Bouncing seismic waves reveal distinct layer in Earth’s inner core
Data captured from seismic waves caused by earthquakes has shed new light on the deepest parts of Earth’s inner core, according to seismologists from The Australian National University (ANU).
By measuring the different speeds at which these waves penetrate and pass through the Earth’s inner core, the researchers believe they’ve documented evidence of a distinct layer inside Earth known as the innermost inner core — a solid “metallic ball” that sits within the centre of the inner core.
Not long ago it was thought Earth’s structure was composed of four distinct layers: the crust, the mantle, the outer core and the inner core. The findings, published in Nature Communications, confirm there is a fifth layer.
“The existence of an internal metallic ball within the inner core, the innermost inner core, was hypothesized about 20 years ago. We now provide another line of evidence to prove the hypothesis,” Dr Thanh-Son Phạm, from the ANU Research School of Earth Sciences, said.
Professor Hrvoje Tkalčić, also from ANU, said studying the deep interior of Earth’s inner core can tell us more about our planet’s past and evolution.
“This inner core is like a time capsule of Earth’s evolutionary history — it’s a fossilised record that serves as a gateway into the events of our planet’s past. Events that happened on Earth hundreds of millions to billions of years ago,” he said.
The researchers analysed seismic waves that travel directly through the Earth’s centre and “spit out” at the opposite side of the globe to where the earthquake was triggered, also known as the antipode. The waves then travel back to the source of the quake.
The ANU scientists describe this process as similar to a ping pong ball bouncing back and forth.
“By developing a technique to boost the signals recorded by densely populated seismograph networks, we observed, for the first time, seismic waves that bounce back-and-forth up to five times along the Earth’s diameter. Previous studies have documented only a single antipodal bounce,” Dr Phạm said.
“The findings are exciting because they provide a new way to probe the Earth’s inner core and its centremost region.”
One of the earthquakes the scientists studied originated in Alaska. The seismic waves triggered by this quake “bounced off” somewhere in the south Atlantic, before travelling back to Alaska.
The researchers studied the anisotropy of the iron-nickel alloy that comprises the inside of the Earth’s inner core. Anisotropy is used to describe how seismic waves speed up or slow down through the material of the Earth’s inner core depending on the direction in which they travel. It could be caused by different arrangement of iron atoms at high temperatures and pressures or preferred alignment of growing crystals.
They found the bouncing seismic waves repeatedly probed spots near the Earth’s centre from different angles. By analysing the variation of travel times of seismic waves for different earthquakes, the scientists infer the crystallised structure within the inner core’s innermost region is likely different to the outer layer.
They say it might explain why the waves speed up or slow down depending on their angle of entry as they penetrate the innermost inner core.
According to the ANU team, the findings suggest there could have been a major global event at some point during Earth’s evolutionary timeline that led to a “significant” change in the crystal structure or texture of the Earth’s inner core.
“There are still many unanswered questions about the Earth’s innermost inner core, which could hold the secrets to piecing together the mystery of our planet’s formation,” Professor Tkalčić said.
The researchers analysed data from about 200 magnitude-6 and above earthquakes from the last decade.
Meet the Canadian astronauts up for a seat on the Artemis II mission to the moon – iHeartRadio.ca
This Sunday, NASA and the Canadian Space Agency (CSA) will announce the four astronauts that will be blasting off to fly around the moon for the Artemis II mission, one of whom will be a Canadian astronaut.
The Artemis II mission will be the first crewed mission to orbit the moon in half a century, and the inclusion of a Canadian astronaut on the mission will make Canada the second country to have an astronaut fly around the moon.
In November 2024, NASA’s Kennedy Space Center in Florida will launch the four astronauts into space for the Artemis II mission. They will pilot the Orion spacecraft around the Earth and then around the moon before returning home.
It’s the second step of a project that started last year with the unmanned Artemis I mission. The Artemis missions help to test the launch system and the spacecraft itself. The end goal is for scientists to construct a Lunar Gateway at the moon — a space station that could serve as a jumping off point for further deep space exploration.
A trailer for the crew announcement was posted by NASA on Wednesday.
There are currently four active Canadian astronauts, but we won’t know until Sunday who will be the first Canadian astronaut to fly around the moon.
Kutryk was born in Fort Saskatchewan, Alberta and grew up on a cattle farm in eastern Alberta. He is a member of the Canadian Armed Forces, and has been deployed in Libya and Afghanistan in the past.
