abiogenesis - How did the nucleobases in the Murchison meteorite form?

It is interesting to note that, in the Wikipedia article, it states that

The amino acids were racemic (that is, the chirality of their enantiomers are equally left- and right-handed), indicating that they are not present due to terrestrial contamination".

This implies that, if a 'life form' did create these proteins, they are fundamentally quite different to life on earth. (Particularly in light of the 70 unique amino acids they described!).

We cannot ever 'know' how they were made, unless a pretty revolutionary discovery is made that undisputably confirms evidence for extra-terrestrial life (although this is the best evidence yet!), so we are left to speculation.

The nucleobases either formed 'randomly' in one of the countless celestial events (although the chances of this seem pretty remote given the complexity of the molecules and the homogeneity in the sample), or they were made by extra-terrestrial 'life' (much more exciting, and indeed probably more likely, as we will see). (Or the 3rd option: intelligent design, however this is dramatically less probable than either of the other two).

The Miller-Urey experiment to which you refer has been subsequently enhanced, and evidence for the "catalytic potential of cosmic dust" is now reasonably robust (Hill, 2004). They demonstrate that simple nebular iron silicate catalysts can yield methane and water from CO₂ and H₂, and ammonia from N₂ and H₂. Allowing these to react yields nitrogen-containing organics such as methyl amine.

It is not a huge jump to suppose that with enough time, mass and energy, these reactants could combine and form a molecule (chain of amino-acid-like molecules - a protein) capable of faithfully replicating itself, and thus initiate life. There is no reason to suppose that Earth is unique in this respect; there are billions of suns in our galaxy alone, and billions of years of time for these reactions to take place.

Could a small Mars Cycler be used for repeated sample and big data transfers?

I'm not sure data return in a physical format is worthwhile. Samples are another question, of course.

If we're already willing to wait seven years for it all to come in, why not transmit data slowly throughout that period via a relay satellite? This means you can start interpreting it early (and help inform the ongoing sample collection work); you avoid the "all your eggs in one basket" problem; you escape the risk of physical data corruption; and, best of all, you get flexibility. You can relay information from other orbiters, from other (non-sample-return) vehicles, etc.

But surely a relay satellite is too slow? Well, not really. Conveniently, we have a figure for the amount of data returned by the Mars Reconnaissance Orbiter over its first seven and a bit years; over 200 terabits (25 TB). It's reasonable to assume that a dedicated relay satellite would have the ability to exceed this, and if we can transfer dozens of TB every seven years, we're seriously competing with the physical storage approach.

Only a small fraction of the data sent through MRO is relayed from the surface, but if we knew there would be a dedicated and high-capacity relay satellite, rovers and landers would no doubt be built to rely on that infrastructure, and high-bandwidth relay uplinks on them could be prioritised.

Yes, we'd still have to keep the data relay satellite working. But we're doing pretty well with Mars orbiters - every orbiter that's made it to Mars in the past fifteen years is still going - and if we built a cycler, we'd have to worry about keeping that going.

All told, from the data transfer perspective, it's probably unnecessary.

human biology - Can an adult without genetic lactase persistence still develop a tolerance for dairy foods?

Here are my thoughts on the topic.

Dairy good is not only milk, but also the following milk products: sour milk products (like yougurt, kefir, katik, buttermilk, etc.), cheese, etc. These products can contain less lactose than in the milk solids (due to fermentation during processing). It is also common for some of these products to contain living lactase-active bacteria, that can digest lactose.

Regular intake of these products can lead to certain changes in our small intestine microflora, so that the lacking lactase activity is substituted by the bacteria and thereby the tolerance grows. Maybe this is the intend of the Chinese government? Maybe they encourage the intake of sour milk products and not solid milk?

It is known, for example, that children with congenital/primary enzymatic deficiency develop the tolerance at the age of 6-10 years so that no special diet is needed anymore. This is true at least for such common enzymatic deficiencies like phenylketonuria and coeliacia.

In Russia, where I got my medical degree, it is common to use bacteria in the treatment of many types of primary intolerance combining this treatment with dietary support.

What are the prerequisites for a meteorite to reach the ground?

Your first resource here can be the impact effects calculator, It can show you when it is likely that a high velocity impact will occur. Somewhat surprisingly, faster objects are less likely to hit the ground at hyper-velocity, as they are more likely to break up and explode at altitude. They will likely form multiple meteorites, as the Chelyabinsk meteor did

If you are interested in meteorite formation, rather than craters, then most impactors will in some part survive the fall, provided they are rocky rather than icy. Objects smaller than 5cm are mostly cometary in origin. Larger than that and they are more likely to be rocky.

solar system - Could the trajectories of non-periodic comets be used to infer properties of the 'ninth planet'?

