We found the world's oldest asteroid strike in Western Australia. It might have triggered a global thaw

The world's oldest remaining asteroid crater is at a place called Yarrabubba, southeast of the town of Meekatharra in Western Australia. Our new study puts a precise age on the cataclysmic impact - showing Yarrabubba is the oldest known crater and dating it at the right time to trigger the end of an ancient glacial period and the warming of the entire planet. Yarrrabubba holds the eroded remnants of a crater 70 kilometres wide that was first described in 2003, based on minerals at the site that showed unique signs of impact. But its true age was not known.We studied tiny "impact-shocked" crystals found at the site, which show the crater formed 2.229 billion years ago (give or take 5 million years). This new, precise date establishes Yarrabubba as the oldest recognised impact structure on Earth. It is some 200 million years older than the next oldest, the Vredefort impact in South Africa. More intriguing, the geological record shows the Earth had glacial ice before the time of the impact - but afterwards, ice disappeared for hundreds of millions of years. Was the Yarrabubba impact a trigger for global climate change? An asteroid strike is one of the most violent geologic events. In an instant, Earth's crust is squeezed to unimaginable pressures, before exploding and ejecting carnage across the landscape. Large impacts leave behind scars the size of a small city. The basin formed by an impact will partly fill with molten and pulverised rock from the Earth and from the asteroid itself. The edge of the crater forms a ring of mountains; over time erosion gradually erases the story.

Today, Yarrabubba has been worn down into a minor feature on a barren landscape.

To place the Yarrabubba event in a geologic context, we had to find its age. To find the age, we had to look carefully at minerals in the rocks shocked by the impact.

Geologists date events using "isotopic clocks" in minerals like zircon and monazite. These minerals contain small amounts of uranium, which gradually decays into lead at a known rate.

Asteroid strikes raise the temperature in rocks they hit, causing minerals to lose their accumulated lead, which resets the clock. After impact, the isotopic clocks start ticking again as new lead accumulates.

So by measuring the isotopes of uranium and lead in these minerals, we can calculate how much time has passed since the impact.

At Yarrabubba, we identified tiny crystals of zircon and monazite - each about the width of human hair - with textures that show they had been heated by a massive impact.

We analysed the amounts of lead and uranium isotopes in these crystals using mass spectrometry, and found their clocks had been reset 2.229 billion years ago (give or take five million years). That's when we realised Yarrabubba coincided with a major change in Earth's climate.

A different Earth
The Yarrabubba impact occurred during a period in Earth's history called the Proterozoic eon. Long before plants, fish, or dinosaurs, life at this time consisted of simple, multicellular organisms.

These simple bacteria had already begun changing the composition of air. Previously dominated by carbon dioxide and methane, Earth's atmosphere gradually became oxygenated by life about 2.4 billion years ago.

As oxygen levels built up, rocks started weathering more, and the atmosphere cooled down. And then ice came, plunging Earth into globally frigid conditions.

Earth has repeatedly dipped into glacial conditions over the last 4.5 billion years. We know about these periods because of deposits of solidified rock and mud that were ground up by glaciers as they bulldozed across Earth's surface.

Studies have found multiple periods in Earth's history in which glacial deposits occur in rocks of the same age across many continents. These deposits may represent worldwide glacial conditions, often referred to as a "Snowball Earth" event.

In these periods, ice forms from the poles well into the tropics, covering nearly all of Earth.

There is geological evidence that Earth was in an icy phase during the Yarrabubba impact. Rocks in South Africa show that glaciers were present at this time. But it's not clear if the amount of ice was similar to today, or if it covered the world.

Fire and ice
So we found Earth's oldest preserved impact crater, and worked out when the asteroid hit. We also know Earth had ice at the time, but not how much.

To understand the effect of the impact on an ice-covered world, we used computer models based on the physics of shockwaves to estimate how much ice would end up in the atmosphere as water vapour. As it turns out, it's quite a lot.

Our models show that if the Yarrabubba asteroid hit an ice sheet 5 kilometres thick (not an unreasonable estimate), more than 200 billion tons of water vapour would be ejected into the atmosphere. That's about 2% of the total amount of water vapour in today's atmosphere, but would have been a much bigger fraction back then.

Water vapour is a serious greenhouse gas. It's responsible for about half of the heat absorption from solar radiation today.

Global climate models don't yet exist for the Proterozoic Earth, so we don't yet know for sure if the Yarrabubba impact pushed the planet past a tipping point that led to more warming and the end of a possible Snowball Earth.

