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December 29[edit]

meteorites from EARTH to Mars, rather than vice versa[edit]

Hi, what i read is that about a ton of meteorites of mars origin land on earth every year. How often would the reverse happen given Earth's stronger gravity? Less often I'm sure but how less often? Is there an approximate formula based on gravitys and distance from sun etc? Thanks68.65.169.66 (talk) 01:20, 29 December 2012 (UTC)[reply]

When was the last time a meteorite impact on Earth was storng enough to eject material into space? This is not just a matter of stronger gravity -- it's also a matter of Earth having a dense atmosphere that all but prevents any Earth material from being ejected into space as meteors. 24.23.196.85 (talk) 01:37, 29 December 2012 (UTC)[reply]

I don't know when the last one was, but a meteorite impact on Earth, if it did bang stuff off of earth, even many millions of years ago, could be a continuing source of meteorites to Mars. Also, i wonder about (Earth)volcanoes shooting material away from Earth.68.65.169.66 (talk) 02:09, 29 December 2012 (UTC)[reply]

No volcano has ever been powerful enough to launch stuff into space -- the rocks fly thousands of feet into the air at most, while the volcanic ash usually goes up into the stratosphere and just hangs there for some weeks. 24.23.196.85 (talk) 02:51, 29 December 2012 (UTC)[reply]

No volcano on Earth. There have been (water) volcanoes that launched material into space. Some of Saturn's rings are from one (see Enceladus (moon)). StuRat (talk) 04:05, 29 December 2012 (UTC)[reply]

No volcano in historical times has come anywhere close to achieving an orbital launch. Large modern eruptions send volcanic bombs (i.e. large rocks) up to 500 m or so above the volcano. However, we have good evidence of volcanic explosions 10-100 times larger having occurred over geologic times. This makes it likely that at least occasionally volcanic eruptions might send rocks miles into the sky, and just possibly the very largest eruptions might approach escape trajectories. Back in the early twentieth century, there was a theory in geology that large, suborbital volcanic ejecta was responsible for creating impact craters (e.g. verneshot). We now know that most impact craters have a extraterrestrial origin (i.e. meteors), but I don't think one can completely rule out the possibility of an extremely large, extremely rare (e.g. 1 per 100 million years) volcanic eruption being capable of launching some rocks off the planet. If it has ever happened though, it certainly doesn't happen often. Dragons flight (talk) 05:12, 29 December 2012 (UTC)[reply]

What about meteorite impacts?64.9.234.141 (talk) 05:58, 29 December 2012 (UTC)[reply]

It would require a pretty big meteorite impact. Still not very common, since big impacts are themselves rare—maybe once every 10 million years or so at most. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:59, 29 December 2012 (UTC)[reply]

I thank you for your answer. I'm not sure how you get your estimate, or even if your estimate is at least from intuition gained from experience and study. My original question was how much Earth material gets to mars relative to the reverse process, (which hopefully the scientists who claim about 1 ton/year have their reasons). But if you are correct that such meteorite impacts are on average 1 every 10 million years, how much transfer would we expect to mars? Is it likely or unlikely that there been in the last 100million years meteor impacts that ejected millions of tons of matter from Earth?(I ask the large amount of a million tons because I bet the odds of any given particle of it ever getting to mars, let alone in a given year, are small.) Could we say perhaps then that extremely tiny amounts of Earth end up on Mars, like a teaspoon per year?Thanks again.64.9.234.141 (talk) 08:02, 29 December 2012 (UTC)[reply]

Terrene meteorites in the moon: its relevance for the study of the origin of life in the Earth Here somebody wants to look what the earth meteorites look like to search for the beginning of life on earth.
doi:10.1016/0012-821X(94)00232-N Here somebody wants to know how life spread from earth with meteorites.
Testing interplanetary transfer of bacteria between Earth and Mars as a result of natural impact phenomena and human spaceflight activities Bacterial transfer in the solar system. --Stone (talk) 09:06, 29 December 2012 (UTC)[reply]

