ST/ ‘Pack ice’ tectonics reveal Venus’ geological secrets

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Paradigm

36 min readJul 1, 2021

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Space biweekly vol.29, 17th June — 1st July

TL;DR

A new analysis of Venus’ surface shows evidence of tectonic motion in the form of crustal blocks that have jostled against each other like broken chunks of pack ice.
Scientists have identified 2,034 nearby star-systems — within the small cosmic distance of 326 light-years — that could find Earth merely by watching our pale blue dot cross our sun.
A new analysis of known exoplanets has revealed that Earth-like conditions on potentially habitable planets may be much rarer than previously thought. The work focuses on the conditions required for oxygen-based photosynthesis to develop on a planet, which would enable complex biospheres of the type found on Earth.
Motions of a remarkable cosmic structure have been measured for the first time, using NASA’s Chandra X-ray Observatory. The blast wave and debris from an exploded star are seen moving away from the explosion site and colliding with a wall of surrounding gas.
New findings shed light on the molecular triggers of rapid cardiac atrophy. Findings have potential implications for space travel.
Data from 500 young stars observed with the Atacama Large Millimeter/submilliter Array (ALMA) is giving scientists a window back through time, allowing them to predict what exoplanetary systems looked like through each stage of their formation. And it all starts with a link between higher mass stars, disks with gaps in them, and a high occurrence of observed exoplanets.
A new study suggests that the NASA James Webb Space Telescope (JWST), scheduled to launch in November, will be sensitive enough to observe the birth of galaxies directly.
Scientists have developed an innovative way to use NASA satellite data to track the movement of tiny pieces of plastic in the ocean.
New research suggests that carbon, oxygen, and hydrogen cosmic rays travel through the galaxy toward Earth in a similar way, but, surprisingly, that iron arrives at Earth differently. The international research team analyzed data from the CALET instrument on the International Space Station to arrive at the results, which help address the age-old question: How is matter generated and distributed across the universe?
Astronomers have identified an extremely magnetized and rapidly rotating ultra-massive white dwarf. Several telescopes characterized the dead star.
The most accurate distance measurement yet of ultra-diffuse galaxy (UDG) NGC1052-DF2 (DF2) confirms beyond any shadow of a doubt that it is lacking in dark matter. The newly measured distance of 22.1 +/-1.2 megaparsecs are based on 40 orbits of NASA’s Hubble Space Telescope, with imaging by the Advanced Camera for Surveys and a ‘tip of the red giant branch’ (TRGB) analysis.
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The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates

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A globally fragmented and mobile lithosphere on Venus

by Paul K. Byrne, Richard C. Ghail, A. M. Celal Sengor, Peter B. James, Christian Klimczak, Sean C. Solomon in Proceedings of the National Academy of Sciences

A new analysis of Venus’ surface shows evidence of tectonic motion in the form of crustal blocks that have jostled against each other like broken chunks of pack ice. The movement of these blocks could indicate that Venus is still geologically active and give scientists insight into both exoplanet tectonics and the earliest tectonic activity on Earth.
“We’ve identified a previously unrecognized pattern of tectonic deformation on Venus, one that is driven by interior motion just like on Earth,” says Paul Byrne, associate professor of planetary science at North Carolina State University and lead and co-corresponding author of the work. “Although different from the tectonics we currently see on Earth, it is still evidence of interior motion being expressed at the planet’s surface.”

The finding is important because Venus has long been assumed to have an immobile solid outer shell, or lithosphere, just like Mars or Earth’s moon. In contrast, Earth’s lithosphere is broken into tectonic plates, which slide against, apart from, and underneath each other on top of a hot, weaker mantle layer.

A network of crustal blocks in the Vinmara Planitia region. (A) Magellan radar image mosaic of a portion of Vinmara Planitia, with named landforms labeled. The approximate and inferred outlines of the network of campi in this region are marked by dashed and dotted yellow lines, respectively. (B) Orthogonal shortening within part of Ahsonnutli Dorsa, which demarcates the western margin of a campus. © Extensional structures within Surupa Dorsa, which defines the eastern margin of that campus. (D) Examples of sigmoidal folds within an unnamed ridge belt that together indicate left-lateral transpressional deformation. The radar look direction is from the left for each image. All images are in azimuthal equidistant projection, centered at 69.3°N, 210.7°E (A); 68.9°N, 201.7°E (B); 70.3°N, 213.5°E ©; and 65.7°N, 225.1°E (D). The black polygons are gores.

Byrne and an international group of researchers used radar images from NASA’s Magellan mission to map the surface of Venus. In examining the extensive Venusian lowlands that make up most of the planet surface, they saw areas where large blocks of the lithosphere seem to have moved: pulling apart, pushing together, rotating and sliding past each other like broken pack ice over a frozen lake.

The team created a computer model of this deformation, and found that sluggish motion of the planet’s interior can account for the style of tectonics seen at the surface.

“These observations tell us that interior motion is driving surface deformation on Venus, in a similar way to what happens on Earth,” Byrne says. “Plate tectonics on Earth are driven by convection in the mantle. The mantle is hot or cold in different places, it moves, and some of that motion transfers to Earth’s surface in the form of plate movement.
“A variation on that theme seems to be playing out on Venus as well. It’s not plate tectonics like on Earth — there aren’t huge mountain ranges being created here, or giant subduction systems — but it is evidence of deformation due to interior mantle flow, which hasn’t been demonstrated on a global scale before.”

The deformation associated with these crustal blocks could also indicate that Venus is still geologically active.

“We know that much of Venus has been volcanically resurfaced over time, so some parts of the planet might be really young, geologically speaking,” Byrne says. “But several of the jostling blocks have formed in and deformed these young lava plains, which means that the lithosphere fragmented after those plains were laid down. This gives us reason to think that some of these blocks may have moved geologically very recently — perhaps even up to today.”

The researchers are optimistic that Venus’ newly recognized “pack ice” pattern could offer clues to understanding tectonic deformation on planets outside of our solar system, as well as on a much younger Earth.

Viscosity profiles used for each of the seven model calculations shown in Fig. 4C and D, and SI Appendix, Fig. S6. The viscosities, μ, are normalized by an arbitrary reference viscosity, μ0, and the normalized viscosities are plotted on a logarithmic scale. The choice of reference viscosity does not affect our calculated stresses, since the reference viscosity is inversely proportional to the amplitudes of the resulting strain rates. For all models, a minimum normalized viscosity of 10–2 is assumed for the deep mantle. The curves have been shifted slightly to avoid overlaps and so aid legibility.