OSIRIS-REx completes closest flyover of sample site Nightingale

Preliminary results indicate that NASA's OSIRIS-REx spacecraft successfully executed a 0.4-mile (620-m) flyover of site Nightingale yesterday as part of the mission's Reconnaissance B phase activities. Nightingale, OSIRIS-REx's primary sample collection site, is located within a crater high in asteroid Bennu's northern hemisphere.To perform the pass, the spacecraft left its 0.75-mile (1.2-km) safe home orbit and flew an almost 11-hour transit over the asteroid, aiming its science instruments toward the 52-ft (16-m) wide sample site before returning to orbit. Science observations from this flyover are the closest taken of a sample site to date. The primary goal of the Nightingale flyover was to collect the high-resolution imagery required to complete the spacecraft's Natural Feature Tracking image catalog, which will document the sample collection site's surface features - such as boulders and craters. During the sampling event, which is scheduled for late August, the spacecraft will use this catalog to navigate with respect to Bennu's surface features, allowing it to autonomously predict where on the sample site it will make contact. Several of the spacecraft's other instruments also took observations of the Nightingale site during the flyover event, including the OSIRIS-REx Thermal Emissions Spectrometer (OTES), the OSIRIS-REx Visual and InfraRed Spectrometer (OVIRS), the OSIRIS-REx Laser Altimeter (OLA), and the MapCam color imager.

A similar flyover of the backup sample collection site, Osprey, is scheduled for Feb. 11. Even lower flybys will be performed later this spring - Mar. 3 for Nightingale and May 26 for Osprey - as part of the mission's Reconnaissance C phase activities. The spacecraft will perform these two flyovers at an altitude of 820 feet (250 m), which will be the closest it has ever flown over asteroid Bennu's surface.

Ученые выяснили, откуда в Солнечную систему прибыла комета 2I/Borisov

Согласно предположениям учёных, первая межзвёздная комета 2I/Borisov могла прибыть к нам из нескольких звёздных систем – Ross 573, GJ 4384 либо HD 34327. Факт того, что тело пролетало предельно близко к Ross 573, может говорить о происхождении тела именно оттуда. Правда, раз в 120 млн лет происходит сближение кометы со звёздной системой, поэтому реальность может быть другой. Как отмечается в журнале Astronomy & Astrophysics, расстояние до Ross 573 составило 14 тыс. астрономических единиц, что довольно близко в масштабах космоса. Вполне возможно, что комета вылетела из данной звёздной системы. Ross 573 – холодный красный карлик, который находится в 60 световых годах от Земли. Сейчас специалисты в разных уголках мира вычисляют форму орбиты объекта. Учёным уже удалось обнаружить воду в комете 2I/Borisov, по составу тело подобно объектам из Солнечной системы. Когда комета подлетит к Солнцу, ученые смогут более детально её изучить. 2I/Borisov была открыта 30.09.2019 астрономом-любителем Геннадием Борисовым. Сейчас в изучении тела заинтересованы многие учёные.

Meteorite contains the oldest material on Earth: 7-billion-year-old stardust

Stars have life cycles. They're born when bits of dust and gas floating through space find each other and collapse in on each other and heat up. They burn for millions to billions of years, and then they die. When they die, they pitch the particles that formed in their winds out into space, and those bits of stardust eventually form new stars, along with new planets and moons and meteorites. And in a meteorite that fell fifty years ago in Australia, scientists have now discovered stardust that formed 5 to 7 billion years ago-the oldest solid material ever found on Earth. "This is one of the most exciting studies I've worked on," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of a paper describing the findings in PNAS. "These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy." The materials Heck and his colleagues examined are called presolar grains-minerals formed before the Sun was born. "They're solid samples of stars, real stardust," says Heck. These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before the solar system.. But presolar grains are hard to come by. They're rare, found only in about five percent of meteorites that have fallen to Earth, and they're tiny-a hundred of the biggest ones would fit on the period at the end of this sentence. But the Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Australia in 1969 and that the people of Murchison, Victoria, made available to science. Presolar grains for this study were isolated from the Murchison meteorite for this study about 30 years ago at the University of Chicago.

"It starts with crushing fragments of the meteorite down into a powder ," explains Jennika Greer, a graduate student at the Field Museum and the University of Chicago and co-author of the study. "Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic-it smells like rotten peanut butter."

This "rotten-peanut-butter-meteorite paste" was then dissolved with acid, until only the presolar grains remained. "It's like burning down the haystack to find the needle," says Heck.

Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were. "We used exposure age data, which basically measures their exposure to cosmic rays, which are high-energy particles that fly through our galaxy and penetrate solid matter," explains Heck. "Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form.

"I compare this with putting out a bucket in a rainstorm. Assuming the rainfall is constant, the amount of water that accumulates in the bucket tells you how long it was exposed," he adds. By measuring how many of these new cosmic-ray produced elements are present in a presolar grain, we can tell how long it was exposed to cosmic rays, which tells us how old it is.

The researchers learned that some of the presolar grains in their sample were the oldest ever discovered-based on how many cosmic rays they'd soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were even older than 5.5 billion years. For context, our Sun is 4.6 billion years old, and the Earth is 4.5 billion.

