生成一个有趣的科普视频---**Textual Information:** Title: DEADLY ASTEROID CLOSE CALLS Words by: ANDREW MAY Topic Label: SPACE Subtitle/Caption: Asteroid 2024 YR4 may not be the serious threat it was once thought to be, but scientists are still concerned about the possibility of future asteroid collisions **Image Description:** Type: Illustration/Artwork Main Elements: - Two asteroids are depicted in the foreground, appearing to be entering or passing close to Earth's atmosphere. - The asteroids are irregularly shaped and show signs of intense heat, with fiery trails and glowing surfaces. One asteroid is larger and more prominent, positioned in the mid-right, showing a heavily cratered surface glowing red-orange. The other is smaller and positioned in the upper-right, trailing fire and debris. - Below the asteroids, the curved surface of the Earth is visible, partially obscured by clouds or atmosphere. The Earth's atmosphere is depicted with gradients of color, suggesting a sunrise, sunset, or atmospheric heating. - The background is dark space filled with scattered stars. - A blue rectangular label with a stylized rocket icon is present in the upper-left corner, containing the word "SPACE". **Textual Information:** DID YOU KNOW? In 1989, the large asteroid 4581 Asclepius, 300 metres across, came within 425,000 miles of hitting Earth [Paragraph starting with A] As Earth travels through space, it's constantly colliding with anything that crosses its path. This ranges from extremely small objects to much larger ones, with far more of the former than the latter. At the small end of the spectrum are tiny particles of cosmic dust, much too small to be seen without a microscope, that end up in gutters and drains. At a larger scale are the rock-like meteorites sometimes seen in museums – small chunks of asteroids that have survived the journey through Earth's atmosphere. This journey slows them down to relatively modest speeds, so even if they hit a car or building when they reach the ground, they rarely do much damage. Their main significance is scientific in what they can tell us about the nature and composition of interplanetary material. Of course, people often focus on much larger impact events, such as the Chicxulub asteroid that caused the extinction of the dinosaurs. That was around six miles across – so big that the atmosphere barely slowed it down at all. It still had as much energy as a billion atomic bombs when it smashed into Earth's surface. Fortunately, such occurrences are extremely few and far between. The Chicxulub event was 66 million years ago, and nothing remotely comparable has happened to Earth since then. If ordinary meteorites cause so little damage, and asteroids large enough to trigger a global catastrophe are so rare, is there any cause for worry at all? The answer is maybe. Between those two extremes, there's the possibility of an asteroid big enough to destroy a town or city, and that's something astronomers are taking increasingly seriously. At the same time, it's important to keep things in perspective, because nothing of this kind is known to have happened in human history. There have, however, been several close calls. Perhaps the most famous of these was the Tunguska event of 1908, when a 30-metre-diameter asteroid exploded above Russia. Fortunately this happened in a remote area of forest, and the only casualties were the millions of trees that were knocked down by the blast. However, with a thousand times as much energy as an atomic bomb, the effects would be disastrous if the same thing were to happen over a populated area. Another close call occurred in 2013, when a scaled-down version of the Tunguska event played out in a different part of Russia. This involved an asteroid about 20 metres across, which exploded above the city of Chelyabinsk. Fortunately, the explosion occurred way up in the atmosphere, at an altitude of 18.6 miles. As a result, there was little damage at ground level beyond a lot of broken windows – and minor injuries to people who were close enough to those windows to be struck by flying glass. The Chelyabinsk event helped bring the dangers of an asteroid impact home to astronomers, who now put considerable effort into locating potentially hazardous objects before they become a serious collision risk. [Did You Know? Box] Did you know? Bits of the Chelyabinsk meteor are now in museums [The Torino Scale Section] THE TORINO SCALE Thousands of asteroids travel around the Sun on orbits that periodically bring them close to Earth. While astronomers refer to these as 'potentially hazardous asteroids', the emphasis is on 'potentially'. In most cases, there is zero chance of a collision with our planet in the foreseeable future. For the small number of exceptions, the International Astronomical Union employs a classification system called the Torino scale, after the Italian name for Turin where it originated. The scale runs from zero to ten, where zero means there's no chance of an asteroid colliding for at