Astronomy

Humans may have shaped the development of aromatic herbs like lavender and mint, but did herbs also shape our own evolution?

Humans may have shaped the development of aromatic herbs like lavender and mint, but did herbs also shape our own evolution?

When June 2024's Strawberry Moon is almost full, it will occult the bright star Antares.

Earth’s protective atmosphere has sheltered life for billions of years, creating a haven where evolution produced complex lifeforms like us. The ozone layer plays a critical role in shielding the biosphere from deadly UV radiation. It blocks 99% of the Sun’s powerful UV output. Earth’s magnetosphere also shelters us.

But the Sun is relatively tame. How effective are the ozone and the magnetosphere at protecting us from powerful supernova explosions?

Every million years—a small fraction of Earth’s 4.5 billion-year lifetime—a massive star explodes within 100 parsecs (326 light-years) of Earth. We know this because our Solar System sits inside a massive bubble in space called the Local Bubble. It’s a cavernous region of space where hydrogen density is much lower than outside the bubble. A series of supernovae explosions in the previous 10 to 20 million years carved out the bubble.

Supernovae are dangerous, and the closer a planet is to one, the more deadly its effects. Scientists have speculated on the effects that supernova explosions have had on Earth, wondering if it triggered mass extinctions or at least partial extinctions. A supernova’s gamma-ray burst and cosmic rays can deplete Earth’s ozone and allow ionizing UV radiation to reach the planet’s surface. The effects can also create more aerosol particles in the atmosphere, increasing cloud coverage and causing global cooling.

A new research article in Nature Communications Earth and Environment examines supernova explosions and their effect on Earth. It is titled “Earth’s Atmosphere Protects the Biosphere from Nearby Supernovae.” The lead author is Theodoros Christoudias from the Climate and Atmosphere Research Center, Cyprus Institute, Nicosia, Cyprus.

The Local Bubble isn’t the only evidence of nearby core-collapse supernovae (SNe) in the last few million years. Ocean sediments also contain 60Fe, a radioactive isotope of iron with a half-life of 2.6 million years. SNe expel 60Fe into space when they explode, indicating that a nearby supernova exploded about 2 million years ago. There’s also 60Fe in sediments that indicate another SN explosion about 8 million years ago.

This graphic from the research article shows the potential atmospheric and climate impacts of a nearby supernova. Gamma rays can deplete the ozone, allowing more UV radiation to reach Earth’s surface. Some UV radiation is ionizing, meaning it can damage DNA. Cosmic rays can also create more condensation nuclei, meaning more clouds and potential global cooling, Image Credit: Christoudias et al. 2024

Researchers have correlated an SN explosion with the Late Devonian extinction about 370 million years ago. In one paper, researchers found plant spores burned by UV light, an indication that something powerful depleted Earth’s ozone layer. In fact, Earth’s biodiversity declined for about 300,000 years prior to the Late Devonian extinction, suggesting that multiple SNe could’ve played a role.

Earth’s ozone layer is in constant flux. As UV energy reaches it, it breaks ozone molecules (O3) apart. That dissipates the UV energy, and the oxygen atoms combine into O3 again. The cycle repeats. That’s a simplified version of the atmospheric chemistry involved, but it serves to illustrate the cycle. A nearby supernova could overwhelm the cycle, depleting the ozone column density and allowing more deadly UV to reach Earth’s surface.

But in the new paper, Christoudias and his fellow authors suggest that Earth’s ozone layer is much more resilient than thought and provides ample protection against SNe within 100 parsecs. While previous researchers have modelled Earth’s atmosphere and its response to a nearby SN, the authors say that they’ve improved on that work.

They modelled Earth’s atmosphere with an Earth Systems Model with Atmospheric Chemistry (EMAC) model to study the impact of nearby SNe explosions on Earth’s atmosphere. Using EMAC, the authors say they’ve modelled “the complex atmospheric circulation dynamics, chemistry, and process feedbacks” of Earth’s atmosphere. These are needed to “simulate stratospheric ozone loss in response to elevated ionization, leading to ion-induced nucleation and particle growth to CCN” (cloud condensation nuclei.)

“We assume a representative nearby SN with GCR (galactic cosmic ray) ionization rates in the atmosphere that are 100 times present levels,” they write. That correlates with a supernova explosion about 100 parsecs or 326 light-years away.

