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Dimitar D. Sasselov

Publications and source records attributed to Dimitar D. Sasselov.

At least 19 recordsLinked to original sources
arXiv2026

Prebiotic magnetite enables chirality-magnetic surface feedback

The emergence of biomolecular homochirality requires both an initial symmetry-breaking event and a mechanism to amplify and preserve a chiral imbalance. Magnetic minerals have been shown to function as chiral agents through the chiral-induced spin selectivity (CISS) effect and may have enabled homochirality on early Earth, yet the magnetic properties of magnetite formed under realistic prebiotic conditions remain unexplored. Here we show that magnetite synthesized through two geochemically plausible pathways - UV-driven photo-oxidation and nitrite-mediated oxidation of Fe(II) - produces particles dominated by single-vortex and multi-vortex magnetic domain states. Magnetic measurements and electron microscopy confirm that these populations differ markedly from the nano-fabricated thin-film substrates conventionally used in previous CISS experiments. Using 3D micromagnetic simulations, we demonstrate that single-domain and vortex-state grains undergo irreversible, exchange-driven re-magnetization when interacting with spin-polarized homochiral compounds. This magnetic irreversibility provides a robust mechanism for storing and reinforcing weak chiral bias, suggesting that prebiotic magnetite could have contributed to the emergence and stabilization of persistent chiral bias on the early Earth.

physics.chem-ph↗
arXiv2026

Temperature-Enhanced Coercive Field by Chiral Molecules

The chiral-induced spin selectivity (CISS) effect demonstrates a strong coupling between electron spin and molecular chirality, enabling spin-controlled interactions between chiral molecules and magnetic surfaces. While CISS experiments have revealed robust changes in the spin-polarization properties of magnetic materials upon chiral molecular adsorption, the temperature dependence of these effects remains poorly understood. Here, we investigate the temperature dependence of the chirality-induced increase in magnetic coercivity by ribose-aminooxazoline (RAO) crystals on ferromagnetic surfaces. RAO was selected as a conglomerate-forming, thermodynamically stable crystalline chiral organic molecule with prebiotic relevance that has previously been shown to induce strong spin-dependent changes in magnetic minerals. Contrary to classical expectations that magnetic coercivity weakens at elevated temperatures, we observe a significant increase in magnetic coercivity (1 mT over a 60 C temperature change) with increasing temperature. These results support a vibronic contribution to CISS arising from electron-phonon interactions and demonstrate that spin-dependent interactions between chiral molecules and magnetic surfaces can become more effective at higher temperatures, providing new insight into the microscopic origins of CISS and the environmental robustness of spin-controlled asymmetric processes.

physics.chem-ph↗
arXiv2024

Chiral Phonons Enhance Ferromagnetism

Recent experiments suggest that the conditions for ferromagnetic order in, e.g., magnetite, can be modified by adsorption of chiral molecules. Especially, the coercivity of magnetite was increased by nearly 100 \%, or 20 times the earth magnetic flux density, at room temperature. The coercivity was, moreover, demonstrated to increase linearly with temperature in a finite range around room temperature. Based on these results, a mechanism is proposed for providing the necessary enhancement of the magnetic anisotropy. It is shown that nuclear vibrations (phonons) coupled to ferromagnetic spin excitations (magnons) absorb the thermal energy in the system, thereby diverting the excess energy that otherwise would excite magnons in the ferromagnet. This energy diversion, not only restores the ferromagnetic order but also enhances its stability by increasing the anisotropy energy for magnon excitations. The coupling between phonons with magnons is enabled by chirality due to the lack of inversion symmetry.

cond-mat.mtrl-sci↗
arXiv2023

The central dogma of biological homochirality: How does chiral information propagate in a prebiotic network?

