10 research outputs found
Tensile Strength of Porous Dust Aggregates
Comets are thought to have information about the formation process of our
solar system. Recently, detailed information about comet
67P/Churyumov-Gerasimenko has been found by a spacecraft mission Rosetta. It is
remarkable that its tensile strength was estimated. In this paper, we measure
and formulate the tensile strength of porous dust aggregates using numerical
simulations, motivated by porous dust aggregation model of planetesimal
formation. We perform three-dimensional numerical simulations using a monomer
interaction model with periodic boundary condition. We stretch out a dust
aggregate with a various initial volume filling factor between and
0.5. We find that the tensile stress takes the maximum value at the time when
the volume filling factor decreases to about a half of the initial value. The
maximum stress is defined to be the tensile strength. We take an average of the
results with 10 different initial shapes to smooth out the effects of initial
shapes of aggregates. Finally, we numerically obtain the relation between the
tensile strength and the initial volume filling factor of dust aggregates. We
also use a simple semi-analytical model and successfully reproduce the
numerical results, which enables us to apply to a wide parameter range and
different materials. The obtained relation is consistent with previous
experiments and numerical simulations about silicate dust aggregates. We
estimate that the monomer radius of comet 67P has to be about 3.3--220
to reproduce its tensile strength using our model.Comment: 12 pages, 12 figures, accepted for publication in Ap
Formulating Compressive Strength of Dust Aggregates from Low to High Volume Filling Factors with Numerical Simulations
Compressive strength is a key to understanding the internal structure of dust
aggregates in protoplanetary disks and their resultant bodies, such as comets
and asteroids in the Solar System. Previous work has modeled the compressive
strength of highly-porous dust aggregates with volume filling factors lower
than 0.1. However, a comprehensive understanding of the compressive strength
from low () volume filling factors is lacking. In this
paper, we investigate the compressive strength of dust aggregates by using
aggregate compression simulations resolving constituent grains based on JKR
theory to formulate the compressive strength comprehensively. We perform a
series of numerical simulations with moving periodic boundaries mimicking the
compression behavior. As a result, we find that the compressive strength
becomes sharply harder when the volume filling factor exceeds 0.1. We succeed
in formulating the compressive strength comprehensively by taking into account
the rolling motion of aggregates for low volume filling factors and the closest
packing of aggregates for high volume filling factors. We also find that the
dominant compression mechanisms for high volume filling factors are sliding and
twisting motions, while rolling motion dominates for low volume filling
factors. We confirm that our results are in good agreement with previous
numerical studies. We suggest that our analytical formula is consistent with
the previous experimental results if we assume the surface energy of silicate
is . Now, we can apply our results to
properties of small compact bodies, such as comets, asteroids, and pebbles.Comment: 15 pages, 12 figures, accepted for publication in Ap
The K2-ESPRINT Project III: A Close-in Super-Earth around a Metal-rich Mid-M Dwarf
We validate a planet on a close-in orbit
( days) around K2-28 (EPIC 206318379), a metal-rich
M4-type dwarf in the Campaign 3 field of the K2 mission. Our follow-up
observations included multi-band transit observations from the optical to the
near infrared, low-resolution spectroscopy, and high-resolution adaptive-optics
(AO) imaging. We perform a global fit to all the observed transits using a
Gaussian process-based method and show that the transit depths in all passbands
adopted for the ground-based transit follow-ups () are within of the K2 value. Based on a model of
the background stellar population and the absence of nearby sources in our AO
imaging, we estimate the probability that a background eclipsing binary could
cause a false positive to be . We also show that K2-28
cannot have a physically associated companion of stellar type later than M4,
based on the measurement of almost identical transit depths in multiple
passbands. There is a low probability for a M4 dwarf companion (), but even if this were the case, the size of K2-28b
falls within the planetary regime. K2-28b has the same radius (within
) and experiences a similar irradiation from its host star as the
well-studied GJ~1214b. Given the relative brightness of K2-28 in the near
infrared ( mag and mag) and relatively deep
transit (), a comparison between the atmospheric properties of these
two planets with future observations would be especially interesting.Comment: 11 pages, 9 figures, accepted to Ap
Size Dependence of the Bouncing Barrier in Protoplanetary Dust Growth
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