astronomy (50)

Nano Racetracks...

In this image, optical pulses (solitons) can be seen circling through conjoined optical tracks. (Image: Yuan, Bowers, Vahala, et al.) An animated gif is at the original link below.

Topics: Applied Physics, Astronomy, Electrical Engineering, Materials Science, Nanoengineering, Optics

(Nanowerk News) When we last checked in with Caltech's Kerry Vahala three years ago, his lab had recently reported the development of a new optical device called a turnkey frequency microcomb that has applications in digital communications, precision timekeeping, spectroscopy, and even astronomy.

This device, fabricated on a silicon wafer, takes input laser light of one frequency and converts it into an evenly spaced set of many distinct frequencies that form a train of pulses whose length can be as short as 100 femtoseconds (quadrillionths of a second). (The comb in the name comes from the frequencies being spaced like the teeth of a hair comb.)

Now Vahala, Caltech's Ted and Ginger Jenkins, Professor of Information Science and Technology and Applied Physics and executive officer for applied physics and materials science, along with members of his research group and the group of John Bowers at UC Santa Barbara, have made a breakthrough in the way the short pulses form in an important new material called ultra-low-loss silicon nitride (ULL nitride), a compound formed of silicon and nitrogen. The silicon nitride is prepared to be extremely pure and deposited in a thin film.

In principle, short-pulse microcomb devices made from this material would require very low power to operate. Unfortunately, short light pulses (called solitons) cannot be properly generated in this material because of a property called dispersion, which causes light or other electromagnetic waves to travel at different speeds, depending on their frequency. ULL has what is known as normal dispersion, and this prevents waveguides made of ULL nitride from supporting the short pulses necessary for microcomb operation.

In a paper appearing in Nature Photonics ("Soliton pulse pairs at multiple colors in normal dispersion microresonators"), the researchers discuss their development of the new micro comb, which overcomes the inherent optical limitations of ULL nitride by generating pulses in pairs. This is a significant development because ULL nitride is created with the same technology used for manufacturing computer chips. This kind of manufacturing technique means that these microcombs could one day be integrated into a wide variety of handheld devices similar in form to smartphones.

The most distinctive feature of an ordinary microcomb is a small optical loop that looks a bit like a tiny racetrack. During operation, the solitons automatically form and circulate around it.

"However, when this loop is made of ULL nitride, the dispersion destabilizes the soliton pulses," says co-author Zhiquan Yuan (MS '21), a graduate student in applied physics.

Imagine the loop as a racetrack with cars. If some cars travel faster and some travel slower, then they will spread out as they circle the track instead of staying as a tight pack. Similarly, the normal dispersion of ULL means light pulses spread out in the microcomb waveguides, and the microcomb ceases to work.

The solution devised by the team was to create multiple racetracks, pairing them up so they look a bit like a figure eight. In the middle of that '8,' the two tracks run parallel to each other with only a tiny gap between them.

Conjoined 'racetracks' make new optical devices possible, Nanowerk.

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Dark Matter, Ordinary Matter...

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Topics: Astronomy, Astrophysics, Dark Matter, Research, Theoretical Physics

Dark matter, composed of particles that do not reflect, emit, or absorb light, is predicted to make up most of the matter in the universe. However, its lack of interactions with light prevents its direct detection using conventional experimental methods.

Physicists have been trying to devise alternative methods to detect and study dark matter for decades, yet many questions about its nature and its presence in our galaxy remain unanswered. Pulsar Timing Array (PTA) experiments have been trying to probe the presence of so-called ultralight dark matter particles by examining the timing of an ensemble of galactic millisecond radio pulsars (i.e., celestial objects that emit regular millisecond-long radio wave pulses).

The European Pulsar Timing Array, a multinational team of researchers based at different institutes that are using 6 radio-telescopes across Europe to observe specific pulsars, recently analyzed the second wave of data they collected. Their paper, published in Physical Review Letters, sets more stringent constraints on the presence of ultralight dark matter in the Milky Way.

"This paper was basically the result of my first Ph.D. project," Clemente Smarra, co-author of the paper, told Phys.org. "The idea arose when I asked my supervisor if I could carry out research focusing on gravitational wave science, but from a particle physics perspective. The main aim of the project was to constrain the presence of the so-called ultralight dark matter in our galaxy."

Ultralight dark matter is a hypothetical dark matter candidate, made up of very light particles that could potentially address long-standing mysteries in the field of astrophysics. The recent study by Smarra and his colleagues was aimed at probing the possible presence of this type of dark matter in our galaxy via data collected by the European Pulsar Timing Array.

