Do Red Dwarfs Provide Enough Sunlight for Plants to Grow? – Universe Today
To date, 5,250 extrasolar planets have been confirmed in 3,921 systems, with another 9,208 candidates awaiting confirmation. Of these, 195 planets have been identified as “terrestrial” (or “Earth-like“), meaning that they are similar in size, mass, and composition to Earth. Interestingly, many of these planets have been found orbiting within the circumsolar habitable zones (aka. “Goldilocks zone”) of M-type red dwarf stars. Examples include the closest exoplanet to the Solar System (Proxima b) and the seven-planet system of TRAPPIST-1.
These discoveries have further fueled the debate of whether or not these planets could be “potentially-habitable,” with arguments emphasizing everything from tidal locking, flare activity, the presence of water, too much water (i.e., “water worlds“), and more. In a new study from the University of Padua, a team of astrobiologists simulated how photosynthetic organisms (cyanobacteria) would fare on a planet orbiting a red dwarf. Their results experimentally demonstrated that oxygen photosynthesis could occur under red suns, which is good news for those looking for life beyond Earth!
The study was led by Nicoletta La Rocca and Mariano Battistuzzi, biologists from the Center for Space Studies and Activities (CISAS) at the University of Padua. They were joined by researchers from the National Council of Research of Italy’s Institute for Photonics and Nanotechnologies (CNR-IFN), the National Institute for Astrophysics (INAF), and the Astronomical Observatory of Padua. The paper that describes their findings was published on February 7th, 2023, in the Frontiers of Plant Science.
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The subject of M-type stars, photosynthesis, and the implications for astrobiology has been explored at length in recent decades. Not only are red dwarfs the most common type of star in the Universe, accounting for 75% of stars in the Milky Way alone. Recent surveys have shown they are also very good at forming rocky planets that orbit within the parent star’s habitable zone (in many cases, tidally locked with their stars). Given the unstable nature of red dwarfs, their tendency to flare, and other factors, the jury is still out on whether or not they could support life – especially in their early phases. As Dr. Battistuzzi told Universe Today via email:
“M-dwarfs can profoundly change their activity depending on their stage of evolution. 25% of early-life M-dwarfs release X-rays and UV through flares and chromospheric activity. Instead, quiescent stars emit little UV radiation and have no flares. Planets orbiting around M-dwarfs often receive high doses of these kinds of radiation during stellar flares, changing rapidly the radiation environment on the surface and possibly eroding the ozone shield, if present, as well as part of the atmosphere.
“However, it has been pointed out that these planets could remain habitable. Atmospheric erosion could be avoided through a strong magnetic field or with thick atmospheres. Also, in addition to this, possible organisms could develop UV-protecting pigments and DNA repair mechanisms as happens on Earth or develop in subsurface niches, underwater or under the ice, where radiation is less intense.”
On Earth, life is theorized to have emerged during the Archean Eon (ca. 4 billion years ago) in the form of simple, single-celled (prokaryote) bacteria. Earth’s atmosphere was still largely composed of carbon dioxide, methane, and other volcanic gases at this time. Between 3.4 and 2.9 billion years ago, the first photosynthetic organisms – green-blue microbes called cyanobacteria – began flourishing in Earth’s oceans. These organisms metabolized carbon dioxide with water and sunlight to create gaseous oxygen (O2), eventually leading to more complex, multi-celled organisms (eukaryotes).
Hence the concern regarding young red dwarf suns and their rocky planets. These dimmer, cooler stars emit the majority of their radiation in the red and infrared wavelengths (lower energy than the yellow light of the Sun peaks). As a result, scientists have speculated that additional photons would be needed to achieve excitation potentials comparable to those needed for photosynthesis on Earth. For their study, La Rocca and Battistuzzi sought to determine experimentally if this was the case. According to Battistuzzi, this consisted of subjecting cyanobacteria to different wavelengths of light and monitoring the bacteria’s growth:
“We exposed a couple of cyanobacteria to a simulated M-dwarf light spectrum and measured their growth, acclimation responses (for example, the changes in the pigment composition and the organization of the photosynthetic apparatus, crucial to absorbing light and converting it into sugars), and oxygen production capabilities under this light spectrum. We compared these data to 2 different control conditions: a monochromatic far-red light and a solar light spectrum.”
The experiment utilized two types of cyanobacteria. This included Chlorogloeopsis fritschii, a small group of cyanobacteria capable of synthesizing special pigments (chlorophyll d and f) that are able to absorb far-red light. Unlike most other photosynthetic organisms (like plants), this gives this strain the ability to grow and produce oxygen using far-red light alone or in addition to visible light. The second strain, Synechocystis sp., is a broader group of freshwater cyanobacteria that cannot utilize far-red light alone for photosynthesis and needs visible light.
