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Simulation of the density of the Milky Way's dark matter halo

New simulations show how the outer regions of the Milky Way are shaped by the motion of its largest satellite galaxy, the Large Magellanic Cloud (LMC). Using 100 million simulated dark matter particles, a team led by Nicolás Garavito-Camargo (Steward Observatory, University of Arizona) shows that the LMC creates a wake in the Milky Way’s dark matter halo, like a ship traveling across the ocean, as it swings past our galaxy. The friction between the LMC and the Milky Way’s halo will cause the smaller galaxy to lose energy and eventually merge with the Milky Way. The gravitational influence of the LMC introduces an asymmetry into the roughly spherical dark matter halo, which is shown in the above image and in the video below. By pairing simulations like this one with the wealth of data from upcoming all-sky surveys, astronomers should be able to account for this asymmetry and probe the underlying shape of the Milky Way’s dark matter halo to learn more about how our galaxy formed on cosmological timescales. To read more about their results, check out the article below.


Check out this video, which shows how the structures seen in the authors’ simulations relate to the positions of the Milky Way and the LMC. [NASA/JPL-Caltech/NSF/R. Hurt/N. Garavito-Camargo & G. Besla]


“Quantifying the Impact of the Large Magellanic Cloud on the Structure of the Milky Way’s Dark Matter Halo Using Basis Function Expansions,” Nicolás Garavito-Camargo et al 2021 ApJ 919 109. doi:10.3847/1538-4357/ac0b44

close-up image of the interior of an asteroid fragment

two panels showing the interior of two different asteroid fragments

The interior structure of two carbonaceous chondrites: meteorite Los Vientos 123 (top) and meteorite El Médano 463 (bottom). Click to enlarge. [Pinto et al. 2021]

Have you ever wanted to look inside an asteroid? Today’s image (see the full version to the right) shows the interior structure of a type of meteorite called a carbonaceous chondrite — a remnant of a rocky, carbon-containing asteroid thought to have formed far from the Sun early in solar system history. A team led by Gabriel Pinto (Université de Lorraine, France) determined the composition of several carbonaceous chondrites by bombarding them with high-energy electrons and measuring the electrons that bounced back (top panel; meteorite Los Vientos 123) or the X-rays that were emitted (bottom panel; meteorite El Médano 463). The shading colors in the bottom panel indicate the chemical element, while the outline colors in both panels indicate the component type — for example, iron-oxide-rich components that formed in a high-temperature environment are outlined in blue. The authors found that the sizes and types of components in these meteorites support the theory that planetesimals formed via gravitational collapse of clumps of small particles. For more information, check out the article below!


“Constraints on Planetesimal Accretion Inferred from Particle-size Distribution in CO Chondrites,” Gabriel A. Pinto et al 2021 ApJL 917 L25. doi:10.3847/2041-8213/ac17f2

Set of four images showing close-ups of the rocky surface of Ceres.

The images above show two regions on the surface of Ceres, the only dwarf planet in the inner solar system. The larger-scale views of the two regions (left panels) and their zoom-ins (right panels) reveal fine-debris landslides tumbling down the walls of a crater on this airless body. In a new publication led by Elizabeth Palmer (University of Southern California), a team of scientists has combined existing observations of Ceres with laboratory experiments to better understand the properties of this dwarf planet’s surface. They find that Ceres’s uppermost surface layer is much more porous than other bodies like it, providing an opportunity for it to retain small, hidden pockets of volatiles — substances that should normally evaporate from airless bodies — across its surface. The authors speculate that Ceres’s porous surface is created by activity like avalanches of fine particles, as seen above. To learn more about the authors’ results, check out the original article below.


“Exploring Ceres’s Unusual Regolith Porosity and Its Implications for Volatile Retention,” Elizabeth M. Palmer et al 2021 Planet. Sci. J. 2 182. doi:10.3847/PSJ/ac0b3e

Image of the surface of a small, rocky, rough asteroid, overlaid with a grid of ~50 colored tiles.