Non-periodic comets are comets which have very long orbital periods (>200 years or more), spending most of their time in the outer solar system.

Planet X, recently revived by researchers at Caltech, is a proposed planet orbiting in the farthest reaches of the outer solar system. The Caltech researchers infer its presence from to its effect on the orbits of Kuiper belt objects.

If such a planet exists, and is the cause of the Kuiper belt object alignments, could it not also knock such objects in to the inner solar system, creating non-periodic comets with huge aphelion orbital distances? Could our current observations of non-periodic comets be used to infer properties of the planet?

How much time do INS1-E and MIN6 cells need after splitting?

I am currently doing an experiment on cells to test the internalization of a protein.
Normally, I seeded my cells the day before the incubation. This worked well for Hela, CHL or PANC1 cells. However, when I did the same with INS1-E and MIN6 (both beta-cells) after the incubation and the washing step the majority of the cells were gone. This was better in the control where I did not put in the compound, but still a lot of cells were detached.

Therefore, I wonder if I should seed the INS1-E and MIN6 cells earlier, more like 2-3 days before. Do these cell lines need more time after splitting to attach again?

human biology - Is it correct that the body only responds to the most painful stimulus?

Your question statement is a little bit incorrect or, better say, imprecise.

First of all it is not clear what you mean by the "body response" here? Pain is sensed by peripherial receptors (several types of receptors, mostly purinergic, are assumed to play role in pain preception) and then this sensation is propagated into CNS. So, the local "response to pain" (like swelling, increase of the blood perfusion) is not the response to the pain stimulus, but rather a methabolic response to the cell injures and release of many humoral factors like interleukins, "wound hormones" etc.

And this is true that out of many different pain inputs the one with highest intensity seems to "outshine" all other inputs and ultimately the pain perception is constrained to a single body part. However, if you consciously focus your perception on other parts of your body you may be able to percieve the pain originating from these parts even if this pain is lower.

This principle is known as a smaller particular case of a more general principle known as "the dominance principle of Ukhtomsky". Wikipedia has only the Russian language version about this principle (as well as about Ukhtomsky, a prominent Russian physiologist) and it seems to be not really known outside of the Russian scientific community (this is the only page I found about him in English).

The more general principle of Ukhtomsky postulates the following: one certain input may lead to the formation of the dominance center in the cortex. The domaninace center is characterized by the higher level of nerve cell excitation, whereas the rest of the cortex undergoes an inhibition so that different, even unrelated inputs converge here, helping this center to exist for longer time. The only way how this center can be ceased is to form another dominance center by a extremely high stimulus (for example a startle sound). Here the most insensive pain leads to the formation of such a center and all substantial pain stimuli just contribute to the persistence of this center: the pain is however percieved to originate from the place where the first stimulus, responsible for dominance center formation, originated from.

zoology - Is there such thing as Animal non-verbal body language?

Have there been any studies done on the animal use of their bodies to signal, communicate or express their emotions, particularly to members of other species (ex: humans)?

I've been observing a very intelligent indoor-outdoor cat who has been doing the same sideways stretching posture every day he met me. There has been a number of other postures that the cat has been using - tearing at a carpet with claws, or dragging himself against the carpet by using claws that I've repeatedly observed.

Another cat was thumping her head against a door to "knock" and indicate that the cat is outside.

To me, these gestures appeared as clear expressions of intent or emotional state.

Other experiment involved "trained" geese at a local pond who would indirectly approach humans to ask for food. Their body, neck and head position appear to indicate intent (is the animal grazing towards the human or away from the human).

Yet another experiment involves nesting birds who start to clearly express their displeasure at me located near their nesting area. They repeatedly produce high pitched screech until I move away.

For example I repeatedly see geese assume this gesture to intimidate other geese.

As a human, I'm very conditioned to vocal and eye related coordination, and this "non-verbal" language is fascinating to me.

Have there been any studies in how indoor/outdoor - partially domesticated animals communicate with humans?

Is it true that this communication uses their entire body and not just the vocal cords?

Is there some "foundation" language that would be similar among members of the same species, or is it entirely a learned skill that has nothing to do with evolutionary adaptation?

Finally, is there some sort of a brain complexity cut off at which level the animals can no longer understand if they are being communicated with?

observation - why does venus flick?

Because planets actually do twinkle. Most people were told that the major difference between stars and planets is that only the former twinkle - but that's an oversimplification. Given the right conditions, planets will twinkle too, it just happens more rarely.

