50499 and HD 73267. We finally estimate the frequency of inner low mass (10–30 M⊕) planets in the presence of outer giant planets as fp < 9.84% for P < 150 days. Conclusions. Our preliminary estimate of fp is significantly lower than the literature values for similarly defined mass and period ranges; the lack of inner candidate planets found in our sample can also be seen as evidence corroborating the inwards-migration formation model for super-Earths and mini-Neptunes. Our results also underline the need for high-cadence and high-precision followup observations as the key to precisely determine the occurence of solar system analogues.

Properties of the single Jovian planet population and the pursuit of Solar system analogues

While the number of exoplanets discovered continues to increase at a rapid rate, we are still to discover any system that truly resembles the Solar system. Existing and near future surveys will likely continue this trend of rapid discovery. To see if these systems are Solar system analogues, we will need to efficiently allocate resources to carry out intensive follow-up observations. We seek to uncover the properties and trends across systems that indicate how much of the habitable zone is stable in each system to provide focus for planet hunters. We study the dynamics of all known single Jovian planetary systems, to assess the dynamical stability of the habitable zone around their host stars. We perform a suite of simulations of all systems where the Jovian planet will interact gravitationally with the habitable zone, and broadly classify these systems. Besides the system's mass ratio (Mpl/Mstar), and the Jovian planet's semi-major axis (apl) and eccentricity (epl), we find that there are no underlying system properties which are observable that indicate the potential for planets to survive within the system's habitable zone. We use Mpl/Mstar, apl and epl to generate a parameter space over which the unstable systems cluster, thus allowing us to predict which systems to exclude from future observational or numerical searches for habitable exoplanets. We also provide a candidate list of 20 systems that have completely stable habitable zones and Jovian planets orbiting beyond the habitable zone as potential first order Solar system analogues.

A next-generation Very Large Array

AbstractIn this proceeding, we summarize the key science goals and reference design for a next-generation Very Large Array (ngVLA) that is envisaged to operate in the 2030s. The ngVLA is an interferometric array with more than 10 times the sensitivity and spatial resolution of the current VLA and ALMA, that will operate at frequencies spanning ~1.2 – 116 GHz, thus lending itself to be highly complementary to ALMA and the SKA1. As such, the ngVLA will tackle a broad range of outstanding questions in modern astronomy by simultaneously delivering the capability to: unveil the formation of Solar System analogues; probe the initial conditions for planetary systems and life with astrochemistry; characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; use pulsars in the Galactic center as fundamental tests of gravity; and understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy.

Formation of solar system analogues – I. Looking for initial conditions through a population synthesis analysis

Population synthesis models of planetary systems developed during the last $\sim$15 years could reproduce several of the observables of the exoplanet population, and also allowed to constrain planetary formation models. We present our planet formation model, which calculates the evolution of a planetary system during the gaseous phase. The code incorporates relevant physical phenomena for the formation of a planetary system, like photoevaporation, planet migration, gas accretion, water delivery in embryos and planetesimals, a detailed study of the orbital evolution of the planetesimal population, and the treatment of the fusion between embryos, considering their atmospheres. The main goal of this work, unlike other works of planetary population synthesis, is to find suitable scenarios and physical parameters of the disc to form solar system analogs. We are specially interested in the final planet distributions, and in the final surface density, eccentricity and inclination profiles for the planetesimal population. These final distributions will be used as initial conditions for N-body simulations, to study the post-oligarchic formation in a second work. We then consider different formation scenarios, with different planetesimal sizes and different type I migration rates. We find that solar system analogs are favored in massive discs, with low type I migration rates, and small planetesimal sizes. Besides, those rocky planets within their habitables zones are dry when discs dissipate. At last, the final configurations of solar system analogs include information about the mass and semimajor-axis of the planets, water contents, and the properties of the planetesimal remnants.

The fates of Solar system analogues with one additional distant planet

The potential existence of a distant planet ("Planet Nine") in the Solar system has prompted a re-think about the evolution of planetary systems. As the Sun transitions from a main sequence star into a white dwarf, Jupiter, Saturn, Uranus and Neptune are currently assumed to survive in expanded but otherwise unchanged orbits. However, a sufficiently-distant and sufficiently-massive extra planet would alter this quiescent end scenario through the combined effects of Solar giant branch mass loss and Galactic tides. Here, I estimate bounds for the mass and orbit of a distant extra planet that would incite future instability in systems with a Sun-like star and giant planets with masses and orbits equivalent to those of Jupiter, Saturn, Uranus and Neptune. I find that this boundary is diffuse and strongly dependent on each of the distant planet's orbital parameters. Nevertheless, I claim that instability occurs more often than not when the planet is as massive as Jupiter and harbours a semimajor axis exceeding about 300 au, or has a mass of a super-Earth and a semimajor axis exceeding about 3000 au. These results hold for orbital pericentres ranging from 100 to at least 400 au. This instability scenario might represent a common occurrence, as potentially evidenced by the ubiquity of metal pollution in white dwarf atmospheres throughout the Galaxy.