Biological systems are homochiral, raising the question of how a racemic mixture of prebiotically synthesized biomolecules could attain a homochiral state at the network level. Based on our recent results, we aim to address a related question of how chiral information might have flowed in a prebiotic network. Utilizing the crystallization properties of the central RNA precursor known as ribose-aminooxazoline (RAO), we showed that its homochiral crystals can be obtained from its fully racemic solution on a magnetic mineral surface, due to the chiral-induced spin selectivity (CISS) effect. Moreover, we uncovered a mechanism facilitated by the CISS effect through which chiral molecules, like RAO, can uniformly magnetize such surfaces in a variety of planetary environments in a persistent manner. All this is very tantalizing, because recent experiments with tRNA analogs demonstrate high stereoselectivity in the attachment of L-amino acids to D-ribonucleotides, enabling the transfer of homochirality from RNA to peptides. Therefore the biological homochirality problem may be reduced to ensuring that a single common RNA precursor (e.g. RAO) can be made homochiral. The emergence of homochirality at RAO then allows for the chiral information to propagate through RNA, then to peptides, and ultimately, through enantioselective catalysis, to metabolites. This directionality of the chiral information flow parallels that of the central dogma of molecular biology--the unidirectional transfer of genetic information from nucleic acids to proteins.

physics.bio-ph↗
arXiv2023

Chirality-Induced Magnetization of Magnetite by an RNA Precursor

Life is homochiral and homochirality is a fundamental feature of living systems on Earth. While the exact mechanism that led to homochirality is still not fully understood, any realistic scenario on the origins of life needs to address the emergence of homochirality. In order to impose and maintain chirality in a prebiotic network, an environmental factor functioning as a chiral agent is demanded. Magnetized surfaces are prebiotically plausible chiral agents, shown to be effective in enantioseparation of ribose-aminooxazoline (RAO), a ribonucleic acid (RNA) precursor, due to the chiral-induced spin selectivity (CISS) effect. As such, mechanisms for breaking the magnetic symmetry of magnetic minerals are of the utmost importance. Here we report the avalanche magnetization of magnetite $(Fe_{3}O_{4})$ by the crystallization of enantiopure RAO. The observed breaking of the magnetic symmetry is induced by the chiral molecules due to the CISS effect and spreads out across the magnetic surface like an avalanche, providing a way to uniformly magnetize a magnetic surface without fully covering it. Considered together with our previous results on enantioseparation by crystallization on a magnetic surface, chirality-induced avalanche magnetization paves the way for a cooperative feedback between chiral molecules and magnetic surfaces. With this feedback, a weak natural bias in the net magnetization can be amplified and spin-selective processes can be accommodated on magnetic minerals on a persistent basis.

physics.chem-ph↗
arXiv2023

Origin of Biological Homochirality by Crystallization of an RNA Precursor on a Magnetic Surface

Homochirality is a signature of life on Earth yet its origins remain an unsolved puzzle. Achieving homochirality is essential for a high-yielding prebiotic network capable of producing functional polymers like ribonucleic acid (RNA) and peptides. However, a prebiotically plausible and robust mechanism to reach homochirality has not been shown to this date. The chiral-induced spin selectivity (CISS) effect has established a strong coupling between electron spin and molecular chirality and this coupling paves the way for breaking the chiral molecular symmetry by spin-selective processes. Magnetic surfaces can act as chiral agents due to the CISS effect and they can be templates for the enantioselective crystallization of chiral molecules. Here we studied the spin-selective crystallization of racemic ribo aminooxazoline (RAO), an RNA precursor, on magnetite ($Fe_3O_4$) surfaces, achieving an unprecedented enantiomeric excess of about 60$\%$. Following the initial enrichment, we then obtained homochiral crystals of RAO after a subsequent crystallization. Our work combines two necessary features for reaching homochirality: chiral symmetry-breaking induced by the magnetic surface and self-amplification by conglomerate crystallization of RAO. Our results demonstrate a prebiotically plausible way of achieving systems level homochirality from completely racemic starting materials.

physics.bio-ph↗
arXiv2022

EOS Manual

The exoplanet field now abounds with new discoveries of planets and planetary systems. It is of great interest for the scientific community to understand the compositions and internal structures of these new planets outside our own solar system, and then infer their formation scenarios. In particular, the proper implementation of the equation-of-states of various matters into the calculation of internal structure is crucial. Thus, we have come up with this write-up that provides the detailed steps to turn an equation-of-state (EOS) into a mass-radius relation of exoplanets, and highlight the physics and chemistry involved in these calculations. It must be visualized!

astro-ph.EP↗
arXiv2022

On the Origins of Life's Homochirality: Inducing Enantiomeric Excess with Spin-Polarized Electrons