“The monochromatic far-red light was used as a control to ensure different responses of the far-red utilizing cyanobacterium and the non-far utilizing one: the first should grow in far-red, and the second one should not,” added Battistuzzi. “The simulated solar light spectrum was used as a control to check the growth, acclimation responses, and oxygen production in optimal conditions (terrestrial organisms evolved under the Sun’s spectrum, so they are adapted to it).”
As they indicate in their study, the results were surprisingly encouraging. Both cyanobacteria grew at a similar rate under the red dwarf and Solar light conditions. This was impressive, considering that visible light is rather scarce in the M-type stellar spectrum. In the case of C. fritschii, the results could be explained by its capability of synthesizing the necessary pigments to harvest far-red light and its ability to harness visible light. While Synechocystis sp. did not grow under far-red light alone, it could also grow at a similar rate to C. fritschii when exposed to both. While the exact cause is not certain, Battistuzzi and La Rossa have some theories:
“This could be explained by recent studies on plants showing that far-red light just helps oxygenic photosynthesis when in combination with visible light, while instead is poorly utilized when provided alone (as demonstrated in this work by Synechocystis sp., which could not grow under this only light source).
“The acclimations of both cyanobacteria moreover led to efficient O2 evolution under the M-dwarf light spectrum. This shows the potentiality of cyanobacteria to utilize light regimes that could arise on tidally locked planets orbiting the Habitable Zone of M-dwarf stars, and also their potential in producing O2 biosignatures detectable from remote.”
In a previous study conducted in 2021, La Rocca, Battistuzzi, and their teammates conducted a similar experiment where they studied the growth and acclimation of cyanobacteria. This study was led by Riccardo Claudi of the Astronomical Observatory of Padua (INAF-OAPD), a co-author of the current paper. For this experiment, the team relied on solid media to cultivate cyanobacteria as biofilms, which allowed them to obtain results more rapidly but limited the amount and the type of experiments they could conduct.
This time, the cyanobacteria were cultivated in liquid media, which yielded more samples. This, in turn, allowed far more detailed examinations of the growth, acclimation processes, and oxygen evolution of cyanobacteria exposed to different light conditions. The implications of these latest experiments and what they revealed are potentially groundbreaking. According to Battistuzzi, this includes a new understanding under which photosynthesis can occur, better prospects for red dwarf habitability, and new opportunities for detected biotic oxygen in exoplanet atmospheres:
“Even if the visible light in the M-dwarf spectrum is very low, it can still be utilized by some oxygenic photosynthetic organisms efficiently. This highlights the importance of taking into account the huge diversity of oxygenic photosynthetic organisms, which not only comprise plants but also basal plants, and microalgae, down to the simplest cyanobacteria.
“It is also important to consider how the new findings demonstrate the role of far-red light in helping photosynthetic performance and the growth of all photosynthetic organisms (higher plants included). If life evolved oxygenic photosynthesis on an exoplanet orbiting the habitable zone of an M-dwarf, this process could be far more similar to what happens on Earth than previously anticipated.”
“If oxygenic photosynthesis evolved in M-dwarf’s exoplanets, with the right conditions, oxygen could, in theory, accumulate in their atmospheres, as happened on Earth billions of years ago during the Great Oxidation Event, becoming a permanent component. This would allow astronomers to detect such biologically produced oxygen, a biosignature, in the atmosphere and infer from that the presence of life from remote.”
This last implication is especially significant, as astronomers and astrobiologists have explored the possibility that when it comes to red dwarfs, oxygen might not be the smoking gun we tend to think it is. Red dwarfs have an extended pre-main sequence phase (roughly 1 billion years), which means that planets orbiting in what will eventually become their habitable zones would be exposed to elevated radiation. This could trigger a runaway greenhouse effect where water is evaporated and broken down by radiation exposure into hydrogen and oxygen (photolysis).
The hydrogen gas would then be lost to space while the oxygen would be retained as a thick abiotic oxygen atmosphere. Such atmospheres would be inherently hostile to photosynthetic bacteria and other terrestrial organisms that existed when the Earth was young. In short, what is considered a leading biosignature and indicator of life could actually be an indication that a planet is sterile. But as Battistuzzi adds, there is plenty of uncertainty here, and more research is needed before any conclusions can be drawn:
“Of course, these are big ifs. It is not a guarantee that life would evolve even if habitability conditions are met on an exoplanet orbiting an M-dwarf, and it is not a guarantee that life would evolve oxygenic photosynthesis at all, as it could also evolve anoxygenic photosynthesis, a kind of photosynthesis which still uses light but does not produce oxygen as a by-product.”
