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24

Pluto is now classified as a dwarf planet. The main difference between a planet and a dwarf planet has to do with the requirement that a planet clear out the material in and near its orbit. Planets do this, dwarf planets do not. The reclassification was triggered by the discovery of many additional object (the Edgeworth-Kuiper Belt) out beyond the orbit ...


22

First, the speed of other galaxies isn't too helpful. For example, the radial velocity of the Andromeda galaxy relatively to us is 300 km/s, i.e. 0.1% of the speed of light only. Moreover, internally, everything in that galaxy moves by pretty much the same speed and is confined to the vicinity of that galaxy which makes us pretty sure that no piece will ...


20

Why don't we observe any relativistic asteroids? The answer to this question would not be complete without mentioning the virial theorem. Considering our galaxy as a system of $N$ gravitating objects, according to the virial theorem, twice the average total kinetic energy of all objects, plus the average total potential energy of these objects, adds up ...


12

Apophis is of no real concern to us as far as we can tell. That said, it doesn't mean another asteroid doesn't have our name on it... According to the most reliable data we have regarding this particular asteroid it only has a 1 chance in about 250,000 of hitting the earth. University of Hawaii states: “Our new orbit solution shows that Apophis will ...


10

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. ...


9

The NASA Dawn mission sees a craft headed toward the Asteroid belt as we speak - they intend to do well, navigating to Ceres and Vesta, and more. Our intuitive knowledge of the universe tells that there will be both semblance chaos and order, with bodies having dominating factors, creating mini, seemingly orderly systems which could or would eventually ...


7

Dr. Phil Plait has written about this extensively. He has a book (Death from the Skies) with a chapter that deals with this. He has a blog entry about this very subject as well (in addition to a link to one just talking about getting hit by a meteorite). Here is an excerpt: what are the odds of getting killed by one? Turns out, they’re a lot ...


7

Yes, but just barely (i.e. only one so far), and only for the L4 point. And this was only recently discovered. Dr. Phil Plait (an Astronomer) covers this at his Discover Magazine blog in his usual easy to read style. NASA’s Wide-field Infrared Survey Explorer (WISE) has found the very first asteroid that (more or less) shares an orbit with Earth! ...


6

It all depends on the size of the asteroids that you're talking about. The asteroid belt in our solar system is so vast that even if you go down to ~1-meter sized objects, each one can have over 4000 square kilometers all to itself. And that's without factoring in the fact that the asteroid belt has a third dimension to it. But, there are clumps, ...


6

I don't think this question can really be answered in any factual way. There's a general definition of "dwarf planet" but the IAU is not known for its rapid turn-arounds. There is also a mathematical way to figure out when mass is sufficient to spherize a body under self-gravity, but exact parameters of the body itself result in ambiguity in many cases ... ...


6

When an object comes within the Roche limit, it breaks up because of tidal stresses - the part closest to the earth feels a stronger gravitational attraction than the furthest part. Hence, the closest part will fall a little faster than the trailing parts. As a result, "disintegration" does not mean that the body will fly apart like a bomb. Instead, it ...


5

Forget Armageddon and Deep Impact. Movie physics is not real. It's a movie, after all. Should some large dinosaur killer class asteroid or comet be on a trajectory that eventually impacts the Earth, our only hope is to detect that object decades in advance. A large number of options exist given adequate advance warning. No options exist were we to detect ...


5

I think you're referring to asteroid 2005 YU55 which is making an approach on November 8. This article on NASA JPL's Asteroid Watch site gives some details including: The asteroid's surface is darker than charcoal at optical wavelengths. Amateur astronomers who want to get a glimpse at YU55 will need a telescope with an aperture of 6 inches (15 ...


5

The answers so far leave out an important consideration, which is that of the Nice model and effects it would have had, and the evidence for the Late Heavy Bombardment. To start with, models predict that Jupiter would have formed rather quickly. The mass of Jupiter - even if it was not quite where it is now in the solar system - will perturb material out ...


4

Have a look at http://impact.arc.nasa.gov/biblio.cfm for a comprehensive list of papers on the subject of asteroid deflection, or Google "deflecting asteroids site:nasa.gov" for a list of popular articles. The summary of the Near Earth Orbit Program mentions the use of nuclear explosions, but makes it clear that a small device would be needed to prevent the ...


4

Dr. Marc D. Rayman, Chief Engineer of the Dawn mission, gives some better statistics and analogies here: Dawn Journal: November 27, 2009 Dawn will travel 7.7 astronomical units (AU), or nearly 1.2 billion kilometers (almost 720 million miles), to its July 2011 rendezvous with Vesta. Yet in all that time, and across all that distance, the closest the ...


4

An asteroid within the Roche Limit of a planet will experience a tidal stress tending to pull it apart that's stronger than the gravitational pull of the body's own gravity, tending to hold it together. If the body is more than twice as dense as the planet, the Roche Limit is below the surface of the planet, and tides won't break it up before it collides ...


3

Ceres is the most important asteroid, having over half the mass of the entire asteroid belt. Vesta is the third largest, and smallest one to have enough gravity to crunch into a spherical shape. Any time two bodies collide or, if they are large enough to have significant gravity, nearly collide, they are going to change their direction of travel. Typically, ...


3

Earth is really, really big (in comparison to that projectile). In order for an object to completely penetrate it, it would need to have enough force to go through 12,742 kilometers of solid and liquid. It would need either extreme mass or extreme speed. in the case of extreme mass, at a certain point, the object wouldn't go straight through earth as much ...


3

The answer to your question depends upon what you mean by "the asteroids" and "really." The vast majority of the material in the asteroid belt today was probably originally there by the end of solar system formation. Objects in their current size and orbits, not so much. Size-wise, the asteroid belt has gone through something like 4.5 billion years of ...


3

To put it simply, every sci-fi movie that ever featured one does grotesque disservice to what an asteroid field is really like. In fact, an X-wing pilot, for instance, rather than having to swoop and dodge, would probably have a difficult time telling that he is even in an asteroid field. I'll also endorse Stuart R.'s link working through the math, ...


3

Yes. Well, you wouldn't fall back and forth forever because space in the asteroid belt isn't a true vacuum. The density is very low, but there would be some drag and it would bring you to a halt eventually. However you would oscillate for a very long time. But then you could argue that wouldn't Ceres orbit the Sun forever (assuming it doesn't get hit by ...


2

The original mass of the solar disk at that position in the Solar System is speculated to be about the same as Earth. Due to gravitational perturbations of Jupiter and Mars, the Asteroid Belt was too chaotic to allow a planet to fully form. Instead of relatively gentle collisions, allowing them to accrete, the impacts of planetesimals were highly energetic. ...



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