# Tag Info

70

There seems to be a fundamental misunderstanding as to how movement in space works. In space there is no air friction, that is, once you are moving toward your destination, you don't need a continuous source of power to keep going. Landing on a comet doesn't buy you anything, since in order to land you must first match the comet's orbit, at which point the ...

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 ...

13

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 ...

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).

12

As @ChrisWhite has already stated, catching up with Halley's comet offers no appreciable benefit since you'd already need to be traveling at the same speed in a frictionless environment. Where you could get a big boost is if your probe was positioned in the comet's path, either coming across it at an oblique angle or simply stationary, relative to the ...

8

The Wikipedia article refers to a fireball, but as Wikipedia itself explains the word fireball has many meanings and doesn't necessarily literally mean a fire as in the combustion of a material in oxygen. In this case it means a ball of very high temperature gas. The gas is heated by the impact and gets hot enough to emit light just like the gas heated in a ...

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.

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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

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 $t ... 4 The asteroid "1566 Icarus" has a perihelion distance of 0.187 au and a semi-major axis of$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 The sense in which a comet could be a "free taxi" is that it is a big source of volatile compounds. A probe that lands on a comet could, in principle, use these to refuel. A comet may be easier to use for this purpose than a large icy moon because of its low gravity. 3 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 ... 3 Conservation of energy means that it would take you just as much energy to catch up with the comet and make a soft landing (in the ideal case where you ignore the extra fuel costs for landing) as you would need to launch the spacecraft in a similar orbit as the comet. What you could do is let the comet give a bounce to the spacecraft, but I don't think this ... 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 ... 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/ 2 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 ... 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

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

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 ...

2

As earlier answers have stated this method doesn't work to save fuel directly, however it might still be useful to hitch a ride on a comet using it for a gravitational assist that the probe would not survive without more shielding than is practical. Placing the body of the comet between the Sun and the probe would presumably shield it from much of the solar ...

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