“The thickness of a planet’s lithosphere depends mainly upon how hot it is, both in the interior and on the surface,” Byrne says. “Heat flow from the young Earth’s interior was up to three times greater than it is now, so its lithosphere may have been similar to what we see on Venus today: not thick enough to form plates that subduct, but thick enough to have fragmented into blocks that pushed, pulled, and jostled.”

NASA and the European Space Agency recently approved three new spacecraft missions to Venus that will acquire observations of the planet’s surface at much higher resolution than Magellan. “It’s great to see renewed interest in the exploration of Venus, and I’m particularly excited that these missions will be able to test our key finding that the planet’s lowlands have fragmented into jostling crustal blocks,” Byrne says.

Efficiency of the oxygenic photosynthesis on Earth-like planets in the habitable zone

by Giovanni Covone, Riccardo M Ienco, Luca Cacciapuoti, Laura Inno in Monthly Notices of the Royal Astronomical Society

A new analysis of known exoplanets has revealed that Earth-like conditions on potentially habitable planets may be much rarer than previously thought. The work focuses on the conditions required for oxygen-based photosynthesis to develop on a planet, which would enable complex biospheres of the type found on Earth.

The number of confirmed planets in our own Milky Way galaxy now numbers into the thousands. However planets that are both Earth-like and in the habitable zone — the region around a star where the temperature is just right for liquid water to exist on the surface — are much less common.

Photons flux in two differently defined PAR ranges at the surface of planets at the two edges of the HZ (dark blue lines for an upper limit of 800 nm and light blue for an upper limit of 750 nm), as a function of the star effective temperature, in units of 1020 photons s−1m−2 (HZ inner edge: continuous line; HZ outer edge: dotted line). The green dot and circle show the photon flux in PAR range on the Earth surface, yellow dots and circles the estimated photon flux on the surface of known Earth analogues, respectively, with an upper limit for the PAR range of 800 nm (dots) and 750 nm (circles). The red dotted line shows the average photon flux which is necessary to sustain the Earth biosphere. The green dotted line - the typical lower threshold for OP on Earth.

At the moment, only a handful of such rocky and potentially habitable exoplanets are known. However the new research indicates that none of these has the theoretical conditions to sustain an Earth-like biosphere by means of ‘oxygenic’ photosynthesis — the mechanism plants on Earth use to convert light and carbon dioxide into oxygen and nutrients.

Only one of those planets comes close to receiving the stellar radiation necessary to sustain a large biosphere: Kepler-442b, a rocky planet about twice the mass of the Earth, orbiting a moderately hot star around 1,200 light years away.

The study looked in detail at how much energy is received by a planet from its host star, and whether living organisms would be able to efficiently produce nutrients and molecular oxygen, both essential elements for complex life as we know it, via normal oxygenic photosynthesis.

By calculating the amount of photosynthetically active radiation (PAR) that a planet receives from its star, the team discovered that stars around half the temperature of our Sun cannot sustain Earth-like biospheres because they do not provide enough energy in the correct wavelength range. Oxygenic photosynthesis would still be possible, but such planets could not sustain a rich biosphere.

Planets around even cooler stars known as red dwarfs, which smoulder at roughly a third of our Sun’s temperature, could not receive enough energy to even activate photosynthesis. Stars that are hotter than our Sun are much brighter, and emit up to ten times more radiation in the necessary range for effective photosynthesis than red dwarfs, however generally do not live long enough for complex life to evolve.

*Exergetic efficiency versus the host star effective temperature for planets at the edges of the HZ for the two different PAR ranges. Red lines: PAR range.*

“Since red dwarfs are by far the most common type of star in our galaxy, this result indicates that Earth-like conditions on other planets may be much less common than we might hope,” comments Prof. Giovanni Covone of the University of Naples, lead author of the study.
He adds: “This study puts strong constraints on the parameter space for complex life, so unfortunately it appears that the “sweet spot” for hosting a rich Earth-like biosphere is not so wide.”

Future missions such as the James Webb Space Telescope (JWST), due for launch later this year, will have the sensitivity to look to distant worlds around other stars and shed new light on what it really takes for a planet to host life as we know it.

Probing cosmic dawn: Ages and star formation histories of candidate z ≥ 9 galaxies

by N Laporte, R A Meyer, R S Ellis, B E Robertson, J Chisholm, G W Roberts-Borsani in Monthly Notices of the Royal Astronomical Society

Cosmic dawn, when stars formed for the first time, occurred 250 million to 350 million years after the beginning of the universe, according to a new study led by researchers at University College London (UCL) and the University of Cambridge.

The study suggests that the NASA James Webb Space Telescope (JWST), scheduled to launch in November, will be sensitive enough to observe the birth of galaxies directly.

The UK-led research team examined six of the most distant galaxies currently known, whose light has taken most of the universe’s lifetime to reach us. They found that the distance of these galaxies away from Earth corresponded to a “look back” time of more than 13 billion years ago, when the universe was only 550 million years old.

Analysing images from the Hubble and Spitzer Space Telescopes, the researchers calculated the age of these galaxies as ranging from 200 to 300 million years, allowing an estimate of when their stars first formed.

Lead author Dr Nicolas Laporte (University of Cambridge), who started the project while at UCL, said: “Theorists speculate that the universe was a dark place for the first few hundred million years, before the first stars and galaxies formed.
“Witnessing the moment when the universe was first bathed in starlight is a major quest in astronomy.
“Our observations indicate that cosmic dawn occurred between 250 and 350 million years after the beginning of the universe, and, at the time of their formation, galaxies such as the ones we studied would have been sufficiently luminous to be seen with the James Webb Space Telescope.”

Spectral energy distributions and best-fitting BAGPIPES (Carnall et al. 2018) models for the six galaxies in Table 1. The blue points represent photometric data or limits, and the red points represent the predicted fluxes. All models incorporate contributions from nebular emission. The right-hand inset panel shows the redshift probability distribution, while the left-hand inset panel shows the posterior distribution of the stellar mass as a function of the age of the stellar population. HST upper limits are showed at 1σ, IRAC limits are at 2σ.

The researchers analysed starlight from the galaxies as recorded by the Hubble and Spitzer Space Telescopes, examining a marker in their energy distribution indicative of the presence of atomic hydrogen in their stellar atmospheres. This provides an estimate of the age of the stars they contain.

This hydrogen signature increases in strength as the stellar population ages but diminishes when the galaxy is older than a billion years. The age-dependence arises because the more massive stars that contribute to this signal burn their nuclear fuel more rapidly and therefore die first.

