Two versions of the Charon-lit image of Pluto’s southern hemisphere recovered. with different image-processing techniques (top right and bottom left). The top left and bottom right panels show the viewing orientation. [Lauer et al. 2021]
“The Dark Side of Pluto,” Tod R. Lauer et al 2021 Planet. Sci. J. 2 214. doi:10.3847/PSJ/ac2743
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
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]
“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
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
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
How does the Sun’s outermost atmosphere — the solar corona — become heated to a million degrees Kelvin? The answer may lie in what’s pictured here: the quiet Sun. This extreme ultraviolet image, taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in 2019, shows a region of the Sun spanning roughly 300 x 350 arcseconds (click for the full view). The image captures the quiet Sun — the ordinary, background roiling of the corona, unblemished by large magnetic features like active regions or coronal holes. In a new study, scientists Vishal Upendran and Durgesh Tripathi (Inter University Centre for Astronomy and Astrophysics, India) combine SDO AIA images of the quiet Sun with new models to better understand how heat may be injected into the solar corona on a continuous basis — even when the Sun is quiet. They show that impulsive events — tiny, constantly occurring nanoflares — can pump enough energy into the quiet-Sun corona to explain its mysteriously large temperature. For more information, check out the original article below.
“On the Impulsive Heating of Quiet Solar Corona,” Vishal Upendran and Durgesh Tripathi 2021 ApJ 916 59. doi:10.3847/1538-4357/abf65a
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
Examples from DSHARP of some of the structure observed in protoplanetary disks. Click to enlarge. [Andrews et al. 2018]
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.
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
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
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