NEWS FROM SPACE
Alien meteors, ancient eclipses and a second Chicxulub
DINO DOUBLE WHAMMY?
Seismic data from the Atlantic floor off the west coast of Africa collected by Uisdean Nicholson, a geologist at Heriot Watt University in Edinburgh, has revealed the existence of a second major impact crater from around the time of the extinction of the dinosaurs. Nicholson was collecting the data to study plate tectonics, but the results also revealed traces of a massive, ancient crater hidden under about 3,000ft (900m) of water and 1,300ft (400m) of sediment. It showed up as a roughly circular hole approximately 5.3 miles (8.5km) from rim to rim and about 131ft (40m) deep. Deformation of the rock around the hole was consistent with a meteor impact and there was a “central uplift” in the depression, which is a tell-tale sign of an impact. “The crater is very striking, and unlike anything that I had ever seen before,” Nicholson said. While the data strongly points to the structure being an impact crater, to confirm this will require drilling to collect samples to see if the rocks in the crater contain shocked quartz crystals that can only be created by a meteor impact. Based on the rock layers around the structure, now named the Nadir Crater, it can be dated to about 66 million years ago. This puts it at about the same time as the Chicxulub crater off Central America, widely credited as the site of the impact that caused the extinction of the dinosaurs, raising the possibility that the Nadir Crater could have been caused by another part of the Chicxulub asteroid that broke off in space and hit the Earth within a few hours or days of the main impact. It is impossible to say for certain as the crater can only be dated to within about 800,000 years, and so may be completely unrelated to that impact. livescience.com, 19 Aug 2022.
ALIEN TECH?
A rather smaller impact, this time in the Pacific Ocean, has attracted the attention of Harvard Astronomer Avi
Loeb. “I found the catalogue that the government compiled of meteorites that were detected by government sensors from our missile warning system. I asked my student to check if any of the meteors, the fastest moving meteors, could have arrived on Earth from outside the Solar System,” Loeb said. The student, Amir Siraj, turned up one candidate that, based on the speed of the meteor and how much of it burned up in the atmosphere, looked likely to have originated outside the Solar System. The data also suggested it was made of a material tougher than iron. Sometime after Loeb and Siraj wrote up their findings they got confirmation of their suspicions. “After a few years, the release of a letter from the US Space Command in the Department of Defense stated explicitly that this meteor at the 99.999% confidence level came from outside the Solar System.” With this confirmation, Loeb now wants to mount an expedition to find the remains of the object on the Pacific floor.
Knowing the object’s trajectory, composition and the behaviour of local ocean currents, he is confident that he can recover some of its remains, even though it is likely to be in fragments smaller than a penny in size, and he is attempting to raise the $1.5 million that is needed to search the area off New Guinea where the interstellar object impacted. While he has raised the possibility of the object being some form of alien technology, Loeb still believes it is worth searching for even if it is just a meteorite, as it would be the first material from outside the Solar System scientists have been able to examine first hand. “This could be the most important scientific discovery that humanity ever made. Because if you think about it, it will change our perspective about our place in the Universe,” he says. nbcboston.com,
12 Aug 2022.
Data suggests the meteor was made of material tougher than iron
ANCIENT ECLIPSES
Reports of ancient eclipses describing the path of totality (the area where it became dark enough to see stars) are important for working out variations in the length of a day on Earth for times in the distant past. If the descriptions of where the totality was seen differ from astronomers’ estimates, a variation in the day length must have been responsible. Knowing this, in turn, is useful for research into things like past sea levels and ice cover. A team of Japanese researchers have been combing ancient records for clues about times, locations, and extents of historical eclipses observed around the Eastern Mediterranean in the fourth-seventh centuries, a time for which few eclipse records were previously known. “Although original eyewitness accounts from this period have mostly been lost, quotations, translations, etc., recorded by later generations provide valuable information,” said Koji Murata of the University of Tsukuba, one of the lead researchers on the project. “In addition to reliable location and timing information, we needed confirmation of eclipse totality… We were able to identify the probable times and locations of five total solar eclipses from the fourth to seventh centuries in the Eastern Mediterranean region, in 346, 418, 484, 601, and 693 AD.”
For the 19 July 418 eclipse, they found a description from Constantinople that described the eclipse as so complete that stars appeared in the sky; the previous estimate for that eclipse’s path would have made that impossible, so the researchers were able to use that to correct the value for day length variation for the fifth century, revising it upwards. Similar information discovered for the other eclipses also enabled the values for the sixth and seventh centuries to be revised downward. heritagedaily. com, 15 Sept 2022.
FAST EARTH
It’s not only the day length in the past that looks like it needs adjusting. Due to its interaction with the Moon, the Earth’s rotation is slowing down at an infinitesimal rate, so the day should increase by about 1.8 milliseconds (thousandths of a second) per century, on average. This means that 1.4 billion years ago the day was just 19 hours long. As a result, the body that measures day length, the International Earth Rotation and Reference Systems Service (IERS), periodically add a leap second to compensate for the slower spin to ensure things like GPS remain properly calibrated. However, recently, the Earth has bucked this trend and its rotation has started to speed up. In 2020 the IERS recorded the 28 shortest days since 1960, although the variations are still counted in just milliseconds. The trend paused in 2021, but on 29 June 2022 the planet recorded its fastest ever spin, with the day ending 1.59 milliseconds sooner than was expected. Soon after, 19 July came in 1.47 milliseconds short, and then the end of 26 July came 1.5 milliseconds early.
No one is entirely sure why this is happening, but there are several possible explanations: the melting of the glaciers means less weight on the poles, increasing the planet’s angular momentum, the motion of our planet’s inner molten core can affect it too, and earthquakes also have the potential to redistribute the planet’s mass and affect the rotation, as does the “Chandler wobble”– the movement of Earth’s geographical poles across its surface. No one is sure which of these is the culprit, or indeed if it is the result of something else entirely. In the longer term, though, the planet’s rotation is likely to continue to slow, but in the immediate future, if the speeding up does continue, the IERS might need to subtract a “negative leap second”, known as a drop second, from the Earth’s official period of rotation to temporarily shorten the day so that GPS and other technologies that rely on millisecondaccurate timekeeping do not go permanently out of synch. forbes. com, 28 Jul 2022.
SAUSAGE STAR
When the James Webb Space Telescope began scientific operations on 12 July, the world was treated to a torrent of stunning images that showed the Universe in far greater detail than had been previously possible. One of the most widely circulated, though, was not quite what it seemed. Physicist Étienne Klein, director of France’s Alternative Energies and Atomic Energy Commission, tweeted a picture to his 91,000 followers saying “Picture of Proxima Centauri, the nearest star to the Sun, located 4.2 light years away from us. It was taken by the James Webb Space Telescope. This level of detail... A new world is unveiled everyday.” The only problem was that it wasn’t actually a picture of a star – it was a slice of chorizo photographed on a black background. The image was commented on and widely retweeted before Klein confessed his hoax and apologised, explaining that his intention was “to urge caution regarding images that seem to speak for themselves”. editions. cnn.com, 8 Aug 2022.