Life as we know it is homochiral, but the origins of biological homochirality on early Earth remain elusive. Shallow closed-basin lakes are a plausible prebiotic environment on early Earth, and most are expected to have significant sedimentary magnetite deposits. We hypothesize that UV (200-300nm) irradiation of magnetite deposits could generate hydrated spin-polarized electrons sufficient to induce chirally selective prebiotic chemistry. Such electrons are potent reducing agents that drive reduction reactions where the spin polarization direction can alter enantioselectively the reaction kinetics. Our estimate of this chiral bias is based on the strong effective spin-orbit coupling observed in the chiral-induced spin selectivity (CISS) effect, as applied to energy differences in reduction reactions for different isomers. In the original CISS experiments, spin selective electron transmission through a monolayer of dsDNA molecules is observed at room temperature - indicating a strong coupling between molecular chirality and electron spin. We propose that the chiral symmetry breaking due to the CISS effect, when applied to reduction chemistry, can induce enantioselective synthesis on the prebiotic Earth and thus facilitate the homochiral assembly of life's building blocks.

physics.chem-ph↗
arXiv2022

New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State

Recent astronomical observations obtained with the Kepler and TESS missions and their related ground-based follow-ups revealed an abundance of exoplanets with a size intermediate between Earth and Neptune. A low occurrence rate of planets has been identified at around twice the size of Earth, known as the exoplanet radius gap or radius valley. We explore the geometry of this gap in the mass-radius diagram, with the help of a Mathematica plotting tool developed with the capability of manipulating exoplanet data in multidimensional parameter space, and with the help of visualized water equations of state in the temperature-density graph and the entropy-pressure graph. We show that the radius valley can be explained by a compositional difference between smaller, predominantly rocky planets and larger planets that exhibit greater compositional diversity including cosmic ices (water, ammonia, methane) and gaseous envelopes. In particular, among the larger planets, when viewed from the perspective of planet equilibrium temperature, the hot ones are consistent with ice-dominated composition without significant gaseous envelopes, while the cold ones have more diverse compositions, including various amounts of gaseous envelopes.

astro-ph.EP↗
arXiv2021

UV Transmission in Natural Waters on Prebiotic Earth

Ultraviolet (UV) light plays a key role in surficial theories of the origin of life, and numerous studies have focused on constraining the atmospheric transmission of UV radiation on early Earth. However, the UV transmission of the natural waters in which origins-of-life chemistry (prebiotic chemistry) is postulated to have occurred is poorly constrained. In this work, we combine laboratory and literature-derived absorption spectra of potential aqueous-phase prebiotic UV absorbers with literature estimates of their concentrations on early Earth to constrain the prebiotic UV environment in marine and terrestrial natural waters, and consider the implications for prebiotic chemistry. We find that prebiotic freshwaters were largely transparent in the UV, contrary to assumptions by some models of prebiotic chemistry. Some waters, e.g., high-salinity waters like carbonate lakes, may be deficient in shortwave ($\leq220$ nm) UV flux. More dramatically, ferrous waters can be strongly UV-shielded, particularly if the Fe$^{2+}$ forms highly UV-absorbent species like Fe(CN)$_6^{4-}$. Such waters may be compelling venues for UV-averse origin-of-life scenarios, but are disfavorable for some UV-dependent prebiotic chemistries. UV light can trigger photochemistry even if attenuated through photochemical transformations of the absorber (e.g., $e^{-}_{aq}$ production from halide irradiation), which may have both constructive and destructive effects for prebiotic syntheses. Prebiotic chemistries invoking waters containing such absorbers must self-consistently account for the chemical effects of these transformations. The speciation and abundance of Fe$^{2+}$ in natural waters on early Earth is a major uncertainty, and should be prioritized for further investigation as it plays a major role in UV transmission in prebiotic natural waters.

astro-ph.EP↗
arXiv2021

The TESS Mission Target Selection Procedure

We describe the target selection procedure by which stars are selected for 2-minute and 20-second observations by TESS. We first list the technical requirements of the TESS instrument and ground systems processing that limit the total number of target slots. We then describe algorithms used by the TESS Payload Operation Center (POC) to merge candidate targets requested by the various TESS mission elements (the Target Selection Working Group, TESS Asteroseismic Science Consortium, and Guest Investigator office). Lastly, we summarize the properties of the observed TESS targets over the two-year primary TESS mission. We find that the POC target selection algorithm results in 2.1 to 3.4 times as many observed targets as target slots allocated for each mission element. We also find that the sky distribution of observed targets is different from the sky distributions of candidate targets due to technical constraints that require a relatively even distribution of targets across the TESS fields of view. We caution researchers exploring statistical analyses of TESS planet-host stars that the population of observed targets cannot be characterized by any simple set of criteria applied to the properties of the input Candidate Target Lists.

