Hot answers tagged

88

Impacting solar system objects would have relative closing speeds from around 11 to 72 km/s. We could take the optimal case that the asteroid approaches whilst fully lit by the Sun (which I think precludes the minimum and maximum speed in the range quoted above) and then scale from another similar body - say the asteroid Vesta. This has a diameter of around ...


34

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 ...


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 ...


19

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 ...


15

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. ...


13

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 ...


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 ...


12

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!" ...


11

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? ...


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

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 ...


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

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 atmosphere of ...


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 ...


10

The key finding why we think Earth's water came from Asteroids (big rocks) and not Comets (small rocks) is the Deuterium/Hydrogen ratio that we can measure in several sources. When a star forms, it has an initial value of D/H that came from the nucleosynthesis in its progenitor nebular / star. In a protoplanetary disc, as dust grows to rocks grow to planets ...


10

Was it Comet Hale-Bopp? It was discovered in 1995, but made a very close approach in 1997, earning it the nickname "The Great Comet of 1997". Wikipedia states As it passed perihelion on April 1, 1997 the comet developed into a spectacular sight. It shone brighter than any star in the sky except Sirius, and its dust tail stretched 40–45 degrees across the ...


10

Given that moons commonly orbit planets, why do we never encounter a comet orbiting a planet? By definition, it would no longer be a comet, but rather a moon (or more properly a satellite). Comets are icy bodies that orbit the Sun, satellites are any body which orbits a larger body than itself, other than the Sun. There are many examples of asteroids and ...


10

Wordy answer, mostly light on Math: The key word here (and the article uses this word) is "long period comets". First there's Jupiter impacts, but that's a relatively low percentage, cause even large Jupiter is quite small compared to it's orbit. Even if you extend it out to it's Roche limit where a comet could break apart, it's still a very small ...


9

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 ...


9

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 hail 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 ...


8

Shoemaker Levy 9 was estimated to have released kinetic energy equivalent to 300 gigatons of TNT. That is 1.255×1021 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 that's only my ...


8

This paper estimates "another 2300 close perihelion passages". Multiplied with around 76 years per period, we get roughly 175,000 years. That's probably only a very rough estimate. If we take the estimated mass of $2.2\cdot 10^{17}g$ and divide it naively by the estimated 1910 mass loss of $2.8\cdot 10^{14}g$, we get just 786 periods or roughly 60,000 years....


8

A comet is usually characterized by its tail. A dead comet has lost all its ices and gases (responsible for producing this tail), leaving just a rocky core. The Halloween comet is such a dead comet, in that it has no tail, but furthermore it resembles a skull, making it particularly relevant for Halloween.


8

This was a hard one to answer, primarily because of the difficulty in tracking down information. The Observations of MU69 The extended mission for New Horizons involved adjusting its orbit to do a close fly-by of a Kuiper Belt Object (KBO). The annoying part about this was that they needed to find one first! Ground based observations were unsuccessful due ...


8

Interesting question indeed, especially since it's still a matter of investigation in meteor research area! Here are some elements of answer (but definitely not all elements...): This observed asymetry is especially true for the Geminids, and less for the Perseids. Best is to check the activity profile, available e.g. at imo.net: https://www.imo.net/...


7

See Jeans Escape. If the average velocity of the volatile molecules is above escape velocity, volatiles will escape. And the with the shallow gravity wells of comets, escape velocity is very low. The earth and Mars have lots volatile gases and ice. But with their deeper gravity wells, sublimated volatile ices aren't hurled into space as they are with ...


7

This is a very brief answer but I hope it helps. Distance Hayabusa collected samples from a near-earth asteroid while Philae landed on a comet after traveling a distance of over 6.4 billion kilometers. The Type Of Mission Hayabusa's did not literally land on the asteroid. It just touched down and collected samples. While, Philae had to land, steady ...


Only top voted, non community-wiki answers of a minimum length are eligible