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A research group has developed a new COVID-19 testing system using Janus particles -- microparticles with two sides possessing distinctive molecular properties. These particles are engineered to bind specifically to target antigens, such as viral proteins, creating a low-cost, accurate, and rapid means of testing for viral diseases. The system's versatility means it can potentially be used to test for other diseases and biomarkers linked to other conditions.

A single treatment session, which includes the video game Tetris, can reduce symptoms of post-traumatic stress disorder (PTSD). This has been shown in a new study carried out with healthcare professionals working during the COVID-19 pandemic.

Large language models (LLMs) have developed rapidly in recent years and are becoming an integral part of our everyday lives through applications like ChatGPT. An article explains the opportunities and risks that arise from the use of LLMs for our ability to collectively deliberate, make decisions, and solve problems.

Although most potentially habitable worlds orbit red dwarf stars, we know larger and brighter stars can harbor life. One yellow dwarf star, for example is known to have a planet teaming with life, perhaps even intelligent life. But how large and bright can a star be and still have an inhabited world? That is the question addressed in a recent article in the Astrophysical Journal.

Stable main-sequence stars such as the Sun are categorized by color or spectral type, with each type assigned a letter designation. For historical reasons the categories aren’t alphabetical. Red dwarf stars, the coolest stars with the smallest mass, are M type. Then with each brighter, bluer, and more massive category is K, G, F, A, B, and finally O. The Sun falls into the G category as a yellow star. Each spectral type is then broken into smaller sections, numbered 0 – 9. The Sun is G2 star because it is at the warmer end of G-type stars.

As you go up the scale, the potentially habitable zone shifts farther from the star but also gets larger. That makes it more likely for a planet to be in the zone. But larger stars also have shorter lives, which might not give life enough time to evolve on a world. Then there are other factors that can be harmful for life. The largest stars emit a tremendous amount of ionizing radiation, which could strip planets of their atmospheres, or sterilize the surface of a planet. Because of this, the largest stars of the B and O types aren’t likely to harbor life.

How habitable zones differ by spectral type. Credit: NASA, ESA and Z. Levy (STScI)

But what about F-type stars? They are a bit brighter than the Sun and more white than yellow in color. They are also stable for around 4 billion years, which is long enough for life to evolve and thrive. And they also emit more ultraviolet radiation, which may have helped life arise on Earth. What are the odds of a habitable F-type planet?

To answer this question, the team went through the database of known exoplanets. About 80 F-type main-sequence stars are known to have at least one planet. Of those, 18 systems have exoplanets that spend at least part of their orbit in the habitable zone of the star. And in one case, the exoplanet 38 Virginis b, the planet is always in the habitable zone. Statistically around 5% – 20% of F-type stars have potential for life.

What’s interesting about 38 Virginis b is that it is a gas giant about 4 times more massive than Jupiter, so it isn’t likely to be habitable. But it could have Earth-sized moons, similar to the Galilean moons of Jupiter. A world orbiting a Jovian planet could be a perfect home for life.

F-type stars only comprise 3% of main-sequence stars in the Milky Way, and it’s possible that their excess UV light could rule out habitable worlds. But alien astronomers might make similar arguments about G-type stars like the Sun. As this study shows, we shouldn’t rule out the Sun’s brighter cousins in the search for living worlds.

Reference: Patel, Shaan D., Manfred Cuntz, and Nevin N. Weinberg. “Statistics and Habitability of F-type Star–Planet Systems.” The Astrophysical Journal Supplement Series 274.1 (2024): 20.

The post Could Stars Hotter Than the Sun Still Support Life? appeared first on Universe Today.

Here’s what members of the New Scientist editorial team are keenest to catch at the world’s greatest festival of ideas and discovery, which runs from 12 to 13 October

I recently wrote a piece for Skeptic titled “Ranking Presidents: Does It Make Any Sense?”, in which I outlined three reasons why ranking Presidents against one another is a fool’s errand: presentism, the evolving role of the presidency, and sui generis.1 The current trend of the first of these criteria, presentism, becomes problematic when applied to entertainment made for previous generations. Viewing and evaluating the culture of the past through a contemporary lens has led to erasing history in at least three relatively recent incidents. This is, I believe, a slippery slope toward censorship and a missed opportunity for valuable lessons about our collective past.

