# Tag Info

92

The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could also be much longer than this if the object was a cometary body. Details: Impacting solar system objects would have relative closing speeds from around 11 to 72 km/s. We could take the optimal case that the ...

55

There are two forces that can cause the formation of a tail: the solar wind and radiation pressure. The first misconception in your question is "the dust [travels] slower than the nucleus". The tail is not left trailing behind the comet, it is pushed away from the comet by the sun. When the comet is moving away from the sun, the tail is in front of the ...

37

The answer to this is surprising: We are. And many (if not all) other galaxies. And they move faster than light. See, the universe is expanding, at an accelerating rate. The fabric of spacetime itself stretches out, so that galaxies seem to move away from each other. The interesting thing is that relativity does not forbid these from moving away faster ...

35

First, there is not just one tail, it is several, but when traveling far from a star, they are "aligned". When it gets closer the different materials behave differently, both depending on the temperature they start to vaporise and how they are affected by solar winds. I think this picture shows it in a good way. https://community.dur.ac.uk/physics....

30

The comet sheds material each time it get close to the sun. The sun heats this dirty snow ball, the ice evaporates and tears dust and smaller rocks with it. These dust particles then follow a similar orbit around the sun as the comet. But as they are ejected with some velocity and react differently to the solar wind & radiation, their orbit is slightly ...

23

Each time Halley's comet passes us, we can make a pretty good estimate of its current orbit, and determine how close it will get to the massive bodies of the solar system like Jupiter, Saturn, Uranus, or Neptune on its next orbit. We can make good estimates of gravitational perturbation effects, and thereby know where to look for it. In fact, astronomers ...

20

Yes and here's a video of "a Giant Comet Hitting the Sun": https://www.youtube.com/watch?v=Mat4dWpszoQ The impact occurred sometime during May 10-11, 2011. The comet was not named but believed to be a member of the Kreutz family of comets Many close calls Before this spectacular plunge we had witnessed several other comets graze (come close without ...

17

There is also another mediator particle which moves at the speed of light other than the photon. This is the gluon, which is the exchange particle for the strong force. The odd thing about the gluon is that it's never seen by itself (that is, outside of collections of other gluons). Also, though neutrinos do in fact have mass, they are neutral particles. ...

15

The rate of loss of mass from a comet is perhaps surprisingly low. A paper The calculation of $Af\rho$ and mass loss rate for comets gives a rate for a "typical" comet at 1.29AU as 153kg/s. A typical comet has a mass of about $10^{13}kg$. Even if the comet is constantly active (and they are not) it would have enough material for over 2000 years. In fact ...

15

Its very unlikely for a comet to become a satellite of an inner solar system planet. Much less likely than it is for an asteroid. Most asteroids are on fairly circular orbits, and so the relative velocity between asteroids and planets is quite low. In comparison comets have very elliptical orbits, and their relative velocities to the planets are much larger. ...

14

Yes, binary comets do exist; 8P/Tuttle is an example of one. This is an area that is still being heavily researched, but it is suspected that binary comets can "form from collision, mutual capture, or fission." In recent news, the comet 67P/Churyumov-Gerasimenko has also been revealed to be a contact-binary by the European Space Agency's Rosetta spacecraft. ...

14

There are plenty of rapidly moving objects in astrophysics. A good place where one can get moving relativistically is near an event horizon of a black hole. A simple Newtonian estimate illustrates the point. Black hole has all its mass $M$ hidden under an event horizon of the radius of order $r_{g}=\dfrac{2GM}{c^2}$. An object moving circularly in the ...

14

I also googled "iridium content of comets", and the first result was https://news.dartmouth.edu/news/2013/04/dartmouth-researchers-say-comet-killed-dinosaurs Now there is currently no consensus on the nature of the Chicxulub impactor. The observations of iridium and osmium suggest an asteroid. A minority opinion is that a comet may be responsible. The ...

14

The confusion comes from the difference between the nucleus and the coma. The nucleus is a small icy body, only a few km across. The coma is the cloud of gas and dust released from the nucleus as it warms up. With not much gravity, the coma spreads out into space, and it can be hard to say exactly where the edge of the coma lies, however, a coma "the size ...

13

Key factors: How close is perihelion? Too close and it may be destroyed on its first pass. We know Halley's Comet, which has a perihelion of about 0.6AU, has been orbiting for over 2000 years, passing the sun every 74-76 years and is still going strong. How big is it? Every pass loses material, so a bigger comet could last longer. What is its composition? ...

