Planet seminar is held at 15:00 every Monday (Organizers: Kazumasa Ohno, Yuhito Shibaike)
| Date | Speaker | Title | Remarks | Person in charge |
|---|---|---|---|---|
| 2025/1/17 | Yuya Fukuhara | TBD | Yuhito Shibaike | |
| 2025/1/10 | Kanon Nakazawa | TBD | Instrument Development Building 3, 3F | Yuhito Shibaike |
| 2025/1/7 | Tamami Okamoto | TBD | Tuesday, 13:00 | Yuhito Shibaike |
| 2024/12/20 | Hiroto Mitani | TBD | Yuhito Shibaike | |
| 2024/12/17 | Hanno Rein | TBD | Tuesday, 13:30(?) | Kazumasa Ohno |
| 2024/11/22 | Helong Huang | ExoLyn: A Balanced Exoplanet Cloud Model for Retrieval | Friday, 13:00 (Insei seminar room) | Kazumasa Ohno |
| 2024/11/22 | Shuo Huang | The resonances of planets across their formation and evolution | Friday, 13:00 (Insei seminar room) | Kazumasa Ohno |
| 2024/11/19 | Chris Ormel | ALMA rings as planet factories | Tuesday, 13:00 | Yuhito Shibaike |
| 2024/10/18 | Jeehyun Yang | Cross-Disciplinary Characterization of Exoplanet Atmospheres: Observation, Theory, and Experiment | Friday, 13:00 (ALMA 102) | Kazumasa Ohno |
| 2024/10/15 | Tenri Jinno | Global N-body simulation of planetary formation: The origins of ice giants | Tuesday, 13:00 | Yuhito Shibaike |
| 2024/9/9 | Yinhao Wu | Combining numerical simulations and observations to study MHD disk winds and disk substructures | Kazumasa Ohno | |
| 2024/9/4 | Wen-Han Zhou | The Binary Yarkovsky Effect: A New Mechanism for Changing the Mutual Orbits of Binary Asteroids | Wednesday, 15:00 | Yuhito Shibaike, Kazumasa Ohno |
| 2024/8/1 | Yasuhiro Hasegawa | Testing theories of planetary growth and disk evolution | Thursday, 15:30 | Yuhito Shibaike |
| 2024/7/5 | Bin Cheng | Asteroid Kamo`oalewa’s Journey from Lunar Crater Giordano Bruno to Earth 1:1 Resonance | Yuhito Shibaike | |
| 2024/7/1 | Ryo Sawada | The Origin of Short-Lived Radioactive Nuclides 26Al in the Early Solar… | Yuhito Shibaike | |
| 2024/6/24 | Lorenzo Mugnai | Simulations for Exoplanet Population Studies: a Guide for the Future | 14:30 | Kazumasa Ohno |
| 2024/6/17 | Yukun Huang | A Rogue Planet Hypothesis for the Formation of the Trans-Neptunian Solar… | Yuhito Shibaike | |
| 2024/6/10 | Ji Wang | Early Accretion of Large Amounts of Solids for Directly-Imaged Exoplanets | Kazumasa Ohno | |
| 2024/6/3 | Taiki Kagetani | Close-in Giant Planets around Low-mass Stars | Kazumasa Ohno |
|
| 2024/5/22 | Yixian Chen | Unorthodox planet-disk interaction: Eccentricity, Turbulence and Winds | Wednesday, 13:00 | Yuhito Shibaike |
Helong Huang (Tsinghua University),
ExoLyn: A Balanced Exoplanet Cloud Model for Retrieval
With the launch of JWST, we are embracing an era of precise measurement of exoplanet atmosphere’s transmission and emission spectrum. In interpreting these data, the presence of clouds plays a crucial role, as clouds obscures the spectral signature and their formation consumes vapor, changing the molecular inventory. However, in retrieval methods, clouds are typically imposed by parameters such as cloud deck pressure, mixing ratio. Here, we have developed a streamlined 1D cloud model, ExoLyn, that solves for the steady state cloud profile, following, but vastly improving on, Ormel & Min (2019). The model includes particle transport, growth, and can cope with an arbitrary large number of condensate species. A novel relaxation method ensures rapid and robust convergence under arbitrary conditions. The general setup of our model allows computation of cloud structure in hot-Jupiters, super-Earths and self-luminous planets. For hot-Jupiter planets, we find layers of MgSiO3, Fe and Al2O3 clouds, recovering the characteristics of physically more complex models. The composition of the cloud particles can be constrained from the spectrum, for example, MgSiO3 and Mg2SiO4 components give rise to an absorption feature at 8-10 um. We investigate the dependence of the cloud structure on the bulk elemental composition of the planet and find that SiO2-dominated clouds forms on metal-rich planet and Fe clouds with strong extinction effect forms on C-rich planet. With the computational cost on the order of seconds on a regular PC, ExoLyn can be embedded into the majority of existing atmosphere retrieval codes.