These panels from the research letter show the ozone column percentage decrease from a 100-fold increase in GCR intensity over nominal. The left vertical axis represents Earth’s latitude, and the x-axis shows the time of year. Ozone loss is more pronounced over the poles due to the effect of Earth’s magnetosphere, where it’s weaker. a is present-day Earth, while b represents an ancient Earth with only 2% oxygen during the pre-Cambrian. Image Credit: Christoudias et al. 2024

“The maximum ozone depletion over the poles is less than the present-day anthropogenic ozone hole over Antarctica, which amounts to an ozone column loss of 60–70%,” the authors explain. “On the other hand, there is an increase of ozone in the troposphere, but it is well within the levels resulting from recent anthropogenic pollution.”

But let’s cut to the chase. We want to know if Earth’s biosphere is safe or not.

The maximum mean stratospheric ozone depletion from 100 times more ionizing radiation than normal, representative of a nearby SN, is about 10% globally. That’s about the same decrease as our anthropogenic pollution causes. It wouldn’t affect the biosphere very much.

“Although significant, it is unlikely that such ozone changes would have a major impact on the biosphere, especially because most of the ozone loss is found to occur at high latitudes,” the authors explain.

But that’s for modern Earth. During the pre-Cambrian, before life exploded in a multiplication of forms, the atmosphere had only about 2% oxygen. How would an SN affect that? “We simulated a 2% oxygen atmosphere since this would likely represent conditions where the emerging biosphere on land would still be particularly sensitive to ozone depletion,” the authors write.

“Ozone loss is about 10–25% at mid-latitudes and an order of magnitude lower in the tropics,” the authors write. At minimum ozone levels at the poles, ionizing radiation from an SN could actually end up increasing the ozone column. “We conclude that these changes of atmospheric ozone are unlikely to have had a major impact on the emerging biosphere on land during the Cambrian,” they conclude.

What about global cooling?

Global cooling would increase, but not to a dangerous extent. Over the Pacific and Southern oceans, CCN could increase by up to 100%, which sounds like a lot. “These changes, while climatically relevant, are comparable to the contrast between the pristine pre-industrial atmosphere and the polluted present-day atmosphere.” They’re saying that it would cool the atmosphere by about the same amount as we’re heating it now.

These two panels from the research help illustrate the global cooling effect from a nearby SN exposing Earth to 100 times more ionizing radiation. b shows the fractional change in CCN relative to the present day. d shows the fractional change in outgoing solar radiation relative to the present day due to increased cloud albedo. Image Credit: Christoudias et al. 2024

The researchers point out that their study concerns the entire biosphere, not individuals. “Our study does not consider the direct health risks to humans and animals resulting from exposure to elevated ionizing radiation,” they write. Depending on individual circumstances, individuals could be exposed to dangerous levels of radiation over time. But overall, the biosphere would hum along despite a 100-fold increase in UV radiation. Our atmosphere and magnetosphere can handle it.

“Overall, we find that nearby SNe are unlikely to have caused mass extinctions on Earth,” the authors write. “We conclude that our planet’s atmosphere and geomagnetic field effectively shield the biosphere from the effects of nearby SNe, which has allowed life to evolve on land over the last hundreds of million years.”

This study shows that Earth’s biosphere will not suffer greatly as long as supernova explosions keep their distance.

The post Earth’s Atmosphere is Our Best Defence Against Nearby Supernovae appeared first on Universe Today.

NOAA's GOES-R series constellation will be complete in space with the launch of its GOES-U satellite at the end of June. This will mark the first time a NOAA satellite will be transported to space using a SpaceX Falcon Heavy rocket.

NASA has rescheduled last week's EVA, which was called off only an hour before the astronauts were set to exit the station.

Boeing's Starliner will come back to Earth with its two astronauts no earlier than June 26. The four-day extension will allow for more thruster testing at the ISS.

SpaceX is poised to launch the SES Astra 1P telecom satellite after standing down due to elevated winds at the launch site.

This image of Galveston was taken on Nov. 23, 2022, from the International Space Station as it orbited 224 miles above Earth. While President Abraham Lincoln issued the Emancipation Proclamation in 1863, word that enslaved people were free did not reach Galveston until well into 1865. When Union troops arrived that year to share the news, spontaneous celebrations broke out in African American churches, homes, and other gathering places. As years passed, the picnics, barbecues, parades, and other celebrations that sprang up to commemorate June 19th became more formalized as freed men and women purchased land, or “emancipation grounds,” to hold annual Juneteenth celebrations.

