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Earth is naked without its protective barrier. The planet’s magnetic shield surrounds Earth and shelters it from the natural onslaught of cosmic rays. But sometimes, the shield weakens and wavers, allowing cosmic rays to strike the atmosphere, creating a shower of particles that scientists think could wreak havoc on the biosphere.

This has happened many times in our planet’s history, including 41,000 years ago in an event called the Laschamps excursion.

Cosmic rays are high-energy particles, usually protons or atomic nuclei, that travel through space at relativistic speeds. Normally, they’re deflected into space and away from Earth by the planet’s magnetic shield. But the shield is a natural phenomenon and its strength fluctuates, as does its orientation. When that happens, cosmic rays strike the Earth’s atmosphere.

That creates a shower of secondary particles called cosmogenic radionuclides. These isotopes become embedded in sediments and ice cores and even in the structure of living things like trees. There are different types of these isotopes, including ones like Calcium 41 and Carbon 14.

Showers of high-energy particles occur when energetic cosmic rays strike the top of the Earth's atmosphere. Illustration Credit: Simon Swordy (U. Chicago), NASA.
Showers of high-energy particles occur when energetic cosmic rays strike the top of the Earth’s atmosphere. Illustration Credit: Simon Swordy (U. Chicago), NASA.

Some of the isotopes are stable, and some are radioactive. The radioactive ones have half-lives ranging from only 20 minutes (Carbon 11) up to 15.7 million years (Xenon 129.)

When Earth’s shield weakens, more of these isotopes reach the planet’s surface and collect in sediments and ice. By studying these cores and sediments, scientists can determine the magnetic shield’s history. Their observations show that Earth experienced a geomagnetic excursion or reversal 41,000 years ago. It’s called the Laschamps excursion after the Laschamps lava flows in France, where geomagnetic anomalies revealed its occurrence.

Every few hundred thousand years, the Earth’s magnetic poles flip. North becomes South and vice versa. In between those major events are more minor events called excursions. During excursions, the poles shift around for a while without swapping places. The excursions weaken the Earth’s shield and can last from a few thousand to tens of thousands of years. When that happens, more cosmic rays strike the atmosphere, creating more radionuclides that shower down onto Earth.

Scientists often focus on one particular radioactive isotope in paleomagnetic studies. Beryllium 10 has a relatively long half-life of 1.36 million years and tends to accumulate on the soil surface.

Sanja Panovska is a researcher at GFZ Potsdam, Germany, who studies geomagnetism. At the recent European Geosciences Union (EGU) General Assembly 2024, Panovska presented new research on the Laschamps excursion. She found that during the Laschamps excursion, production of Be 10 was twice as high as normal.

To understand the Laschamps excursion more thoroughly, Panovska combined cosmogenic radionuclide and paleomagnetic data to reconstruct the Earth’s magnetic field at the time. She found that when the field decreased in strength, it also shrank. The transition from normal field to reversed field took about 250 years, and it stayed flipped for about 440 years. During the transition, the Earth’s shield weekend to as little as 5% of its normal strength. When it was fully reversed, it was at about 25% of its regular strength. This weakening allowed more Be 10 and other cosmogenic radionuclides to reach Earth’s surface.

Each map shows the intensity of Earth's geomagnetic field at different snapshots in time, according to Panovska's reconstructions that are constrained by both paleomagnetic data and records of cosmogenic beryllium-10 radionuclides. DM stands for Dipole Moment, which is a measure of the field's polarity or separation of positive and negative. Age [ka BP] is the age measures in thousands of years before the present. Image Credit: Sanja Panovska. Did you miss our previous article…
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The Inner and Outer Milky Way Aren’t the Same Thickness, and that’s Surprising

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At first glance, the universe and night sky seem largely unchanging. The reality is very different, even now, a gas cloud is charging toward the Milky Way Galaxy and is expected to crash into us in 27 million years. A team of astronomers hoping to locate the exact position of the expected impact site have been unsuccessful but have accidentally measured the thickness of the Milky Way! Analysing radio data, they have been able to deduce the thickness of the inner and outer regions and discovered a dramatic difference between the two. 

The team of astronomers from the US National Science Foundation’s Green Bank Observatory were attempting to study the Smith Cloud. This high velocity cloud of hydrogen gas is located in the constellation Aquila at a distance of somewhere between 36,000 and 45,000 light years. Previous studies from the Green Bank Observatory have shown the cloud contains at least 1 million times the mass of the Sun and measures 9,800 light years long by 3,300 light years wide. 

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A false-color image of the Smith Cloud made with data from the Green Bank Telescope (GBT). New analysis indicates that it is wrapped in a dark matter halo. Credit: NRAO/AUI/NSF

The plan was simple enough, to observe the spot where the cloud is currently interacting with the Milky Way. The observation is tricky enough though as the cloud is on the far side of the Milky Way and there is a lot of stuff in the way! The team, led by Toney Minter used the 20m Green Bank Telescope to search for dust and emissions from hydroxyl molecules (composed of a hydrogen and oxygen molecule.)  What the team expected to see was a difference in composition in the region of the Milky Way interacted with the cloud which, should have very little dust and hydroxyl molecules. Clouds in the Milky Way tend to have both so a difference should be detectable. 

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The Robert C. Byrd Green Bank Telescope. Credit: Jay Young.

Minter was candidly open about the study joking ‘I knew there was a low probability that I’d find what I was looking for—and I didn’t,. But this is all part of the scientific process. You learn from what you DO and DON’T find.’

