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Earth's oldest rock found on Moon: Study

An international team associated with Center for Lunar Science and Exploration (CLSE) in the US found evidence that the rock was launched from Earth by a large impacting asteroid or comet.

Houston: Scientists say they have discovered what may be the Earth's oldest rock in a lunar sample returned from the Moon by the Apollo 14 astronauts.

An international team associated with Center for Lunar Science and Exploration (CLSE) in the US found evidence that the rock was launched from Earth by a large impacting asteroid or comet.

This impact jettisoned material through Earth's primitive atmosphere, into space, where it collided with the surface of the Moon -- which was three times closer to Earth than it is now -- about four billion years ago, researchers said.

The rock was subsequently mixed with other lunar surface materials into one sample, according to the study published in the journal Earth and Planetary Science Letters.

The team developed techniques for locating impactor fragments in the lunar regolith, which prompted CLSE Principal Investigator David A Kring to challenge them to locate a piece of Earth on the Moon.

The researchers found a two-gramme fragment of rock composed of quartz, feldspar, and zircon, all commonly found on Earth and highly unusual on the Moon.

Chemical analysis of the rock fragment shows it crystallised in a terrestrial-like oxidised system, at terrestrial temperatures, rather than in the reducing and higher temperature conditions characteristic of the Moon.

"It is an extraordinary find that helps paint a better picture of early Earth and the bombardment that modified our planet during the dawn of life," said Kring, a Universities Space Research Association (USRA) scientist at the Lunar and Planetary Institute (LPI).

It is possible that the sample is not of terrestrial origin, but instead crystallised on the Moon, however, that would require conditions never before inferred from lunar samples, researchers said.

It would require the sample to have formed at tremendous depths, in the lunar mantle, where very different rock compositions are anticipated, they said.

The simplest interpretation is that the sample came from Earth, according to researchers. The rock crystallised about 20 kilometres beneath Earth's surface 4.0 to 4.1 billion years ago. It was then excavated by one or more large impact events and launched into lunar space.

Previous work by the team showed that impacting asteroids at that time were producing craters thousands of kilometres in diameter on Earth, sufficiently large to bring material from those depths to the surface, researchers said.

Once the sample reached the lunar surface, it was affected by several other impact events, one of which partially melted it 3.9 billion years ago, and which probably buried it beneath the surface.

The sample is, therefore, a relic of an intense period of bombardment that shaped the solar system during the first billion years. After that period, the Moon was affected by smaller and less frequent impact events.

Space

Saturn's Rings Could Have Formed During the Dinosaur Age, New Analysis Suggests

Artist’s concept of Cassini in Saturn’s rings

Saturn’s rings might have formed relatively recently—like, in the past hundred million years or so—according to new research.

A team of scientists analyzed Saturn’s gravitational field and the mass of its rings, based on data from the Cassini mission, which ended in 2017. Their measurements led to insights about the planet’s composition and the rings’ young age, at least from an astronomy standpoint.

“Perhaps a big collision formed the rings around the age of the dinosaurs,” Luciano Iess, the study’s lead author from Sapienza Università of Rome in Italy, told Gizmodo. “But for me, the real surprise was the interior structure.”

The scientists assessed Saturn’s gravitational field by measuring a microwave signal that Cassini sent to receivers on Earth during its “Grand Finale orbits.” During these 22 “Grand Finale” orbits, the spacecraft was positioned such that it would graze Saturn’s cloud tops on each pass and send its signals to Earth without being blocked by Saturn. The researchers picked six of these orbits, measuring how the gravitational field around Saturn changed Cassini’s velocity, and in turn, the microwave signal.

After inferring the strength of the gravitational field from the planet and its rings, the researchers were able to pick out the rings’ total mass: around 15 quintillion kilograms. That’s about 7,000 times less massive than Earth’s Moon, or around 0.4 times the mass of the small Saturnian moon Mimas. The team estimated the rings’ age at around 10 million to 100 million years old, compared to the planet’s age of 4.5 billion years. They published their results in Science.

Iess was especially excited by the measurements of the planet itself, which revealed that its gravitational field differed from initial expectations.

“There were people thinking that once we determined the interior of Jupiter, one could know what the interior structure of Saturn was. It turned out to be wrong, because they’re quite different,” he said. It appeared as if the planet’s atmosphere flows and moves around deep into the planet, perhaps 9,000 kilometers (5,600 miles) beneath its cloud tops. But there are still mysterious, unattributable pieces of the planet’s gravity that might be caused by convection, turbulence, or oscillations. They don’t know, said Iess.

This is just one piece of evidence about Saturn’s rings and gravity, of course. “It’s an important piece of the puzzle, but it’s not the only one,” said Kelly Miller, research scientist at Southwest Research Institute who was not involved in the study. She thought that the paper was of intrinsic interest, and noted that more data on rings’ chemical composition could confirm estimates surrounding their age. Iess echoed the sentiment, but noted that this would require sending a probe to sample the rings.