The chemical composition of Pluto and Triton suggests they originated in the same region of the outer solar system before the latter was pulled into Neptune’s orbit

The chemical composition of Pluto and Triton suggests they originated in the same region of the outer solar system before the latter was pulled into Neptune’s orbit

Image: Metallic Mars

According to Lego, the Milky Way Galaxy is made up of love hearts, frogs, flowers and coffee mugs — and it's absolutely fabulous.

Why does this mysterious woman keep popping up in the Doctor's timeline? And what's her connection to the season's Big Bad?

Driverless cars seem to have fewer accidents than human drivers under routine conditions, but higher crash risks when turning or in dim light – although researchers say more accident data is necessary

Driverless cars seem to have fewer accidents than human drivers under routine conditions, but higher crash risks when turning or in dim light – although researchers say more accident data is necessary

It was the first time ever.

There are many scary claims about excess time on digital devices for children and teenagers. Here’s a guide to the real risks - and what to do about them

There are many scary claims about excess time on digital devices for children and teenagers. Here’s a guide to the real risks - and what to do about them

The newest phase of China’s lunar exploration project is soon coming to an end. On June 20th, the Chang’e 6 sample return mission starts its journey back to Earth from the far side of the Moon, having already collected samples and blasted itself back into lunar orbit. But since a picture is worth a thousand words, let’s look at some of the more memorable images that have come out of this mission so far.

China’s National Space Agency (CNSA) released up close and personal images of the Chang’e-6 landers/ascender system on June 14th. They were taken by a small, autonomous rover that descended from the lander, maneuvered to a suitable position, framed a photograph, and took one, all without input from its human overlords. 

Weighing in at only 5 kg, the rover showed what is possible for autonomous operation with relatively light hardware. It also shows an impressive amount of autonomy for a lunar rover, especially one operational only on the “far” side of the Moon.

Shot of the Chang’e-6 lander/ascender taken by its companion autonomous rover.
Credit – CNSA

It wasn’t the only observer that captured an interesting image of China’s sixth mission in a series named after Chang’e, the Chinese Moon goddess. NASA’s Lunar Reconnaissance Orbiter captured the orbiter from overhead space and showed a dramatic change in its surroundings. 

In the image, the lander itself appears as a bright white dot. However, the surrounding area also appears significantly lighter. This had to do with the blast radius of the lander’s retrograde rockets for its soft landing. Those powerful rockets blew away the dark lunar regolith that had remained untouched for millions of years. The picture was snapped on June 7th, after the Chang’e-6 ascent vehicle had launched back off the surface and rendezvoused with the orbiter that will take the samples it collected back to Earth. In so doing, it likely blew away plenty of material with its own ascent rockets.

During its time on the Moon, Chang’e-6 collected 2 kg of samples, which it will return to a laboratory on Earth. This is the second time CNSA has planned such a mission and the first time one has taken place on the far side that humans cannot see from Earth. 

Fraser discusses the Chang’e-6 mission to collect lunar samples in this news update.

The next in the sequence of Chinese moon missions is Chang’e-7, which will focus its research efforts on the lunar south pole. Scientists predict water ice might be abundant there and that it might be the potential future site of a crewed Chinese moon base. Chang’e-7 will also include a hopping rover to explore the local environs surrounding its lander, but it isn’t scheduled for launch until 2026.

Currently, the Chang’e-6 mission orbiter, which has already successfully docked with the ascent vehicle containing the collected samples, is waiting for the opportune time to return to Earth. It will also serve as the return vehicle, which is planned to land back on Earth on June 25th. If all goes according to plan, there will soon be more lunar samples for scientists to explore and another successful mission for the CSNA that will have been documented in some pretty astounding pictures.

Learn More:
CGTN – Unraveling Chang’e-6: Discover the mini rover that snapped a photo of Chang’e-6 probe
NASA – NASA’s LRO Spots China’s Chang’e 6 Spacecraft on Lunar Far Side
UT – Chinese Probe Collects Moon Samples and Heads for Earth
UT – Chinese Probe Lands on Moon’s Far Side to Collect Samples for Return

Lead Image:
This image from NASA’s Lunar Reconnaissance Orbiter shows China’s Chang’e 6 lander in the Apollo basin on the far side of the Moon on June 7, 2024. The lander is the bright dot in the center of the image. The image is about 0.4 miles wide (650 meters); lunar north is up.
Credit: NASA/Goddard/Arizona State University

The post There’s Chang’e-6 on the Far Side of the Moon appeared first on Universe Today.