PROBABILISTIC MASS–RADIUS RELATIONSHIP FOR SUB-NEPTUNE-SIZED PLANETS

ABSTRACT The Kepler Mission has discovered thousands of planets with radii <4 , paving the way for the first statistical studies of the dynamics, formation, and evolution of these sub-Neptunes and super-Earths. Planetary masses are an important physical property for these studies, and yet the vast majority of Kepler planet candidates do not have theirs measured. A key concern is therefore how to map the measured radii to mass estimates in this Earth-to-Neptune size range where there are no Solar System analogs. Previous works have derived deterministic, one-to-one relationships between radius and mass. However, if these planets span a range of compositions as expected, then an intrinsic scatter about this relationship must exist in the population. Here we present the first probabilistic mass–radius relationship (M–R relation) evaluated within a Bayesian framework, which both quantifies this intrinsic dispersion and the uncertainties on the M–R relation parameters. We analyze how the results depend on the radius range of the sample, and on how the masses were measured. Assuming that the M–R relation can be described as a power law with a dispersion that is constant and normally distributed, we find that , a scatter in mass of , and a mass constraint to physically plausible densities, is the “best-fit” probabilistic M–R relation for the sample of RV-measured transiting sub-Neptunes (R pl < 4 ). More broadly, this work provides a framework for further analyses of the M–R relation and its probable dependencies on period and stellar properties.

First detection of gas-phase ammonia in a planet-forming disk

Nitrogen chemistry in protoplanetary disks and the freeze-out on dust particles is key to understand the formation of nitrogen bearing species in early solar system analogs. So far, ammonia has not been detected beyond the snowline in protoplanetary disks. We aim to find gas-phase ammonia in a protoplanetary disk and characterize its abundance with respect to water vapor. Using HIFI on the Herschel Space Observatory we detect, for the first time, the ground-state rotational emission of ortho-NH$_3$ in a protoplanetary disk, around TW Hya. We use detailed models of the disk's physical structure and the chemistry of ammonia and water to infer the amounts of gas-phase molecules of these species. We explore two radial distributions ( confined to $<$60 au like the millimeter-sized grains) and two vertical distributions (near the midplane where water is expected to photodesorb off icy grains) to describe the (unknown) location of the molecules. These distributions capture the effects of radial drift and vertical settling of ice-covered grains. We use physical-chemical models to reproduce the fluxes with assuming that water and ammonia are co-spatial. We infer ammonia gas-phase masses of 0.7-11.0 $\times$10$^{21}$ g. For water, we infer gas-phase masses of 0.2-16.0 $\times$10$^{22}$ g. This corresponds to NH$_3$/H$_2$O abundance ratios of 7\%-84\%, assuming that water and ammonia are co-located. Only in the most compact and settled adopted configuration is the inferred NH$_3$/H$_2$O consistent with interstellar ices and solar system bodies of $\sim$ 5\%-10\%. Volatile release in the midplane may occur via collisions between icy bodies if the available surface for subsequent freeze-out is significantly reduced, e.g., through growth of small grains into pebbles or larger.

STEALING THE GAS: GIANT IMPACTS AND THE LARGE DIVERSITY IN EXOPLANET DENSITIES

ABSTRACT Although current sensitivity limits are such that true solar system analogs remain challenging to detect, numerous planetary systems have been discovered that are very different from our own solar system. The majority of systems harbor a new class of planets, bodies that are typically several times more massive than the Earth but orbit their host stars well inside the orbit of Mercury. These planets frequently show evidence for large hydrogen and helium envelopes containing several percent of the planet’s mass and display a large diversity in mean densities. Here we show that this wide range can be achieved by one or two late giant impacts, which are frequently needed to achieve long-term orbital stability in multiple planet systems once the gas disk has disappeared. We demonstrate using hydrodynamical simulations that a single collision between similarly sized exoplanets can easily reduce the envelope-to-core-mass ratio by a factor of two and show that this leads to a corresponding increase in the observed mean density by factors of two to three. In addition, we investigate how envelope mass loss depends on envelope mass, planet radius, semimajor axis, and the mass distribution inside the envelope. We propose that a small number of giant impacts may be responsible for the large observed spread in mean densities, especially for multiple-planet systems that contain planets with very different densities and have not been significantly sculpted by photoevaporation.