astro-ph.IM↗
arXiv2021

The TESS Objects of Interest Catalog from the TESS Prime Mission

We present 2,241 exoplanet candidates identified with data from the Transiting Exoplanet Survey Satellite (TESS) during its two-year prime mission. We list these candidates in the TESS Objects of Interest (TOI) Catalog, which includes both new planet candidates found by TESS and previously-known planets recovered by TESS observations. We describe the process used to identify TOIs and investigate the characteristics of the new planet candidates, and discuss some notable TESS planet discoveries. The TOI Catalog includes an unprecedented number of small planet candidates around nearby bright stars, which are well-suited for detailed follow-up observations. The TESS data products for the Prime Mission (Sectors 1-26), including the TOI Catalog, light curves, full-frame images, and target pixel files, are publicly available on the Mikulski Archive for Space Telescopes.

astro-ph.EP↗
arXiv2019

Growth Model Interpretation of Planet Size Distribution

The radii and orbital periods of 4000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. The radii show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) and larger intermediate-size planets, respectively. While only the masses of the planets orbiting the brightest stars can be determined by ground-based spectroscopic observations, these observations allow calculation of their average densities placing constraints on the bulk compositions and internal structures. Yet an important question about the composition of planets ranging from 2 to 4 Earth radii still remains. They may either have a rocky core enveloped in a H2-He gaseous envelope (gas dwarfs) or contain a significant amount of multi-component, H2O-dominated ices/fluids (water worlds). Planets in the mass range of 10-15 Earth masses, if half-ice and half-rock by mass, have radii of 2.5 Earth radii, which exactly match the second peak of the exoplanet radius bimodal distribution. Any planet in the 2-4 Earth radii range requires a gas envelope of at most a few mass percentage points, regardless of the core composition. To resolve the ambiguity of internal compositions, we use a growth model and conduct Monte Carlo simulations to demonstrate that many intermediate-size planets are water worlds.

astro-ph.EP↗
arXiv2019

Nitrogen Oxide Concentrations in Natural Waters on Early Earth

A key challenge in origins-of-life studies is estimating the abundances of species relevant to the chemical pathways proposed to have contributed to the emergence of life on early Earth. Dissolved nitrogen oxide anions (NO$_{X}^{-}$), in particular nitrate (NO$_{3}^{-}$) and nitrite (NO$_{2}^{-}$), have been invoked in diverse origins-of-life chemistry, from the oligomerization of RNA to the emergence of protometabolism. Recent work has calculated the supply of NO$_{X}^{-}$ from the prebiotic atmosphere to the ocean, and reported steady-state [NO$_{X}^{-}$] to be high across all plausible parameter space. These findings rest on the assumption that NO$_{X}^{-}$ is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NO$_{X}^{-}$ is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron (Fe$^{2+}$) suppress [NO$_{X}^{-}$] by several orders of magnitude relative to past predictions. For pH$=6.5-8$ and $T=0-50^\circ$C, we find that it is most probable that NO$_{X}^{-}$]$<1~μ$M in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [NO$_{X}^{-}$]$\geq 1~μ$M. As on modern Earth, most NO$_{X}^{-}$ on prebiotic Earth should have been present as NO$_{3}^{-}$, due to its much greater stability. These findings inform the kind of prebiotic chemistries that would have been possible on early Earth. We discuss the implications for proposed prebiotic chemistries, and highlight the need for further studies of NO$_{X}^{-}$ kinetics to reduce the considerable uncertainties in predicting [NO$_{X}^{-}$] on early Earth.

astro-ph.EP↗
arXiv2018

Survival Function Analysis of Planet Size Distribution with GAIA Data Release 2 Updates