least a century. To score one or higher, an asteroid must be at least 20 metres across, with a chance of hitting Earth in the next hundred years of at least one in a hundred million. The higher the chance, or the larger the asteroid, the higher up the scale it appears. The Torino scale can be visualised as a two-dimensional chart **Chart Description:** Type: Two-dimensional classification grid chart / Heatmap. Title: The Torino Scale Axes: * X-axis: * Label: COLLISION PROBABILITY * Scale/Labels: $10^{-9}$, $10^{-6}$, $10^{-4}$, $10^{-2}$, $>0.99$ * Y-axis: * Label: KINETIC ENERGY (MT) * Scale/Labels (with corresponding approximate sizes): $10^3$ (5 Km), $10^2$ (1 Km), $10^1$ (100 m), $10^0$ (20 m) Grid Content: The grid contains numbers representing the Torino Scale level, ranging from 0 to 10. The cells are colored and correspond to severity levels/regions listed on the right side. * Numbers in cells: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. * Severity/Region Labels (aligned with Y-axis values): Global, Regional, Local, No Consequence. Legend: Five colored squares with descriptive text. * White: Events having no likely consequences * Green: Events meriting careful monitoring * Yellow: Events meriting concern * Orange: Threatening Events * Red: Certain collisions Source/Credit: ©AdobeStock / Shutterstock / ESA **Textual Information:** **Title:** SPACE **Image Description:** Asteroid Bennu, as seen from close quarters by NASA's OSIRIS-REx spacecraft **Left Panel - Process Steps:** 1 INITIAL DETECTION This may come from a spacecraft or ground-based observatory, or even from an amateur astronomer. 2 COMBINING DATA All new asteroid data goes into a central repository at the International Astronomical Union's Minor Planet Center. 3 RISK ANALYSIS Two independent groups do this: NASA's Center for Near-Earth Object Studies and the European Space Agency's Near-Earth Object Coordination Centre in Italy. 4 COMPUTER PREDICTIONS The risk assessment centres around computer modelling of the asteroid's orbit and its likelihood of colliding with Earth. 5 COMPARE RESULTS When the two risk assessments have been completed, the results are compared to check they agree with each other. 6 WARNING If a collision is imminent, which has never happened so far, then warnings will be passed to appropriate authorities. **Center Right Panel:** WHAT'S THE RISK? Asteroid threat assessment is the process astronomers use to decide how dangerous a newly discovered asteroid is **Did you know? Box:** Did you know? Comets pose collision risks as well as asteroids **Labels within Diagram:** IAU MPC NASA CNEOS eesa NEOCC ORBIT COMPUTATION IMPACT PREDICTION CROSS-VALIDATE IMPACT RISKS **Chart/Diagram Description:** **Type:** Flowchart / Infographic **Main Elements:** * The infographic is set against a dark blue background with stars and star trails, representing space. * It illustrates the process of asteroid threat assessment in six numbered steps, depicted visually as a flowchart. * **Step 1 (Initial Detection):** Shown near the top left, above a depiction of Earth. Icons represent potential sources: a spacecraft/satellite, a ground-based observatory/telescope on a hill next to a building, and possibly an amateur astronomer's setup (a smaller telescope next to a building). A small asteroid icon is also shown entering the Earth's sphere of influence, represented by a dashed circle. * **Step 2 (Combining Data):** An arrow leads from the Earth depiction down to a circular icon containing multiple documents, representing data collection. This is connected by an arrow to a building labeled "IAU MPC", representing the International Astronomical Union's Minor Planet Center. * **Step 3 (Risk Analysis):** Arrows lead from the IAU MPC building to two separate buildings: one labeled "NASA CNEOS" (NASA's Center for Near-Earth Object Studies) and another labeled "eesa NEOCC" (European Space Agency's Near-Earth Object Coordination Centre). Both buildings are connected by dashed lines to the next step. * **Step 4 (Computer Predictions):** This step is represented by a dashed rectangular box. Inside the box, there are two icons: * "ORBIT COMPUTATION": Shows the Sun, Earth, and an asteroid following an elliptical orbit around the Sun. * "IMPACT PREDICTION": Shows the Earth with a fiery red asteroid approaching and an exclamation mark symbol (alert). * Arrows point from the NASA and ESA buildings towards this box. * **Step 5 (Compare Results):** An arrow leads from the "Computer Predictions" box to a label "CROSS-VALIDATE IMPACT RISKS". This label is connected by an arrow to a dashed rectangular box for Step 5. Inside this box, a globe of the Earth is shown with two location markers, indicating data comparison points. * **Step 6 (Warning):** An arrow leads from the Step 5 box to a dashed rectangular box for Step 6. Inside the box are icons representing results and dissemination: a document with an exclamation mark (warning report), a group of six stylized human figures (stakeholders/authorities), and an information symbol "i" with a surrounding circle of radio waves, potentially indicating communication. * Dotted lines and arrows connect the steps, showing the flow of information and the sequence of the process. * A photograph of asteroid Bennu is placed in the top left corner. * A hexagonal box in the bottom right contains the "Did you know?" text. **Title:** DID YOU KNOW? 2024 YR4 was discovered by the dramatically named Asteroid Terrestrial-impact Last Alert System (ATLAS) **Section: NEO SURVEYOR** The Near-Earth Object Surveyor is an upcoming NASA mission designed to search for potentially hazardous asteroids. Scheduled for launch in 2027, it will consist of an infrared space telescope located part way between Earth and the Sun. This vantage point will allow it to observe asteroids on the Sun side of Earth - something that has proven difficult for ground-based or Earth-orbiting telescopes. Originally proposed as long ago as 2006, the mission repeatedly failed to secure funding from NASA's science budget due to competition from other proposed projects. In the end, because of the wider importance of the mission, it was decided to fund it as a matter of national security instead. *Chart/Diagram Description:* Type: Artist's impression/rendering of a spacecraft. Main Elements: - Image shows a spacecraft with various components, including a telescope-like structure, solar panels (implied), and body sections. - The background is a starry sky with scattered dots representing stars. - The spacecraft appears to be in space. - Caption: Artist's impression of the NEO Surveyor spacecraft in its operational configuration **Section: OBSERVING ASTEROID 2024 YR4** Earlier this year, astronomer Olivier Hainaut gave his thoughts on this potentially high-risk asteroid How is the risk of collision calculated, and could it change? You measure the position of the asteroid in front of the background stars over as many nights as possible, then solve for the orbit, which is the 3D trajectory of the asteroid in space. The longer you can measure, the better you know the orbit. Currently, we could observe YR4 for a little less than two months over its four-year orbit, so we need to extrapolate a lot, hence the large uncertainty. As we observe more, the orbit will be refined, and we will know better where the asteroid will be in 2032. [Although the chances of 2024 YR4 hitting Earth in 2032 have now been calculated to be negligible, there's a stronger possibility that it will hit the Moon in the same year.] "The longer you measure, the better you know the orbit" If 2024 YR4 was on a collision course with Earth, what could we do to stop it or prepare for its impact? First, refine the orbit to determine whether it will hit or not. If it will, then nudge it to slightly change its orbit so that it misses Earth. The sooner the better, as a later nudge will need to be larger. To nudge it, refer to NASA's Double Asteroid Redirection Test, which did this as a test on an asteroid about twice the size of YR4. But don't break the asteroid up, as you would end up with many more fragments to deal with. How worrying was this? It's typical to start preparing for disaster relief when the probability goes above one per cent. Astronomers did not make that number up - it's what is customarily used for all kinds of disasters. Keep in mind that if the asteroid does impact, it's not a large one - possibly a few times larger than the one that blasted above Chelyabinsk in 2013. *Image Description:* Type: Portrait photo of a person. Main Elements: - Shows a man with a beard, glasses, and a maroon shirt. - Caption: Dr Olivier Hainaut is a Belgian astronomer working at the European Southern Observatory in Chile *Image Description:* Type: Illustration of two asteroids. Main Elements: - Two rocky objects, appearing to be asteroids, are depicted with fiery trails. - They are shown against a background with diagonal lines. **Section: 5 DANGEROUS SPACE ROCKS** It's not likely, but one of these may hit Earth **1. 2024 YR4** CHANCE TO HIT: 3.1% This asteroid briefly peaked at three on the Torino scale before being downgraded to zero. It now has a chance of just 0.00082% of hitting Earth in 2032. **2. APOPHTS** CHANCE TO HIT: 2.7% Almost 500 metres across - around ten times as big as 2024 YR4 - this was once rated at four on the Torino scale, but fortunately this has now dropped to zero. **3. BENNU** CHANCE TO HIT: 0.037% This is another large asteroid that might pose a threat in the future - but not for more than a century. As such, it hasn't been given a Torino rating. **4. 2023 TL4** CHANCE TO HIT: 0.003% Briefly given a Torino score of one, this has now been downgraded to zero. The asteroid's chance of hitting Earth in 2119 is now just 0.00055%. **5. 1950 DA** CHANCE TO HIT: 0.33% The chance of collision has now been reduced to 0.0029%, and even then not until 2880 - much too far in the future to register on the Torino scale. **Source/Credit:** Illustration: ESA / NASA