In 1991, Disney released a video version of their 1940 masterpiece Fantasia, describing it as “a meticulously restored version of the original, full-length film.” It wasn’t, though. The version Disney released omitted an original scene in which a Black centaurette named Sunflower is shown shining shoes of a White centaur.2 Seen today, Sunflower is a patently offensive stereotype.3 Ten years later Disney released the censored version for the film’s 60th anniversary DVD.4 Disney’s use of racist stereotypes is not limited to Fantasia. In varying degrees, such tropes are seen in Dumbo (1941),5 Peter Pan (1953),6 The Aristocats (1970),7 and Aladdin (1992).8

In 2020, the company (admirably, in my view) took steps toward addressing this controversy by adding disclaimers to their films on their streaming services, noting the “harmful impact” of racist stereotypes. Unlike the quiet actions the company took censoring the re-releases of Fantasia, the films are viewable in their original forms.

This begs the question: If the racism was so apparent, why weren’t these films decried upon initial release? The answer is they weren’t considered offensive by the public at the time, and applying today’s attitudes toward race crystallizes the fallacy of presentism.

In 2014, Ruth Wise, professor emerita of Yiddish and Comparative Literatures at Harvard, criticized Fiddler on the Roof (1971) for sacrificing Jewish identity to make the musical more universally appealing.9 The problem with Wise’s argument is (again) presentism. In the early 1970s, M*A*S*H writers employed rape jokes,10 and America’s most popular sitcom (All in the Family) featured a working-class bigot who employed racial slurs for laughs.11 John Lennon released a song titled “Woman is The (N-word) of the World”12 and Richard Pryor would use the same racial epithet in an album title three years later.13 Our attitudes towards cultural authenticity and appropriation have evolved since the early 1970s.

In 2020, a 1988 Golden Girls episode called “Mixed Feelings” was pulled from the streaming platform Hulu due to “a scene in which Betty White and Rue McClanahan are mistaken for wearing blackface.”14 In the episode, Dorothy’s (White) son introduces his fiancé, a much older Black woman. Blanche and Rose are mortified with embarrassment when they unexpectedly meet the couple wearing cosmetic mud masks.

Were Rose and Blanche revisiting a minstrel show to characterize Black Americans as lazy, hypersexual thieves, ala “Amos ‘n Andy,” as minstrel shows were in the past?15 Of course not. The joke lay in their mutual embarrassment of appearing as if they were in blackface.16 Each Golden Girls actress (Betty White, Bea Arthur, Rue McClanahan, and Estelle Getty) came of age decades before the women’s movement, but their show was considerably progressive for their time. In its seven-year run, The Golden Girls featured episodes centered on then-controversial topics of racism, sexual harassment, same-sex marriage, age discrimination, homelessness, the death of children, and addiction.17 Perhaps most significantly, a 1990 episode titled “72 Hours,” has Rose worried that she may have come in contact with HIV.18 It was only five years prior that President Reagan first addressed the AIDS crisis, by which time 42,600 people had died from the disease. By 1990, that number had spiked to 310,000, a third of which were deaths occurring that same year.19 When one considers the climate of the times, airing the episode was courageous.

The same year “Mixed Feelings” was removed from Hulu, an actor named François Clemmons published Officer Clemmons: A Memoir. Clemmons played “Officer Clemmons” on Mr. Roger’s Neighborhood in the late 1960s, the first African American actor to have a recurring role on a children’s television program.20 In Clemmon’s mostly heartwarming book, he relates an incident in which Fred Rogers called him into his office. His boss said to him, “Someone has informed us that you were seen at the local gay bar downtown. Now, I want you to know, Franc, that if you’re gay, it doesn’t matter to me at all. Whatever you say and do is fine with me, but if you’re going to be on the show as an important member of the Neighborhood, you can’t be out as gay.”