"We were inspired by previous efforts in this field, especially by the work of Porayko and her collaborators," Smarra said. "Thanks to the longer duration and the improved precision of our dataset, we were able to put more stringent constraints on the presence of ultralight dark matter in the Milky Way,"

The recent paper by the European Pulsar Timing Array makes different assumptions than those made by other studies carried out in the past. Instead of probing interactions between dark matter and ordinary matter, it assumes that these interactions only occur via gravitational effects.

"We assumed that dark matter interacts with ordinary matter only through gravitational interaction," Smarra explained. "This is a rather robust claim: in fact, the only sure thing we know about dark matter is that it interacts gravitationally. In a few words, dark matter produces potential wells in which pulsar radio beams travel. But the depth of these wells is periodic in time; therefore, the travel time of the radio beams from pulsars to the Earth changes with a distinctive periodicity as well."

New constraints on the presence of ultralight dark matter in the Milky Way, Ingrid Fadelli, Phys.org.

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Gas Nephilim...

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Artist's depiction of an extra-solar system that is crowded with giant planets. Credit: NASA/Dana Berry

Topics: Astronomy, Astrophysics, Planetary Science, Space Exploration

Giant gas planets can be agents of chaos, ensuring nothing lives on their Earth-like neighbors around other stars. New studies show in some planetary systems, the giants tend to kick smaller planets out of orbit and wreak havoc on their climates.

Jupiter, by far the biggest planet in our solar system, plays an important protective role. Its enormous gravitational field deflects comets and asteroids that might otherwise hit Earth, helping create a stable environment for life. However, giant planets elsewhere in the universe do not necessarily protect life on their smaller, rocky planet neighbors.

An Astronomical Journal paper details how the pull of massive planets in a nearby star system is likely to toss their Earth-like neighbors out of the "habitable zone." This zone is defined as the range of distances from a star that are warm enough for liquid water to exist on a planet's surface, making life possible.

Unlike most other known solar systems, the four giant planets in HD 141399 are farther from their star. This makes it a good model for comparison with our solar system, where Jupiter and Saturn are also relatively far from the sun.

"It's as if they have four Jupiters acting like wrecking balls, throwing everything out of whack," said Stephen Kane, UC Riverside astrophysicist and author of the journal paper.

Taking data about the system's planets into account, Kane ran multiple computer simulations to understand the effect of these four giants. He wanted specifically to look at the habitable zone in this star system and see if an Earth could remain in a stable orbit there.

Giant planets cast a deadly pall: How they can prevent life in other solar systems, Jules Bernstein, University of California - Riverside, Phys.org.

 

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"Boldly Going" Pretty Close...

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Artist's conception of the dwarf planet Sedna in the outer edges of the known solar system. (Image credit: NASA/JPL-Caltech/R. Hurt (SSC))

Topics: Astronomy, Astrophysics, Exoplanets, NASA, Space Exploration

Astronomers are racing to explain the peculiar orbits of faraway objects at the edge of our solar system.

Among the many mysteries that make the furthest reaches of our solar system, well, mysterious, is the exceptionally egg-shaped path of a dwarf planet called 90377 Sedna.

Its 11,400-year orbit, one of the longest of any resident of the solar system, ushers the dwarf planet to seven billion miles (11.3 billion km) from the sun, then escorts it out of the solar system and way past the Kuiper Belt to 87 billion miles (140 billion km), and finally takes it within a loose shell of icy objects known as the Oort cloud. Since Sedna's discovery in 2003, astronomers have struggled to explain how such a world could have formed in a seemingly empty region of space, where it is too far to be influenced by giant planets of the solar system and even the Milky Way galaxy itself.

Now, a new study suggests that a thus far undetected Earth-like planet hovering in that region could be deviating orbits of Sedna and a handful of similar trans-Neptunian objects (TNOs), which are the countless icy bodies orbiting the sun at gigantic distances. Many TNOs have oddly inclined and egg-shaped orbits, possibly due to being tugged at by a hidden planet, astronomers say.

Could an 'Earth-like' planet be hiding in our solar system's outer reaches? Sharmila Kuthunur, Space.com

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Rate of Expansion...

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A University of Minnesota Twin Cities-led team used a first-of-its-kind technique to measure the Universe's expansion rate, providing insight that could help more accurately determine the Universe’s age and help physicists and astronomers better understand the cosmos. Credit: NASA, ESA, and S. Rodney (JHU) and the FrontierSN team; T. Treu (UCLA), P. Kelly (UC Berkeley), and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)

Topics: Astronomy, Astrophysics, Cosmology, General Relativity

Thanks to data from a magnified, multiply-imaged supernova, a team led by University of Minnesota Twin Cities researchers have successfully used a first-of-its-kind technique to measure the universe's expansion rate. Their data provide insight into a longstanding debate in the field and could help scientists more accurately determine the universe's age and better understand the cosmos.

The work is divided into two papers published in Science and The Astrophysical Journal.