Co-author Dr Romain Meyer (UCL Physics & Astronomy and the Max Planck Institute for Astronomy in Heidelberg, Germany) said: “This age indicator is used to date stars in our own neighbourhood in the Milky Way but it can also be used to date extremely remote galaxies, seen at a very early period of the universe.
“Using this indicator we can infer that, even at these early times, our galaxies are between 200 and 300 million years old.”

Top: ALMA contours overplotted on the HST F160W image (left-hand panel) and ALMA band 7 data (right-hand panel) from a 2σ level upwards for MACS0416-JD. The beam size is indicated at the bottom right-hand panel of the ALMA panel. Centre: Extracted 1D spectrum over the full frequency range sampled showing a clear [O iii] 88 μm emission line at 329.69 GHz corresponding to a redshift of z = 9.28. Bottom: Distribution of the pixel signal/noise ratio (SNR) along the line of sight at the position of MACS0416-JD. In the case of non-detection, the histogram shape should be consistent with a Gaussian. The yellow region highlights a deviation from a Gaussian shape at SNR≃6.

In analysing the data from Hubble and Spitzer, the researchers needed to estimate the “redshift” of each galaxy which indicates their cosmological distance and hence the look-back time at which they are being observed. To achieve this, they undertook spectroscopic measurements using the full armoury of powerful ground-based telescopes — the Chilean Atacama Large Millimetre Array (ALMA), the European Very Large Telescope, the twin Keck telescopes in Hawaii, and Gemini-South telescope.

These measurements enabled the team to confirm that looking at these galaxies corresponded to looking back to a time when the universe was 550 million years old.

Co-author Professor Richard Ellis (UCL Physics & Astronomy), who has tracked ever more distant galaxies over his career, said: “Over the last decade, astronomers have pushed back the frontiers of what we can observe to a time when the universe was only 4% of its present age. However, due to the limited transparency of Earth’s atmosphere and the capabilities of the Hubble and Spitzer Space Telescopes, we have reached our limit.

“We now eagerly await the launch of the James Webb Space Telescope, which we believe has the capability to directly witness cosmic dawn.
“The quest to see this important moment in the universe’s history has been a holy grail in astronomy for decades. Since we are made of material processed in stars, this is in some sense the search for our own origins.”

A highly magnetized and rapidly rotating white dwarf as small as the Moon

by Caiazzo, I., Burdge, K.B., Fuller, J. et al. in Nature

Astronomers have discovered the smallest and most massive white dwarf ever seen. The smoldering cinder, which formed when two less massive white dwarfs merged, is heavy, “packing a mass greater than that of our Sun into a body about the size of our Moon,” says Ilaria Caiazzo, the Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Astrophysics at Caltech and lead author of the new study. “It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead regulated by quantum mechanics.”

The discovery was made by the Zwicky Transient Facility, or ZTF, which operates at Caltech’s Palomar Observatory; two Hawai’i telescopes — W. M. Keck Observatory on Maunakea, Hawai’i Island and University of Hawai’i Institute for Astronomy’s Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui — helped characterize the dead star, along with the 200-inch Hale Telescope at Palomar, the European Gaia space observatory, and NASA’s Neil Gehrels Swift Observatory.

White dwarfs are the collapsed remnants of stars that were once about eight times the mass of our Sun or lighter. Our Sun, for example, after it first puffs up into a red giant in about 5 billion years, will ultimately slough off its outer layers and shrink down into a compact white dwarf. About 97 percent of all stars become white dwarfs.

While our Sun is alone in space without a stellar partner, many stars orbit around each other in pairs. The stars grow old together, and if they are both less than eight solar-masses, they will both evolve into white dwarfs.

The new discovery provides an example of what can happen after this phase. The pair of white dwarfs, which spiral around each other, lose energy in the form of gravitational waves and ultimately merge. If the dead stars are massive enough, they explode in what is called a type Ia supernova. But if they are below a certain mass threshold, they combine together into a new white dwarf that is heavier than either progenitor star. This process of merging boosts the magnetic field of that star and speeds up its rotation compared to that of the progenitors.

Astronomers say that the newfound tiny white dwarf, named ZTF J1901+1458, took the latter route of evolution; its progenitors merged and produced a white dwarf 1.35 times the mass of our Sun. The white dwarf has an extreme magnetic field almost 1 billion times stronger than our Sun’s and whips around on its axis at a frenzied pace of one revolution every seven minutes (the zippiest white dwarf known, called EPIC 228939929, rotates every 5.3 minutes).

*Corner plots for the photometric fitting: results for the model atmospheres of Tremblay et al. (left) and Bohlin et al.(right).*

“We caught this very interesting object that wasn’t quite massive enough to explode,” says Caiazzo. “We are truly probing how massive a white dwarf can be.”

What’s more, Caiazzo and her collaborators think that the merged white dwarf may be massive enough to evolve into a neutron-rich dead star, or neutron star, which typically forms when a star much more massive than our Sun explodes in a supernova.

“This is highly speculative, but it’s possible that the white dwarf is massive enough to further collapse into a neutron star,” says Caiazzo. “It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.”

If this neutron star formation hypothesis is correct, it may mean that a significant portion of other neutron stars take shape in this way. The newfound object’s close proximity (about 130 light-years away) and its young age (about 100 million years old or less) indicate that similar objects may occur more commonly in our galaxy.

The LRIS phase-resolved spectra of ZTF J1901+1458 in the red side. Some small variations can be observed in the spectral features with phase: in particular, the feature at ~6,620 Å becomes broader and narrower with phase.

The white dwarf was first spotted by Caiazzo’s colleague Kevin Burdge, a postdoctoral scholar at Caltech, after searching through all-sky images captured by ZTF. This particular white dwarf, when analyzed in combination with data from Gaia, stood out for being very massive and having a rapid rotation.

“No one has systematically been able to explore short-timescale astronomical phenomena on this kind of scale until now. The results of these efforts are stunning,” says Burdge, who, in 2019, led the team that discovered a pair of white dwarfs zipping around each other every seven minutes.

The team then analyzed the spectrum of the star using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS), and that is when Caiazzo was struck by the signatures of a very powerful magnetic field and realized that she and her team had found something “very special,” as she says. The strength of the magnetic field together with the seven-minute rotational speed of the object indicated that it was the result of two smaller white dwarfs coalescing into one.

Data from Swift, which observes ultraviolet light, helped nail down the size and mass of the white dwarf. With a diameter of 2,670 miles, ZTF J1901+1458 secures the title for the smallest known white dwarf, edging out previous record holders, RE J0317–853 and WD 1832+089, which each have diameters of about 3,100 miles.