Was Mr. Rogers homophobic? When Rogers had the conversation with Clemmons, homosexuality was still listed as a disorder in the DSM. It wasn’t until 1974 that it was replaced with “sexual orientation disturbance.”21 In reality, Fred Rogers, a Presbyterian minister, was an LGBTQ ally. He’d intentionally hired gay men and women since the 1960s and rebuffed efforts from his viewers to renounce homosexuality.22

This article appeared in Skeptic magazine 29.2
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In John Hughes’ The Breakfast Club (1985)23 and Jeff Kanus’ Revenge of the Nerds (1984),24 there are scenes of sexual assault upon women played for laughs. Both Gene Siskel and Roger Ebert (renowned film critics) praised each film, neither noting their discomfort with the now-troubling scenes in either review.25, 26, 27 Why did they fail to do so? Were both Siskel and Ebert misogynists willing to overlook scenes of women being sexually assaulted? Of course not. The social mores in the early 1980s didn’t apply to those we share today. Are these scenes excusable? No, but both actresses (Molly Ringwald and Julie Montgomery) have publicly reckoned with the blatant sexism in their roles and neither has insisted the scenes be omitted.28, 29

In 2022, the UK’s Channel 5 aired the 1961 classic Breakfast at Tiffany’s, but bowdlerized scenes of Mickey Rooney as “Mr. Yunioshi,” an over-the-top yellow-face Asian caricature.30 Should Rooney’s role be excised? No. Just like the racist characters in Disney movies of the 1940s–1990s, and the sexual assaults depicted for laughs in 1980s raunchy comedies, the climate in 1961 was different.

Pop culture of the past is just that: of the past. Applying today’s standards to them is at best a fool’s errand and, at worst (as seen in the cases above) a slippery slope toward censorship. Entertainment from yesteryear should be taken in context while viewed in its entirety.

About the Author

John D. Van Dyke is an academic and science educator. His personal website is vandykerevue.org.

References

1. https://bit.ly/3vjUhOj
2. https://bit.ly/48YFeYe
3. https://bit.ly/49UFKaT
4. https://bit.ly/3TFD1w8
5. https://bit.ly/3TpvgcA
6. https://bit.ly/43p6fTb
7. https://bit.ly/43ltjm0
8. https://bit.ly/3TEanM6
9. https://bit.ly/3IHU5vb
10. https://bit.ly/3IJzVRu
11. https://bit.ly/3IHU9uV
12. Miles, B. & Badman, K. (2001). The Beatles Diary After the Break-Up: 1970–2001. Music Sales Group.
13. https://bit.ly/3TgVYE6
14. https://bit.ly/3VoMmKi
15. https://bit.ly/43koCJd
16. https://bit.ly/3IHHGYf
17. https://bit.ly/43lj6G0
18. https://bit.ly/43DFElP
19. https://bit.ly/3v783Ut
20. Clemmons, F. S. (2020). Officer Clemmons: A Memoir. Catapult.
21. https://bit.ly/3vg6XWj
22. https://bit.ly/49XehW4
23. https://bit.ly/4ahrvN1
24. https://bit.ly/3VmOGBu
25. https://bit.ly/3ViAR72
26. https://bit.ly/4cdaDJ4
27. https://bit.ly/4cj1RcG
28. https://bit.ly/3VmZOOP
29. https://bit.ly/492E65L
30. https://bit.ly/4chtAu9

Doug Hayes of Richmond, Virginia, is back with his “Breakfast Crew” series of bird photos (and a new mammalian member of the Crew). His captions and narrative are indented, and you can enlarge the photos by clicking on them.

The gang is back! The past few months have been quiet at the backyard feeders as plenty of food was available in the surrounding wooded areas along the James River. We also had a pair of hawks build a nest a few yards over which kept activity to a minimum. The hawks seem to have moved on now. With the cooler weather, the Breakfast Crew has returned with the usual members, plus a new mammalian member of the crew, Pat the Bunny.

A common grackle (Quiscalus quiscula) chows down at the basket filled with peanuts and sunflower seeds:

A female house finch (Haemorhous mexicanus) levitates while waiting for a male to finish his meal:

Only peanuts will do for the red-bellied woodpeckers (Melanerpes carolinus). They will dig around, tossing aside sunflower seeds and corn until they find a peanut:

We don’t get very many American goldfinches (Spinus tristis) in the yard, even though they are fairly common throughout the neighborhood. This day, four of the little guys showed up:

White-breasted nuthatches (Sitta carolinensis) are regulars in the yard. They tend to be hit and run feeders, snagging a sunflower seed and flying back into the trees to eat:

A juvenile brown-headed cowbird (Molothrus ater):

Carolina chickadees (Poecile carolinensis) are among the regular visitors to the feeders:

This mourning dove (Zenaida macroura) decided to give perching on the crook a try. It stayed there for some time, despite looking uncomfortable:

We had a population explosion among the Northern cardinals (Cardinalis cardinalis) this year. There are nearly a dozen juveniles that show up most mornings, most of them seem to be females:

This male cardinal (Cardinalis cardinalis) was going through a molt a few weeks ago and was completely bald. Now he seems to be regrowing his head and cheek feathers:

Carolina wrens (Thryothorus ludovicianus) are another bird that underwent a population explosion. Dozens of these noisy, curious little birds hang out in the yard most of the day:

A tufted titmouse (Baeolophus bicolor) about to take off with its meal. Another bird that grabs a quick meal and takes it into the trees to eat.