In astronomy, there are two precise measurements of the expansion of the universe, also called the "Hubble constant." One is calculated from nearby observations of supernovae, and the second uses the "cosmic microwave background," or radiation that began to stream freely through the universe shortly after the Big Bang.

However, these two measurements differ by about 10 percent, which has caused widespread debate among physicists and astronomers. If both measurements are accurate, that means scientists' current theory about the makeup of the universe is incomplete.

"If new, independent measurements confirm this disagreement between the two measurements of the Hubble constant, it would become a chink in the armor of our understanding of the cosmos," said Patrick Kelly, lead author of both papers and an assistant professor in the University of Minnesota School of Physics and Astronomy.

First-of-its-kind measurement of the universe's expansion rate weighs in on a longstanding debate. University of Minnesota, Phys.org.

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Einstein Rings...

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Multiple images of a background image created by gravitational lensing can be seen in the system HS 0810+2554. Credit: Hubble Space Telescope / NASA / ESA

Topics: Astronomy, Astrophysics, Dark Matter, Einstein, General Relativity

Physicists believe most of the matter in the universe is made up of an invisible substance that we only know about by its indirect effects on the stars and galaxies we can see.

We're not crazy! Without this "dark matter," the universe as we see it would make no sense.

But the nature of dark matter is a longstanding puzzle. However, a new study by Alfred Amruth at the University of Hong Kong and colleagues, published in Nature Astronomy, uses light's gravitational bending to bring us a step closer to understanding.

Invisible but omnipresent

We think dark matter exists because we can see its gravity's effects on galaxies' behavior. Specifically, dark matter seems to make up about 85% of the universe's mass, and most of the distant galaxies we can see appear to be surrounded by a halo of the mystery substance.

But it's called dark matter because it doesn't give off light or absorb or reflect it, which makes it incredibly difficult to detect.

So what is this stuff? We think it must be some kind of unknown fundamental particle, but beyond that, we're not sure. All attempts to detect dark matter particles in laboratory experiments have failed, and physicists have debated its nature for decades.

Scientists have proposed two leading hypothetical candidates for dark matter: relatively heavy characters called weakly interacting massive particles (or WIMPs) and extremely lightweight particles called axions. Theoretically, WIMPs behave like discrete particles, while axions behave more like waves due to quantum interference.

It has been difficult to distinguish between these two possibilities—but now light bent around distant galaxies has offered a clue.

New look at 'Einstein rings' around distant galaxies just got us closer to solving the dark matter debate, Rossana Ruggeri, Phys.org.

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Where No One Has Gone Before...

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Images of six candidate massive galaxies, seen 500-800 million years after the Big Bang. One of the sources (bottom left) could contain as many stars as our present-day Milky Way but is 30 times more compact. Credit: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology); Image processing: G. Brammer (Niels Bohr Institute’s Cosmic Dawn Center at the University of Copenhagen)

Topics: Astronomy, Astrophysics, Cosmology, Research

Nobody expected them. They were not supposed to be there. And now, nobody can explain how they had formed. 

Galaxies nearly as massive as the Milky Way and full of mature red stars seem to be dispersed in deep-field images obtained by the James Webb Space Telescope (Webb or JWST) during its early observation campaign. They are giving astronomers a headache. 

These galaxies, described in a new study based on Webb's first data release, are so far away that they appear only as tiny reddish dots to the powerful telescope. By analyzing the light emitted by these galaxies, astronomers established that they were viewing them in our universe's infancy, only 500 million to 700 million years after the Big Bang.

Such early galaxies are not in themselves surprising. Astronomers expected that the first star clusters sprung up shortly after the universe moved out of the so-called dark ages — the first 400 million years of its existence when only a thick fog of hydrogen atoms permeated space. 

But the galaxies found in the Webb images appeared shockingly big, and the stars in them were too old. The new findings are in conflict with existing ideas of how the universe looked and evolved in its early years and don't match earlier observations made by Webb's less powerful predecessor, the Hubble Space Telescope.

JWST Discovers Enormous Distant Galaxies That Should Not Exist, Tereza Pultarova, Scientific American/Space.com.

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Ancient Astronomy...

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Antikythera mechanism (Image), website, and publisher: Encyclopædia Britannica, https://www.britannica.com/topic/Antikythera-mechanism#/media/1/1334586/238592, access date: February 20, 2023

Topics: Archaeology, Astronomy, Astrophysics, History

In 1900 diver Elias Stadiatis, clad in a copper and brass helmet and a heavy canvas suit, emerged from the sea shaking in fear and mumbling about a “heap of dead naked people.” He was among a group of Greek divers from the Eastern Mediterranean island of Symi who were searching for natural sponges. They had sheltered from a violent storm near the tiny island of Antikythera, between Crete and mainland Greece. When the storm subsided, they dived for sponges and chanced on a shipwreck full of Greek treasures—the most significant wreck from the ancient world to have been found up to that point. The “dead naked people” were marble sculptures scattered on the seafloor, along with many other artifacts. Soon after, their discovery prompted the first major underwater archaeological dig in history.