But the age of the presolar grains wasn't the end of the discovery. Since presolar grains are formed when a star dies, they can tell us about the history of stars. And 7 billion years ago, there was apparently a bumper crop of new stars forming-a sort of astral baby boom.

"We have more young grains that we expected," says Heck. "Our hypothesis is that the majority of those grains, which are 4.9 to 4.6 billion years old, formed in an episode of enhanced star formation. There was a time before the start of the Solar System when more stars formed than normal."

This finding is ammo in a debate between scientists about whether or not new stars form at a steady rate, or if there are highs and lows in the number of new stars over time. "Some people think that the star formation rate of the galaxy is constant," says Heck. "But thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. This is one of the key findings of our study."

Heck notes that this isn't the only unexpected thing his team found. As almost a side note to the main research questions, in examining the way that the minerals in the grains interacted with cosmic rays, the researchers also learned that presolar grains often float through space stuck together in large clusters, "like granola," says Heck. "No one thought this was possible at that scale."

Heck and his colleagues look forward to all of these discoveries furthering our knowledge of our galaxy. "With this study, we have directly determined the lifetimes of stardust. We hope this will be picked up and studied so that people can use this as input for models of the whole galactic life cycle," he says.

Heck notes that there are lifetimes' worth of questions left to answer about presolar grains and the early Solar System. "I wish we had more people working on it to learn more about our home galaxy, the Milky Way," he says.

"Once learning about this, how do you want to study anything else?" says Greer. "It's awesome, it's the most interesting thing in the world."

"I always wanted to do astronomy with geological samples I can hold in my hand," says Heck. "It's so exciting to look at the history of our galaxy. Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origin of the carbon in our bodies, the origin of the oxygen we breathe. With stardust, we can trace that material back to the time before the Sun."

"It's the next best thing to being able to take a sample directly from a star," says Greer.

Ученые открыли первый в истории "внутривенерианский" астероид

Астрономам впервые удалось обнаружить астероид, орбита которого полностью находится внутри орбиты Венеры. Как сообщает N+1, исследователям и ранее удавалось найти небесные тела, которые подходят к Солнцу ближе Меркурия, но всегда самая дальняя точка орбиты (афелий) находилась за орбитой Венеры. Теперь же участники проекта ZTF (Zwicky Transient Facility) американской Паломарской обсерватории нашли первое исключение из этого правила – астероид 2020 AV2. В настоящее время ученым известно около 800 тысяч астероидов, но только 21 из них имеют орбиту с афелием, который находится в пределах орбиты Земли. Эти тела составляют так называемую группу Атиры или "внутриземных" астероидов (Inner-Earth Objects, IEOs), названную по самому большому члену из группы, астероиду 163693 Атира. У большинства из них расстояния афелия составляют около 0,9 астрономической единицы. Лишь в прошлом году был открыт объект 2019 AQ3 с рекордно малым расстоянием афелия — 0,77 астрономической единицы. 4 января астрономы обнаружили нового представителя семейства Атиры. Несмотря на то, что параметры орбиты нового астероида будут уточняться, уже понятно, что его афелий находится рекордно близко к Солнцу, на расстоянии 0,65 астрономических единицы (афелий и перигелий Венеры находятся на дистанциях 0,73 и 0,72 астрономической единицы).

 Перигелий, ближайшая к Солнцу точка орбиты астероида, находится на дистанции 0,46 астрономической единицы, то есть он "касается" орбиты Меркурия, чей афелий — 0,47.

Dark skies to host Quadrantid meteor shower

The first major meteor shower of 2020, the Quadrantids, will flash across dark, moonless skies during the predawn hours on Saturday morning. The Quadrantids arrive each year during the first week of January. They often put on a great show, featuring up to 100 meteors per hour during the shower's peak, but last year in North America, the timing wasn't quite right. "The reason the peak is so short is due to the shower's thin stream of particles and the fact that the Earth crosses the stream at a perpendicular angle," according to NASA. Last year, viewers in Asia and Europe saw plenty of action, but the curvature of the Earth blocked much of the view for sky-watchers in North America. This year's timing is much better. And a bonus, the skies will be moon-free. The Quadrantids are caused by the trail of debris left by 2003 EH1, an object astronomers think is a rock-comet -- almost an asteroid, not quite a comet. As Earth's orbit passes through the debris, the bits of rock and ice collide with the atmosphere and burn up, creating bright streaks in the night sky. The meteor showers are unique in that they are named for a constellation, "Quadrans Muralis," that isn't officially recognized. In 1795, the French astronomer Jerome Lalande named a group of stars for their likeness to a quadrant, the instrument used to pinpoint the location of stars. But in 1922, when the International Astronomical Union compiled an official list of constellations, they ignored Quadrans Muralis.

"An alternative name for the Quadrantids is the Bootids since the meteors appear to radiate from the modern constellation of Bootes," according to NASA. "Even though, the constellation may no longer be recognized, it was considered a constellation long enough to give the meteor shower its name."