Downy woodpeckers (Picoides pubescens) love peanuts, just like the larger, red-bellied woodpeckers. They will take suet when I put it out:

Pat the Bunny, an Eastern cottontail (Sylvilagus floridanus), has been hanging out in the yard for over a month now. I think Pat lives under one of the sheds at the end of the yard. The rabbit is most active late afternoons, but I have seen it eating scattered seeds under the bird feeders in the morning:

Photo information:  Sony A7RV camera body, Sony FE 200-600 zoom lens + 1.4X teleconverter, iPhoto Cobra 2 monopod, Neewer gimbal tripod head. Auto ISO, shutter speed ranging from 1/650th to 1/2500th of a second, photos resized and tweaked with Adobe Photoshop (Beta) v25.13

Things have been extremely busy! I have

• written a new article for New Scientist about the familiar-sounding words that we use in physics (such as “particle”) and how they can easily mislead the unwary;
• appeared in an extended Know Time podcast, hosted by a non-scientist, in which we discuss fields, particles and the Higgs boson — core material of my book Waves in an Impossible Sea; and
• learned that the audiobook version of the book is now available for pre-order; it comes out September 24th. 

If any of these might interest you, here are the details!

Article on Science and Language in New Scientist

First, about the latest article I’ve written for New Scientist magazine. (My other New Scientist articles can be found at the bottom of this page.) This one is about the interplay between science and language. There are a lot of words in English that have been repurposed by physicists — force, mass, energy, field, etc. — whose meanings for physicists differ, to a greater or lesser extent, from their meanings in ordinary conversational settings.  This definitional mismatch creates all sorts of opportunities for misunderstandings.

I also dealt with this issue, to a certain extent, in my book. From my experience teaching, and also writing on this blog for many years, I have come to the conclusion that one can’t properly explain the most important results of modern physics without close attention to this linguistic challenge. 

Anyway, in this new article, the focus is mostly on three words crucial for modern physics: atom, force, and particle.  I examine how and why their meanings have shifted over time, and the legacies of these shifts for those trying to make sense of physicists’ verbal explanations of how the universe works.

This is my second article of the month; if you missed my article in Quanta Magazine about how the Higgs field truly gives mass to elementary particles, you can find it here.  My approach to this topic (also covered extensively in my book) avoids the false analogies of the Higgs field being like molasses, or soup, or anything else that violates the Principle of Relativity. It also draws attention to the connection of these ideas to those of resonance, which is fundamental to the physics of musical instruments.  

If you find these articles too brief or too oracular, the book can provide far more details without the use of math.  If you actually want some of the math (but not too much), you can find that here on this website, for example here and here. If that’s still not quite what you want, feel free to ask me for guidance, or explore this website further using the Search bar at the upper right of this page.

Know Time Podcast About the Topics of my Book

Shalaj Lawania, on his podcast Know Time, has a terrific series of interviews with a wide variety of interesting people, including but not limited to scientists.   I’m very pleased to be added to his impressive list. It’s a real shame that he has relatively few subscribers, given the high quality of what he is doing. I strongly encourage you to check out his channel.  You will not be disappointed.

As he always does, Lawania curated a well-structured interview. We methodically covered a wide range of topics from my book, as well as some more general issues about science and belief.  The full interview is two hours long!  But no worries if that’s way too much; you can listen to various self-contained excerpts that Lawania has separated out.

The AudioBook is Finally In Sight

Since many people find it convenient to listen to books rather than read their texts, it’s not surprising that I’ve often been asked about the audio version of my book, for which we’ve had to wait over six months. But the wait is over. I’m pleased to tell you that the audiobook will finally become available next Tuesday, September 24th.  (It can be pre-ordered now.) The company who recorded it wanted a professional reader with an in-house recording studio, so they did not offer me the option of reading it myself. But I am reasonably confident in the skills of the reader they selected.