In the future, Caiazzo hopes to use ZTF to find more white dwarfs like this one, and, in general, to study the population as a whole. “There are so many questions to address, such as what is the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type Ia supernovae? How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs? Finding a large population of white dwarfs born from mergers will help us answer all these questions and more.”

Fast Blast Wave and Ejecta in the Young Core-collapse Supernova Remnant MSH 15–52/RCW 89

by Kazimierz J. Borkowski, Stephen P. Reynolds, William Miltich in The Astrophysical Journal

Motions of a remarkable cosmic structure have been measured for the first time, using NASA’s Chandra X-ray Observatory. The blast wave and debris from an exploded star are seen moving away from the explosion site and colliding with a wall of surrounding gas.

Astronomers estimate that light from the supernova explosion reached Earth about 1,700 years ago, or when the Mayan empire was flourishing and the Jin dynasty ruled China. However, by cosmic standards the supernova remnant formed by the explosion, called MSH 15–52, is one of the youngest in the Milky Way galaxy. The explosion also created an ultra-dense, magnetized star called a pulsar, which then blew a bubble of energetic particles, an X-ray-emitting nebula.

Since the explosion the supernova remnant — made of debris from the shattered star, plus the explosion’s blast wave — and the X-ray nebula have been changing as they expand outward into space. Notably, the supernova remnant and X-ray nebula now resemble the shape of fingers and a palm.

Chandra image of RCW 89 in 2018 (red: 0.5–2 keV; green: 2–3 keV; blue: 3–6.5 keV). Soft, thermally emitting compact ejecta knots are in sharp contrast to diffuse and hard X-rays of nonthermal origin. Boxes enclose knots and filaments selected for PM measurements.

Previously, astronomers had released a full Chandra view of the “hand,” as shown in the main graphic. A new study is now reporting how quickly the supernova remnant associated with the hand is moving, as it strikes a cloud of gas called RCW 89. The inner edge of this cloud forms a gas wall located about 35 light-years from the center of the explosion.

To track the motion the team used Chandra data from 2004, 2008, and then a combined image from observations taken in late 2017 and early 2018. These three epochs are shown in the inset of the main graphic.

The rectangle (fixed in space) highlights the motion of the explosion’s blast wave, which is located near one of the fingertips. This feature is moving at almost 9 million miles per hour. The fixed squares enclose clumps of magnesium and neon that likely formed in the star before it exploded and shot into space once the star blew up. Some of this explosion debris is moving at even faster speeds of more than 11 million miles per hour. A color version of the 2018 image shows the fingers in blue and green and the clumps of magnesium and neon in red and yellow.

Selected emission knots and filaments in 2004, 2008, and 2018. Their large motions are apparent. RGB images (bottom right of each knot’s panels, except for regions SS and FS), with contours and coordinate grids drawn over, show them in more detail (red — 2004, green — 2008, blue — 2018). Knots Fs (bottom left) and Ff (top right) are within regions drawn over the 2008 image in panel F. Region FS (in cyan) is where we measured motion of the fast X-ray synchrotron emitting blast wave. Each coordinate grid cell is in size.

While these are startling high speeds, they actually represent a slowing down of the remnant. Researchers estimate that to reach the farthest edge of RCW 89, material would have to travel on average at almost 30 million miles per hour. This estimate is based on the age of the supernova remnant and the distance between the center of the explosion and RCW 89. This difference in speed implies that the material has passed through a low-density cavity of gas and then been significantly decelerated by running into RCW 89.

PMs (magenta arrows, not to scale), and their radial components with respect to the pulsar (cyan arrows), drawn over the broadband (0.5–6.5 keV) Chandra image. The scaling is shown by red arrow pointing radially away from the pulsar. The scale is in counts per image pixel.

The exploded star likely lost part or all of its outer layer of hydrogen gas in a wind, forming such a cavity, before exploding, as did the star that exploded to form the well-known supernova remnant Cassiopeia A (Cas A), which is much younger at an age of about 350 years. About 30% of massive stars that collapse to form supernovas are of this type. The clumps of debris seen in the 1,700-year-old supernova remnant could be older versions of those seen in Cas A at optical wavelengths in terms of their initial speeds and densities. This means that these two objects may have the same underlying source for their explosions, which is likely related to how stars with stripped hydrogen layers explode. However, astronomers do not understand the details of this yet and will continue to study this possibility.

Past, present and future stars that can see Earth as a transiting exoplanet

by L. Kaltenegger, J. K. Faherty in Nature

Scientists at Cornell University and the American Museum of Natural History have identified 2,034 nearby star-systems — within the small cosmic distance of 326 light-years — that could find Earth merely by watching our pale blue dot cross our sun.

That’s 1,715 star-systems that could have spotted Earth since human civilization blossomed about 5,000 years ago, and 319 more star-systems that will be added over the next 5,000 years. Exoplanets around these nearby stars have a cosmic front-row seat to see if Earth holds life, the scientists said.

“From the exoplanets’ point-of-view, we are the aliens,” said Lisa Kaltenegger, professor of astronomy and director of Cornell’s Carl Sagan Institute, in the College of Arts and Sciences.
“We wanted to know which stars have the right vantage point to see Earth, as it blocks the Sun’s light,” she said. “And because stars move in our dynamic cosmos, this vantage point is gained and lost.”

Kaltenegger and astrophysicist Jackie Faherty, a senior scientist at the American Museum of Natural History and co-author of “Past, Present and Future Stars That Can See Earth As A Transiting Exoplanet,” used positions and motions from the European Space Agency’s Gaia eDR3 catalog to determine which stars enter and exit the Earth Transit Zone — and for how long.

“Gaia has provided us with a precise map of the Milky Way galaxy,” Faherty said, “allowing us to look backward and forward in time, and to see where stars had been located and where they are going.”

Of the 2,034 star-systems passing through the Earth Transit Zone over the 10,000-year period examined, 117 objects lie within about 100 light-years of the sun and 75 of these objects have been in the Earth Transit Zone since commercial radio stations on Earth began broadcasting into space about a century ago.

“Our solar neighborhood is a dynamic place where stars enter and exit that perfect vantage point to see Earth transit the Sun at a rapid pace,” Faherty said.

Included in the catalog of 2,034 star-systems are seven known to host exoplanets. Each one of these worlds has had or will have an opportunity to detect Earth, just as Earth’s scientists have found thousands of worlds orbiting other stars through the transit technique.