He worked as an experimental test pilot and fighter pilot in Cold Lake, Alberta before he was recruited by the CSA. He worked on numerous test flight projects as well as on improving the safety of fighter jets such as the CF-18.
Kutryk made it to the top 16 candidates for the CSA in 2009, but wasn’t selected until CSA’s 2017 recruitment campaign.
He obtained the official title of astronaut in January 2020.
Sidey-Gibbons comes from Calgary, Alberta, and first worked with the CSA while studying mechanical engineering at McGill University, where she conducted research on flame propagation in microgravity in collaboration with the agency.
Before joining CSA, she lived and worked in the U.K. as an assistant professor in the Department of Engineering at the University of Cambridge. Her research there focused on how to develop low-emission combusted for gas turbine engines.
She was selected by the CSA in 2017 as a recruit along with Kutryk, and obtained the official title of astronaut in January 2020.
Hansen was born in London, Ontario and spent his childhood first on a farm near Ailsa Craig, Ontario, and then Ingersoll, Ontario. He is married with three children.
By age 17, he had already obtained glider and private pilot licences through the Air Cadet Program. He is a member of the Canadian Armed Forces and served as a CF-18 fighter pilot before becoming an astronaut.
Hansen graduated as an astronaut in 2011, after being selected as one of two recruits for the CSA in 2009. He currently represents the CSA at NASA and works at the Mission Control Center, serving as the point of connection between the ground and the International Space Station (ISS). He also helps to train astronauts at NASA, the first Canadian to do so.
Saint-Jacques grew up in Saint-Lambert, Quebec, near Montreal, and is married with three children.
Before joining the CSA, he worked as a medical doctor in Puvirnituq, Nunavik, an Inuit community in northern Quebec. He also works as an adjunct professor of family medicine at McGill University. As a biomedical engineer, he has worked in France and Hungary, and helped to develop optics systems for telescopes and arrays used at observatories in Japan, Hawaii and the Canary Islands.
He was selected as a recruit in 2009 by the CSA and graduated in 2011 from the NASA astronaut program. He has since worked with the Robotics Branch of the NASA Astronaut Office, as a support astronaut for various ISS missions and as the mission control radio operator for a number of resupply missions for the ISS.
In December 2018, Saint-Jacques flew to the ISS to complete a 204-day mission, which is the longest mission any Canadian astronaut has carried out in space to date. During this time, he became the fourth CSA astronaut to conduct a spacewalk and the first CSA astronaut to catch a visiting spacecraft using the Canadarm2.
Stressed plants emit airborne sounds that can be detected from more than a meter away
What does a stressed plant sound like? A bit like bubble-wrap being popped. Researchers in Israel report in the journal Cell on March 30 that tomato and tobacco plants that are stressed—from dehydration or having their stems severed—emit sounds that are comparable in volume to normal human conversation. The frequency of these noises is too high for our ears to detect, but they can probably be heard by insects, other mammals, and possibly other plants.
“Even in a quiet field, there are actually sounds that we don’t hear, and those sounds carry information,” says senior author Lilach Hadany, an evolutionary biologist and theoretician at Tel Aviv University. “There are animals that can hear these sounds, so there is the possibility that a lot of acoustic interaction is occurring.”
Although ultrasonic vibrations have been recorded from plants before, this is the first evidence that they are airborne, a fact that makes them more relevant for other organisms in the environment. “Plants interact with insects and other animals all the time, and many of these organisms use sound for communication, so it would be very suboptimal for plants to not use sound at all,” says Hadany.
The researchers used microphones to record healthy and stressed tomato and tobacco plants, first in a soundproofed acoustic chamber and then in a noisier greenhouse environment. They stressed the plants via two methods: by not watering them for several days and by cutting their stems. After recording the plants, the researchers trained a machine-learning algorithm to differentiate between unstressed plants, thirsty plants, and cut plants.
The team found that stressed plants emit more sounds than unstressed plants. The plant sounds resemble pops or clicks, and a single stressed plant emits around 30–50 of these clicks per hour at seemingly random intervals, but unstressed plants emit far fewer sounds. “When tomatoes are not stressed at all, they are very quiet,” says Hadany.
Water-stressed plants began emitting noises before they were visibly dehydrated, and the frequency of sounds peaked after five days with no water before decreasing again as the plants dried up completely. The types of sound emitted differed with the cause of stress. The machine-learning algorithm was able to accurately differentiate between dehydration and stress from cutting and could also discern whether the sounds came from a tomato or tobacco plant.