I’m concerned, though, that the audiobook may be harder to follow than the written text. After all, the written text has many figures and a glossary, and it’s more amenable when one wants to review earlier material that appears again in a later section. To mitigate this, I have put the figures, the tables, the glossary, and the endnotes online on this webpage. That way, while you’re listening to the audiobook, you can have the images etc. open in your browser, so that you can access them easily when they are mentioned. 

And I do think you should expect to listen to certain sections of the book twice. The ideas of modern physics are very strange indeed. I’m sure that I myself, before I took physics classes, would have had trouble completely absorbing these concepts the first time through.

Let me know how the audiobook works for you! And if you think there’s anything I can do on this website to make the audiobook easier and more accessible, please let me know.

More to Come

More podcasts and articles are in the works. So is additional supporting material for the book. Stay tuned!

If Drs. Vinay Prasad and Tracy Hoeg want to prove they actually care about routine vaccines, they can do what the should have done a long time ago and openly and unequivocally denounce Mr. Kennedy and his fire hose of anti-vaxx disinformation.

The post A Simple Challenge For Drs. Vinay Prasad and Tracy Hoeg: Denounce Robert Kennedy Jr. For Promoting The Movie Vaxxed 3: Authorized to Kill first appeared on Science-Based Medicine.

As a six-year investigation into the Thwaites glacier in Antarctica wraps up, the scientists involved are pessimistic for the future of this glacier and the consequences for sea level rise

Genetic analysis shows that microbes growing inside the International Space Station have adaptations for radiation and low gravity, and may pose a threat to astronauts

Computers truly are wonderful things and powerful but only if they are programmed by a skilful mind. Check this out… there is an algorithm that mimics the growth of slim mold but a team of researchers have adapted it to model the large scale structure of the Universe. Since the Big Bang, the universe has been expanding while gravity concentrates matter into galaxies and clusters of galaxies. Between them are vast swathes of empty space called voids. The structure, often referred to as the cosmic web.

The cosmic web is the largest scale structure of the universe and it’s made up of filaments of galaxies and dark matter that stretch across the gulf of space. The filaments connect galaxy clusters with immense voids in between. The web-like structure has formed as a result of the force of gravity pulling matter together since the beginning of time. Studying the cosmic web helps us to piece together the evolution of the universe, how matter is distributed and the relationship with dark matter. 

Image from NASA’s Hubble Space Telescope of a galaxy cluster that could contain dark matter (blue-shaded region). (Credit: NASA, ESA, M. J. Jee and H. Ford et al. (Johns Hopkins Univ.))

Since the early 80’s it’s been known that the nature of a galaxy and its environmental properties has an impact on how it grows and evolves. The exact nature and how this happens is still the cause of many debates. A team of researchers believe they may have demonstrated how galaxies evolve using a slime algorithm!

The team, led by Farhanul Hasan, Professor Joe Burchett and eight co-authors, published their findings ‘Filaments of the Slime Mold Cosmic Web and How they Affect Galaxy Evolution’ in August’s edition of the Astrophysical Journal.  In the paper they report how the mold algorithm has helped to unlock mysteries of the cosmos. 

Burchett recommended the slime mold algorithm could be used for an astrophysical application. Hasan worked with Burchett and altered the algorithm to help them visualise the cosmic web. The team worked with graphics rendering expert Oskar Elek to use the slime mold algorithm. The mold algorithm was designed to mimic slime mold that could find its own food by reforming itself into a structure much like the cosmic web. It took the team several years to complete their work. 

In shaping the Universe, gravity builds a vast cobweb-like structure of filaments tying galaxies and clusters of galaxies together along invisible bridges hundreds of millions of light-years long. A galaxy can move into and out of the densest parts of this web throughout its lifetime. Credit: Volker Springel (Max Planck Institute for Astrophysics) et al.

The result produced far more detailed discrete structures than the old method according to Hasan. He added ‘I didn’t know how well it was going to work or not work, but I had a hunch the slime mold method could tell us much more detailed information about how density is structured in the universe, so I decided to give it a try.’