SETI VIA LEAKAGE FROM LIGHT SAILS IN EXOPLANETARY SYSTEMS

The primary challenge of rocket propulsion is the burden of needing to accelerate the spacecraft's own fuel, resulting in only a logarithmic gain in maximum speed as propellant is added to the spacecraft. Light sails offer an attractive alternative in which fuel is not carried by the spacecraft, with acceleration being provided by an external source of light. By artificially illuminating the spacecraft with beamed radiation, speeds are only limited by the area of the sail, heat resistance of its material, and power use of the accelerating apparatus. In this paper, we show that leakage from a light sail propulsion apparatus in operation around a solar system analogue would be detectable. To demonstrate this, we model the launch and arrival of a microwave beam-driven light sail constructed for transit between planets in orbit around a single star, and find an optimal beam frequency on the order of tens of GHz. Leakage from these beams yields transients with flux densities of Jy and durations of tens of seconds at 100 pc. Because most travel within a planetary system would be conducted between the habitable worlds within that system, multiply-transiting exoplanetary systems offer the greatest chance of detection, especially when the planets are in projected conjunction as viewed from Earth. If interplanetary travel via beam-driven light sails is commonly employed in our galaxy, this activity could be revealed by radio follow-up of nearby transiting exoplanetary systems. The expected signal properties define a new strategy in the search for extraterrestrial intelligence (SETI).

The Solar Twin Planet Search

Context. With high-precision radial velocity surveys reaching a sufficiently long time baseline, the domain of long-period planet detections has recently opened up. The search for Jupiter-like planets is especially important if we wish to investigate the prevalence of solar system analogs, but their detection is complicated by the existence of stellar activity cycles on similar timescales. Radial velocity data with sufficiently long-term instrumental precision and robust methods of diagnosing activity are crucial to the detection of extrasolar Jupiters.

PHOTOMETRY’S BRIGHT FUTURE: DETECTING SOLAR SYSTEM ANALOGS WITH FUTURE SPACE TELESCOPES

Time-series transit photometry from the Kepler space telescope has allowed for the discovery of thousands of exoplanets. We explore the potential of yet improved future missions such as PLATO 2.0 in detecting solar system analogues. We use real-world solar data and end-to-end simulations to explore the stellar and instrumental noise properties. By injecting and retrieving planets, rings and moons of our own solar system, we show that the discovery of Venus- and Earth-analogues transiting G-dwarfs like our Sun is feasible at high S/N after collecting 6yrs of data, but Mars and Mercury will be difficult to detect due to stellar noise. In the best cases, Saturn's rings and Jupiter's moons will be detectable even in single transit observations. Through the high number (>1 bn) of observed stars by PLATO 2.0, it will become possible to detect thousands of single-transit events by cold gas giants, analogue to our Jupiter, Saturn, Uranus and Neptune. Our own solar system aside, we also show, through signal injection and retrieval, that PLATO 2.0-class photometry will allow for the secure detection of exomoons transiting quiet M-dwarfs. This is the first study analyzing in-depth the potential of future missions, and the ultimate limits of photometry, using realistic case examples.

The Small Exoplanet Mass-Radius Relation: Quantifying the Astrophysical Scatter

AbstractThe Kepler Mission has discovered thousands of planets with radii &lt;4 R ⊕, paving the way for the first statistical studies of super-Earth dynamics, formation, and evolution. These calculations often require planetary masses, and yet the vast majority of Kepler planet candidates do not have theirs measured. A key concern is therefore how to map the measured radii to mass estimates in a size range that lacks Solar System analogs. While previous works have derived one-to-one relationships between radius and mass, a realistic mass-radius (M-R) relation should account for the range of compositions that we expect within the population. This compositional diversity creates astrophysical scatter in the relation, which we quantify here.

An Overview of Inside-Out Planet Formation

AbstractThe Kepler-discovered Systems with Tightly-packed Inner Planets (STIPs), typically with several planets of Earth to super-Earth masses on well-aligned, sub-AU orbits may host the most common type of planets, including habitable planets, in the Galaxy. They pose a great challenge for planet formation theories, which fall into two broad classes: (1) formation further out followed by inward migration; (2) formation in situ, in the very inner regions of the protoplanetary disk. We review the pros and cons of these classes, before focusing on a new theory of sequential in situ formation from the inside-out via creation of successive gravitationally unstable rings fed from a continuous stream of small (~cm-m size) “pebbles,” drifting inward via gas drag. Pebbles first collect at the pressure trap associated with the transition from a magnetorotational instability (MRI)-inactive (“dead zone”) region to an inner, MRI-active zone. A pebble ring builds up that begins to dominate the local mass surface density of the disk and spawns a planet. The planet continues to grow, most likely by pebble accretion, until it becomes massive enough to isolate itself from the accretion flow via gap opening. This reduces the local gas density near the planet, leading to enhanced ionization and a retreat of the dead zone inner boundary. The process repeats with a new pebble ring gathering at the new pressure maximum associated with this boundary. We discuss the theory's predictions for planetary masses, relative mass scalings with orbital radius, and minimum orbital separations, and their comparison with observed systems. Finally, we discuss open questions, including potential causes of diversity of planetary system architectures, i.e., STIPs versus Solar System analogs.