# Tag Info

16

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 asteorid. One could estimate the mass of the object assuming compositional ratios similar to a certain class of objects and integrating the whole Iridium deposits ...

13

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 into too much detail here, much of the ejecta from a large impactor would not exceed the moon's escape velocity of 2.38 km/s. You can examine Figure 7 from the ...

11

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 are easily mistaken for normal rocks. Meteorite rate Meteorites come in all sizes, from sand grains to dinosaur-annihilating rocks. The size distribution of ...

11

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 dusty regions of Mars. Often what we see is the dark-toned blast zone created by the impact in lower-resolution data, which has a large areal footprint. Then, ...

10

The impact of Phobos, even in one piece (less likely), would be different from Chicxulub. Phobos is probably a little larger than the Chicxulub impactor, but much slower, and comes in almost perfectly tangential. The impact energy would be less than a 10th of the Chicxulub impact, and the energy would be distributed over a large region around the Martian ...

10

Shoemaker Levy 9 was estimated to have released kinetic energy equivalent to 300 gigatons of TNT. That is $1.255 \times 10^{21} {\rm J}$. This release through friction and compression was sufficient to heat the atmosphere to 4000K at first. That in turn should probably be enough to break down the molecular hydrogen and methane, releasing further energy. But ...

10

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 asteroid asteroid, with energy scaling with radius1.65. Disrupting and dispersing a solid 3 km diameter asteroid with a density of 3 g/cc would require a ...

8

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 by air resistance, so they typically hit the surface at just a few hundred kilometers per hour. Reference: http://csep10.phys.utk.edu/astr161/lect/meteors/...

8

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 probability that an incoming meteor is blocked by the Moon, is $\approx$ 1:160000. Thus, the Moon is totally unfeasible to protect us from anything. The debris would ...

7

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 different planet up until 0.3 billion years ago? How could one find out, what kind of investigation would be needed? Certainly giant impacts were fairly ...

7

There are several potential explanation for the cause of the late heavy bombardment. One of them includes a passing star that disturbed the Oort cloud. A "stellar system collision" would have destroyed the solar system, though. While galaxies are mostly empty and a galactic collision won't involve that many actual collisions (if any), the gravitational ...

7

The answer to the first question is: more observations. That is, what process and techniques are used to calculate and increase the accuracy of our collision threat estimation? You just have to know the orbit. But the orbit of asteroids is very complicated to predict, because they are influenced, sometimes dramatically, by the planets and by smaller ...

7

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 and remains operational. As this page says: Arecibo has twice the range and can see three times the volume of Goldstone, while Goldstone, whose greater ...

6

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 (of order 30 km/s) and the individual velocity of the rogue object. Even if you were to arrange it so that the asteroid/comet was diverted by something else so ...

6

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 yield the same result as a 1 m projectile striking at the same speed, provided all distances are scaled by the same ratio of 1,000 = 1 m/1mm and all times are ...

6

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 in Meteoritics and Planetary Science, the energy calculation and atmospheric drag during entry is relatively straightforward physics; things like crater sizes, ...

6

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 (~1.4 km) asteroid with a 2.29 year period. MOID≈4000 km but closest approach between 1900 and 2200 is 0.37 au; orbit rather highly inclined (i=42.3°). (292220) ...

6

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 the Earth's atmosphere, it pressurized the atmosphere and caused faster than 1000 km/hr super-heated winds - https://www.lpi.usra.edu/science/kring/Chicxulub/...

6

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 would sink down as the base crumbled and spread out. The limit on Earth is about 10 km. Besides the strength issue mountains are also floating ("isostasy"...

5

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/) Here are calculations for a 100km stony asteroid... A brute like this would have a good chance of wiping out most complex life on the planet. There has been ...

5

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 inclination is only ~$1.85^{\circ}$. The longitudinal "clumpiness" may be due to erosion rate differences, since the new impacts almost exclusively appear in the ...

5

I'm not aware of any relevant uranium ore deposit, which is related to meteoritic material. Dangerous fallout is by far the most caused by short-lived radioactive isotopes. Those isotopes are rare in meteorites as well as in rock on Earth. Natural nuclear reactors, which would produce short-lived radioactive isotopes, don't occur any more on Earth, since ...

5

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 ...

5

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 from Galileo of SL9-W, a 49 second event involving a 350m comet fragment at 215,000km/h: info from NASA: _Galileo RADIOMETER brightness of L-impact > that of ...

4

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 it hit us (e.g. distance 0). I think you are asking for the closest distance. It appears the main method of detecting asteriods is with telescopes, but we are ...

4

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.

4

... 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... so the literal answer is "yes". But suppose someone asked instead: Can an 'invisible' impact perturb the orbit enough to have a measurable effect on ...

4

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 not really volcanism as in sustained outpouring of magma from the interior of the planet. However, there is a theory that large asteroid impacts could trigger hotspot volcanism at the ...

4

Using the impact effects calculator The energy before impact (making a some reasonable assumptions) is $3.35 × 10^{27}$ Joules = $7.99 × 10^{11}$ MegaTons TNT, most of which would be deposited in the Earth. The impact effects calculator doesn't discuss the formation of antipodal mountains (this is not a well-understood process) but it certainly seems ...

3

Asteroid impacts on the Moon are monitored by researchers and amateurs. The Meteoroid Environment Office has a list of candidate impacts I stumbled upon, Lunar Monitoring Program is another. Videos and photos of Lunar impacts. One impact photo to the left. All recorded impacts 2005-2015 to the right above.

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