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If you take a Universe worth of hydrogen and helium, and let it stew for about 13 billion years, you get us. We are the descendants of the primeval elements. We are the cast-off dust of the first stars, and many generations of stars after that. So our search for the first stars of the cosmos is a search for our own history. While we haven’t captured the light of those first stars, some of their direct children may be in our own galaxy.

The first stars were massive. Without any heavier elements to weigh them down, they needed to be about 300 times that of our Sun in order to trigger nuclear fusion in their core. Because of their size, they went through their fusion cycles rather quickly and lived very short lives. But the supernova explosions signaling their deaths scattered heavier elements such as carbon and iron from which new stars formed. Large second-generation stars also died as supernovae and scattered even more heavy elements. As a result, each generation of stars contained more and more of these elements. In astronomy lingo, we say each generation has a higher metallicity.

Of course, which generation a star is in can be fuzzy. Clearly, the very first stars, forming entirely out of primordial hydrogen and helium are first-generation stars, and stars forming entirely out of the remnants of the first generations are true second-generation stars. But stars form at all different sizes, so it’s quite likely that some massive second-generation stars became supernova before some of the smaller first-generation stars. Many early stars could have formed from mostly first-generation material with a touch of second-generation dust, while others formed mostly from second-generation stars with a sprinkling of first-generation heritage. Stars like our Sun are likely a mix of material from multiple generations.

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The distribution of stars in our galaxy. Credit: NASA, ESA, and A. Feild [STScI]

For modern stars, rather than trying to determine their generation, we categorize them into populations based on their metallicity. A star’s metallicity is taken as the ratio of iron to helium [Fe/He] on a logarithmic scale. Population I stars have an [Fe/He] of at least -1, meaning they have 10% of the Sun’s iron ratio or more. Population II stars have an [Fe/He] of less than -1. The third category, Population III, is reserved for true first-generation stars.

In the Milky Way galaxy, most of the stars in the galactic plane are population I stars like the Sun. They formed much later in the history of our galaxy, and are younger with more metals. Older population II stars are generally found in the halo surrounding our galaxy, or in the old globular clusters that orbit the Milky Way. That makes sense since older stars have had more time to drift out of the galactic plane. Given the evolution of our galaxy, it’s quite likely that some of the population II stars in our halo are truly second-generation stars. But how can we distinguish them from other old stars?

That’s the goal of a new study published on the *arXiv*. It looks at both observations of distant quasars and simulations of population III stars to determine the metallicity of truly second-generation stars. The authors found that while second-generation stars would be rare in the Milky Way halo, some could be lurking there. The key to identifying them is not their abundance of iron relative to helium, [Fe/He], but rather the ratios of carbon and magnesium to iron, [C/Fe] and [Mg/Fe].

populationDid you miss our previous article…
https://mansbrand.com/this-exoplanet-is-probably-a-solid-ball-of-metal/

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Fly Slowly Through Enceladus’ Plumes to Detect Life

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Enceladus is blasting water into space from the jets at its southern pole. This makes it the ideal place to send a dedicated mission, flying the spacecraft through the plumes with life-detection instruments s. A new study suggests that a spacecraft must proceed carefully through the plumes, keeping its speed below 4.2 km/second (2,236 miles per hour). Using a specialized, custom-built aerosol impact spectrometer at these speeds will allow fragile amino acids to be captured by the spacecraft’s sample collector. Any faster, they’ll shatter, providing inclusive results.

One of the biggest surprises of the 20-year Cassini mission to the Saturn system was the discovery of the active geysers at Enceladus. At only about 500 km (310 miles) in diameter, the ice-covered Enceladus should be too small and too far from the Sun to be active. Instead, this little moon is one of the most geologically dynamic objects in the Solar System.

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Geysers spew from Enceladus in this image from the Cassini spacecraft. Credit: NASA/Cassini mission.

Cassini’s stunning backlit images of this moon show plumes erupting in Yellowstone-like geysers, emanating from tiger-stripe-shaped fractures in the moon’s surface. The discovery of the geysers took on more importance when Cassini later determined the plumes contained water ice and organics. Since life as we know it relies on water and a source of energy, this small but energetic moon has been added to the short list of possible places for life in our Solar System.

During three of Cassini’s passes of Enceladus in 2008 and 2009, the spacecraft’s Cosmic Dust Analyser measured the composition of freshly ejected plume grains. The icy particles hit the detector target at speeds of 6.5–17.5 km/s, and vaporized instantly. While electrical fields inside the instrument were able to separate the various constituents of the resulting impact cloud for analysis, for a future mission, scientists would like to measure the particles in the plumes without completely vaporizing them.

Back in 2012, researchers from the University of California San Diego started working on a custom-built unique aerosol impact spectrometer, designed to study collision dynamics of single aerosols and particles at high velocities. Although it wasn’t built specifically to study ice grain impacts, it turns out this instrument might be exactly what planetary scientists are looking for to use at Enceladus, or even at Jupiter’s moon Europa, where there is growing evidence of active plumes of water vapor erupting from its surface.