I don't see how anything ejected from Earth could make it to Mars -- Mars is tens of millions of miles farther from the sun, and the ejected material would have to overcome the sun's gravity for that great distance. Duoduoduo (talk) 13:57, 29 December 2012 (UTC)[reply]

It takes an enormous amount of energy to get off the Earth. The amount of energy to get from Earth to Mars is only about 4 times larger than the amount required to escape the Earth. If you have any scenario that can get you off the Earth, it isn't hard to imagine a scenario with a few times more energy that gets you to Mars. Dragons flight (talk) 15:23, 29 December 2012 (UTC)[reply]

While the escape velocity from the surface of Earth is more than double that of from Mars (11.2 km/s vs 5.0 km/s), I believe that Duoduoduo is mistaken if they think that once the object has escaped from the planet, then somehow the sun's gravity makes it much easier to travel from Mars to Earth than vice versa. Can someone more familiar with orbital mechanics speak to this point? -- ToE 18:18, 29 December 2012 (UTC)[reply]

Well, if you just put an object with no initial momentum just outside Mars's gravity well, it will fall toward the sun, crossing Earth's orbit on the way. But if you put an object with no initial momentum just outside Earth's gravity well, it will also fall toward the sun, hence not crossing Mars's orbit. Duoduoduo (talk) 22:10, 29 December 2012 (UTC)[reply]

Hmmm, but a rock that falls from near Earth orbit should return near to the same distance over and over again... and if so, is there a chance that it will interact again and a gravitational slingshot will get it out some distance? (but then again, it shouldn't be moving very fast relative to Earth, so it shouldn't slingshot very far... I think...) Wnt (talk) 23:16, 29 December 2012 (UTC)[reply]

But that "no initial momentum" (relative to the Sun) assumption is wrong. Anything starting from Earth will have about the same initial momentum as Earth, and anything starting from Mars will have about the same initial momentum as Mars. Therefore, it would take just as much energy, but in an opposite direction, to force an object from an Earth orbit to a Mars orbit as vice-versa. StuRat (talk) 23:21, 29 December 2012 (UTC)[reply]

"No initial momentum" was just intended as an unnecessary simplifying assumption to focus on the issue at hand -- the sun's gravity. This seems simple to me -- from Mars to Earth the sun's gravity is helping, while from Earth to Mars you're working against the sun's gravity. Duoduoduo (talk) 13:09, 30 December 2012 (UTC)[reply]

No, no, StuRat is correct. The "No-Initial-Momentum" assumption is not a good first approximation. Look at Delta-v budget#Delta-vs between Earth, Moon and Mars for an good picture on that topic. It takes about 10 km/s to go from Earth to Low Earth Orbit, and much less than that to reach a Mars Transfer orbit. And the Earth slingshot idea seems quite viable to me. Dauto (talk) 15:55, 30 December 2012 (UTC)[reply]

Forget the "No-Initial-Momentum" assumption -- as I said, it has nothing to do with my point, and I already retracted it. You say that it takes a positive boost to get out to Mars. Part of that boost is needed because you're fighting against the sun's gravity. My point is that it doesn't take that same boost to get from Mars to Earth, since the sun's gravity is helping rather than hurting. In other words, my point was simply that the sun pulls things toward the sun. Or can you get from Earth to Mars without overcoming the sun's gravity?? (And I too like the Earth slingshot idea.) Duoduoduo (talk) 16:48, 30 December 2012 (UTC)[reply]

What we're trying to explain is that it takes just as much energy to force an object in orbit about the Sun, at Mars, down to an Earth orbit, as to do the reverse. Think of the kid's experiment where you swing a ball on a string around your head. It wants to go outward, and it takes an active force to pull it inward. If this wasn't the case, then everything would have fallen into the Sun long ago. And the size of the object doesn't matter (much). Jupiter can orbit the Sun just as a speck of dust can.