One object recovered from the site, a lump the size of a large dictionary, initially escaped notice amid more exciting finds. Months later, however, at the National Archaeological Museum in Athens, the lump broke apart, revealing bronze precision gearwheels the size of coins. According to historical knowledge at the time, gears like these should not have appeared in ancient Greece or anywhere else in the world until many centuries after the shipwreck. The finding generated huge controversy.

The lump is known as the Antikythera mechanism, an extraordinary object that has befuddled historians and scientists for more than 120 years. Over the decades, the original mass split into 82 fragments, leaving a fiendishly difficult jigsaw puzzle for researchers to put back together. The device appears to be a geared astronomical calculation machine of immense complexity. Today we have a reasonable grasp of some of its workings, but there are still unsolved mysteries. We know it is at least as old as the shipwreck it was found in, which has been dated to between 60 and 70 B.C.E., but other evidence suggests it may have been made around 200 B.C.E.

One of the central researchers in the early years of Antikythera research was German philologist Albert Rehm, the first person to understand the mechanism as a calculating machine. Between 1905 and 1906, he made crucial discoveries that he recorded in his unpublished research notes. He found, for instance, the number 19 inscribed on one of the surviving Antikythera fragments. This figure referenced the 19-year period relation of the moon known as the Metonic cycle, named after Greek astronomer Meton but discovered much earlier by the Babylonians. On the same fragment, Rehm found the numbers 76, a Greek refinement of the 19-year cycle, and 223, for the number of lunar months in a Babylonian eclipse-prediction cycle called the saros cycle. These repeating astronomical cycles were the driving force behind Babylonian predictive astronomy.

The second key figure in the history of Antikythera research was British physicist turned historian of science Derek J. de Solla Price. In 1974, after 20 years of research, he published an important paper, “Gears from the Greeks.” It referred to remarkable quotations by the Roman lawyer, orator, and politician Cicero (106–43 B.C.E.). One of these described a machine made by mathematician and inventor Archimedes (circa 287–212 B.C.E.) “on which were delineated the motions of the sun and moon and of those five stars which are called wanderers ... (the five planets) ... Archimedes ... had thought out a way to represent accurately by a single device for turning the globe those various and divergent movements with their different rates of speed.” This machine sounds just like the Antikythera mechanism. The passage suggests that Archimedes, although he lived before we believe the device was built, might have founded the tradition that led to the Antikythera mechanism. It may well be that the Antikythera mechanism was based on a design by Archimedes.

An Ancient Greek Astronomical Calculation Machine Reveals New Secrets, Tony Freeth, Scientific American

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Planet Video...

 

Topics: Astronomy, Astrophysics, Exoplanets, Space Exploration

In 2008, HR8799 was the first extrasolar planetary system ever directly imaged. Now, the famed system stars in its very own video.

Using observations collected over the past 12 years, Northwestern University astrophysicist Jason Wang has assembled a stunning time-lapse video of the family of four planets — each more massive than Jupiter — orbiting their star. The video gives viewers an unprecedented glimpse into planetary motion.

“It’s usually difficult to see planets in orbit,” Wang said. “For example, it isn’t apparent that Jupiter or Mars orbit our sun because we live in the same system and don’t have a top-down view. Astronomical events happen too quickly or slowly to capture in a movie. But this video shows planets moving on a human time scale. I hope it enables people to enjoy something wondrous.”

An expert in exoplanet imaging, Wang is an assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

Watch distant worlds dance around their sun, Amanda Morris, Northwestern University.

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Reimagining ET...

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Life on other planets might not look like any beings we’re used to on Earth. It may even be unrecognizable at first to scientists searching for it. Credit: William Hand

Topics: Astrobiology, Astronomy, Astrophysics, Planetary Science, SETI, Space Exploration

Sarah Stewart Johnson was a college sophomore when she first stood atop Hawaii’s Mauna Kea volcano. Its dried lava surface differed from the eroded, tree-draped mountains of her home state of Kentucky. Johnson wandered away from the other young researchers she was with and toward a distant ridge of the 13,800-foot summit. Looking down, she turned over a rock with the toe of her boot. To her surprise, a tiny fern lived underneath it, sprouting from ash and cinder cones. “It felt like it stood for all of us, huddled under that rock, existing against the odds,” Johnson says.

Her true epiphany, though, wasn’t about the hardiness of life on Earth or the hardships of being human: It was about aliens. Even if a landscape seemed strange and harsh from a human perspective, other kinds of life might find it quite comfortable. The thought opened up the cosmic real estate and the variety of life she imagined might be beyond Earth’s atmosphere. “It was on that trip that the idea of looking for life in the universe began to make sense to me,” Johnson says.