By watching distant exoplanets transit — or cross — their own sun, Earth’s astronomers can interpret the atmospheres backlit by that sun. If exoplanets hold intelligent life, they can observe Earth backlit by the sun and see our atmosphere’s chemical signatures of life.

The Ross 128 system, with a red dwarf host star located in the Virgo constellation, is about 11 light-years away and is the second-closest system with an Earth-size exoplanet (about 1.8 times the size of our planet). Any inhabitants of this exoworld could have seen Earth transit our own sun for 2,158 years, starting about 3,057 years ago; they lost their vantage point about 900 years ago.

The Trappist-1 system, at 45 light-years from Earth, hosts seven transiting Earth-size planets — four of them in the temperate, habitable zone of that star. While we have discovered the exoplanets around Trappist-1, they won’t be able to spot us until their motion takes them into the Earth Transit Zone in 1,642 years. Potential Trappist-1 system observers will remain in the cosmic Earth transit stadium seats for 2,371 years.

“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see Earth transit,” Kaltenegger said. “If we assume the reverse to be true, that provides a healthy timeline for nominal civilizations to identify Earth as an interesting planet.”

The James Webb Space telescope — expected to launch later this year — is set to take a detailed look at several transiting worlds to characterize their atmospheres and ultimately search for signs of life.

The Breakthrough Starshot initiative is an ambitious project underway that is looking to launch a nano-sized spacecraft toward the closest exoplanet detected around Proxima Centauri — 4.2 light-years from us — and fully characterize that world.

“One might imagine that worlds beyond Earth that have already detected us, are making the same plans for our planet and solar system,” said Faherty. “This catalog is an intriguing thought experiment for which one of our neighbors might be able to find us.”

A Stellar Mass Dependence of Structured Disks: A Possible Link with Exoplanet Demographics

by Nienke van der Marel, Gijs D. Mulders in The Astronomical Journal

Using data for more than 500 young stars observed with the Atacama Large Millimeter/Submillimeter Array (ALMA), scientists have uncovered a direct link between protoplanetary disk structures — the planet-forming disks that surround stars — and planet demographics. The survey proves that higher mass stars are more likely to be surrounded by disks with “gaps” in them and that these gaps directly correlate to the high occurrence of observed giant exoplanets around such stars. These results provide scientists with a window back through time, allowing them to predict what exoplanetary systems looked like through each stage of their formation.
“We found a strong correlation between gaps in protoplanetary disks and stellar mass, which can be linked to the presence of large, gaseous exoplanets,” said Nienke van der Marel, a Banting fellow in the Department of Physics and Astronomy at the University of Victoria in British Columbia, and the primary author on the research. “Higher mass stars have relatively more disks with gaps than lower mass stars, consistent with the already known correlations in exoplanets, where higher mass stars more often host gas-giant exoplanets. These correlations directly tell us that gaps in planet-forming disks are most likely caused by giant planets of Neptune mass and above.”

Gaps in protoplanetary disks have long been considered as overall evidence of planet formation. However, there has been some skepticism due to the observed orbital distance between exoplanets and their stars. “One of the primary reasons that scientists have been skeptical about the link between gaps and planets before is that exoplanets at wide orbits of tens of astronomical units are rare. However, exoplanets at smaller orbits, between one and ten astronomical units, are much more common,” said Gijs Mulders, assistant professor of astronomy at Universidad Adolfo Ibáñez in Santiago, Chile, and co-author on the research. “We believe that planets that clear the gaps will migrate inwards later on.”

The new study is the first to show that the number of gapped disks in these regions matches the number of giant exoplanets in a star system. “Previous studies indicated that there were many more gapped disks than detected giant exoplanets,” said Mulders. “Our study shows that there are enough exoplanets to explain the observed frequency of the gapped disks at different stellar masses.”

The correlation also applies to star systems with low-mass stars, where scientists are more likely to find massive rocky exoplanets, also known as Super-Earths. Van der Marel, who will become an assistant professor at Leiden University in the Netherlands beginning September 2021 said, “Lower mass stars have more rocky Super-Earths — between an Earth mass and a Neptune mass. Disks without gaps, which are more compact, lead to the formation of Super-Earths.”

This link between stellar mass and planetary demographics could help scientists identify which stars to target in the search for rocky planets throughout the Milky Way. “This new understanding of stellar mass dependencies will help to guide the search for small, rocky planets like Earth in the solar neighborhood,” said Mulders, who is also a part of the NASA-funded Alien Earths team. “We can use the stellar mass to connect the planet-forming disks around young stars to exoplanets around mature stars. When an exoplanet is detected, the planet-forming material is usually gone. So the stellar mass is a ‘tag’ that tells us what the planet-forming environment might have looked like for these exoplanets.”

And what it all comes down to is dust. “An important element of planet formation is the influence of dust evolution,” said van der Marel. “Without giant planets, dust will always drift inwards, creating the optimal conditions for the formation of smaller, rocky planets close to the star.”

The current research was conducted using data for more than 500 objects observed in prior studies using ALMA’s high-resolution Band 6 and Band 7 antennas. At present, ALMA is the only telescope that can image the distribution of millimeter-dust at high enough angular resolution to resolve the dust disks and reveal its substructure, or lack thereof. “Over the past five years, ALMA has produced many snapshot surveys of nearby star-forming regions resulting in hundreds of measurements of disk dust mass, size, and morphology,” said van der Marel. “The large number of observed disk properties has allowed us to make a statistical comparison of protoplanetary disks to the thousands of discovered exoplanets. This is the first time that a stellar mass dependency of gapped disks and compact disks has been successfully demonstrated using the ALMA telescope.”

“Our new findings link the beautiful gap structures in disks observed with ALMA directly to the properties of the thousands of exoplanets detected by the NASA Kepler mission and other exoplanet surveys,” said Mulders. “Exoplanets and their formation help us place the origins of the Earth and the Solar System in the context of what we see happening around other stars.”

