Future historians might look back on this time and call it the ‘exoplanet age.’ We’ve found over 5,000 exoplanets, and we’ll keep finding more. Next, we’ll move beyond just finding them, and we’ll turn our efforts to finding biosignatures, the special chemical fingerprints that living processes imprint on exoplanet atmospheres.
But there’s more to biosignatures than atmospheric chemistry. On a planet with lots of plant life, light can be a biosignature, too.
The search for biosignatures on exoplanets got a boost of energy when the James Webb Space Telescope began observations. One of the telescope’s science objectives is to characterize exoplanet atmospheres with its powerful infrared spectrometry. If Webb finds large amounts of oxygen, for example, it’s an indication that biological processes might be at work and are changing a planet’s atmosphere. But the JWST and other telescopes could detect another type of biosignature.
Earth’s abundant plant life changes our planet’s ‘light signature.’ The change is based on photosynthesis and how plant life absorbs some light frequencies while reflecting others. The resulting phenomenon is called the vegetation red edge (VRE.)
Exoplanet scientists have worked on the idea of the VRE as a biosignature for a few years. It’s based on the fact that chlorophyll absorbs light in the visible part of the spectrum and is almost transparent in the infrared. Other cellular structures in the vegetation reflect the infrared. This helps plants avoid overheating during photosynthesis. This absorption and reflection make it possible for remote sensing to gauge plant health, coverage, and activity, and agricultural scientists use it to monitor crops.
In a new paper, a team of researchers looked at chlorophyll and its solar-induced fluorescence (SIF.) SIF is the name of the electromagnetic signal emitted by chlorophyll a, the most widely-distributed chlorophyll molecule. Part of the energy absorbed by chlorophyll a is not used for photosynthesis but is emitted at longer wavelengths as a two-peak spectrum. It covers roughly the 650–850 nm spectral range.
The paper is “Photosynthetic Fluorescence from Earth-Like Planets around Sun-Like and Cool Stars,” and it will be published in The Astrophysical Journal. The lead author is Yu Komatsu, a researcher at the National Institutes of Natural Sciences Astrobiology Center, National Astronomical Observatory of Japan.
The paper focuses on how the fluorescence from chlorophyll could be detected on planets similar to Earth. “This study examined the detectability of biological fluorescence from two types of photosynthetic pigments, chlorophylls (Chls) and bacteriochlorophylls (BChls), on Earth-like planets with oxygen-rich/poor and anoxic atmospheres around the Sun and M dwarfs,” the authors explain.
Detecting the presence of chlorophyll on another world is complicated. There’s a complex interplay between plant life, starlight, land/ocean coverage, and atmospheric composition. This study is part of an ongoing effort to understand some of the limitations to detection and what spectroscopic data can tell scientists about exoplanets. Over time, exoplanet scientists want to determine which detections can be biosignatures in different circumstances.
The VRE is a sharp drop in observed light between infrared and visible light. Light in the near-infrared (starting at about 800 nm) is much brighter than the light in the optical (between about 350 to 750 nm.) On Earth, this is the light signature of plant life and its chlorophyll. The chlorophyll absorbs the light up to 750 nm, and other plant tissues reflect light above 750 nm.
Satellites like NASA’s Terra can observe different regions on Earth’s surface over time and watch how the light reflectance changes. Scientists measure what’s called the Normalized Difference Vegetation Index (NVDI.) A dense forest location during peak growing season gives peak values for the NDVI, while vegetation-poor regions give low values.
Scientists can also observe Earthshine, the light reflected from Earth onto the Moon. That light is the entirety of the light reflected by Earth, what scientists call a disk-averaged spectrum. “Whereas remote sensing observes local areas on Earth, Earthshine observations provide disk-averaged spectra of the Earth, leading to fruitful insights into exoplanet applications,” the authors write. “The apparent reflectance change in the Earth’s disk-averaged spectrum due to surface vegetation is less than 2%.”
