Photophoresis on particles hotter/colder than the ambient gas in the free molecular flow

Loesche, C.; Wurm, Gerhard; Jankowski, Tim; Kuepper, Markus

doi:10.1016/j.jaerosci.2016.04.001

Cited by 19 publications

(9 citation statements)

References 26 publications

(51 reference statements)

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“…Further increases in pressure reduce -force as P −2 , which is faster than the P −1 scaling that is typical for the temperature difference forces (20) (see the Supplementary Materials for full formulation). Our model follows the well-established semi-empirical approach (8,13,19,24) to predict the total lift force but not its different components such as area force, edge force, and shear force, which were previously calculated for radiometers (38). While the separation of force components can provide additional theoretical insights, such detailed analysis requires Figure 2A shows the predicted areal density of an object that can be levitated using -force with  = 0.15 ± 0.05 and flux of ~0.5 W _ cm 2 (~5 times the direct sunlight intensity on the surface of Earth and ~4 times the direct sunlight intensity in the upper atmosphere) as well as the results of our experiments with the CNT-covered mylar disk.…”

Section: Resultsmentioning

confidence: 99%

“…Recent photophoresis studies have primarily focused on microscopic particles in atmospheric aerosols (11)(12)(13)(14)(15) and the optical trapping of microscopic particles, for example, to create threedimensional displays (16). In the free molecular regime, where the mean free path  is much larger than the characteristic size a of the object, the photophoretic force results from the difference in the velocity of the incident and departing gas molecules from a hot surface (17)(18)(19). In the continuum regime ( ≪ a), the force is generated through the thermal creep of the gas over the edges of the sample from the cold side to the hot side (20)(21)(22)(23).…”

Section: Introductionmentioning

confidence: 99%

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Controlled levitation of nanostructured thin films for sun-powered near-space flight

et al. 2021

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We report light-driven levitation of macroscopic polymer films with nanostructured surface as candidates for long-duration near-space flight. We levitated centimeter-scale disks made of commercial 0.5-micron-thick mylar film coated with carbon nanotubes on one side. When illuminated with light intensity comparable to natural sunlight, the polymer disk heats up and interacts with incident gas molecules differently on the top and bottom sides, producing a net recoil force. We observed the levitation of 6-mm-diameter disks in a vacuum chamber at pressures between 10 and 30 Pa. Moreover, we controlled the flight of the disks using a shaped light field that optically trapped the levitating disks. Our experimentally validated theoretical model predicts that the lift forces can be many times the weight of the films, allowing payloads of up to 10 milligrams for sunlight-powered low-cost microflyers at altitudes of 50 to 100 km.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Controlled levitation of nanostructured thin films for sun-powered near-space flight

et al. 2021

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“…The experiments and numerical simulations led to better quantification of photophoretic forces, as given by Loesche et al [117] and Loesche and Husmann [118], i.e., at low protoplanetary disk pressures, photophoretic motion due to temperature differences induced by illumination with a given light flux (I) was approximated with high accuracy by [117]:…”

Section: Photophoresismentioning

confidence: 94%

Selective Aggregation Experiments on Planetesimal Formation and Mercury-Like Planets

Wurm¹

2018

Geosciences

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Much of a planet's composition could be determined right at the onset of formation. Laboratory experiments can constrain these early steps. This includes static tensile strength measurements or collisions carried out under Earth's gravity and on various microgravity platforms. Among the variety of extrasolar planets which eventually form are (Exo)-Mercury, terrestrial planets with high density. If they form in inner protoplanetary disks, high temperature experiments are mandatory but they are still rare. Beyond the initial process of hit-and-stick collisions, some additional selective processing might be needed to explain Mercury. In analogy to icy worlds, such planets might, e.g., form in environments which are enriched in iron. This requires methods to separate iron and silicate at early stages. Photophoresis might be one viable way. Mercury and Mercury-like planets might also form due to the ferromagnetic properties of iron and mechanisms like magnetic aggregation in disk magnetic fields might become important. This review highlights some of the mechanisms with the potential to trigger Mercury formation.

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“…The magnitude of this additional force on particles is proportional to the regions' thermal gradient, and the size of the particles themselves (Krauss & Wurm 2005). Thus, it is possible for particles to be size-sorted through this process (Loesche et al 2016). Since the mid-plane of proto-planetary disks is thought to be highly opaque, it is unclear whether this mechanism plays a significant role in altering the chemistry of the material near Mercury's modern orbit (e.g.…”

Section: Iron-enrichment Of the Mercury-forming Planetesimalsmentioning

confidence: 99%

Dynamical avenues for Mercury's origin II: in-situ formation in the inner terrestrial disk

Clement,

Chambers

2021

Preprint

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Modern terrestrial planet formation models are highly successful at consistently generating planets with masses and orbits analogous to those of Earth and Venus. In stark contrast to classic theoretical predictions and inferred demographics of multi-planet systems of rocky exoplanets, the mass ( 10) and orbital period ( 2) ratios between Venus and Earth and the neighboring Mercury and Mars are not common outcomes in numerically generated systems. While viable solutions to the small-Mars problem are abundant in the literature, Mercury's peculiar origin remains rather mysterious. In this paper, we investigate the possibility that Mercury formed in a mass-depleted, inner region of the terrestrial disk (a < 0.5 au). This regime is often neglected in terrestrial planet formation models because of the high computational cost of resolving hundreds of short-period objects over ∼100 Myr timescales. By testing multiple disk profiles and mass distributions, we identify several promising sets of initial conditions that lead to remarkably successful analog systems. In particular, our most successful simulations consider moderate total masses of Mercury-forming material (0.1-0.25 Earth masses). While larger initial masses tend to yield disproportionate Mercury analogs, smaller values often inhibit the planets' formation as the entire region of material is easily accreted by Venus. Additionally, we find that shallow surface density profiles and larger inventories of small planetesimals moderately improve the likelihood of adequately reproducing Mercury.

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Photophoresis on particles hotter/colder than the ambient gas in the free molecular flow

Cited by 19 publications

References 26 publications

Controlled levitation of nanostructured thin films for sun-powered near-space flight

Controlled levitation of nanostructured thin films for sun-powered near-space flight

Selective Aggregation Experiments on Planetesimal Formation and Mercury-Like Planets

Dynamical avenues for Mercury's origin II: in-situ formation in the inner terrestrial disk

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