Measurement of the Iron Spectrum in Cosmic Rays from 10 GeV/n to 2.0 TeV/n with the Calorimetric Electron Telescope on the International Space Station

by O. Adriani, Y. Akaike, K. Asano, Y. Asaoka, E. Berti, G. Bigongiari, W. R. Binns, M. Bongi, P. Brogi, A. Bruno, J. H. Buckley, N. Cannady, G. Castellini, C. Checchia, M. L. Cherry, G. Collazuol, K. Ebisawa, H. Fuke, S. Gonzi, T. G. Guzik, T. Hams, K. Hibino, M. Ichimura, K. Ioka, W. Ishizaki, M. H. Israel, K. Kasahara, J. Kataoka, R. Kataoka, Y. Katayose, C. Kato, N. Kawanaka, Y. Kawakubo, K. Kobayashi, K. Kohri, H. S. Krawczynski, J. F. Krizmanic, J. Link, P. Maestro, P. S. Marrocchesi, A. M. Messineo, J. W. Mitchell, S. Miyake, A. A. Moiseev, M. Mori, N. Mori, H. M. Motz, K. Munakata, S. Nakahira, J. Nishimura, G. A. de Nolfo, S. Okuno, J. F. Ormes, N. Ospina, S. Ozawa, L. Pacini, P. Papini, B. F. Rauch, S. B. Ricciarini, K. Sakai, T. Sakamoto, M. Sasaki, Y. Shimizu, A. Shiomi, P. Spillantini, F. Stolzi, S. Sugita, A. Sulaj, M. Takita, T. Tamura, T. Terasawa, S. Torii, Y. Tsunesada, Y. Uchihori, E. Vannuccini, J. P. Wefel, K. Yamaoka, S. Yanagita, A. Yoshida, K. Yoshida in Physical Review Letters

New findings suggest that carbon, oxygen, and hydrogen cosmic rays travel through the galaxy toward Earth in a similar way, but, surprisingly, that iron arrives at Earth differently. Learning more about how cosmic rays move through the galaxy helps address a fundamental, lingering question in astrophysics: How is matter generated and distributed across the universe?
“So what does this finding mean?” asks John Krizmanic, a senior scientist with UMBC’s Center for Space Science and Technology (CSST). “These are indicators of something interesting happening. And what that something interesting is we’re going to have to see.”

Cosmic rays are atomic nuclei — atoms stripped of their electrons — that are constantly whizzing through space at nearly the speed of light. They enter Earth’s atmosphere at extremely high energies. Information about these cosmic rays can give scientists clues about where they came from in the galaxy and what kind of event generated them.

An instrument on the International Space Station (ISS) called the Calorimetric Electron Telescope (CALET) has been collecting data about cosmic rays since 2015. The data include details such as how many and what kinds of atoms are arriving, and how much energy they’re arriving with. The American, Italian, and Japanese teams that manage CALET, including UMBC’s Krizmanic and postdoc Nick Cannady, collaborated on the new research.

Charge distributions from the combined charge measurement of the two CHD layers in the elemental region between Ca and Ge. Events are selected with 100<ETASC<125 GeV. Flight data (black dots) are compared with Monte Carlo samples comprising chromium, manganese, iron, cobalt, and nickel. Titanium and vanadium are not included in the MC sample because their contamination to iron data is negligible. In Fig. S1 of the SM [51] an enlarged version of this figure is shown, as well as the distribution for the bin 501<ETASC<631 GeV.

Cosmic rays arrive at Earth from elsewhere in the galaxy at a huge range of energies — anywhere from 1 billion volts to 100 billion billion volts. The CALET instrument is one of extremely few in space that is able to deliver fine detail about the cosmic rays it detects. A graph called a cosmic ray spectrum shows how many cosmic rays are arriving at the detector at each energy level. The spectra for carbon, oxygen, and hydrogen cosmic rays are very similar, but the key finding from the new paper is that the spectrum for iron is significantly different.

There are several possibilities to explain the differences between iron and the three lighter elements. The cosmic rays could accelerate and travel through the galaxy differently, although scientists generally believe they understand the latter.

“Something that needs to be emphasized is that the way the elements get from the sources to us is different, but it may be that the sources are different as well,” adds Michael Cherry, physics professor emeritus at Louisiana State University (LSU) and a co-author on the new paper. Scientists generally believe that cosmic rays originate from exploding stars (supernovae), but neutron stars or very massive stars could be other potential sources.

CALET iron flux (multiplied by E2.6) as a function of kinetic energy per nucleon. Error bars of the CALET data (red) represent the statistical uncertainty only, the yellow band indicates the quadrature sum of systematic errors, while the green band indicates the quadrature sum of statistical and systematic errors.

An instrument like CALET is important for answering questions about how cosmic rays accelerate and travel, and where they come from. Instruments on the ground or balloons flown high in Earth’s atmosphere were the main source of cosmic ray data in the past. But by the time cosmic rays reach those instruments, they have already interacted with Earth’s atmosphere and broken down into secondary particles. With Earth-based instruments, it is nearly impossible to identify precisely how many primary cosmic rays and which elements are arriving, plus their energies. But CALET, being on the ISS above the atmosphere, can measure the particles directly and distinguish individual elements precisely.

Iron is a particularly useful element to analyze, explains Cannady, a postdoc with CSST and a former Ph.D. student with Cherry at LSU. On their way to Earth, cosmic rays can break down into secondary particles, and it can be hard to distinguish between original particles ejected from a source (like a supernova) and secondary particles. That complicates deductions about where the particles originally came from.

“As things interact on their way to us, then you’ll get essentially conversions from one element to another,” Cannady says. “Iron is unique, in that being one of the heaviest things that can be synthesized in regular stellar evolution, we’re pretty certain that it is pretty much all primary cosmic rays. It’s the only pure primary cosmic ray, where with others you’ll have some secondary components feeding into that as well.”

Measuring cosmic rays gives scientists a unique view into high-energy processes happening far, far away. The cosmic rays arriving at CALET represent “the stuff we’re made of. We are made of stardust,” Cherry says. “And energetic sources, things like supernovas, eject that material from their interiors, out into the galaxy, where it’s distributed, forms new planets, solar systems, and… us.”

“The study of cosmic rays is the study of how the universe generates and distributes matter, and how that affects the evolution of the galaxy,” Krizmanic adds. “So really it’s studying the astrophysics of this engine we call the Milky Way that’s throwing all these elements around.”

Energy dependence of the spectral index calculated within a sliding energy window for the CALET iron data. The spectral index is determined for each bin by fitting the data using ±3 bins. Red lines indicate statistical errors only. The fit with a constant function (black line) gives a mean spectral index value ⟨γ⟩=−2.61±0.01.

The Japanese space agency launched CALET and today leads the mission in collaboration with the U.S. and Italian teams. In the U.S., the CALET team includes researchers from LSU; NASA Goddard Space Flight Center; UMBC; University of Maryland, College Park; University of Denver; and Washington University.

