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23 votes
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If Theia really crashed into Earth, did it impact Earth's axial tilt?

TL;DR: Yes Long answer: Theia is a hypothesized ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, ...
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17 votes

What if the Earth was hit by a small asteroid having close to the speed of light?

If the Earth was hit by an asteroid having diameter of about 5 km and moving with the speed close to the speed of light? What would happen? According to https://what-if.xkcd.com/20/ The momentum ...
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16 votes
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Could this estimate of the size and mass of the Chicxulub Impactor be accurate?

Well, that article was never accepted for publication in any peer-review journal apparently. That said, estimates may vary widely depending on assumptions about the composition and velocity of the ...
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15 votes
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How many iridium layers do we know, besides the K-Pg one (the dinosaur killer "smoking gun")?

There are other iridium anomalies, particularly the Devonian-Carboniferous boundary (D-C boundary), about 350 Ma ago. The K-Pg boundary is only 66 Ma old. Just because there is an iridium anomaly ...
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  • 1,499
13 votes

How well would the Moon protect the Earth from an Asteroid?

It would be much better for Earth if the impactor hit the moon... In this Worldbuilding answer, I used a paper on ejecta kinematics to do calculations for ejecta velocity upon impact. Without going ...
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13 votes

What if the Earth was hit by a small asteroid having close to the speed of light?

It might be hard to find sources where such collisions have been rigorously modeled, but certainly the amount of kinetic energy available is enough to do some damage. The amount of kinetic energy is ...
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12 votes

Would a killer asteroid shattered into thousands of pieces produce the same devastation?

TL;DR version: Too big and way, way too late. The dispersal can't be done, even at the lower end of that 3-20 km scale. Holsapple claims 5 kilojoule/kg are needed to disrupt and disperse a solid 1 km ...
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12 votes

What if the Earth was hit by a small asteroid having close to the speed of light?

The kinetic energy of a relativistic mass is given by $(\gamma -1)mc^2$, where $m$ is the mass of the object and $\gamma$ is the Lorentz factor $(1 - v^2/c^2)^{-1/2}$, where $v$ is the speed. ...
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11 votes
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What explains the distribution of new impact craters on Mars?

I was on the targeting team for one of the cameras that discovered most of these new impact craters. The reason for the distribution is simply because it's easiest to find "new" impact craters in the ...
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11 votes
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How often do meteorites hit the Earth?

There is definitely not a catalogue of all meteorites hitting Earth. For instance, the ones falling in desert areas and in the ocean aren't found, and even the ones falling in more populous regions ...
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9 votes
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What if a global killer hit Mars?

Imagine a similar asteroid as Chicxulub, the one that likely killed the dinosaurs here on earth. It is thought to have impacted at about 20 km/s. Initial atmospheric effects: When the asteroid entered ...
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9 votes
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What would happen if Venus was hit by a Chicxulub-like meteor?

Question: Would the dense atmosphere and high surface pressure and temperature lead to a different result compared to what happened here on Earth? Short Answer: No. There will not be any significant ...
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8 votes
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How gently could a comet/asteroid/meteorite "hit" Earth?

Yes, spacecraft do it all the time by using air resistance (and sometimes rockets) to slow down. Meteorites enter the atmosphere at high speed, typically 10-70 km/sec, but the smaller ones are slowed ...
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8 votes
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If an Asteroid was to strike the Earth, would it affect the Earth's rotation?

To have a noticeable effect the impactor needs to be BIG. Most questions about "what would happen if ... hits" can be answered by the "Earth impact effects program" (http://impact.ese.ic.ac.uk/) ...
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8 votes
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How well would the Moon protect the Earth from an Asteroid?

The Moon orbits the Earth from $\approx$ 380000 km, but its radius is only $\approx$ 3500 km. The sky has 41253 sq degrees, and the Moon covers only $\approx$ 0.25 sq degree from it. Thus, the ...
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  • 3,102
7 votes

Could an impact have resurfaced Venus 300 million years ago?

Would an impact event leave visible traces like impact basins, or could the entire surface melt and reform as it is today, as I suppose Earth did when the Moon formed? Could Venus have been a very ...
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7 votes
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Are we less safe now that Arecibo is no more?

The linked article is copied from a university press release. Arecibo's article is more matter-of-fact but naturally also emphasizes the value of their own work. NASA Goldstone can do planetary radar ...
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  • 16.6k
6 votes

How gently could a comet/asteroid/meteorite "hit" Earth?

It is difficult to see how. Most comets and asteroids would encounter the Earth on a crossing orbit and the encounter velocity would be roughly the vector sum of the Earth's velocity around the Sun (...
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6 votes
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What percentage of a lunar meteor strike is blown back into space?

There are some invariances that actually lend themselves well to estimating an answer to this question. From the Deep Impact mission white paper: A 1 mm projectile striking a target at 10 km/s will ...
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  • 14.1k
6 votes
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2019OK energy at impact

You can use the Purdue 'Impact Earth!' website to estimate the effects of impacts of objects of various size, speed and composition. As detailed in the accompanying documentation, which was published ...
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6 votes
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Is there any known asteroid or comet whose path goes through the Earth?

JPL and ESA provide tools to search for small bodies meeting user-defined criteria. I tried: H <= 24 MOID <= 1e-4 au with each and got these results in common: (89959) 2002 NT7, an H=16.5 (~1....
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6 votes
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Why do Jupiter impact events look dark brown?

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'...
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5 votes

What explains the distribution of new impact craters on Mars?

The simplest explanation for the latitudinal distribution would be that most small solar system bodies that could impact one of the planets happen to orbit near the ecliptic plane and Mars' orbital ...
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5 votes

What if a global killer hit Mars?

A partial answer to this part: Would any volcanoes erupt? At a local scale (i.e., close to the impact), such an asteroid could melt the rock, see impactite. But this is not volcanism stricto sensu, ...
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5 votes
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What if you 'placed' the Chicxulub asteroid onto the Earth?

An asteroid resting on Earth would be a mountain. Or, for smaller asteroids, a pile of gravel. Mountains are limited in altitude by the strength of stone to resist compression: a too tall mountain ...
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5 votes
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If Planet Nine indeed exists, how large a impact event there should be to be seen from Earth?

We can compare the brightness of a comet hitting planet 9 with the 1994 impact of Shoemaker-Levy 9 / SL9 on Jupiter. It was seen by Hubble, and Galileo which was orbiting Jupiter at the time. View ...
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4 votes
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Detecting Deep Impact

Something to consider might be a large very dark (low albedo) asteroid. I would say it is quite possible a large dark asteroid (e.g. P-type) "could" be headed for us, and we would not know it until ...
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4 votes

Celestial impacts

Yes, there is an observed impact of a comet into a celestial body. A fairly recent one in 1994 is the comet which impacted into Jupiter, Shoemaker-Levy-9 Here's a video of this event happening.
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4 votes

Small changes to Earth's orbit caused by a large impact on the Moon

... and still remain within the habitable zone? Everything perturbs all the time. Every change in the distribution of mass in the solar system (or in the universe) perturbs the orbit of the Earth... ...
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