Later, Johnson became a professional at looking. As an astronomy postdoc at Harvard University in the late 2000s and early 2010s, she investigated how astronomers might use genetic sequencing—detecting and identifying DNA and RNA—to find evidence of aliens. Johnson found the work exciting (the future alien genome project!), but it also made her wonder: What if extraterrestrial life didn’t have DNA, RNA, or other nucleic acids? What if their cells got instructions in some other biochemical way?

As an outlet for heretical thoughts like this, Johnson started writing in style too lyrical and philosophical for scientific journals. Her typed musings would later turn into the 2020 popular science book The Sirens of Mars. Inside its pages, she probed the idea that other planets were truly other. So their inhabitants might be very different, at a fundamental and chemical level, from anything in this world. “Even places that seem familiar—like Mars, a place that we think we know intimately—can completely throw us for a loop,” she says. “What if that’s the life case?”

The Search for Extraterrestrial Life as We Don’t Know It, Sarah Scoles, Scientific American

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At Horizon's Edge...

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An artist’s concept of New Horizons during the spacecraft’s planned encounter with Pluto and its moon Charon. The craft’s miniature cameras, radio science experiments, ultraviolet and infrared spectrometers, and space plasma experiments would characterize the global geology and geomorphology of Pluto and Charon, map their surface compositions and temperatures, and examine Pluto’s atmosphere in detail. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

Topics: Astronomy, Astrophysics, NASA, Planetary Science, Space Exploration

Only two spacecraft have ever left our solar system and lived to tell the tale. In 2012 and 2019, NASA’s Voyager 1 and 2 spacecraft respectively broke through the heliopause, the boundary at which our sun’s sphere of influence gives way to the interstellar medium. They have sent back remarkable riches from this distant location, humanity’s first foray into the limitless bounds beyond our solar system’s edge. Hot pursuit is a far more advanced vehicle, sporting improved instruments, updated optics, and even a means to sample the interstellar medium itself. New Horizons was launched from Earth in 2006 on a mission to visit Pluto, arriving in 2015 and revealing incredible details during its all-too-brief flyby. The spacecraft has continued its cruise toward interstellar frontiers ever since. It has now begun its second extended mission. It is soon set to wake up from a deep hibernation, opening a wealth of new scientific opportunities in the outer solar system. “It takes a long time to get to where our spacecraft is,” says Alice Bowman, mission operations manager for New Horizons at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) in Maryland. “When you have a spacecraft that is out in that part of the solar system, it is a huge asset to the scientific community. There are so many unique things that a spacecraft that is out that far can do. We definitely want to take advantage of that.”

For New Horizons, those “unique things” include unprecedented studies of the planets Uranus and Neptune, sampling of the local dust, studies of the background light in the universe, and more. The sum total will be a new phase of the mission that is “really unique and interdisciplinary in nature,” says Alan Stern, the lead on the mission at the Southwest Research Institute (SwRI) in Texas. In October, this two-year second extended mission officially began, but in 2023 it will pick up the pace as the spacecraft exits hibernation and begins its scientific program in earnest. “There were lots of good ideas for how to do things in astrophysics, heliophysics, and planetary science,” Stern says. “We took the very best of those.” There is even the tantalizing possibility of visiting another object in the Kuiper Belt, the region of asteroids and icy objects that lurks beyond Neptune, in which New Horizons has already visited one object—Arrokoth in 2019—after its Pluto encounter. Even without such a possibility, there was more than enough reason for NASA to extend the mission. “New Horizons is at a unique location in the solar system with an amazing suite of functioning instruments on board,” says Becky McCauley Rench, New Horizons program scientist at NASA Headquarters in Washington, D.C. “[It] can provide valuable insights to the heliosphere and the solar wind, astronomical observations of the cosmic background radiation, and valuable data about Uranus and Neptune that can be applied to our knowledge about ice giant planets.”

NASA’s Pluto Spacecraft Begins New Mission at the Solar System’s Edge, Jonathan O'Callaghan, Scientific American

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Modified Gravity...

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Rotation curve of the typical spiral galaxy M 33 (yellow and blue points with error bars) and the predicted one from the distribution of the visible matter (white line). The discrepancy between the two curves is accounted for by adding a dark matter halo surrounding the galaxy. Credit: Wikipedia

Topics: Astronomy, Astrophysics, Cosmology, Dark Matter

Although dark matter is central to the standard cosmological model, it's not without issues. There continue to be nagging mysteries about the stuff, not the least of which is the fact that scientists have found no direct particle evidence of it.