The Earthshine we see on the Moon is similar to the light we detect from distant exoplanets. It’s the totality of the light vs regional surface light. But there’s an enormous amount of complexity involved in studying that light, and there are no easy comparisons between Earth and exoplanets. “The VRE signals from exoplanets around stars other than a Sun-like star are challenging to predict due to the complexity of photosynthetic mechanisms in different light environments,” the authors explain. But there’s still value in looking for a VRE on exoplanets. If scientists observe an exoplanet frequently, they may be able to recognize how the VRE changes seasonally, and they may recognize a similar VRE-like step in the planet’s spectroscopy, though it could be at different wavelengths than on Earth.
In their paper, the researchers considered an Earth-like planet in different stages of atmospheric evolution. In each case, the planets orbited the Sun, a well-studied red dwarf named Gliese 667 C, or the even more well-known red dwarf TRAPPIST-1. (Both red dwarfs have planets in their habitable zones, and both represent common types of red dwarfs.) They modelled the reflectance from each case for vegetation chlorophyll, bacterial chlorophyll-based vegetation, and biological fluorescence without any surface vegetation.
What they came up with is a collection of light curves that shows what different VREs might look like on Earth-like exoplanets in different stages of atmospheric evolution around different stars. It’s important to look at different stages of atmospheric evolution because Earth’s atmosphere changed from oxygen-poor to oxygen-rich while life was present.
“We considered fluorescence emissions from Chl- and BChl-based vegetation in a clear-sky condition
on an Earth-like planet around the Sun and two M dwarfs,” the authors write.
The study produced a range of reflectance data for Earth-like planets around different stars. The planets were modelled with different atmospheres that correspond to Earth’s different atmospheres over its four billion-year history. The researchers also varied the amount of land cover vs ocean cover, the amount of coastline, and whether the surface was covered in plants or in photosynthetic bacteria.
In the future, we’ll be wielding ever more powerful space telescopes like LUVOIR (Large UV/Optical/IR Surveyor) and HabEx (Habitable Exoplanet Observatory.) Ground-based telescopes like the Thirty Meter Telescope, the Giant Magellan Telescope, and the European Extremely Large Telescope will also be coming online in the near future. These telescopes are going to generate an unprecedented amount of data on exoplanets, and this study is part of preparing for that.
We’re detecting more and more exoplanets and are building a statistical understanding of other solar systems and the distributions, masses, and orbits of exoplanets. The next is to gain a deeper understanding of the characteristics of exoplanets. Telescopes like the E-ELT will do that with its 39.3-meter mirror. It’ll be able to separate an exoplanet’s light from the star’s light and directly image some exoplanets. It’ll unleash a flood of data on exoplanet reflectance and potential biosignatures, and all of that data will have to be evaluated.
If we ever locate an Earth-like planet, one that’s habitable and currently supporting life, it won’t just appear in one of our telescopes and announce its presence. Instead, there’ll be tantalizing hints, there’ll be indications and contra-indications. Scientists will slowly and carefully work their way forward, and one day we might be able to say we’ve found a planet with life. This research has a role to play in the endeavour.
“It is important to quantitatively evaluate the detectability of any potential surface biosignature using expected specifications of specific future missions,” the authors explain. “This study made the first attempt to investigate the detectability of photosynthetic fluorescence on Earth-like exoplanets.”
Rare ‘big fuzzy green ball’ comet visible in B.C. skies, a 50000-year sight
In the night sky, a comet is flying by Earth for the first time in 50,000 years.
Steve Coleopy, of the South Cariboo Astronomy Club, is offering some tips on how to see it before it disappears.
The green-coloured comet, named C/2022 E3 (ZTF), is not readily visible to the naked eye, although someone with good eyesight in really dark skies might be able to see it, he said. The only problem is it’s getting less visible by the day.
“Right now the comet is the closest to earth and is travelling rapidly away,” Coleopy said, noting it is easily seen through binoculars and small telescopes. “I have not been very successful in taking a picture of it yet, because it’s so faint, but will keep trying, weather permitting.”
At the moment, the comet is located between the bowl of the Big Dipper and the North Star but will be moving toward the Planet Mars – a steady orange-coloured point of light- in the night sky over the next couple of weeks, according to Coleopy.
