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.
These two images help illustrate the vegetation red edge and the solar-induced fluorescence. (L) shows the wavelength of the VRE. (Credit: Terrence et al. 2010.) (R) shows the absorption and the fluorescence for two types of chlorophyll: Chl is vegetative chlorophyll, and BChl is bacterial chlorophyll. (Credit: Komatsu et al. 2023.)
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.
Machinery inside the chloroplasts of plant cells converts sunlight to energy, emitting fluorescence in the process. Scientists can detect the fluorescence fingerprint in satellite data. Credit:
NASA Goddard’s Conceptual Image Lab/T. Chase
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 bright sunlit crescent contrasts with the darker lighting of twice-reflected light supplied by sunlight reflecting off our own planet. Credit: Bob King
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.
This figure from the study shows just one set of results the team produced. This is a set of modelled light curves for a modern Earth-like planet with an oxygen atmosphere around three stars: the Sun, the red dwarf GJ667C, and the red dwarf TRAPPIST-1. The column on the left is for a planet with vegetation covering the entire surface; the middle column is for a planet with 70 % ocean, 2% coast, and 28% land covered with vegetation; the right column is for the modern Earth. When scientists study exoplanet light with powerful telescopes in the future, they can compare their observations with this study as part of their interpretation of the data. Image Credit: Komatsu et al. 2023.
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.
This artist’s impression shows the European Extremely Large Telescope (E-ELT) in its enclosure. The E-ELT will be a 39-metre aperture optical and infrared telescope. Image Credit: ESO/L. Calçada
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.”
More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.
That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.
“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”
The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.
Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.
Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.
Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.
Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.
“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”
The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.
North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.
Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”
Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.
Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.
For Dello, the “fingerprints of climate change” were clear.
“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”
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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.
On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.
They call it “Big Sam.”
The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.
It didn’t die alone.
“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.
She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”
“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.
The head alone, she said, is about the size of a baby elephant.
The discovery was a long time coming.
The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.
“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.
When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”
“It contains about 100 to 300 bones per square metre,” she said.
Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.
About a year ago, they found the second adult: Big Sam.
Bamforth said both dinosaurs are believed to have been the elders in the herd.
“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.
“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”
The genders of the two adults are unknown.
Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.
The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.
She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.
“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.
“It’s pretty exciting.”
This report by The Canadian Press was first published Sept. 25, 2024.
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.”