CALET was optimized to detect cosmic ray electrons, because their spectrum can contain information about their sources. That’s especially true for sources that are relatively close to Earth in galactic terms: within less than one-thirtieth the distance across the Milky Way. But CALET also detects the atomic nuclei of cosmic rays very precisely. Now those nuclei are offering important insights about the sources of cosmic rays and how they got to Earth.

“We didn’t expect that the nuclei — the carbon, oxygen, protons, iron — would really start showing some of these detailed differences that are clearly pointing at things we don’t know,” Cherry says.

The latest finding creates more questions than it answers, emphasizing that there is still more to learn about how matter is generated and moves around the galaxy. “That’s a fundamental question: How do you make matter?” Krizmanic says. But, he adds, “That’s the whole point of why we went in this business, to try to understand more about how the universe works.”

A Tip of the Red Giant Branch Distance of 22.1 ± 1.2 Mpc to the Dark Matter Deficient Galaxy NGC 1052–DF2 from 40 Orbits of Hubble Space Telescope Imaging

by Zili Shen, Shany Danieli, Pieter van Dokkum, Roberto Abraham, Jean P. Brodie, Charlie Conroy, Andrew E. Dolphin, Aaron J. Romanowsky, J. M. Diederik Kruijssen, Dhruba Dutta Chowdhury in The Astrophysical Journal Letters

The most accurate distance measurement yet of ultra-diffuse galaxy (UDG) NGC1052-DF2 (DF2) confirms beyond any shadow of a doubt that it is lacking in dark matter. The newly measured distance of 22.1 +/-1.2 megaparsecs was obtained by an international team of researchers led by Zili Shen and Pieter van Dokkum of Yale University and Shany Danieli, a NASA Hubble Fellow at the Institute for Advanced Study.
“Determining an accurate distance to DF2 has been key in supporting our earlier results,” stated Danieli. “The new measurement reported in this study has crucial implications for estimating the physical properties of the galaxy, thus confirming its lack of dark matter.”

The results are based on 40 orbits of NASA’s Hubble Space Telescope, with imaging by the Advanced Camera for Surveys and a “tip of the red giant branch” (TRGB) analysis, the gold standard for such refined measurements. In 2019, the team published results measuring the distance to neighboring UDG NGC1052-DF4 (DF4) based on 12 Hubble orbits and TRGB analysis, which provided compelling evidence of missing dark matter. This preferred method expands on the team’s 2018 studies that relied on “surface brightness fluctuations” to gauge distance. Both galaxies were discovered with the Dragonfly Telephoto Array at the New Mexico Skies observatory.

“We went out on a limb with our initial Hubble observations of this galaxy in 2018,” van Dokkum said. “I think people were right to question it because it’s such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it’s more fun and more interesting if it actually is a weird galaxy.”

In addition to confirming earlier distance findings, the Hubble results indicated that the galaxies were located slightly farther away than previously thought, strengthening the case that they contain little to no dark matter. If DF2 were closer to Earth, as some astronomers claim, it would be intrinsically fainter and less massive, and the galaxy would need dark matter to account for the observed effects of the total mass.

Dark matter is widely considered to be an essential ingredient of galaxies, but this study lends further evidence that its presence may not be inevitable. While dark matter has yet to be directly observed, its gravitational influence is like a glue that holds galaxies together and governs the motion of visible matter. In the case of DF2 and DF4, researchers were able to account for the motion of stars based on stellar mass alone, suggesting a lack or absence of dark matter. Ironically, the detection of galaxies deficient in dark matter will likely help to reveal its puzzling nature and provide new insights into galactic evolution.

While DF2 and DF4 are both comparable in size to the Milky Way galaxy, their total masses are only about one percent of the Milky Way’s mass. These ultra-diffuse galaxies were also found to have a large population of especially luminous globular clusters.

This research has generated a great deal of scholarly interest, as well as energetic debate among proponents of alternative theories to dark matter, such as Modified Newtonian dynamics (MOND). However, with the team’s most recent findings — including the relative distances of the two UDGs to NGC1052 — such alternative theories seem less likely. Additionally, there is now little uncertainty in the team’s distance measurements given the use of the TRGB method. Based on fundamental physics, this method depends on the observation of red giant stars that emit a flash after burning through their helium supply that always happens at the same brightness.

“There’s a saying that extraordinary claims require extraordinary evidence, and the new distance measurement strongly supports our previous finding that DF2 is missing dark matter,” stated Shen. “Now it’s time to move beyond the distance debate and focus on how such galaxies came to exist.”

Moving forward, researchers will continue to hunt for more of these oddball galaxies, while considering a number of questions such as: How are UDGs formed? What do they tell us about standard cosmological models? How common are these galaxies, and what other unique properties do they have? It will take uncovering many more dark matter-less galaxies to resolve these mysteries and the ultimate question of what dark matter really is.

Thbs1 induces lethal cardiac atrophy through PERK-ATF4 regulated autophagy

by Davy Vanhoutte, Tobias G. Schips, Alexander Vo, Kelly M. Grimes, Tanya A. Baldwin, Matthew J. Brody, Federica Accornero, Michelle A. Sargent, Jeffery D. Molkentin in Nature Communications

In many situations, heart muscle cells do not respond to external stresses in the same ways that skeletal muscle cells do. But under some conditions, heart and skeletal muscles can both waste away at fatally rapid rates, according to a new study led by experts at Cincinnati Children’s.

The new findings, based on studies of mouse models, represent an important milestone in a long effort to prevent or even reverse cardiac atrophy, which can lead to fatal heart failure when the body loses large amounts of weight or experiences extended periods of weightlessness in space.

a Western blotting for Thbs1 in heart tissue of mice (8–10 weeks of age) subjected to 2 weeks of TAC, that contained the activated calcineurin A transgene (ΔCnA), or are Csrp3−/−, compared to sham-operated or wild-type (WT) control. Gapdh is shown as a processing and loading control. b Representative immunohistochemistry for endogenous Thbs1 (red) and cell outlines with wheat germ agglutinin (WGA)-FITC (green) with DAPI-stained nuclei (blue) from hypertrophic ΔCnA transgenic and WT control hearts at 8 weeks of age. Scale bars are 10 μm. c Immunohistochemistry for Thbs1 protein (green), vimentin (red) from sham or TAC-operated hearts, 2 weeks later. Scale bars are 50 μm. Nuclei are shown in blue with DAPI. d Schematic diagram depicting the inducible double transgenic (DTG) tetracycline-repressor system for inducible overexpression of Thbs1 in the heart. e Representative Western blots for Thbs1, Thbs3, Armet, BiP, calreticulin (calret.), and Gapdh as a loading control from hearts of tTA cont., Thbs1 DTG, and Thbs3 DTG mice at 6 weeks of age. f Representative immunohistochemistry broken into 2 channels each for overexpressed Thbs1 (green) with WGA-labeled membranes (purple), DAPI for nuclei (blue) and BiP (red) to show ER and the vesicular compartment in Thbs1 DTG hearts at 8 weeks of age. Scale bars are 50 μm. g Representative images of transmission electron microscopy of heart sections from tTA cont. and Thbs1 DTG mice at 6 weeks of age. Upper panels: arrowheads indicate ER in tTA cont., white arrows show expanded ER and vesicles only in Thbs1 DTG hearts. Lower panels: enlargement of white dotted boxed area from upper panels. Scale bars are 1 μm.