Applying the survival function analysis to the planet radius distribution of the Kepler confirmed/candidate planets, we have identified two natural divisions of planet radius at 4 Earth radii and 10 Earth radii. These divisions place constraints on planet formation and interior structure model. The division at 4 Earth radii separates small exoplanets from large exoplanets above. When combined with the recently-discovered radius gap at 2 Earth radii, it supports the treatment of planets 2-4 Earth radii as a separate group, likely water worlds. For planets around solar-type FGK main-sequence stars, we argue that 2 Earth radii is the separation between water-poor and water-rich planets, and 4 Earth radii is the separation between gas-poor and gas-rich planets. We confirm that the slope of survival function in between 4 and 10 Earth radii to be shallower compared to either ends, indicating a relative paucity of planets in between 4-10 Earth radii, namely, the sub-Saturnian desert there. We name them transitional planets, as they form a bridge between the gas-poor small planets and gas giants. Accordingly, we propose the following classification scheme: (<2 Earth radii) rocky planets, (2-4 Earth radii) water worlds, (4-10 Earth radii) transitional planets, and (>10 Earth radii) gas giants.

astro-ph.EP↗
arXiv2018

Exoplanet Science Priorities from the Perspective of Internal and Surface Processes for Silicate and Ice Dominated Worlds

The geophysics of extrasolar planets is a scientific topic often regarded as standing largely beyond the reach of near-term observations. This reality in no way diminishes the central role of geophysical phenomena in shaping planetary outcomes, from formation, to thermal and chemical evolution, to numerous issues of surface and near-surface habitability. We emphasize that for a balanced understanding of extrasolar planets, it is important to look beyond the natural biases of current observing tools, and actively seek unique pathways to understand exoplanet interiors as best as possible during the long interim prior to a time when internal components are more directly accessible. Such pathways include but are not limited to: (a) enhanced theoretical and numerical modeling, (b) laboratory research on critical material properties, (c) measurement of geophysical properties by indirect inference from imprints left on atmospheric and orbital properties, and (d) the purpose-driven use of Solar System object exploration expressly for its value in comparative planetology toward exoplanet-analogs. Breaking down barriers that envision local Solar System exploration, including the study of Earth's own deep interior, as separate from and in financial competition with extrasolar planet research, may greatly improve the rate of needed scientific progress for exoplanet geophysics. As the number of known rocky and icy exoplanets grows in the years ahead, we expect demand for expertise in 'exogeoscience' will expand at a commensurately intense pace. We highlight key topics, including: how water oceans below ice shells may dominate the total habitability of our galaxy by volume, how free-floating nomad planets may often attain habitable subsurface oceans supported by radionuclide decay, and how deep interiors may critically interact with atmospheric mass loss via dynamo-driven magnetic fields.

astro-ph.EP↗
arXiv2018

Highly Volcanic Exoplanets, Lava Worlds, and Magma Ocean Worlds: An Emerging Class of Dynamic Exoplanets of Significant Scientific Priority

Highly volcanic exoplanets, which can be variously characterized as 'lava worlds', 'magma ocean worlds', or 'super-Ios' are high priority targets for investigation. The term 'lava world' may refer to any planet with extensive surface lava lakes, while the term 'magma ocean world' refers to planets with global or hemispherical magma oceans at their surface. 'Highly volcanic planets', including super-Ios, may simply have large, or large numbers of, active explosive or extrusive volcanoes of any form. They are plausibly highly diverse, with magmatic processes across a wide range of compositions, temperatures, activity rates, volcanic eruption styles, and background gravitational force magnitudes. Worlds in all these classes are likely to be the most characterizable rocky exoplanets in the near future due to observational advantages that stem from their preferential occurrence in short orbital periods and their bright day-side flux in the infrared. Transit techniques should enable a level of characterization of these worlds analogous to hot Jupiters. Understanding processes on highly volcanic worlds is critical to interpret imminent observations. The physical states of these worlds are likely to inform not just geodynamic processes, but also planet formation, and phenomena crucial to habitability. Volcanic and magmatic activity uniquely allows chemical investigation of otherwise spectroscopically inaccessible interior compositions. These worlds will be vital to assess the degree to which planetary interior element abundances compare to their stellar hosts, and may also offer pathways to study both the very young Earth, and the very early form of many silicate planets where magma oceans and surface lava lakes are expected to be more prevalent. We suggest that highly volcanic worlds may become second only to habitable worlds in terms of both scientific and public long-term interest.

astro-ph.EP↗