Shuo Huang (Tsinghua University),
The resonances of planets across their formation and evolution
Planets form in protoplanetary disks, where they start to migrate (usually inwards) after growing to Earth masses. Planet migration naturally results in orbital resonances. In this talk, I will first explain why migration leads to orbital resonance. We find that resonance trapping is guaranteed only when both planet migration and eccentricity damping is gentle in the disk. Therefore, the formation/migration history imprints itself on the resonant architecture of mature exoplanet systems. We then list TRAPPIST-1 system as an example, uncovering the planet formation history there. However, only a small fraction (about 15%) of the observed exoplanets are in resonance. To ease the tension between planet formation theory and the observed exoplanet architecture, I will review several mechanisms: inefficient planet migration (gas-poor formation), dynamical instability during disk dispersal, collision with planet embryos, and stellar flybys (for planets on wide orbits).
Chris Ormel (Tsinghua University),
ALMA rings as planet factories
Almost 10 years ago, ALMA first discovered substructure in the HL tau
system, in the forms of bright rings and dark lanes. This and other
substructure is now ubiquitously seen in continuum and line emission.
The standard (but not exclusive) explanation for substructure is
sculpting by planets. Massive planets will open gaps in the disk,
creating pressure maxima that collects solids, and changes the local gas
rotation speeds, which can be traced by molecular line observations.
Nevertheless, some of these indicators for planets are contradictory and
direct evidence for planets in the form of H-alpha detection are rare.
Here, in a turnaround of the classical chicken-egg dilemma, we instead
propose that these dense ALMA rings are the ideal sites to form planets.
We show that, inside the ring, the threshold of the pebble accretion
process is met as soon as planetesimals form and that planets grow
rapidly. After reaching ~10 Earth mass, planets migrate away from the
ring, which continues to produce planets as long as the pebble supply
lasts. Next, I will highlight the role of pebble accretion in changing
the chemical composition of the gas through ice sublimation. I will
conclude by applying these ideas to the MWC-480 system.
Jeehyun Yang (Jet Propulsion Laboratory),
Cross-Disciplinary Characterization of Exoplanet Atmospheres: Observation, Theory, and Experiment
With the advent of JWST, the need for detailed chemical and photochemical models of exoplanet atmospheres has increased. Traditionally, building reaction networks required manually tracking species and reactions, a process that is both time-consuming and prone to errors, often limited to specific conditions. We introduce an automated approach using a computer-aided chemical reaction network generator combined with 1D photochemical kinetic-transport modeling, applied to various exoplanet atmospheres from hot Jupiters to temperate sub-Neptunes.