Of the conclusion, Hasan and team found that the impact on galaxies seems to have taken the proverbial u-turn. In earlier epochs, the growth of a galaxy was stimulated by proximity to larger structures. In the near universe, and therefore in cosmologically recent times, we see that galaxy growth is limited by proximity to larger structures. This wasn’t possible without the modified slime mold algorithm. We can now map out the gas around the real universe using the algorithm across many different times to help understand how the web has changed and the universe evolved. 

Source : NMSU astronomy research uses slime mold to model galaxies

The post Slime Mold Can Teach Us About the Cosmic Web appeared first on Universe Today.

The beliefs we hold develop from a complex dance between our internal and external lives. A recent study uses well-known formalisms in statistical physics to model multiple aspects of belief-network dynamics. This multidimensional approach to modeling belief dynamics could offer new tools for tackling various real-world problems such as polarization or the spread of disinformation.

By staring into the hellish landscape of Jupiter's moon Io -- the most volcanically active location in the solar system -- astronomers have been able to study a fundamental process in planetary formation and evolution: tidal heating.

Engineers developed a new kind of reconfigurable masonry made from 3D-printed, recycled glass. The bricks could be reused many times over in building facades and internal walls.

Chemists have developed a generative AI model that can make it much easier to determine the structures of powdered crystal materials. The prediction model could help researchers characterize materials for use in batteries, magnets, and many other applications.

Chemists have developed a generative AI model that can make it much easier to determine the structures of powdered crystal materials. The prediction model could help researchers characterize materials for use in batteries, magnets, and many other applications.

Scientists design a process that merges metal extraction, alloying and processing into one single, eco-friendly step.

Making hydrogen from seawater can be tricky because the salt is corrosive and the process can create toxic chlorine gas – new electrodes can split ocean water to make the clean fuel more easily

Photosynthesis changed Earth in powerful ways. When photosynthetic organisms appeared, it led to the Great Oxygenation Event. That allowed multicellular life to evolve and resulted in the ozone layer. Life could venture onto land, protected from the Sun’s intense ultraviolet radiation.

But Earth’s photosynthetic organisms evolved under the Sun’s specific illumination. How would plants do under other stars?

Our Sun is a G-type star, sometimes called a yellow dwarf. It seems like a normal star to us, but yellow dwarfs aren’t that common. Only about 7% to 8% of stars in the Milky Way are G-type stars. When it comes to understanding habitability on exoplanets, we need to understand the more plentiful types of stars.

Some scientists propose that K-dwarf stars are the most optimal host stars for habitable exoplanets. They’re between about 50% and 80% as massive as G-type stars, are more abundant and have stable luminosities for billions of years longer than Sun-like stars. The Sun will be stable on the main sequence for about 10 billion years, while K-type stars can be stable for up to 70 billion years. Despite this, much exoplanet habitability research focuses on M-dwarfs, or red dwarfs, which may actually be far more inhospitable to life because of flaring and tidal locking.

In a new study, a trio of researchers simulated the light output from a K-dwarf star and grew two photosynthetic organisms in those conditions to see how they responded. The research article is “Observation of significant photosynthesis in garden cress and cyanobacteria under simulated illumination from a K dwarf star.” It’s published in the International Journal of Astrobiology, and the lead author is Iva Vilovi?, a PhD student in the Astrobiology Research Group at the Technical University of Berlin.

These figures from the article show the spectra for both the Sun and a K-dwarf star, and the simulated spectra for both. Image Credit: Vilovi? et al. 2024.

Garden cress, whose Latin name is Lepidium sativum, is a common garden green used in salads, soups, and sandwiches. It’s an adaptable plant that grows rapidly. The cyanobacterium Chroococcidiopsis is an extremophile known for lying dormant for 13 million years and remaining viable. It can resist radiation, desiccation, and extreme temperatures and is of interest in astrobiology.

We expect photosynthesis to play a role in astrobiology. Starlight provides the energy for organisms to synthesize organic compounds. In order to understand photosynthesis in astrobiology, we need to understand how other stars could power photosynthesis. “Therefore, understanding any planet in the context of its stellar environment is an essential step in assessing its habitability,” the authors write.

Astronomers search for Earth-like planets around Sun-like stars because that’s the only life we know of. They also pay special attention to M-dwarfs because they’re so plentiful and are known to host many rocky exoplanets in their habitable zones. Scientists have demonstrated that photosynthetic organisms from Earth can grow under simulated M-dwarf light. But M-dwarf habitability faces a whole host of potential barriers.