“I have found it best to view the comet after 3:30 in the morning, after the moon sets,” he said. “It is still visible in binoculars even with the moon still up, but the view is more washed out because of the moonlight.”
He noted the comet looks like a “big fuzzy green ball,” as opposed to the bright pinpoint light of the stars.
“There’s not much of a tail, but if you can look through the binoculars for a short period of time, enough for your eyes to acclimatize to the image, it’s quite spectacular.”
To know its more precise location on a particular evening, an internet search will produce drawings and pictures of the comet with dates of where and when the comet will be in each daily location.
Coleopy notes the comet will only be visible for a few more weeks, and then it won’t return for about 50,000 years.
Extreme species deficit of nitrogen-converting microbes in European lakes
Sampling of Lake Constance water from 85 m depth, in which ammonia-oxidizing archaea make up as much as 40% of all microorganisms
An international team of researchers led by microbiologists from the Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH in Braunschweig, Germany, shows that in the depths of European lakes, the detoxification of ammonium is ensured by an extremely low biodiversity of archaea. The researchers recently published their findings in the prestigious international journal Science Advances. The team led by environmental microbiologists from the Leibniz Institute DSMZ has now shown that the species diversity of these archaea in lakes around the world ranges from 1 to 15 species. This is of particularly concern in the context of global biodiversity loss and the UN Biodiversity Conference held in Montreal, Canada, in December 2022. Lakes play an important role in providing freshwater for drinking, inland fisheries, and recreation. These ecosystem services would be at danger from ammonium enrichment. Ammonium is an essential component of agricultural fertilizers and contributes to its remarkable increase in environmental concentrations and the overall im-balance of the global nitrogen cycle. Nutrient-poor lakes with large water masses (such as Lake Constance and many other pre-alpine lakes) harbor enormously large populations of archaea, a unique class of microorganisms. In sediments and other low-oxygen environments, these archaea convert ammonium to nitrate, which is then converted to inert dinitrogen gas, an essential component of the air. In this way, they contribute to the detoxification of ammonium in the aquatic environment. In fact, the species predominant in European lakes is even clonal and shows low genetic microdiversity between different lakes. This low species diversity contrasts with marine ecosystems where this group of microorganisms predominates with much greater species richness, making the stability of ecosystem function provided by these nitrogen-converting archaea potentially vulnerable to environmental change.
Maintenance of drinking water quality
Although there is a lot of water on our planet, only 2.5% of it is fresh water. Since much of this fresh water is stored in glaciers and polar ice caps, only about 80% of it is even accessible to us humans. About 36% of drinking water in the European Union is obtained from surface waters. It is therefore crucial to understand how environmental processes such as microbial nitrification maintain this ecosystem service. The rate-determining phase of nitrification is the oxidation of ammonia, which prevents the accumulation of ammonium and converts it to nitrate via nitrite. In this way, ammonium is prevented from contaminating water sources and is necessary for its final conversion to the harmless dinitrogen gas. In this study, deep lakes on five different continents were investigated to assess the richness and evolutionary history of ammonia-oxidizing archaea. Organisms from marine habitats have traditionally colonized freshwater ecosystems. However, these archaea have had to make significant changes in their cell composition, possible only a few times during evolution, when they moved from marine habitats to freshwaters with much lower salt concentrations. The researchers identified this selection pressure as the major barrier to greater diversity of ammonia-oxidizing archaea colonizing freshwaters. The researchers were also able to determine when the few freshwater archaea first appeared. Ac-cording to the study, the dominant archaeal species in European lakes emerged only about 13 million years ago, which is quite consistent with the evolutionary history of the European lakes studied.
Slowed evolution of freshwater archaea
The major freshwater species in Europe changed relatively little over the 13 million years and spread almost clonally across Europe and Asia, which puzzled the researchers. Currently, there are not many examples of such an evolutionary break over such long time periods and over large intercontinental ranges. The authors suggest that the main factor slowing the rapid growth rates and associated evolutionary changes is the low temperatures (4 °C) at the bottom of the lakes studied. As a result, these archaea are restricted to a state of low genetic diversity. It is unclear how the extremely species-poor and evolutionarily static freshwater archaea will respond to changes induced by global climate warming and eutrophication of nearby agricultur-al lands, as the effects of climate change are more pronounced in freshwater than in marine habitats, which is associated with a loss of biodiversity.