Applying this new framework to temperate sub-Neptunes reveals that the atmospheric CO2/CH4 ratio can infer the deep interior H2O/H2 ratio. Applying this to recent JWST observations, we suggest that K2-18 b likely has an interior with 50% water enrichment, indicating significant ice accretion during its formation. Conversely, our model suggests that TOI-270 d’s interior is about 25% water, consistent with a metallicity exceeding 100x solar metallicity. Additionally, our models identify carbonyl sulfide (OCS) and sulfur dioxide (SO2) as key indicators for temperate sub-Neptunes with at least 10% water content.
As a future study, investigating extensive sulfur (photo)chemistry will be crucial. This research should combine ab-initio calculations with experimental measurements, enabling a cross-disciplinary characterization of exoplanet atmospheres.
Tenri Jinno (Kobe University),
Global N-body simulation of planetary formation: The origins of ice giants
In the standard theory of planet formation, planets are thought to have formed “in-situ” around their current orbits. However, it has long been pointed out that assuming “in-situ” formation for ice giants results in formation times that exceed the age of the Solar System. Moreover, recent observations of exoplanets have revealed the existence of a diverse planetary systems that cannot be explained without considering migration of planets. One of the leading mechanisms for planetary migration is Planetesimal-Driven Migration (hereafter, PDM), where planets migrate due to gravitational interactions between planetesimals and planets. It has been known that PDM not only causes planets to migrate toward the central star (inward PDM) but also migrate outward (outward PDM). This dynamic migration through PDM is expected to explain the outward migration of ice giants and the diversity of exoplanets.
In this study, we conducted self-consistent, large-scale N-body simulations of planet formation using the supercomputer “Fugaku”, which included self-stirring, planet-disk gas interactions, and the process of planetary growth from planetesimals. Our results show that protoplanets formed in the inner disk migrate outward while growing through PDM. Furthermore, these protoplanets, formed in the inner disk, repel smaller protoplantes located further outward, leading to the outward migration of multiple protoplanets.
The results of our global self-consistent N-body simulations of planet formation suggest that planets can dynamically migrate within the protoplanetary disk during their growth process. This not only potentially explains the origins of ice giants but also provides theoretical support for the origin of Plutino, believed to form due to the outward migration of Neptune.
Yinhao Wu (University of Leicester),
Combining numerical simulations and observations to study MHD disk winds and disk substructures
Recent observations suggest that protoplanetary disks are not as turbulent as previously predicted by theoretical models. To explain angular momentum transfer and accretion processes in non-viscous disks, astronomers have turned their attention to the MHD disk wind mechanism. In this talk, I will introduce our 2D multi-fluid hydrodynamic simulations with a simplified prescription of MHD disk winds, that study the formation of substructures in disks when angular momentum transfer dominated by MHD disk winds, as opposed to traditional viscosity-dominated disks. By identifying different observational signatures of these substructures, we may be able to directly determine the presence of MHD disk winds in disks through ALMA imaging. Additionally, I will discuss how this method has been applied in my latest research to explain the asymmetric structures and high accretion rates observed in the well-known DM Tau system. Lastly, I will present my recently submitted work on how MHD disk winds affect planet migration.
Wen-Han Zhou (Observatoire de la Côte d’Azur),
The Binary Yarkovsky Effect: A New Mechanism for Changing the Mutual Orbits of Binary Asteroids
Binary asteroids form from gravitational collapse in the protoplanetary disks or collisions and rotational disruption in the asteroid belt. Understanding their long-term dynamics is crucial to tracing back their evolution, estimating their lifetime, and learning the physical properties and geologic structures of asteroids. The commonly considered mechanisms include the tidal effect and the binary YORP (BYORP) effect. The former arises from the gravitational perturbation due to shape deformation and the latter comes from the anisotropic irradiation from an irregular shape. Recently I found that another mechanism, namely the Yarkovsky effect, also affect significantly the long-term evolution of binary asteroids.