“NASA is very interested in cardiac atrophy,” says Jeffery Molkentin, PhD, Co-Director of the Heart Institute at Cincinnati Children’s. “It might be the single biggest issue for long-period space flights and astronaut health, especially when re-entering a higher-gravity situation, whether that’s arriving at Mars or returning to Earth.”

Astronauts and cosmonauts have been exercising in orbit to minimize loss of muscle mass ever since doctors observed years ago that returning spacefarers have often been barely able to walk upon returning to Earth. Along the way, clinicians also have observed increased risk of heart trouble during the recovery period.

The new findings from Molkentin and colleagues help explain why the heart also is affected by muscle-wasting conditions, which in turn suggests potential new ways to prevent or treat the problem.

The research team studied mouse models in several ways to trace the withering of heart cells to a three-step molecular process. Like skeletal muscle, the heart can either grow larger or smaller depending on workload. The new research identifies a process whereby the gene thrombospondin-1 can result in a dramatic loss of heart mass.

The overexpression of thrombospondin-1 in the hearts of mice lead to rapid and lethal loss of heart mass, called atrophy, by directly activating the signaling protein called PERK. Excessive PERK activity, in turn, triggers a response from the transcription factor ATF4, which together directly program the atrophy of heart muscle cells.

The longer these genes are active, the more severe the atrophy becomes. Eliminating or reducing the activity of these genes would block or reduce the atrophy response, which could be an attractive new strategy for addressing loss of heart muscle during extended periods of space travel.

“Our findings describe a new pathway of muscle mass loss,” Molkentin says. “More research is needed to develop methods or drugs that can interrupt this signaling pathway through these genes to stop cardiac atrophy once detected.”

***ATF4 is sufficient to induce cardiac atrophy. a*** Schematic diagram depicting the experimental protocol. Either 0.5E11 or 1E10 genomic copies (gc) of AAV9-ATF4 or AAV9-Lucif. control were injected into the mediastinum of 7-day-old wild-type mouse pups. Hearts were harvested at 4 weeks of age for further analysis. b Representative western blots for PERK and ATF4 from cardiac protein extracts of 4-week-old mice treated with the indicated AAV9. Gapdh serves as a loading control. c, d Representative heart sections with Masson’s Trichrome staining © and immunohistochemistry for ATF4 (green) and WGA (purple)-stained membranes and nuclei with DAPI (blue) (d) of AAV9-ATF4 or AAV9-Lucif. injected mice (both 0.5E11 gc) at 4 weeks of age. Scale bars are 2 mm and 100 μm, respectively. e CSA of AAV9-Lucif. versus AAV9-ATF4 positive cardiomyocytes determined by ATF4 and WGA staining of histological sections as shown in panel “d”. *P = 0.0548 vs AAV9-Lucif. f Representative Masson’s trichrome stained images of hearts from mice injected with 1E10 gc AAV9-Lucif or -ATF4 and harvested at 4 weeks of age. Scale bar is 2 mm. g HW/BW ratio at 4 weeks of age in the indicated groups of mice. *P = 0.0235 vs AAV9-Lucif. h Representative immunohistochemistry for ATF4 (green), nuclei with DAPI (blue) and WGA (purple)-stained membranes from heart sections of AAV9-ATF4 or AAV9-Lucif. injected mice (both 1E10 gc) at 4 weeks of age. Scale bars are 100 μm. i CSA of ATF4 positive cardiomyocytes determined by ATF4 and WGA staining as shown in panel “h”. *P = 0.0116 vs AAV9-Lucif. j Representative western blots for LC3b, p62, and ubiquitin-conjugated proteins (Ubiq.) from cardiac protein extracts of 4-week-old mice treated with 1E10 gc AAV9-Lucif. or -ATF4. Gapdh serves as a loading control. k, l Representative micrographs of fluorescent LC3 puncta (k) and quantification thereof (l) in cultured primary neonatal rat ventricular myocytes 48 h after infection with adenoviruses to overexpress tandem mRFP-GFP-LC3 (Ad-tf-LC3) and ATF4 or βgal expressing control. Yellow dots represent autophagosomes, whereas red dots indicate autolysosomes. Scale bars are 50 μm. *P < 0.0001 vs Adβgal.

Researchers still need to confirm that the process observed in mice also occurs in people. More work also is needed to determine whether drugs exist (or need to be developed) that can safely manage the molecular activity the research team has identified.

In humans, even though we lack the ability to replace lost heart muscle tissue, it should be possible to rehabilitate weakened or atrophied heart muscle cells back to their original state.

Toward the Detection and Imaging of Ocean Microplastics With a Spaceborne Radar

by Madeline C. Evans, Christopher S. Ruf in IEEE Transactions on Geoscience and Remote Sensing

Scientists from the University of Michigan have developed an innovative way to use NASA satellite data to track the movement of tiny pieces of plastic in the ocean.

Microplastics form when plastic trash in the ocean breaks down from the sun’s rays and the motion of ocean waves. These small flecks of plastic are harmful to marine organisms and ecosystems. Microplastics can be carried hundreds or thousands of miles away from the source by ocean currents, making it difficult to track and remove them. Currently, the main source of information about the location of microplastics comes from fisher boat trawlers that use nets to catch plankton — and, unintentionally, microplastics.

The new technique relies on data from NASA’s Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight small satellites that measures wind speeds above Earth’s oceans and provides information about the strength of hurricanes. CYGNSS also uses radar to measure ocean roughness, which is affected by several factors including wind speed and debris floating in the water.

Working backward, the team looked for places where the ocean was smoother than expected given the wind speed, which they thought could indicate the presence of microplastics. Then they compared those areas to observations and model predictions of where microplastics congregate in the ocean. The scientists found that microplastics tended to be present in smoother waters, demonstrating that CYGNSS data can be used as a tool to track ocean microplastic from space.