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4

The minimum diameter of the dinosaur-killing impactor is 11 km (according to the wikipedia page on the Chicxulub impact) . Let's use that as our basis for calculation. Larger objects could be seen further away. Objects impacting the Earth can have relative speeds of about 11 to 90 km/s. Let's assume our object is in the middle of this range (the answer will ...


3

There are a few other aspects to this question. As already mentioned, space is big and the Earth is a relatively small moving target. The Earth's orbital speed is around 29.8 km/s, thus it covers a distance equal to its own diameter in around 7 minutes. If you want to determine if some rogue body is going to hit the Earth, your trajectory calculations need ...


12

An object's absolute magnitude (how bright it would appear at full phase, 1 au from both Earth and Sun) is related to its size and easier to determine. A ~1 km asteroid has absolute magnitude H ≈ 17.75. The Chicxulub impactor, estimated between 11 and 80 km, was probably 9 ≤ H ≤ 12. Comet C/2019 U6 (Lemmon) is smaller (H = 13.3) but a good example of modern ...


4

The initial impacts are brighter. The team that observed the shoemaker levy impacts described them as "fireballs" and the initial pictures showed spots glowing bright after impact, though I'm not sure how much those images used the infra-red range, so, grain of salt, because I think you're asking about the visible spectrum. Jupiter's bands are ...


1

What you are seeing is the top of a huge cloud of dust and smoke that forms in the Jovian atmosphere. It doesn't look "red" because it cools down quite rapidly. In fact the same is true when an asteroid impacts Earth. There is a cloud of dust and smoke (that looks white because it is lit by the sun and is seen against the sky) If there is a ...


27

It could be as little notice as a few days. There is a large variation in the amount of warning we would have before an asteroid strike similar in energy to Chicxulub. Let’s examine the case in which we would have the least warning. The lower bound to the estimated energy released by the Chicxulub collision is 1.3e24 joules https://en.wikipedia.org/wiki/...


17

There are two classes of object. One is "asteroids" and the other is "comets". Asteroids orbit in fat ellipses, mostly between Mars and Jupiter, but some come closer and a few can come close to Earth. They are never very far from Earth and we discover new small ones all the time. These are "potentially hazardous objects". If ...


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