Recently, the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft traveled to the near-Earth asteroid (101955) Bennu and spent two years studying the surface of this rocky body. An example view OSIRIS-REx captured using its MapCam color imager is shown as the background layer of the photo above (click for the full image!); the ~50 overlaid colored regions are tiles from a high-resolution shape model. Scientists use shape models to better interpret MapCam’s photometry of Bennu’s rough surface, since we must account for variations in the asteroid’s surface texture, color, albedo, and composition. In a new study led by Dathon Golish (Lunar and Planetary Laboratory, University of Arizona), a team of scientists has worked to improve our analysis of asteroid Bennu with photometric models. To read more about the authors’ work and results, check out the original article below.


“Regional Photometric Modeling of Asteroid (101955) Bennu,” D. R. Golish et al 2021 Planet. Sci. J. 2 124. doi:10.3847/PSJ/abfd3c

A gold-wrapped spacecraft sits on the right side of the image, in a room completely covered in blue conical protrusions.

On the right side of this photograph is the integrated payload and spacecraft of Chandrayaan-2, an Indian Space Research Organisation (ISRO) lunar exploration mission. In the image, the mission’s Dual-Frequency synthetic aperture radar (DFSAR) instrument is being tested prior to launch in an anechoic chamber — a room designed to minimize reflections and echos at specific wavelengths, allowing scientists to evaluate the function of an instrument. Chandrayaan-2 launched in 2019 and is currently orbiting the Moon, mapping out the lunar surface and exploring its thin atmosphere. In a new publication, a team of scientists led by Sriram Bhiravarasu (Space Applications Centre, ISRO) provides a preliminary report on DFSAR’s performance and describes what we may be able to learn from the radar polarization measurements made by this instrument — for instance, how the rockiness of craters evolve with time on the Moon’s surface. To learn more (and to see some cool radar images of the Moon’s surface), check out the original article below.


“Chandrayaan-2 Dual-frequency Synthetic Aperture Radar (DFSAR): Performance Characterization and Initial Results,” Sriram S. Bhiravarasu et al 2021 Planet. Sci. J. 2 134. doi:10.3847/PSJ/abfdbf

a cross section of a disk shows streamlines with swirls and swoops illustrating the motion of dust

full DSHARP gallery

Examples from DSHARP of some of the structure observed in protoplanetary disks. Click to enlarge. [Andrews et al. 2018]

In the simulated cross-section of a protoplanetary disk shown above (see the full figure below), dust swirls around as a consequence of the recent passage of an orbiting planet. This simulation was led by Jiaqing Bi (毕嘉擎; University of Victoria, Canada) to explore what happens to the disk of gas and dust surrounding a young star when a baby planet orbits within it.

Protoplanetary disks often exhibit a dramatic structure of gaps and rings. But in some systems, the edges of gaps are puffy and ill-defined, suggesting agitated dust; in others, the gaps are sharp and well-defined, suggesting the dust there is well-settled. Could the presence of an orbiting planet explain both kinds of structure?

Bi and collaborators use their 3D simulations to model how a planet stirs up the gas and dust at the edges of gaps, and show how the properties of both the planet and the dust affect how quickly the dust settles after the planet’s passage — and thus, how sharp the disk gaps appear. To find out more about the authors’ results, check out the original article below.

Two plots show a disk in cross-section with overplotted streamlines showing gas and dust motion.

Streamlines showing the gas (top) and dust (bottom) motion in a disk, shown in cross-section, due to a planet orbiting at R/Rref=1. [Bi et al. 2021]


“Puffed-up Edges of Planet-opened Gaps in Protoplanetary Disks. I. Hydrodynamic Simulations,” Jiaqing Bi et al 2021 ApJ 912 107. doi:10.3847/1538-4357/abef6b

Two images showing swirls and eddies in the atmospheres of a hot jupiter; the left represents the planet's nightside, and the right represents the planet's dayside.