The Binary Yarkovsky effect on a binary consists of two sub-effects: the eclipse-induced Yarkovsky-Schach (YS) effect and the planetary Yarkovsky effect. The YS effect is caused by the elimination of the satellite irradiation by sunlight when it is located in the primary shadow and the related asymmetric thermal cooling and heating of the secondary after it enters and exits the shadow. The planetary Yarkovsky effect is simply the Yarkovsky effect caused by the primary’s radiation instead of the Sun . We find that YS dominates over the planetary Yarkovsky effect and the net effect is to move the object toward the synchronous orbit. The timescale for the orbital migration of the Yarkovsky effect is roughly 0.1 Myrs, depending on the physical properties of the binary. Therefore, we propose that the Binary Yarkovsky effect on the secondary asteroid (BYS) accounts for the synchronization of binary asteroids. Moreover, the Binary Yarkovsky on the primary asteroid (BYP) continues to modify the mutual orbital and could account for the observed orbital drift rate of several binary asteroids. This newly discovered Binary Yarkovsky effect, along with BYORP allows us to build a unified theory about the radiation effect on the binary asteroid system and have potential applications on planet-satellite/ring systems.
Yasuhiro Hasegawa (Jet Propulsion Laboratory, California Institute of Technology),
Testing theories of planetary growth and disk evolution
The discoveries of a large number of exoplanets are one of the biggest achievements in astronomy today. Observed exoplanets exhibit great diversity in their properties and challenge our current understanding of planet formation. Such challenges led to the proposition of various hypotheses, and as a result, it becomes of fundamental importance to determine which hypothesis is most dominant to understand observations. In this talk, I will discuss two of my recent efforts, wherein new theoretical models are developed to examine certain hypotheses. For the first part, I will discuss how sequential accretion of gas and solids, which is one key ingredient of core accretion, will be verified, using the bulk and atmospheric metallicities of exoplanets. For the second part, I will discuss how the origin of gas in debris disks will be constrained, by focusing on cold water vapor. These studies thus provide new probes of testing theories of planetary growth and disk evolution currently proposed in the literature.
Bin Cheng (Tsinghua University),
Asteroid Kamo`oalewa’s Journey from Lunar Crater Giordano Bruno to Earth 1:1 Resonance
Among the nearly 30,000 known near-Earth asteroids (NEAs), only tens possess Earth co-orbital characteristics with semi-major axes ~1 au. In particular, 469219 Kamo‘oalewa (2016 HO3), an upcoming target of China’s Tianwen-2 asteroid sampling mission, exhibits a meta-stable 1:1 mean-motion resonance with Earth. Intriguingly, recent ground-based observations show that Kamo‘oalewa has spectroscopic characteristics similar to space-weathered lunar silicates, hinting at a lunar origin instead of an asteroidal one like the vast majority of NEAs. Here we use numerical simulations to demonstrate that Kamo‘oalewa’s physical and orbital properties are compatible with a fragment from a crater larger than 10–20 km formed on the Moon in the last few million years. The impact could have ejected sufficiently large fragments into heliocentric orbits, some of which could be transferred to Earth 1:1 resonance and persist today. This leads us to suggest the young lunar crater Giordano Bruno (22 km diameter, 1–10 Myr age) as the most likely source, linking a specific asteroid in space to its source crater on the Moon. The hypothesis will be tested by the Tianwen-2 mission when it returns a sample of Kamo‘oalewa. And the upcoming NEO Surveyor mission may help us to identify such a lunar-derived NEA population.
Ryo Sawada (Institute for Cosmic Ray Research The University of Tokyo),
The Origin of Short-Lived Radioactive Nuclides 26Al in the Early Solar System (and some topics)
Meteoritic material formed in the early Solar System is known to contain an excess of short-lived radionuclides (SLRs). This suggests that our Solar System experienced the injection of SLRs from core-collapse supernova (CCSN) explosions somewhere during the formation process from the molecular cloud core. However, it is still unclear when, where and how these SLRs were injected from supernova explosions into the early Solar System.