Further Reading: arXiv
Boeing's first-ever crewed mission in Starliner ISS spacecraft delayed to late July – The Register
Boeing’s debut Starliner spacecraft launch carrying its first-ever crew of astronauts to the International Space Station is being postponed again, and is not expected to fly until 21 July at the earliest.
A Boeing Starliner landing system is tested for reliability in White Sands Space Harbor in New Mexico. Photo credit: NASA/Boeing
Steve Stich, manager of Commercial Crew Program at NASA, confirmed the delay in a media teleconference on Wednesday. Officials from the space agency and Boeing need more time to assess the capsule, and to avoid conflicts with upcoming flights scheduled to the ISS.
Boeing’s Crew Flight Test (CFT) mission has suffered repeated setbacks, and was originally slated to fly in April. “We’ve deliberated and decided that the best launch attempt is no earlier than July 21st,” Stitch said.
“Where we’re at right now is really getting through the certification work… it is a large amount of work which has been going on for well over a year. There’s 600 components that have to be qualified on the Starliner for NASA and Boeing to review jointly [and] over 70 hazard reports. And then a total of what we call 370 verifications,” he added.
They are both paying close attention to the parachute system on the Starliner deployed to land the spacecraft safely back on Earth. Ground tests will examine the parachute’s ability to launch properly and slow the Starliner to splash down safely for the return of astronauts Butch Wilmore and Suni Williams, who will fly and spend eight days docked to the ISS in the CFT.
Joel Montalbano, manager of NASA’s International Space Station Program, said that activities onboard the ISS are jam packed over the next few months. The Soyuz MS-23 currently docked to the space station will be relocated to another module. Russian cosmonauts and American astronauts will also be performing separate spacewalks to adjust for incoming solar arrays and retrieve hardware.
There are also upcoming cargo deliveries as well as the Axiom-2 mission, the second private crewed mission to the ISS, which will send the first Saudi Arabian woman, Rayyanah Barnawi, to space. Barnawi’s crewmates include Ali Alqarni, a second Saudi representative, Peggy Whitson, a NASA veteran, and John Shoffner, an investor and pilot.
All that means is Boeing will have to find a flight slot after these events.
“We’re very close,” said Mark Nappi, vice president and program manager of the CST Starliner at Boeing. He said the company was working hard to inspect the spacecraft’s hardware, build the service module, refurbish the crew module, and verify its flight software.
“Most of the areas that needed to be completed are going to be completed by the end of April. In the one area that Steve talked about, which is the parachute, the verification closure notice and the hazard report will poke out into May,” he said.
The next major milestone will be loading the propellant into the spacecraft about 40 days prior to its launch. ®
When is the next planetary alignment in Vancouver in 2023?
An uncommon celestial cluster dotted the sky over Vancouver last night.
A planetary alignment including Jupiter, Mercury, Venus, Uranus, and Mars, was seen over the city Tuesday (March 28) night.
Though planetary alignments aren’t rare, alignments involving so many planets aren’t common either.
Vancouver locals snapped photos of the astronomical spectacle.
When is the next planetary alignment visible in Vancouver?
According to the educational astronomy app Star Walk, Earth-dwellers will have plenty more opportunities to see clusters of planets in the sky this year. The next chance to spot Mercury, Uranus, Venus, and Mars lined up will be on April 11.
However, the next most noteworthy planetary alignment won’t take place until Sept. 8, 2040. On this night, stargazers will be able to see five planets– Venus, Mercury, Mars, Jupiter, and Saturn– with the naked eye, along with the crescent Moon between Venus and Saturn.
The next major alignment will occur 40 years later on March 15, 2080, with six planets– Venus, Mercury, Jupiter, Saturn, Mars, and Uranus– all visible in the morning sky. It will also feature the “great conjunction” of Saturn and Jupiter.
There is one exciting celestial event that will take place over a century later. On May 19, 2161, all the planets in the solar system, including Earth, will end up on one side of the Sun which means earthlings can observe every planet in the sky.
As for 2023, here is when you can spot the next planetary alignment in Vancouver:
- April 11 – Mercury, Uranus, Venus, Mars; small evening alignment with 35-degree sky sector
- April 24 – Mercury, Uranus, Venus, Mars; small evening alignment with 40-degree sky sector
- May 29 – Mercury, Uranus, Jupiter, Saturn; small morning alignment with 70-degree sky sector
- June 17 – Mercury, Uranus, Jupiter, Neptune; large morning alignment with 95-degree sky sector
- July 26 – Mercury, Venus, Mars; mini evening alignment with 15-degree sky sector
- August 24
- at sunset: setting Mercury and Mars, rising Saturn; mini alignment with 175-degree sky sector
- at night: Uranus, Jupiter, Neptune, Saturn; small alignment with 80-degree sky sector
Don’t Read Too Much into River Otters’ Return
Standing at the foot of a rocky sandstone cliff, biologist Michelle Wainstein inspected her essentials: latex gloves, two long cotton swabs, glass vials, and tubes filled with buffer solution. She placed them in a blue dry bag, rolled it up, and clipped it to a rope wrapped around her waist. It was late afternoon, and she was slick with dirt and sweat from navigating the dense terrain. Her destination lay across the frigid river: two small logs of otter fecal matter resting on a mossy boulder. In she plunged.