13

The objects you are refering to are actually two different objects: asteroids and comets. Meteor and meteorite are other names for an asteroid, at a given time of its interaction with our planet. We'll get to that. So first, what is the difference between an asteroid and a comet? A comet is a small solar system body that display a "coma" (an ...

13

Halley's comet orbits the sun and its orbit lasts 75 years. The orbit is a long elliptical orbit. For most of those 75 years it is a cold black dot, and frozen solid in the outer solar system. But a short period during that orbit it gets close to the sun. The ice and gas begin to boil of its surface and gets blown back by the solar wind of the sun. It then ...

13

A very interesting question. Neither Bruce McClure at EarthSky nor I knew the answer, despite the fact that the observed gradual rise in numbers for the Perseids - and their quick drop-off - is something we've both observed for decades. So we asked a true expert on meteor showers, Robert Lunsford of the American Meteor Society. He also said: "Good question!" ...

13

The time of the orbit is not well known but the inclination can't change as much (small changes in velocity due to outgassing can significantly change the orbital period, but can't change the inclination much. So, while we have a good idea of it's orbital track close to perihelion, we just don't know when it will be there. We don't know where the Earth will ...

13

No. Halley's Comet has an aphelion of 35 AU, which is far less than the believed boundaries of the Oort cloud. Any object on an elliptical orbit with a perihelion of 0.6 AU and an aphelion of 2,000 AU has a semimajor axis of about 1,000 AU, and orbital period of about 31,600 years, much longer than Halley's Comet's current orbital period of 75-76 years. To ...

13

Yes, comets spin although measuring it can be tricky due to the coma and outgassing from the nucleus. It's easiest to measure the rotation period when the comet is inactive near aphelion although this is more difficult as the comet is fainter, necessitating a large amount of large (>4m) telescope time which is difficult to obtain. Searching the JPL Small ...

11

The tail of a comet is not actually "slowing down and falling away" from the comet, like you might expect to see when smoke streams out from behind a moving object on earth. The tail of a comet is actually being pushed away from the sun by the solar winds and radiation. That's why the tail of a comment always points away from the sun, and doesn't stream out ...

11

There is, believe it or not, a scientific theory regarding this: panspermia. According to the panspermia hypothesis, microbes "hitch" a lift on bodies leaving a planet. They then travel through space and eventually land somewhere else. Panspermia involves three difficult phases of travel: Launch (as well as the impact event) Travel in the harsh environment ...

11

One thing to keep in mind is that the Kepler instrument is not a telescope like Hubble. It is a photometer and though it uses CCDs to look at the sky, it doesn't return a picture in the usual sense. The way it operates is that you only look at the pixels around the object you're interested in because otherwise you'd never get all those pixels transmitted ...

11

A carbonaceous condrite has the same reflectivity as the moon at around 7-13%. If there was ice, if the tail was 10 times smaller than Hale-Bopp, it would have auspiciously covered half of the sky. it could have made an incredible display in the 1-2 days preceding the collision, because it was as close to the sun as Hale-Bopp, the brightest astronomical ...

11

Close, but not quite right - the blue light is indeed emission from CO$^+$, but it's from the CO$^+$ ions themselves, with no need for recombination to CO; that (ionized) molecule has a strong set of energy transitions around 425 nm (4250 Angstroms), which is in the blue part of the visible spectrum: Spectrum of Comet C/2016 R2 (Pan-STARRS), Figure 2 from ...

11

The comet releases lots of dust particles. The sunlight pushes these particles into orbits not quite the same as the comet Some particles will be pushed into faster orbits, some will be pushed into slower orbits. Over time the dust particles get spread out in a band that goes all the way around the sun. So we don't just see meteors in the years that the ...

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

ISON slingshot past the Sun close enough (around one Solar diameter) for its surface temperature pointed towards it to reach 6,000 °C and it wasn't a fast spinner either to help this temperature average out along its total surface. In a nutshell, it melted to its nucleus into a hot gaseous plasma of materials it was composed of long before it reached ...

10

Ahh, I see you've met our friend, the hypothetical star known as Nemesis. I don't know which scientist(s) you're referring to, but the idea goes back quite a while. The original theory was created by Raup and Sepkoski way back in 1984. Their paper analyzed mass extinctions in the past and concluded that there was a pattern. Note, though, that the paper does ...

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