One scenario that has long been proposed is that a nearby CCSN contracted the molecular cloud core and triggered star formation. On the other hand, a scenario in which SLRs are injected from a nearby CCSN after the already formation of the proto-solar disk has also been proposed. However, the shock wave from a nearby CCSN may not inject SLRs into the disk, but rather destroy it. In this study, we focus on 26Al and investigate the conditions under which a CCSN is suitable as a nuclide injection event without destroying the disk.
Lorenzo Mugnai (The Cardiff University),
Simulations for Exoplanet Population Studies: a Guide for the Future
This seminar focuses on the use of simulators to prepare for exoplanet population studies, a crucial aspect for the success of future space missions like Ariel and JWST. By simulating spectroscopic observations, it is possible to predict instrument performance, analyze hundreds of targets in minutes, and develop strategies for data reduction. The seminar will explore the challenges related to data reduction and interpretation, using examples from spectroscopic studies of exoplanets observed with HST-WFC3 and comparing data obtained with different pipelines. Innovative strategies to handle the vast amount of data expected from future missions and the use of atmospheric models to simulate observed planetary spectra will be presented.
Ji Wang (The Ohio State University),
Early Accretion of Large Amounts of Solids for Directly-Imaged Exoplanets
As the number of planetary mass objects (PMOs, <13 M_J) at wider separation (>10 AU) grows, there is emerging evidence that they form differently from their higher-mass brown-dwarf (BD) counterparts. Namely, PMOs’ atmospheres are enriched by metals which is usually interpreted as a sign of solid accretion. As a first step toward a population-level study of the amount and timing of solid accretion, we analyze a sample of five directly-imaged exoplanets with measured stellar and planetary chemical abundances (51 Eri b, beta Pic b, HIP 65426 b, and HR 8799 c and e). Our analysis uses existing data of stellar and planetary atmospheric metallicities, and adopts a Bayesian framework that marginalizes the probabilities of disk conditions, formation locations, planet structures, and accretion physics. We show that these PMOs accrete large amounts of solids regardless of formation channels. On average >50 M_Earth solids (ranging from 38.2 to 294.6 M_Earth for individual systems) are accreted to enrich planet atmospheres. The result implies that the solid accretion process and therefore the planet formation process likely take place at an early stage (<1 Myr) when large amounts of solids are available in young protoplanetary disks.
Taiki Kagetani (University of Tokyo/NAOJ),
Close-in Giant Planets around Low-mass Stars
More than four hundred close-in giant planets around solar-type stars have been discovered to date, with an occurrence rate of ~1 %. For giant planets around solar-type stars, there is a positive correlation between planetoccurrence and stellar metallicity, which is consistent with the predictions of the core-accretion theory. In the framework of the core-accretion theory, it is difficult to form Jupiter-sized giant planets around low-mass stars because of insufficient amounts of materials. However, in recent years, close-in giant planets around low-mass stars have been gradually discovered by TESS, and more are expected to be found in the future. Increasing the sample size and investigating the correlations between the planetary and stellar properties are required to reveal the formation mechanisms of close-in giant planets around low-mass stars. In this talk, I will introduce the mass measurements of TOI-519b, a close-in giant planet around a mid-M dwarf, and present a statistical study using the occurrence rate.
Yixian Chen (Princeton University),
Unorthodox planet-disk interaction: Eccentricity, Turbulence and Winds
When a circular planet is embedded within a laminar protoplanetary disk, the classical circumplanetary flow pattern is prograde – in other words, aligned with the global orbital angular momentum. However, this is non-trivial as the background Keplerian shear is retrograde, and the tidal gravity field must significantly influence the flow to maintain its prograde nature. Using 3D global hydrodynamic simulations, we show that when planet eccentricity is large enough, the circumplanetary flow can become retrograde due to impact velocity relative to the background flow. Likewise, presence of strong turbulence also introduces constantly fluctuating impact velocities, leading to possible randomization of the circumplanetary flow pattern as well as migration torque. On the other hand, in regimes of low turbulence, accretion may be driven by MHD wind instead of turbulent viscosity. We show that the gas radial inflow structure in a windy disk can cause migration torque saturation and gap-opening process to be different from laminar disks, possibly producing distinct dust substructures in sub-millimeter observations.
