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 “pale orange dot.” Artist’s impression of what early Earth would have looked like. Credit: NASA/Goddard Space Flight Center/Francis Reddy
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).
Artist’s impression of the Archean Eon. Credit: Tim Bertelink
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).”
Three of the TRAPPIST-1 planets – TRAPPIST-1e, f, and g – dwell in their star’s so-called “habitable zone.” Credit: NASA/JPL
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.
Artist’s impression of a water world, where half of its mass consists of water. Just like our Moon, the planet is bound to its star by tidal forces and always shows the same face to its host star. Credit: Pilar Montañés
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.”
Artist’s conception of a rocky Earth-mass exoplanet like Wolf 1069 b orbiting a red dwarf star. If the planet has retained its atmosphere, chances are high that it would feature liquid water and habitable conditions over a wide area of its dayside. Credit: NASA/Ames Research Center/Daniel Rutter
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.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