Artist’s impression of a flaring red dwarf star orbited by an exoplanet. Red dwarfs can flare violently, which could make planets in their habitable zones unable to support life. Planets in their habitable zones are also often tidally locked, which is another barrier to habitability. Credit: NASA, ESA, and G. Bacon (STScI)

In this work, the researchers focused on K-dwarfs. They lack the magnetic activity that appears to generate extremely powerful flaring on M-dwarfs, flaring so powerful that it could sterilize planets in their liquid-water habitable zone. The habitable zones around K-dwarfs are also far enough away that planets wouldn’t be tidally locked, another potential barrier to habitability that affects M-dwarfs. K-dwarfs also become habitable sooner in their lives than M-dwarfs due to their rapidly weakening FUV and X-ray fluxes.

“All things combined, K dwarfs can be considered the ‘Goldilocks stars’ in the search for potentially life-bearing planets,” the authors write.

This table from the research article shows the conditions that the researchers recreated in their study. Image Credit: Vilovi? et al. 2024.

The trio of researchers exposed watercress seedlings to three different light regimes: sunlight, K-dwarf light, and no light. Visually, the solar and K-dwarf samples were similar, though most of the time, the seeds sprouted a day or two earlier than under solar light. The K-dwarf sample also had marginally larger leaf surface area.

The researchers grew garden cress (Lepidium sativum) on a sand substrate with one hundred initial seedlings under Solar (effective temperature 5800 K), K dwarf (effective temperature 4300 K) and dark conditions. This image shows the visual results for selected days. Garden cress under K dwarf radiation sprouts sooner relative to Solar and dark conditions. Image Credit: Vilovi? et al. 2024.

After seven days, a side view of the samples showed that height and stem elongation were different. Under the K-dwarf lighting, the watercress grew taller.

The watercress grew taller under K-dwarf lighting than under Solar conditions. Image Credit: Vilovi? et al. 2024.

The researchers also measured water content and dry mass. Under K-dwarf conditions, the watercress had slightly higher water content, while the dry content was lower compared to solar conditions.

These figures show the water content and dry content for all three garden cress samples. Image Credit: Vilovi? et al. 2024.

The researchers also tested the photosynthetic efficiency and found no significant difference between the solar and K-dwarf samples.

The hardy extremophile Cyanobacterium Chroococcidiopsis sp. CCMEE 029 is at the other end of the spectrum from the quick-growing garden cress. It’s a survivor that can withstand long periods of dormancy and extreme growing conditions. The researchers also cultivated it under Solar, K-dwarf and dark conditions.

They measured the average integrated density (IntD) of the cyanobacterium, which is an indicator of culture growth. They found that the K-dwarf sample exhibited higher values than the solar sample, but the differences were not considered significant. Predictably, “Cyanobacteria under constant dark conditions failed to exhibit significantly measurable IntD,” the authors write in their paper.

This figure from the research article shows incremental ratios and integrated densities of the cyanobacterium on selected days under Solar, K dwarf and dark conditions. Though the integrated density was higher under K-dwarf conditions, the difference isn’t significant, according to the researchers. Image Credit: Vilovi? et al. 2024.

They point out that their study didn’t replicate natural conditions completely. Sunlight intensity changes throughout the day, but they didn’t include that in their study. “Sunlight intensity on Earth varies throughout the day, with peak intensities occurring during the central hours. This variation is crucial for plants to adapt and respond to changing light conditions, including the activation of non-photochemical quenching (NPQ) to mitigate the effects of excess light,” they write. NPQ helps plants cope with periods of excess light, meaning light above what it can photosynthesize, by dissipating it as heat.

“Understanding the effects of K-dwarf radiation on photosynthesis and growth is of foremost importance not only for the assessment of its viability for phototrophic organisms but also for the interpretation of atmospheric biosignatures outside of the Solar System,” the authors explain. Other research in this area has focused on M-dwarfs, and this trio of researchers say that to the best of their knowledge, theirs is the first to look at photosynthesis and K-dwarfs.

“These results can bring us closer to addressing which stellar environments could be the optimal candidates in the search for habitable worlds,” the authors write. “These findings not only highlight the coping mechanisms of photosynthetic organisms to modified radiation environments but also they imply the principal habitability of exoplanets orbiting K dwarf stars.”

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