| Date | Speaker | Title | Remarks | Person in charge |
|---|---|---|---|---|
| Previous semesters | ||||
| 2023/7/20 | Huan-Yu Teng | Exploring Planetary Systems around Evolved Stars through the Radial Velocity Method — The latest results from EAPS-Net | Yuichi Ito | |
| 2023/7/27 | Kei Tanaka | Hot Disks in Massive Star Formation | Kenji Furuya | |
| 2023/8/3 | Yukihiko Hasegawa | Collisional Growth and Fragmentation of Dust Aggregates | Given in Japanese | Kenji Furuya |
| 2023/10/24 | Yuhito Shibaike | Constraints on PDS70 b and c with the dust continuum emission from the circumplanetary discs | Kenji Furuya | |
| 2023/11/14 | Sota Arakawa | Numerical investigations on collisional behaviors of dust aggregates | Kenji Furuya | |
| 2023/11/21 | Yuki Nakamura | Impacts of solar energetic particles on the Martian atmosphere | Yuichi Ito | |
| 2023/11/28 | Takahiro Ueda | A Comprehensive Model of Gravitationally Self-Regulated Protoplanetary Disks Supported by Multiple Observations of the IM Lup Disk | Kenji Furuya | |
| 2024/1/8 | Xiaoyi Ma | Vortex-induced substructures in protoplanetary disks | Akimasa Kataoka Yuichi Ito |
|
| 2024/1/15 | Xinting Yu | Unlocking the Nature of Sub-Neptunes -Atmospheric Characterization in the JWST era | Monday from 14:00 | Kazumasa Ohno Kenji Furuya |
| 2024/1/16 | Nicolas Kaufmann | Population level study of the influence of planetesimal fragmentation on planet formation | Yuhito Shibaike Yuichi Ito |
|
| 2024/2/6 | Yoshiharu Shinnaka | Comet observations | Kenji Furuya | |
Huan-Yu Teng (Tokyo Institute of Technology),
Exploring Planetary Systems around Evolved Stars through the Radial Velocity Method — The latest results from EAPS-Net
The formation of giant planets is debated, with observational evidence needed to refine and augment the theories. In this study, we conduct the continuation of our radial velocity planet survey, the Okayama Planet Search Program (OPSP) and its collaborative East Asian Planet Search Network (EAPS-Net), to search for and characterize planets targeting evolved stars. We have validated diverse planet populations orbiting stars with wide mass range, investigated the correlation between planetary and stellar properties, and discussed planet formation and migration theories for specific planetary systems within OPSP and EAPS-Net framework. In the presentation, I will mainly introduce the latest planet discovery status from EAPS-Net, and focus on the correlation between planetary characteristics and stellar properties, as well as the inference on planet formation from our observations.
Kei Tanaka (Tokyo Institute of Technology),
Hot Disks in Massive Star Formation
Recent high-resolution observations have revealed detailed structures and chemistry in protoplanetary disks around low-mass stars. However, these observations are mostly limited to regions outside the water snowlines with temperatures of <200K. In contrast, accretion disks around massive stars have been found to reach temperatures as high as ~200-1000 K or even hotter due to the intense stellar radiation and high accretion heating. These conditions provide unique opportunities to investigate the physics and chemistry of gas and dust at such high temperatures (e.g., the collisional growth of silicate grains, sublimation of refractory materials, and evaporation of photoionized gas. In this talk, I will introduce our theoretical and observational studies on “hot disks” around massive stars and also discuss some future perspectives for this research in the ngVLA era.