Robert Continetti’s one-of-a-kind aerosol impact spectrometer was used in this experiment. Ice grains impact the microchannel plate detector (far right) at hypervelocity speeds, which can then be characterized in-situ.

Continetti and several colleague have now tested the device in a laboratory, showing that amino acids transported in ice plumes — like at Enceladus — can survive impact speeds of up to 4.2 km/s. Their research is published in The Proceedings of the National Academy of Sciences (PNAS).

“This apparatus is the only one of its kind in the world that can select single particles and accelerate or decelerate them to chosen final velocities,” said Robert Continetti, a professor from UC San Diego, in a press release. “From several micron diameters down to hundreds of nanometers, in a variety of materials, we’re able to examine particle behavior, such as how they scatter or how their structures change upon impact.”

From Cassini’s measurements, scientists estimate the ice plumes at Enceladus blast out at approximately .4 km/s (800 miles per hour). A spacecraft would have to fly at the right speeds to make sure the particles could be captured intact.

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This composite image shows suspected plumes of water vapour erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The plumes, photographed by Hubble’s Imaging
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The International Space Station Celebrates 25 Years in Space

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NASA recently celebrated the 25th anniversary of the International Space Station (ISS) with a space-to-Earth call between the 7-person Expedition 70 crew and outgoing NASA Associate Administrator, Bob Cabana, and ISS Program Manager, Joel Montalbano. On December 6, 1998, the U.S.-built Unity module and the Russian-built Zarya module were mated in the Space Shuttle Endeavour cargo bay, as Endeavour was responsible for launching Unity into orbit that same day, with Zarya having waited in orbit after being launched on November 20 from Kazakhstan.

“I cannot believe it was 25 years ago today that we grappled Zarya and joined it with the Unity node,” said Cabana during the call from NASA Headquarters in Washington, D.C. “Absolutely amazing.”

While this milestone marks 25 years since the first two ISS modules were attached, it would be another two years until the ISS had a crew, Expedition 1, which arrived at the ISS in November 2000 and stayed until March 2001, beginning an uninterrupted human presence on the ISS that continues today. During the two-year period between the first mating and Expedition 1, the Russian-built Zvedza module was attached to the Unity and Zarya modules on July 26, 2000, after launching from Kazakhstan two weeks earlier. Assembly of the large modules of the ISS would continue until 2021 when the Roscosmos-funded Nauka module was attached in July 2021.

Now in its final configuration, the ISS is approximately the size of an American gridiron football field consisting of 8 solar arrays that provide the station’s power while maintaining an average altitude of 400 kilometers (250 miles). Its massive size consists of a pressurized module length along the major axis of 67 meters (218 feet), a truss (primary body) length of 94 meters (310 feet), a solar array length (measured along the truss) of 73 meters (239 feet), and a total mass of 419,725 kilograms (925,335 pounds).

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Artist rendition of the ISS compared to an American gridiron football field. (Credit: NASA)
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Image of the ISS taken by SpaceX Crew-2 mission on November 8, 2021 after it successfully undocked from the ISS Harmony module. (Credit: NASA)

Ever since the 3-person Expedition 1 crew first took command of the ISS, a total of 273 individuals from 21 countries have visited the orbiting laboratory and have been comprised of trained astronauts and private visitors. From most visitors to least, the following visitor countries include the United States, Russia, Japan, Canada, Italy, France, Germany, Saudi Arabia, United Arab Emirates, Belgium, Brazil, Denmark, Great Britain, Israel, Kazakhstan, Malaysia, Netherlands, South Africa, South Korea, Spain, and Sweden.

“One of my favorite aspects of the International Space Station is the international part of it,” said NASA Astronaut and Expedition 70 Flight Engineer, Jasmin Moghbeli, during the call. “We each bring our unique perspectives, not just from our different nationalities, but also our different backgrounds. I think we’re definitely strengthened by the international partnership. It’s just like gaining redundancy when you have multiple partners working together. It’s stronger and more resilient to any sort of problems or obstacles that come our way and so it definitely makes us stronger. And I think that’s why we have had the International Space Station up here for 25 years now.”

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Starship | Second Flight Test

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On November 18, 2023, Starship successfully lifted off at 7:02 a.m. CT from Starbase on its second integrated flight test.

While it didn’t happen in a lab or on a test stand, it was absolutely a test. What we did with this second flight will provide invaluable data to continue rapidly developing Starship.

The test achieved a number of major milestones, helping us improve Starship’s reliability as SpaceX seeks to make life multiplanetary. The team at Starbase is already working final preparations on the vehicles slated for use in Starship’s third flight test.

Congratulations to the entire SpaceX team on an exciting second flight test of Starship!

Follow us on X.com/SpaceX for continued updates on Starship’s progress

Did you miss our previous article…
https://mansbrand.com/for-its-final-trick-chandrayaan-3-brings-its-propulsion-module-to-earth-orbit/

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