Now, you are correct that an object with no initial momentum relative to the Sun would fall into it, but this just won't be the case with either Mars or Earth meteorites. StuRat (talk) 00:20, 31 December 2012 (UTC)[reply]

I'm looking for some intuition as to why the required energy would be identical in either direction. Is it this?: Denote orbital velocity to maintain a Mars-radius orbit as m and to maintain Earth-radius orbit as e. To go from Earth-radius orbit to Mars-radius orbit, the entirety of what you have to do is to decelerate from e to m, and to go from Mars-radius orbit to Earth-radius orbit the entirety of what you have to do is accelerate from m to e. Since the absolute change in velocity is the same in either case, the energy is the same in either case. Is that it? Duoduoduo (talk) 16:03, 31 December 2012 (UTC)[reply]

Yes, that's a good way to picture it. StuRat (talk) 06:43, 1 January 2013 (UTC)[reply]

But that only gives equality of energy needed if in both directions you are slowing down or speeding up to the second planet's orbital speed. But a meteorite doesn't have to do that -- it can just hit while attempting to cross the planet's orbit, without havng to enter orbit. So I return to my original notion that a key difference is which way the sun is pulling the meteorite. Duoduoduo (talk) 16:16, 1 January 2013 (UTC)[reply]

And I return to my statement that any meteorite kicked loose from a planet will have an orbital speed about the Sun very similar to the source planet. The Earth is orbiting the Sun at 29.78 km/s, and has an escape velocity of 11.186 km/s, while Mars orbits at 24.077 km/s with an escape velocity of 5.027 km/s. So, for an object to "fall" from Mars to the Earth, it would have to leave Mars at nearly 5 times the escape velocity, in just the right direction, to not have any momentum relative to the Sun. This is extremely unlikely, and the much greater amount of energy required to do this (rather than just barely escape Mars) would vaporize the object, so it would be gas, not a meteorite, and probably split Mars in half in the process. StuRat (talk) 03:02, 2 January 2013 (UTC)[reply]

Please bear with me, as I'm trying to learn something here. What I'm saying is I think analogous to the following from Delta-v budget#Near earth objects:

The delta-v to return from them [near earth objects] are usually quite small, sometimes as low as 60 m/s....However, the delta-v to reach near earth objects is usually higher, over 3.8 km/s

Duoduoduo (talk) 17:04, 30 December 2012 (UTC)[reply]

Following the reference from that section, I see that the 3.8 km/s delta-v is from Low Earth Orbit to the NEA, so most of that is needed to escape Earth's gravity well. -- ToE 18:01, 3 January 2013 (UTC)[reply]

From an earlier post: When was the last time a meteorite impact on Earth was storng [sic] enough to eject material into space?

Well, I doubt it was the last, but there's at least one big one, though it obviously didn't make it to Mars.

— The Hand That Feeds You:^Bite 00:08, 31 December 2012 (UTC)[reply]

Even though we haven't had any large impactors here on Earth very recently - my "gut feel" wonders whether it might be the case that the velocity of the debris will follow some kind of (gaussian?) velocity distribution? While the average velocity might not be enough to reach escape velocity - wouldn't it be possible for a freak particle out on the far end of the distribution to make it out? The energy equation ought to allow it - providing the piece of debris is small enough. SteveBaker (talk) 04:28, 31 December 2012 (UTC)[reply]

Yes, but those small particles would burn up in the atmosphere of Earth, unless you're talking about an impact so great it blows a good bit of the atmosphere away with it. And that distribution would also mean the Earth would be surrounded by a ring of all the objects which failed to reach escape velocity, although that ring might be rather unstable, due to the Moon, resulting in more of a cloud. StuRat (talk) 06:46, 1 January 2013 (UTC)[reply]

Confusion in article Atomic mass and bond order greater than 6[edit]

While reading the article Atomic_mass#Mass_defects_in_atomic_masses, I read in the linked section "deviation is positive or negative". What does deviation and positive/negative mean in the context ?
No two elements in the periodic table can form a bond with greater order than 6. Why ? Sunny Singh (DAV) (talk) 13:51, 29 December 2012 (UTC)[reply]