Although the study focused on tomato and tobacco plants because of their ease to grow and standardize in the laboratory, the research team also recorded a variety of other plant species. “We found that many plants—corn, wheat, grape, and cactus plants, for example—emit sounds when they are stressed,” says Hadany.
The exact mechanism behind these noises is unclear, but the researchers suggest that it might be due to the formation and bursting of air bubbles in the plant’s vascular system, a process called cavitation.
Whether or not the plants are producing these sounds in order to communicate with other organisms is also unclear, but the fact that these sounds exist has big ecological and evolutionary implications. “It’s possible that other organisms could have evolved to hear and respond to these sounds,” says Hadany. “For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision.”
Other plants could also be listening in and benefiting from the sounds. We know from previous research that plants can respond to sounds and vibrations: Hadany and several other members of the team previously showed that plants increase the concentration of sugar in their nectar when they “hear” the sounds made by pollinators, and other studies have shown that plants change their gene expression in response to sounds. “If other plants have information about stress before it actually occurs, they could prepare,” says Hadany.
Sound recordings of plants could be used in agricultural irrigation systems to monitor crop hydration status and help distribute water more efficiently, the authors say.
“We know that there’s a lot of ultrasound out there—every time you use a microphone, you find that a lot of stuff produces sounds that we humans cannot hear—but the fact that plants are making these sounds opens a whole new avenue of opportunities for communication, eavesdropping, and exploitation of these sounds,” says co-senior author Yossi Yovel, a neuro-ecologist at Tel Aviv University.
“So now that we know that plants do emit sounds, the next question is—’who might be listening?'” says Hadany. “We are currently investigating the responses of other organisms, both animals and plants, to these sounds, and we’re also exploring our ability to identify and interpret the sounds in completely natural environments.”
Lilach Hadany, Sounds emitted by plants under stress are airborne and informative, Cell (2023). DOI: 10.1016/j.cell.2023.03.009. www.cell.com/cell/fulltext/S0092-8674(23)00262-3
Stressed plants emit airborne sounds that can be detected from more than a meter away (2023, March 30)
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After sunset, see the 5 planets in the sky or via video
How to see 5 planets
This week (late March 2023), you can see five planets lined up in our evening sky: Venus and Uranus, Jupiter and Mercury and Mars. Gianluca Massi of the Virtual Telescope Project in Rome, Italy, showed them through a telescope earlier today (March 29). To enjoy his presentation, watch the video below. In addition, you can see them in the sky, perhaps, if your sky conditions are very good, and you have a sharp eye.
As soon as the sun sets, the planets are positioned in a gentle arc across the evening sky, following the sun’s path across our sky. Likewise, the Moon and the planets also follow the eclipse.
How can we see the planets? Go out around sunset and look west. Among them you can easily spot the bright planet Venus.
Then use binoculars to scan the planet Uranus next to Venus.
Then aim your binoculars low in the sky, near the point where the sun is setting. That is where you will find Jupiter and Mercury.
Then look high in the sky — still see the eclipse or the path of the Sun — to Mars.
Guide to Planetary Viewing
Venus and Uranus. Of these five planets, Venus is the brightest and Uranus is the dim. These two are close together in the sky. Venus is easily visible to the eye. It is the first “star” (actually, planet) to come into view. Uranus shines at +5.8 magnitudes. This is theoretically obvious. But, in practice, you need a dark sky and a telescope to find it. It was roughly 1.5 degrees or three moon widths from Venus earlier this week. Uranus will be closest to Venus on Thursday, March 30.
Thursday and Wednesday. Jupiter is the 2nd brightest planet. But it is now near sunset and visible only in bright twilight. Bright twilight skies make Jupiter more difficult to find. But Jupiter is still visible to the naked eye very close to sunset. And Wednesday? It is fainter than Jupiter (though still brighter than most stars). But it is near sunset. Shortly after sunset, start looking for the pair on the western horizon. You need clear skies and an unobstructed western view to catch them. A telescope should help. They disappear only 30 minutes after sunset. So, when the sun sets, the clock chimes.
tuesday, now the 5th planet in the evening sky, was easy to spot earlier this week because it’s not far from the Moon in our sky’s dome. A bright red light near the moon on Tuesday evening, March 28, 2023. Mars is bright. It is brighter than most stars. And it is clearly red. Even after the sun goes away, you can still spot Mars by its color and by the fact that it doesn’t shine like stars.
Some inventor charts
Bottom line: You have a chance to see five planets tonight and throughout this week. Here are illustrations and information, including where to look in the video.
For more celestial events, visit EarthSky’s Night Sky Guide.
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