Disappointingly the team did not detect any differences in composition but what they did find was equally as interesting. The study revealed information about the Milky Way itself and the structure of its inner regions. Minter and his team had to look through the Milky Way’s inner regions for their study and what they were able to determine was the thickness of the layer of molecules in the inner Galaxy. The information enabled them to deduce the scale height of the clouds of molecular gas in the inner Milky Way. The results showed that the layer of molecules in the inner region measured 330 light years thick while those in the outer parts measured twice as much, around 660 light years.

The discovery still leaves questions unanswered. The observation certainly shows the difference in thickness between the inner and outer regions but it doesn’t give any clue as to what is driving the difference. Further observations are now required to follow up on this discovery to try and model the underlying process. Of course one other question remains unanswered and that is the nature and mechanics of the Smith Cloud and how it will impact our own Galaxy. Far from being disappointed though, Minter stated ‘That’s why astronomy is exciting, our knowledge is always evolving’

Source : While Aiming for
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Catching Comet 13P Olbers This Summer

Comet 13P Olbers by William R. Brooks

A little known periodic comet graces northern hemisphere summer skies.

Short summer nights present a tough dilemma for nighttime astronomy: to stay up late, or wake up early? Summer 2024 gives you at least one reason to opt for the former, as periodic Comet 13P/Olbers graces the evening sky.

The History of the Comet

The comet was first spotted on the night of March 6th, 1815 by astronomer Heinrich Olbers (of Olbers’ Paradox fame) observing from Bremen, Germany. The orbit was later described by Carl Gauss and Friedrich Bessel as just shy of 74 years, about five years off of the present value.

Olbers
A sketch of Comet 13P Olbers from 1887 by William Robert Brooks. Credit: Public Domain

The Comet’s Orbit

Comet 13P/Olbers is on a 69 year orbit, which takes it from a perihelion 1.175 Astronomical Units (AU) from the Sun just outside of the Earth’s orbit, out to an aphelion of 32.5 AU out beyond the orbit of Neptune.

Perihelion for the comet occurs June 30th, 2024 at 1.175 AU from the Sun and 1.919 AU from the Earth.

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The orbit of Comet 13P Olbers. Credit: NASA/JPL

Synopsis of the Current Apparition

In 2024, Comet 13P Olbers loiters low to the west this summer for northern observers at dusk. This is because it’s approaching Earth along our line of sight. The comet will seem to hang about 20-30 degrees above the horizon on summer evenings for mid-latitude northern hemisphere observers.

June 15
The location of the comet in the evening sky in mid-June. Credit: Stellarium

Here’s our look at what to expect from the comet month-by-month. Unless otherwise noted, ‘Passes near’ means a closest approach of less than one angular degree:

June

17-The orbital path of the comet is edge on as seen from our point of view, and the comet may exhibit a spiky anti-tail.

19-Passes into the constellation of the Lynx.

28-Passes near the +4.3 magnitude star 31 Lyncis.

Path
The celestial path of the comet
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Starliner Has Five Leaks

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Many space fans have been following the successful launch of the Boeing Starliner, another commercial organisation aiming to make space more accessible. It successfully reached the International Space Station, delivering Butch Wilmore and Suni Williams into orbit but it wasn’t without a hitch. Three of its thrusters experienced problems and there were ‘five small leaks on the service module.’ The crew and ground teams are working through safety checks of power and habitability. To ensure a safe return of the astronauts NASA has extended the mission by four days to 18th June. 

Boeing Starliner is a reusable (partly) spacecraft designed to transport crews to low Earth orbit. NASA is the lead customer so, once certification has been achieved, will be used to deliver astronauts regularly to the ISS. It consists of a crew capsule that can be used ten times and an expendable service module. Measuring 4.6 metres in diameter it is slightly larger than the Apollo Command module that was a part of the historic Armstrong, Aldrin and Collins mission to the Moon.

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The Apollo 10 command/service module nicknamed “Charlie Brown” orbiting the Moon as seen from the lunar module. Credit: NASA

The Boeing Starliner launch marked its first crewed trip into orbit, with the objective of data collection for certification by NASA for regular crewed missions to ISS. The tests are numerous and include; running the spacecraft in minimal power mode (for when docked to ISS), checking suitability to support crew on its own in the event of an emergency, performing habitability studies for a four person crew and a multitude of other system checks. The module has been docked to ISS since 6th June.

Teething problems for any new module are always expected but when the word ‘leak’ pops up it is most definitely a cause for concern. In the case of Starliner, five small leaks have been detected in the service module helium manifolds. When Starliner launched, the ground team already knew there was one leak in the propulsion system but now, four more have been detected! The flight engineers initially suspected a flaw in a manifold seal or possibly even faulty installation but now, with the four additional leaks they’re trying to understand if there is a common problem.

The leaks are not the only problem that has been experienced. As Starliner approached ISS, it relied upon precise pulses from the 28 reaction control thrusters. During this critical phase of the docking process, five of them failed. More accurately, the spacecraft control software deduced they were not working and deselected them. The first docking window was missed as a result but the crew were able to test and restart four of the five engines allowing them to safely dock. Engineers are still looking into the thruster problem but are confidence it will allow the safe return of the astronauts. 

ISS
International Space Station. Credit: NASA

As for the helium leak, flight engineers have examined the leak rate and confirmed that Starliner has sufficient margin to support a return trip to Earth. With Starliner docked to the ISS the manifolds are all closed preventing any helium loss until the return trip which takes just seven hours. Even with the manifolds open and the rate of leak there is sufficient helium to support 70 hours of flight time.

Ground support teams are continuing to work through the problems and the return plan. They will explore tolerances and possible operational mitigations for the remainder of the mission. As the
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