Despite numerous searches, we have yet to detect dark matter particles. Some astronomers favor an alternative, such as modified Newtonian dynamics (MoND) or the modified gravity model. And a new study of galactic rotation seems to support them.

The idea of MoND was inspired by galactic rotation. Most of the visible matter in a galaxy is clustered in the middle, so you'd expect that stars closer to the center would have faster orbital speeds than stars farther away, similar to the planets of our solar system. We observe that stars in a galaxy all rotate at about the same speed. The rotation curve is essentially flat rather than dropping off. The dark matter solution is that a halo of invisible matter surrounds galaxies, but in 1983 Mordehai Milgrom argued that our gravitational model must be wrong.

At interstellar distances, the gravitational attraction between stars is essentially Newtonian. So rather than modifying general relativity, Milgrom proposed modifying Newton's universal law of gravity. He argued that rather than the force of attraction as a pure inverse square relation, gravity has a small remnant pull regardless of distance. This remnant is only about ten trillionths of a G, but it's enough to explain galactic rotation curves.

New measurements of galaxy rotation lean toward modified gravity as an explanation for dark matter, Brian Koberlein, Universe Today/Phys.org.

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Cosmic Family Portraits...

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Credit: NASA, ESA, CSA, and Jupiter ERS Team; Image processing by Ricardo Hueso/UPV/EHU and Judy Schmidt

Topics: Astronomy, Astrophysics, Planetary Science, Space Exploration

Jupiter's rings, its moons Amalthea (the bright point at left), Adrastea (the faint dot at the left tip of rings), and even background galaxies are visible in this image from JWST's NIRCam instrument. Whiter areas on the planet represent regions with more cloud cover, which reflects sunlight, especially Jupiter's famous Great Red Spot; darker spots have fewer clouds. Perhaps the most stunning feature is the blue glow of the planet's auroras at the north and south poles. This light shows results when high-energy particles streaming off the sun hit atoms in Jupiter's atmosphere. Auroras are found on any planet with an atmosphere and a magnetic field, which steers the sun's particles to the poles; besides Earth and Jupiter, telescopes have seen auroras on Saturn, Uranus, and Neptune.

The Best of JWST’s Cosmic Portraits, Clara Moskowitz, Scientific American

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Dinosaurs and Dodos...

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Credit: Andrzej Puchta/Alamy Stock Photo

Topics: Asteroids, Astronomy, Astrophysics, Civilization, Computer Modeling

The following article, since it simulated the destruction of my hometown, two days after my sixtieth birthday, is a little personal.

*****

On August 16, 2022, an approximately 70-meter asteroid entered Earth’s atmosphere. At 2:02:10 P.M. EDT, the space rock exploded eight miles over Winston-Salem, N.C., with the energy of 10 megatons of TNT. The airburst virtually leveled the city and surrounding area. Casualties were in the thousands.

Well, not really. The destruction of Winston-Salem was the storyline of the fourth Planetary Defense Tabletop Exercise, run by NASA’s Planetary Defense Coordination Office. The exercise was a simulation where academics, scientists, and government officials gathered to practice how the United States would respond to a real planet-threatening asteroid. Held February 23–24, participants were both virtual and in-person, hailing from Washington D.C., the Johns Hopkins Applied Physics Lab (APL) campus in Laurel, Md., Raleigh, and Winston-Salem, N.C. The exercise included more than 200 participants from 16 different federal, state, and local organizations. On August 5, the final report came out, and the message was stark: humanity is not yet ready to meet this threat.

On the plus side, the exercise was meant to be hard—practically unwinnable. “We designed it to fall right into the gap in our capabilities,” says Emma Rainey, an APL senior scientist who helped to create the simulation. “The participants could do nothing to prevent the impact.” The main goal was to test the different government and scientific networks that should respond in a real-life planetary defense situation. “We want to see how effective operations and communications are between U.S. government agencies and the other organizations that would be involved, and then identify shortcomings,” says Lindley Johnson, planetary defense officer at NASA headquarters.

NASA Asteroid Threat Practice Drill Shows We’re Not Ready, Matt Brady, Scientific American

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Death of Chrysalis...

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A view of Saturn from NASA's Hubble Space Telescope captures details of its ring system and atmospheric details on June 20, 2019. NASA, ESA, A. Simon (GSFC), M.H. Wong (University of California, Berkeley), and the OPAL Team/Handout via REUTERS

Topics: Astronomy, Astrophysics, NASA, Planetary Science

WASHINGTON, Sept 15 (Reuters) - Call it the case of the missing moon.

Scientists using data obtained by NASA's Cassini spacecraft and computer simulations said on Thursday the destruction of a large moon that strayed too close to Saturn would account both for the birth of the gas giant planet's magnificent rings and its unusual orbital tilt of about 27 degrees.

