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43

The maximum speed of an object that orbits the Sun at a certain distance $r$ is known as the escape velocity: $$ v_\text{esc} = \sqrt{\frac{2GM_\odot}{r}}, $$ where $M_\odot$ is the mass of the Sun. If the object would have a greater speed, it would eventually leave the solar system. So I'd say that the absolute maximum possible speed of any object in the ...


12

It depends. There are collisions amongst asteroids that have been caught on film that had no effect on us whatsoever. In your scenario, they would have to have a resultant vector towards us in order to cause any problems. Then there is the question of how many resultant particles are big enough to cause any problems (that is, big enough to get through our ...


12

When there aren't comets falling into the sun, Mercury is hard to beat. This NASA fact sheet lists Mercury's orbital velocity around the sun as varying from $38.86$ to $58.98$ km/sec, not so much greater than Earth (less than a factor $2$, even at maximum).


11

There are several points of evidence that the Oort Cloud exists, though it is indeed still a hypothesis and lacks direct observation. The first is indirectly observational, as proposed by Ernst Öpik back in 1932 as the source of long-period comets. This was revised by Jan Oort in 1950. All you need to determine an orbit is three observations of the ...


11

At the risk of being snarky (each definition is from wikipedia)... Comet - A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. ...


8

It is unlikely that comets are a feature unique to our Solar System. Since comets are simply remnants of star and planetary formation, then anywhere stars and planets have formed would be fertile ground to expect comets. Their individual masses are relatively very small compared to discovered planets. For example, Halley's Comet has a mass of roughly ...


8

I'm not a professional, but I'll try to answer anyway. Meteor showers occur when the Earth passes through the orbit of a comet (or, in at least one case, an asteroid). Over time, the debris spreads over the entire orbit of the comet. A shower can last for several days, which is an indication of how wide the debris stream is. Assuming a duration of 1 day, ...


7

The Moon has no atmosphere, so meteors would not heat up and glow as they descended, as they do on Earth. Comets, however, reflect light from the Sun, and thus can be seen from any sufficiently dark location.


6

An estimate of impacts from long-period comets is available at this NASA JPL site. They appear to be randomly distributed . Given detection at about 5 AU, we'd only have a year of warning for potential impactors. Their mean impact velocity is in the order of 52 km/s with an impact probability crossing Earth's orbit of 2.2 - 2.5x${10^{ - 9}}$ per perihelion ...


5

A comet doesn't need to impact the sun in order to come very close to solar escape velocity at perihelion. There is a class of comets known as sungrazers that pass very close to the sun. Although small ones evaporate on their first pass near the sun, larger ones can survive several orbits, and be considered periodic comets. There is a class of sungrazing ...


4

The asteroid "1566 Icarus" has a perihelion distance of 0.187 au and a semi-major axis of $a=1.078$ au, an orbital period of 1.119 years and eccentricity $e=0.827$. Using $$v_{\rm peri} = \sqrt{\frac{GM}{a}\frac{(1+e)}{(1-e)}},$$ where $M$ is a solar mass, then its fastest speed is 93.5 km/s. So this does not come close to Comet Lovejoy (mentioned in other ...


4

There are a few phenomena that can cause sound to be heard from a meteorite. Here it says that sonic booms as well as shock waves due to larger fragments breaking up can reach and be detected by the human ear. There is also the so-called electrophonic effect. Given that most meteorites burn up at ~100km altitude, sonic boom and shock waves would take $ t ...


3

It seems Comet Elenin broke up on this pass through the inner Solar System, and that's why it is not visible. http://www.msnbc.msn.com/id/45050612/ns/technology_and_science-space/t/comet-elenin-dead-along-doomsday-predictions/


3

There's vapour in our atmosphere all the time but it doesn't escape, at least not quickly enough to be of any concern. With the exceptions of hydrogen and helium, which really are escaping (not heavy enough), our atmosphere is stable in the medium-long term. And that includes water (you may recall that water vapour eventually comes back down as rain). A ...


2

Kepler's Three Laws of Planetary Motion are particularly helpful when addressing this question. They state that (in informal language) The shape of a planet's orbit in an ellipse, with the Sun at one focus of the ellipse. As planets move around their elliptical orbits, the imaginary line drawn from the planet to the Sun sweeps out equal regions of equal ...


2

As you rightly pointed out, the fact that 67P is oddly-shaped should alter its gravitational attraction on various parts of the comet. That said, if we were to go by Wikipedia in a rather off-hand manner, we find that the lander is $100 kg$ (as @fibonatic rightly pointed out) and 67P has an acceleration due to gravity of $\textbf{g'} = 10^{-3} m/s^2$. Its ...


2

The appeared weight of an object does not only depend on the mass of the celestial body by which it is attracted. If you simplify to spherical symmetry, which is not definitely not that case for the comet 67P (in to a lesser extend also not for the Earth) you can approximate the ratios of weight by using Newton's law of universal gravitation: $$ ...


2

As the comet approaches the Sun, it starts to melt. It means that what was once rock and ice is exposed to very high temperatures and forms a liquid which flows over and behind the comet. The above is a picture of fluid boundary layer on a sphere. Notice how the fluid motion is visible, and my guess is that the fluid drags along with it, some of the ...


1

Very near where the sun will rise, i.e. east. Lovejoy is still close to the sun. Good luck!!


1

I'd heard about a really detailed simulation of an India-Pakistan nuclear war, and found an oblique reference to it on Wikipedia. The money quote is "Five million tons of soot would be released, which would produce a cooling of several degrees over large areas of North America and Eurasia, including most of the grain-growing regions. The cooling would last ...


1

I would try here, generate an ephemeris for the object of interest (some objects may already be in the database.) HORIZONS Web-Interface This tool provides a web-based limited interface to JPL's HORIZONS system which can be used to generate ephemerides for solar-system bodies. Full access to HORIZONS features is available via the primary telnet interface. ...


1

Wild unsubstantiated guess: Could it be flow of the sand down an incline, more like a glacier than sand dunes. Maybe the flow gets a boost from tidal forces flexing the comet whenever it passes near a massive body. Some of the patterns in the sand in the lower left corner look like what happens when sand slips down a critical incline like on an over ...


1

Since there is effectively no atmosphere and thus little chance for any type of erosion, the individual "dirty sand" particles are most likely very jagged like the lunar regolith. Thus, I doubt that small distortions in the shape of the comet are to blame as these particles do not slip past each other as easily as, say, sand on Earth. So my best guess is ...


1

Astronomy -- especially exoplanet science -- has gotten very good at detecting impossibly faint signals. In this case a very recent Nature article, Two families of exocomets in the β Pictoris system, claims to see thousands of exocomet signatures in the not-too-distant β Pictoris system. This is a very young system with an edge-on debris disk -- essentially ...


1

The fastest moving object that does not get destroyed by crashing into the sun would be the apollo asteroids that get very close to the sun. For example Icarus gets going pretty fast at perihelion, (0.18665203 AU from the sun) at just under 100 km/sec.



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