The river, the Green-Duwamish in Washington State, trickles out of the Cascade Range and empties 150 kilometers downstream into Puget Sound. The last eight kilometers of the run—known as the lower Duwamish—is so polluted the US Environmental Protection Agency designated it a Superfund site in 2001. For a century, Seattle’s aviation and manufacturing industries routinely dumped waste chemicals like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) into the water.
“A lot of the river is still really polluted,” says Jamie Hearn, the Superfund program manager at Duwamish River Community Coalition. “The mud is thick and black, and you can smell it.”
Despite the pollution, river otters are everywhere along the waterway, even in the most contaminated areas near the river’s mouth. “I would be walking the docks looking for scat,” remembers Wainstein, “and a couple of times we were lucky enough to see moms with their pups.”
For several weeks in the summer of 2016 and 2017, Wainstein surveyed otter poop she collected from a dozen sites along the river. Comparing contaminant concentrations in the otters’ poop between the river’s industrial and rural zones, Wainstein uncovered the lingering legacy of the region’s toxic past. The poop from otters in the lower Duwamish contained nearly 26 times more PCBs and 10 times more PAHs than poop from their cousins in cleaner water upstream. PCBs disrupt hormonal and neurological processes and affect reproduction in mammals. Both PCBs and PAHs are human carcinogens.
The discovery that otters along the lower Duwamish are living with such high levels of contamination upends a common narrative: that river otters’ return to a once-degraded landscape is a sign that nature is healing.
In Singapore, where smooth-coated otters have reappeared in canals and reservoirs, they have been embraced as new national mascots. “It plays into that rhetoric that government agencies want to project,” says environmental historian Ruizhi Choo, “that we’ve done such a good job that nature is coming back. That image of a city in nature is the new marketing branding.”
In Europe, the once-common Eurasian otter similarly began reappearing in the late 20th century following successful river cleanup campaigns. Conservationist Joe Gaydos at the SeaDoc Society thinks that this phenomenon has helped form the mental link between otters and ecosystem health.
“The number of animals is our first indicator,” Gaydos says. But few seem to ask the next question: are those animals healthy?
As Wainstein’s study suggests, perhaps not. The otters she analyzed in the lower Duwamish have some of the highest concentrations of PCBs and PAHs ever recorded in wild river otters. Previous research has found a correlation between PCB exposure and health risks in wild river otters, including increased bone pathologies, reproductive and immunological disorders, organ abnormalities, and hormonal changes.
Even so, the contamination is not manifesting in physically obvious ways. “They’re not washing up on shore with tumors all over their bodies,” Wainstein says, and neither is their population dwindling. “They’re not setting off this direct alarm with a big change in their ability to survive.”
The otters’ ability to bear such a heavy contaminant burden suggests that a population resurgence alone may not reflect the quality of an environment. They just become as toxic as the environments they inhabit.
However, their localized bathroom habits, mixed diet of fish, crustaceans, and mammals, and persistence in the face of pollution make them useful indicators of environmental contamination.
River otters have played this role before. Following the 1989 Exxon Valdez oil spill, river otters lingered in oil-drenched waterways, allowing scientists like Larry Duffy at the University of Alaska Fairbanks to track the effectiveness of the oil cleanup. In 2014, scientists in Illinois discovered dieldrin in otter organ tissue even though the insecticide had already largely been banned for 30 years. In these cases, the collection of long-term pollution data was made possible by the creatures’ resilience in contaminated waterways. Wainstein wants to similarly use the Green-Duwamish River otters as biomonitors of the Superfund cleanup over the next decade.
Watching workers dismantle a portion of the river’s levied banks to make channels for salmon, Wainstein thinks about the seabirds, shorebirds, and small mammals, like beaver and mink, that were driven out by industrial contamination. She wonders if one day the rumbling machinery dredging up clawfuls of sediment from the riverbed will be taken over by the piercing cries of marbled murrelets, the croaks of tufted puffins, and the bubbling twittering of western snowy plovers.
“How long will it take? And will it actually work?” she says of the cleanup effort. The otters might hold the answer.
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