One atomic unit of mass is 1/12-th of the mass of Carbon-12 atom. Hydrogen-1 (proton+electron) has mass higher than this unit. So, the mass deviation is positive. Atoms heavier than carbon (up to nickel) generally have negative deviations. Ruslik_Zero 15:37, 29 December 2012 (UTC)[reply]

For your second question, see this article. Septuple bonds are not possible between two atoms of any elements with atomic numbers 100 and below. They might be possible in the early superactinides, but their half-lives may not be enough for chemical characterization (except, possibly, for a few elements around the magic number Z = 126). Double sharp (talk) 07:17, 30 December 2012 (UTC)[reply]

We have a Sextuple bond article that includes that ref. DMacks (talk) 20:45, 30 December 2012 (UTC)[reply]

Biochemistry of Seizures[edit]

What are the biochemical processes involved in a seizure. Is it different for every cause I.e.for low blood pressure, transplant rejection, high fever, allergy etc. — Preceding unsigned comment added by 176.27.208.210 (talk) 16:39, 29 December 2012 (UTC)[reply]

Don't know, but in the case of an epileptic seizure, dogs can apparently predict them, which points to a chemical odor, which means there must be chemical reactions leading up to it. StuRat (talk) 23:24, 29 December 2012 (UTC)[reply]

I think you're probably correct about chemical odors. But it seems to me there some chance that dogs detect it by other means instead. Their eyes are very sensitive to motion, perhaps especially of human motion, and they hear at some frequencies humans can't.199.33.32.40 (talk) 00:25, 30 December 2012 (UTC)[reply]

Thanks for your answers. Im pretty sure that every biochemical process in the human body involves chemical reactions and that most symptoms of illnesses are also caused by biochemical reactions. My question is specifically which biochemical processes/reactions cause seizures. 176.27.208.210 (talk) 02:48, 30 December 2012 (UTC)[reply]

I don't think that's true. A heart attack can be caused by a blockage, and a stroke can be caused by a break in a blood vessel. Neither requires any chemical reactions immediately leading up to it. StuRat (talk) 03:13, 30 December 2012 (UTC)[reply]

True but surely there's chemical processes which lead to blockages or burst vessels. 176.27.208.210 (talk) 13:23, 30 December 2012 (UTC)[reply]

Seizures have many causes (e.g, hyponatremia, hypoglycemia, hypocalcemia). The muscle activity and alterations of breathing can produce some common post-ictal chemical changes (e.g., elevated prolactin). Doctors pay more attention to the chemistry of possible causes than to the chemistry of the consequences. alteripse (talk) 06:27, 30 December 2012 (UTC)[reply]

Rather than writing a long response I'm just going to give a pointer to our article on epilepsy. Looie496 (talk) 14:32, 30 December 2012 (UTC)[reply]
The OP seems to be asking for an explanation at the wrong level of causation. Seizures are neurological events, and have to do with malfunctions of neurons and their signalling of each other and the body. See action potential and neurotransmitter for relevant articles. There isn't some sort of general chemical reaction going on like combustion that causes a seizure as such. All the normal sorts of chemical events that are going on in normal functioning will be found during seizures, but in the circumstance of improperly coordinated actions of the cells. Asking for a chemical explanation as such is about as relevant as it would be to ask what sort of chemical reactions are going on during a senate filibuster or a ferry capsizing. μηδείς (talk) 20:39, 30 December 2012 (UTC)[reply]

One intriguing piece of the puzzle has to do with a fall in the carbon dioxide tension before a seizure, particularly in patients with fever or hypoxic-ischemic encephalopathy. A fall in pCO2 is thought to lower the seizure threshold. The relationship between CO2 and seizures has been studied since at least the 1920s, but specific clinical interventions (like supplemental CO2 administration) have only been investigated in the last few years. I wish I understood it better on a biochemical level, but the potential clinical applications are exciting. EricEnfermero ^Howdy! 23:30, 30 December 2012 (UTC)[reply]