Yukihiko Hasegawa (Tohoku University),
Collisional Growth and Fragmentation of Dust Aggregates
The dust grains grow and fragment through collisions between dust grains in protoplanetary disks. To clarify the evolution process of dust grains, we need to know the detailed physical properties of collisions between dust grains. In this seminar, I’ll talk about collisional outcomes of water-ice dust aggregates with various mass ratios; we particularly focus on unequal-mass offset collisions. We carried out three-dimensional numerical N-body simulations of collisions between two dust aggregates in a wide range of the mass ratio 1-64. First, we found that the mass transfer from a larger target to a smaller projectile is a dominant process in collisions with a mass ratio higher than 3. As a result, the critical velocity for fragmentation of the largest body is considerably reduced due to the mass transfer for such unequal-mass collisions; the critical velocity of collisions with a mass ratio of 3 is about half of that obtained from equal-mass collisions. Next, we derived analytic expressions of the mass distribution of large remnants and small fragments by numerical fitting to the simulation results. Our analytic formulae for masses of the large remnants can reproduce the contribution of mass transfer from a larger target to a smaller projectile. Our fragment model can roughly reproduce the results of our simulations and be applied to statistical simulations of the dust evolution.
Yuhito Shibaike (NAOJ),
Constraints on PDS70 b and c with the dust continuum emission from the circumplanetary discs
A young T Tauri star PDS70 has two gas accreting planets sharing one large gap in a pre-transitional disc. Dust continuum emission from PDS70 c has been detected by Atacama Large Millimeter/submillimeter Array (ALMA) Band 7, considered as the evidence of the circumplanetary disc (CPDs). However, there has been no detection of the dust emission from the CPD of PDS70 b. We constrained the planet mass and the gas accretion rates of the planets by introducing a dust evolution model to the CPDs and reproducing the observations, which is the first case to succeed in obtaining the constraints on the planet properties with the dust continuum emission from CPDs. Summarizing the obtained constraints, I will also discuss a possible scenario for the two planets explaining consistently their observations.
Sota Arakawa (JAMSTEC),
Numerical investigations on collisional behaviors of dust aggregates
Understanding the collisional behavior of dust aggregates is essential in the context of planet formation. It is known that low-velocity collisions of dust aggregates result in bouncing rather than sticking when the filling factor of colliding dust aggregates is higher than a threshold value. However, a large discrepancy between numerical and experimental results on the threshold filling factor was reported so far. In this study, we perform numerical simulations using soft-sphere discrete element methods and demonstrate that the sticking probability decreases with increasing aggregate radius. Our results suggest that the large discrepancy in the threshold filling factor may reflect the difference in the size of dust aggregates in earlier numerical simulations and laboratory experiments.
Yuki Nakamura(The University of Tokyo),
Impacts of solar energetic particles on the Martian atmosphere
Solar energetic particles (SEPs) are high-energy (from a few tens of keV to GeV) charged particles consisting mainly of electrons and protons ejected from the Sun associated with solar flares and coronal mass ejections. Precipitation of SEPs into planetary atmospheres causes changes in atmospheric chemical composition through ionization, dissociation, and excitation of atmospheric molecules. In contrast to the Earth’s atmosphere, where the destruction of ozone by SEPs in the polar mesosphere has been studied by observations and models for decades, the effect of SEPs on the atmospheric composition on Mars is far from understood. Understanding the effects of solar energetic particles (SEPs) on the atmospheric chemistry on Mars is of astrobiological interest because the precipitation of SEPs into the early Martian atmosphere could have facilitated the prebiotic chemistry. In this talk, I will introduce recent updates on the impacts of SEPs on the Martian atmosphere.