The researchers named this hypothesized moon Chrysalis and said it may have been torn apart by tidal forces from Saturn's gravitational pull perhaps 160 million years ago - relatively recent compared to the date of the planet's formation more than 4.5 billion years ago.

About 99% of the Chrysalis wreckage appears to have plunged into Saturn's atmosphere while the remaining 1% stayed in orbit around the planet and eventually formed the large ring system that is one of the wonders of our solar system, the researchers said. They chose the name Chrysalis for the moon because it refers to a butterfly's pupal stage before it transforms into its glorious adult form.

"As a butterfly emerges from a chrysalis, the rings of Saturn emerged from the primordial satellite Chrysalis," said Jack Wisdom, a professor of planetary science at the Massachusetts Institute of Technology and lead author of the study published in the journal Science.

Violent death of moon Chrysalis may have spawned Saturn's rings, Will Dunham, Reuters Science

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Proxima Oceans...

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An artist’s impression of the newly discovered planet orbiting Proxima Centauri.Credit: ESO/L. Calçada

Topics: Astronomy, Astrophysics, Exoplanets, Space Exploration, Spaceflight

Astronomers have discovered a third planet orbiting Proxima Centauri, the star closest to the Sun. Called Proxima Centauri d, the newly spotted world is probably smaller than Earth and could have oceans of liquid water.

“It’s showing that the nearest star probably has a very rich planetary system,” says Guillem Anglada-Escudé, an astronomer at the Institute of Space Sciences in Barcelona, Spain, who led the team that, in 2016, discovered the first planet to be seen orbiting Proxima Centauri.

Astronomer João Faria and his collaborators detected Proxima Centauri d by measuring tiny shifts in the spectrum of light from the star as the planet’s gravity pulled at it during orbit. The team used a state-of-the-art instrument called the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) at the Very Large Telescope, a system of four 8.2-meter telescopes at the European Southern Observatory in Cerro Paranal, Chile. The results were published on 10 February in Astronomy & Astrophysics.

Earth-like planet spotted orbiting Sun’s closest star, Davide Castelvecchi, Nature

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Cosmic Existentialism...

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An illustration of a black hole and its event horizon. (Image credit: Nicholas Forder/Future Publishing)

Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

"Small" black holes are estimated to make up 1% of the universe's matter.

Scientists have estimated the number of "small" black holes in the universe. And no surprise: It's a lot.

This number might seem impossible to calculate; after all, spotting black holes is not exactly the simplest task. Because there are as pitch-black as the space they lurk in, the light swallowing cosmic goliaths can be detected only under the most extraordinary circumstances — like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling toward enormous collisions that unleash gravitational waves.

But that hasn't stopped scientists from finding some ingenious ways to guess the number. Using a new method, outlined Jan. 12 in The Astrophysical Journal, a team of astrophysicists has produced a fresh estimate for the number of stellar-mass black holes — those with masses 5 to 10 times that of the sun — in the universe.

And it's astonishing: 40,000,000,000,000,000,000, or 40 quintillions, stellar-mass black holes populate the observable universe, making up approximately 1% of all normal matter, according to the new estimate.

So how did the scientists arrive at that number? By tracking the evolution of stars in our universe they estimated how often the stars — either on their own or paired into binary systems — would transform into black holes, said first author Alex Sicilia, an astrophysicist at the International School of Advanced Studies (SISSA) in Trieste, Italy.

40 quintillion stellar-mass black holes are lurking in the universe, a new study finds, Ben Turner, Space.com

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Dyson Sphere Feedback...

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Image: Artist’s impression of a Dyson sphere under construction. Credit: Steve Bowers.

Topics: Astronomy, Astrophysics, Dyson Sphere, SETI

Although the so-called Dysonian SETI has been much in the air in recent times, its origins date back to the birth of SETI itself. It was in 1960 – the same year that Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia to study Epsilon Eridani and Tau Ceti – that Freeman Dyson proposed the Dyson sphere. In fiction, Olaf Stapledon had considered such structures in his novel Star Maker in 1937. As Macy Huston and Jason Wright (both at Penn State) remind us in a recent paper, Dyson’s idea of energy-gathering structures around an entire star evolved toward numerous satellites around the star rather than a (likely unstable) single spherical shell.

We can’t put the brakes on what a highly advanced technological civilization might do, so both solid sphere and ‘swarm’ models can be searched for, and indeed have been, for in SETI terms we’re looking for infrared waste heat. And if we stick with Dyson (often a good idea!), we would be looking for structures orbiting in a zone where temperatures would range in the 200-300 K range, which translates into searching at about 10 microns, the wavelength of choice. But Huston and Wright introduce a new factor, the irradiation from the interior of the sphere onto the surface of the star.