But the young age of the rings has important implications. It means that the feature that we most identify with Saturn might be a new thing, cosmologically, possibly the result of some chaotic collision that occurred millions of year ago, or maybe something stranger. And combined with recent data suggesting that the planet’s rings might be gone in another 100 million years, we’re lucky to live in an age when Saturn has rings, said Iess

It’s wild to think that Saturn only acquired its iconic rings during the time of the dinosaurs or even more recently. And studies like these could reveal more about how Saturn and its rings formed and how disks in space behave more generally. Now, we’ll just need to send a new probe to Saturn.

Space

Hypernova Observations Reveal the Death of the Massive Stars

The end of a star’s life can occur in a tranquil manner in the case of low mass stars, such as the Sun. This is not the case, however, for very massive stars, which suffer such extreme explosive events that they can outshine the brightness of the whole galaxy that hosts them. An international group of astronomers has published a detailed study of the death of a high-mass star that produced a gamma-ray burst (GRB) and a hypernova, in which they have detected a new component in this type of events. The study, published in Nature, provides a link that completes the scenario that relates hypernovae with GRBs.

“The first hypernova was detected in 1998 as a very energetic type of supernova that followed a gamma-ray burst. This was the first evidence of the connection between both phenomena” says Luca Izzo, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC), and leader the study.

The scenario that has been proposed to explain the phenomena involves a star over 25 times more massive than the Sun that, once it has exhausted its fuel, suffers the collapse of its core. During this collapse, the nucleus of the star transforms either into a neutron star or a black hole, and at the same time, two polar jets of matter are ejected. These jets drill through the external layers of the star and, once out of the star, produce detectable gamma-rays (the so-called GRB). Finally, the external layers of the star are ejected, generating a hypernova explosion, tens of times brighter than a typical supernova.

This is an artist representation of the hypernova. The interaction of the jet with the outer layers of the star forms a cocoon that surrounds the head of the jet and begins to propagate laterally with respect to the direction of the jet. The jet is capable of completely perforating the envelope of the parent star, emitting high energy gamma rays, responsible for GRB. Credit: Anna Serena Esposito

Although the connection between GRBs and hypernovae has been well established over the last 20 years, the opposite is not so clear, since there have been several hypernovae that do not have associated GRBs. “This work has allowed us to find the missing link between these two types of hypernova through the detection of an additional component: A sort of hot cocoon generated around the jet, as it propagates through the outer layers of the progenitor star – indicates Dr. Izzo (IAA-CSIC) -. The jet transfers a significant part of its energy to the cocoon and, if it manages to reach the surface of the star, will produce the gamma-ray emission that we know as a GRB”.

This is an image of the explosion obtained by the Gran Telescopio Canarias in the period of maximum brightness of the event. Credit: Gran Telescopio Canarias

On the other hand, the jet can fail to pierce the external layers of the star and never emerge into the circumstellar medium if it lacks the necessary energy. In this case we would observe a hypernova but not a GRB. The cocoon detected in this study is the link between the two subtypes of hypernovae that had been studied until now, and the chocked jets would naturally explain the observed differences.

THE STORY OF THE EVENT

On December 5, 2017, GRB 171205A was detected in a galaxy located 500 million light years from Earth. However far this may seem, this makes it the fourth closest long GRB ever observed. “Such events occur on average every ten years, so we immediately started an intense observing campaign to observe the emerging hypernova from the very early phases on – says Christina Thöne, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who participated in the discovery -. In fact, with our early observations we managed to obtain the earliest detection of a hypernova to date, less than one day after the collapse of the star”.

And indeed, very early on the first features of a hypernova were detected with the Gran Telescopio Canarias, on the island of La Palma. “This was only possible because the luminosity of the jet was much weaker than usual, as typically the jets outshine the hypernova during the first week – says Antonio de Ugarte Postigo, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who participated in the paper -. What we saw, however, was a very peculiar component, which showed unprecedented expansion velocities and chemical abundances that were different to the ones seen in similar events”.

This peculiar chemical composition and the high expansion velocities matched the expectations for the existence of a cocoon accompanying the jet at the surface of the star. This had been predicted but had been never observed before. The cocoon observed during the first days dragged material out from the interior of the star, and its chemical composition was determined in this study. After a few days, this component faded away, and the hypernova evolved in a similar way as the ones previously observed.

The total energy emitted by the cocoon during these first days was larger than that of the GRB, implying that the jet transferred a large part of its energy to the cocoon. However, it also indicates that the energy of the GRB depends to some degree on the interaction between the jet and the stellar material, and on this new component, the cocoon. This discovery also implies that the models must be revised: “While in the standard model of supernovae the collapse of the nucleus leads to quasi-spherical explosions, the evidence of such an energetic emission produced by the cocoon suggests that the jet plays an important role in core-collapse supernovae which means we will need to consider it in supernova explosion models”, concludes Izzo (IAA-CSIC).

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Earth's oldest rock found on Moon: Study

An international team associated with Center for Lunar Science and Exploration (CLSE) in the US found evidence that the rock was launched from Earth by a large impacting asteroid or comet.

Saturn's Rings Could Have Formed During the Dinosaur Age, New Analysis Suggests

Hypernova Observations Reveal the Death of the Massive Stars