Publication: Ngugi DK, Salcher MM, Andre A-S, Ghai R., Klotz F, Chiriac M-C, Ionescu D, Büsing P, Grossart H-S, Xing P, Priscu JC, Alymkulov S, Pester M. 2022. Postglacial adaptations enabled coloniza-tion and quasi-clonal dispersal of ammonia oxidizing archaea in modern European large lakes. Science Advances: https://www.science.org/doi/10.1126/sciadv.adc9392
PhDr. Sven-David Müller, Head of Public Relations, Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH
Phone: ++49 (0)531/2616-300
About the Leibniz Institute DSMZ
The Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures is the world’s most diverse collection of biological resources (bacteria, archaea, protists, yeasts, fungi, bacteriophages, plant viruses, genomic bacterial DNA as well as human and animal cell lines). Microorganisms and cell cultures are collected, investigated and archived at the DSMZ. As an institution of the Leibniz Association, the DSMZ with its extensive scientific services and biological resources has been a global partner for research, science and industry since 1969. The DSMZ was the first registered collection in Europe (Regulation (EU) No. 511/2014) and is certified according to the quality standard ISO 9001:2015. As a patent depository, it offers the only possibility in Germany to deposit biological material in accordance with the requirements of the Budapest Treaty. In addition to scientific services, research is the second pillar of the DSMZ. The institute, located on the Science Campus Braunschweig-Süd, accommodates more than 82,000 cultures and biomaterials and has around 200 employees. www.dsmz.de
Scientists are closing in on why the universe exists
Particle astrophysicist Benjamin Tam hopes his work will help us understand a question. A very big one.
“The big question that we are trying to answer with this research is how the universe was formed,” said Tam, who is finishing his PhD at Queen’s University.
“What is the origin of the universe?”
And to answer that question, he and dozens of fellow scientists and engineers are conducting a multi-million dollar experiment two kilometres below the surface of the Canadian Shield in a repurposed mine near Sudbury, Ontario.
The Sudbury Neutrino Observatory (SNOLAB) is already famous for an earlier experiment that revealed how neutrinos ‘oscillate’ between different versions of themselves as they travel here from the sun.
This finding proved a vital point: the mass of a neutrino cannot be zero. The experiment’s lead scientist, Arthur McDonald, shared the Nobel Prize in 2015 for this discovery.
The neutrino is commonly known as the ‘ghost particle.’ Trillions upon trillions of them emanate from the sun every second. To humans, they are imperceptible except through highly specialized detection technology that alerts us to their presence.
Neutrinos were first hypothesized in the early 20th century to explain why certain important physics equations consistently produced what looked like the wrong answers. In 1956, they were proven to exist.
Tam and his fellow researchers are now homing in on the biggest remaining mystery about these tiny particles.
Nobody knows what happens when two neutrinos collide. If it can be shown that they sometimes zap each other out of existence, scientists could conclude that a neutrino acts as its own ‘antiparticle’.
Such a conclusion would explain how an imbalance arose between matter and anti-matter, thus clarifying the current existence of all the matter in the universe.
It would also offer some relief to those hoping to describe the physical world using a model that does not imply none of us should be here.
Guests in this episode (in order of appearance):
Benjamin Tam is a PhD student in Particle Astrophysics at Queen’s University.
Eve Vavagiakis is a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellow in the Physics Department at Cornell University. She’s the author of a children’s book, I’m A Neutrino: Tiny Particles in a Big Universe.
Erica Caden is a research scientist at SNOLAB. Among her duties she is the detector manager for SNO+, responsible for keeping things running day to day.
*This episode was produced by Nicola Luksic and Tom Howell. It is part of an on-going series, IDEAS from the Trenches, some stories are below.
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