This is intriguing because it extends our notions of Dyson spheres well beyond the habitable zone as we consider just what an advanced civilization might do with them. It also offers up the possibility of new observables. So just how does such a Dyson sphere return light back to a star, affecting its structure and evolution? If we can determine that, we will have a better way to predict these potential observables. As we adjust the variables in the model, we can also ponder the purposes of such engineering.

Think of irradiation as Dyson shell ‘feedback.’ We immediately run into the interesting fact that adding energy to a star causes it to expand and cool. The authors explain this by noting that total stellar energy is a sum of thermal and gravitational energies. Let’s go straight to the paper on this. In the clip below, E* refers to the star’s total energy, with Etherm being thermal energy:

When energy is added to a star (E increases), gravitational energy increases and thermal energy decreases, so we see the star expand and cool both overall (because Etherm is lower) and on its surface (because being larger at the same or a lower luminosity its effective temperature must drop). A larger star should also result in less pressure on a cooler core, so we also expect its luminosity to decrease.

Dyson Sphere ‘Feedback’: A Clue to New Observables? Paul Gilster, Centauri Dreams

Evolutionary and Observational Consequences of Dyson Sphere Feedback, Macy Huston, Jason Wright, Astrophysical Journal

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Exomoon Two...

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Artist’s impression of an exomoon (left) orbiting a giant planet around a distant star. Credit: Helena Valenzuela Widerström

Topics: Astronomy, Astrophysics, Exomoon, Exoplanets

And then there were two—maybe. Astronomers say they have found a second plausible candidate for a moon beyond our solar system, an exomoon, orbiting a world nearly 6,000 light-years from Earth. Called Kepler-1708 b-i, the moon appears to be a gas-dominated object, slightly smaller than Neptune, orbiting a Jupiter-sized planet around a sunlike star—an unusual but not wholly unprecedented planet-moon configuration. The findings appear in Nature Astronomy. Confirming or refuting the result may not be immediately possible, but given the expected abundance of moons in our galaxy and beyond, it could further herald the tentative beginnings of an exciting new era of extrasolar astronomy—one focused not on alien planets but on the natural satellites that orbit them and the possibilities of life therein.

There are more than 200 moons in our solar system, and they have an impressive array of variations. Saturn’s moon Titan possesses a thick atmosphere and frigid hydrocarbon seas on its surface, possibly an analog of early Earth. Icy moons such as Jupiter’s Europa are frozen balls that hide subsurface oceans, and they may be prime habitats for life to arise. Others still, such as our own moon, are apparently barren wastelands but could have water ice in their shadowed craters and maze-like networks of tunnels running underground. An important shared trait among these worlds, however, is their mere existence: six of the eight major planets of our solar system have moons. Logic would suggest the same should be true elsewhere. “Moons are common,” says Jessie Christiansen of the California Institute of Technology. “In our solar system, almost everything has a moon. I am very confident that moons are everywhere in the galaxy.”

Astronomers Have Found Another Possible ‘Exomoon’ beyond Our Solar System, Jonathan O'Callaghan, Scientific American

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Moments and Metaphors...

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Credit: Pete Saloutos/Getty Images

Topics: Astronomy, Astrophysics, Comets, Philosophy, Science Fiction

On a recent morning, in Lower Manhattan, 20 scientists, including me, gathered for a private screening of the new film Don’t Look Up, followed by lunch with the film’s director, Adam McKay.

The film’s plot is simple. An astronomy graduate student, Kate Dibiasky (Jennifer Lawrence), and her professor, Randall Mindy (Leonardo DiCaprio), discover a new comet and realize that it will strike the Earth in six months. It is about nine kilometers across, like the one that wiped out the dinosaurs 66 million years ago. The astronomers try to alert the president, played by Meryl Streep, to their impending doom.

“Let’s just sit tight and assess,” she says, and an outrageous, but believable comedy ensues, in which the astronomers wrangle an article in a major newspaper and are mocked on morning TV, with one giddy host asking about aliens and hoping that the comet will kill his ex-spouse.

At last, mainstream Hollywood is taking on the gargantuan task of combatting the rampant denial of scientific research and facts. Funny, yet deadly serious, Don’t Look Up is one of the most important recent contributions to popularizing science. It has the appeal, through an all-star cast and wicked comedy, to reach audiences that have different or fewer experiences with science.

Don’t Look Up isn’t a movie about climate change, but one about planetary defense from errant rocks in space. It handles that real and serious issue effectively and accurately. The true power of this film, though, is in its ferocious, unrelenting lampooning of science deniers.

After the screening, in that basement theater in SoHo, McKay said: “This film is for you, the scientists. We want you to know that some of us do hear you and do want to help fight science denialism.”

Hollywood Can Take On Science Denial: Don’t Look Up Is a Great Example, Rebecca Oppenheimer, curator, and professor of astrophysics at the American Museum of Natural History/Scientific American

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