Hot Jupiters are giant exoplanets that orbit very close to their host stars, generally in a 1:1 spin–orbit ratio that ensures they always present the same face to their host. How does the atmosphere of a hot Jupiter respond to the bombardment of radiation on only one side of the planet? In a new study led by James Cho (CCA, Flatiron Institute), a team of scientists has conducted detailed simulations to find out. The delicate vorticity maps above (click for a closer look) show the nightside (left) and dayside (right) of a simulated hot Jupiter atmosphere. Cho and collaborators’ high-resolution simulations are designed to accurately capture small-scale eddies and waves that arise in the atmosphere as the unequal heating drives flows. The authors show that intense storms result across the hot Jupiter on both small and large scales, leading to global variability and chaotic mixture of the atmosphere. To learn more about the authors’ results, check out the original article below.


“Storms, Variability, and Multiple Equilibria on Hot Jupiters,” James Y-K. Cho et al 2021 ApJL 913 L32. doi:10.3847/2041-8213/abfd37

Photograph of the Sun during an eclipse reveals large-scale stalks extending through the sun's corona. Two are labeled "streamer" and one is labeled "pseudostreamer".

This stunning image of the Sun during a total solar eclipse, included in today’s article with permission from astrophotographer Nicolas Lefaudeux, illustrates an intriguing structure in the solar corona: a pseudostreamer. Streamers and pseudostreamers structure the Sun’s outer atmosphere — the corona — on enormous scales. True streamers, which are long-lived and relate to the global dipole magnetic field of the Sun, separate regions of opposite magnetic field in the corona. Pseudostreamers, on the other hand, are transient structures that separate regions of the same polarity. Can you tell which is which in the image above? Click on the image to see the labels. A team of scientists led by Roger Scott (US Naval Research Laboratory) has now created the first detailed 3D numerical simulations of the formation of a pseudostreamer and explored the implications for the origins of the extremely variable slow solar wind, a stream of magnetized particles that flows from the Sun. To learn more about the team’s results, check out the original article below.


“The Dynamic Formation of Pseudostreamers,” Roger B. Scott et al 2021 ApJ 913 64. doi:10.3847/1538-4357/abec4f

Six panels show different magnetic field line configurations where reconnection may occur.

Magnetic reconnection — when magnetic fields rearrange themselves, breaking neighboring field lines and rejoining them in a new configuration — is a critical process in astrophysical plasmas. This rearrangement converts energy stored in the magnetic fields into kinetic and thermal energy, playing a major role in phenomena like solar flares or the Earth’s aurora. But reconnection is not yet well understood — especially when operating in three dimensions! In particular, it’s notoriously difficult to identify the sites where reconnection occurs in 3D. In a recent study, scientist Giovanni Lapenta (Space Science Institute; KU Leuven University, Belgium) presents a new indicator that can be used to detect reconnection sites in both observations and simulations of 3D plasmas. The images above, adapted from figures in the study, show the magnetic field configurations for six different probable reconnection sites identified via Lapenta’s process in a 3D simulation of a turbulent outflow. To learn more, check out the original article below.


“Detecting Reconnection Sites Using the Lorentz Transformations for Electromagnetic Fields,” Giovanni Lapenta 2021 ApJ 911 147. doi:10.3847/1538-4357/abeb74

Compilation of 12 images of the sun taken during a solar eclipse, so the extended solar corona and streams of solar wind are visible.

The figure above (click for the full view) contains 6 pairs of images of the Sun captured during different total solar eclipses between 2008 and 2020. During an eclipse, the Moon blocks the bright light of the solar disk and reveals the complex structure of the Sun’s corona. Each beautifully detailed pair of images above shows a white-light picture (left), and an overlay of white light with Fe XI 789.2 nm (red) and Fe XIV 530.3 nm (green) emission (right). A team of scientists led by Shadia Habbal (Institute for Astronomy, University of Hawaii) has used these images and complementary in situ observations from NASA’s Advanced Composition Explorer — a spacecraft that measures the properties of solar wind particles — to explore the source regions of different solar wind streams. By studying where solar wind streams arise, the authors are able to better understand the physical processes that shape these flows of energetic particles from our host star. To learn more about their work (and to see more spectacular images!), check out the article below.


“Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle,” Shadia R. Habbal et al 2021 ApJL 911 L4. doi:10.3847/2041-8213/abe775

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