Takahiro Ueda (MPIA),
A Comprehensive Model of Gravitationally Self-Regulated Protoplanetary Disks Supported by Multiple Observations of the IM Lup Diskgetic particles on the Martian atmosphere
Protoplanetary disk, a birthplace of planets, is believed to be gravitationally unstable in its early phase of evolution. We develop a theoretical model of the gravitationally self-regulated disk around IM Lup, comprehensively explaining multiple observations of the disk. Our findings indicate that dust particles need to be fragile in order to maintain a sufficient amount responsible for the observed millimeter emission. Preferably, the dust should be moderately porous to account for the observed millimeter polarization. Another key finding is that the inner region is likely heated by gas accretion. The accretion heating naturally accounts for the bright millimeter emission within 20 au around IM Lup. The actively-heated inner region cast a 100-au-scale shadow, which is in good agreement with the previous near-infrared scattered light observation. The fragile dust is also preferred to maintain enough optical thickness for accretion heating to be the dominant source of heating. The fragile dust makes it unlikely for a giant planet to form beyond 50 au within IM Lup’s age, suggesting that any giant planet responsible for the substructures seen in the ALMA observations, if present, likely formed via gravitational instability. Conversely, the less turbulent inner region with abundant pebbles is favorable for the formation of planetesimals/planets within 1 Myr.
Xiaoyi Ma (University of Victoria),
Vortex-induced substructures in protoplanetary disks
The presence of both crescents and rings has been observed in protoplanetary disks through dust continuum emission. The crescents in continuum emission have been proposed to be dust-trapping vortices produced by the Rossby Wave Instability (RWI). Our hypothesis suggests that these RWI vortices may induce rings and gaps by driving density waves, analogous to those induced by planets. To explore this, we investigate the properties of density waves and substructures generated by the vortices through 2D hydrodynamic simulations conducted with Athena++ for a shearing box. Our work successfully confirms that the vortices can produce rings and gaps in the disk, comparable to ALMA dust continuum observations.
Xinting Yu (University of Texas San Antoni),
Unlocking the Nature of Sub-Neptunes: Atmospheric Characterization in the JWST era
In the upcoming era of the James Webb Space Telescope (JWST), the field of exoplanet research is poised for transformative discoveries. This talk will delve into my recent work on leveraging atmospheric characterization techniques to identify surface conditions on sub-Neptunes. These enigmatic worlds, which defy easy classification, offer a unique opportunity to study planetary formation, evolution, and even habitability. I will discuss the methodologies employed in transmission spectroscopy to probe the atmospheres of sub-Neptunes and how these data can be used to infer surface conditions. I will also touch on some experimental works on planetary hazes that support exoplanet characterization in the JWST era.
Nicolas Kaufmann (University of Bern),
Population level study of the influence of planetesimal fragmentation on planet formation
The size distribution of solids in the protoplanetary disk is still ill constrained and evolves significantly throughout plant formation by various processes. As the planets grow, they excite the mutual random velocities among planetesimals, making collisions between them destructive. This leads to their fragmentation changing the typical size of solids accreted by protoplanets. I will show the impact planetesimal collisional fragmentation has on planet formation employing a population synthesis approach. The synthesis is performed by varying the initial conditions based on observations of disks to generate synthetic exoplanet populations. Our results show that planetesimal fragmentation, in conjunction with radial drift and the interactions with the gas disk, can either promote or hinder planet formation, depending on the typical size of fragments produced in collisions. In addition, the enhanced radial drift of the smaller fragments also changes the typical origin of accreted solids affecting the composition of the forming planets.
Shinnaka Yoshiharu (Kyoto Sangyo University),
Comet observations: science background and open questions
Comets are thought to be one of the pristine objects in our solar system, holding crucial clues about its early stages. In this presentation, I will introduce recent advancements in cometary science, primarily based on our observational results. The focus will be on exploring the relationship between derived physical parameters (such as chemical compositions, isotopic ratios, mineral compositions, and more) and the conditions under which comets formed in the solar nebula. Additionally, I will highlight recent studies on interstellar objects, which represent potential pristine objects beyond our solar system.