Several factors that contribute to it:

• lots of air turbulence; or, as astronomers call it, "bad seeing"




• closeness to horizon; if the planets are high in the sky, the air column is shorter so there's less chance they will twinkle; but when they are low, their light goes through more air and so it is perturbed to a larger degree

The observation you've made, Venus twinkling, is not very unusual. Many stargazers are used to seeing that once in a while. I've seen Venus scintillate several times in the past, always at sunset when it was about to drop below horizon; I would presume you could see the same behavior very early in the morning as Venus has just risen.

genetics - Origin, or source, of rhesus negative in human blood

This is my first post here, so please be gentle. I recently learned that I have Rh- blood (I'm A-), and was idly looking into blood types on Wikipedia. I was surprised to find that relatively few (~15% of all) humans have it, and most of those seem to be European. Looking just a little further, I found a bunch of crackpot-looking sites that try to explain how people got Rh- blood, and what weird abilities they possess as a result.

I managed to find one site that seemed at least less laughable, which suggested that interbreeding with Homo neanderthalensis (or possibly Homo sapiens neanderthalensis, since the site seemed to indicate that there was some question about how different H. s. sapiens were from H. neanderthalensis) might have accounted for the introduction of the condition.

It seems that from more reputable (medical) sources, the only difference between Rh+ and Rh- is that complications can arise during pregnancy if the mother is Rh- and the fetus is Rh+. Indeed, most sites (e.g., WebMD) seem to explicitly state that there are no other differences of note.

I am not a biologist, or an anthropologist, or a life-science kind of guy at all. However, as a computer scientist, I like to think that I have both an open mind but one which demands scientific and/or logico-mathematical evidence for claims. Lots of the pseudo-scientific, paranormal, etc. theories on the web I basically dismiss out of hand, as explanations which are almost certainly fantasies, but most definitely baseless and untestable.

My question:

What, if any, is the current scientific understanding of the origin, or source, of rhesus negative blood in human beings? Do individuals with Rh- blood have any common (in a statistically significant sense) characteristics or health issues, aside from the issue with pregnancy and tending to be more European than not? Is there anything to continuing to look into this?

For context, I got started down this rabbit hole while looking into different dieting strategies, and found the "blood type diet". Just as an aside, I don't think there's a lot of merit to that diet... sounds like a fad thing. Any sources or information or help on this subject are appreciated.

EDIT:

I have been looking a little more, and I stumbled across a paper entitled, "The influence of RhD phenotype on toxoplasmosis and age-associated changes in personality profile of blood donors" which looks at the effect of the Rh- trait on personality changes caused by toxoplasmosis (if you Google the title, you should be able to download). Using Cloninger's and Cattel's personality factors, they seem to show a variety of things, including (a) personality differences between Rh+ and Rh- individuals not affected by toxoplasmosis, and (b) different reactions to prolonged toxoplasmosis affection in Rh+ and Rh- individuals.

I didn't even know that parasites could affect your behavior; that seems frightening on the one hand, but on the other, it's fascinating if it's for real, especially since the incidence of toxoplasmosis is not insignificant in most people. Anybody who knows anything about this or who reads the paper and can help me understand what it's saying would be doing me a great favor to answer/comment/chat. Thanks!

galactic dynamics - Is the motion of the Sun around the Galaxy a result of gravitational pull?

I would say the answer to your question is yes and no. Yes that the orbit of our Sun in the Milky Way is due solely to gravitational forces as you suggest, but no in that they are not all radial towards the center of the galaxy.

The motion of the Sun around the center of our galaxy can be broken into two motions. The first is an "azimuthal" orbital motion around the center of the galaxy due to radial gravitational forces from mass interior to our orbit (be it stars, gas/dust, dark matter, dragons, etc.). The other type of motion is an oscillation into and out of the plane of the milky way. This is also caused by gravitational forces, albeit not radial forces from the center of the milky way. As the sun moves "above" the plane of the Milky Way, there is more mass below than above and it gets pulled "down". When it is in the plane it has residual energy from "falling down" and continues to fall "below" the plane where it then gets pulled back "up". This type of oscillatory motion is constant and analogous to a mass on a spring.

botany - How do trees manage to grow equally in all directions?

There are some other good answers which provide part of the picture, but I think there is a fundamental organising principle which has been missed. Konrad has touched on it in his answer.

The reason trees, and most plants, tend to grow equally in all directions is that they have iteratively generated branching and radial symmetry which is controlled in a feedback loop of the growth promoting hormone auxin and auxin-sensitive auxin transporters. This is an elegant biological algorithm which explains all branching growth.

The things Konrad identifies (phototropism, gravitropism, etc.) serve as orientation cues which help the plant determine which axes to grow along, but fundamentally the process is about auxin gradients. There are exceptions, as others have pointed out in their answers, and they usually result from severe imbalances in the orientation cues.

I'll try to explain the growth process clearly (and it gives me an opportunity to try my hand at diagramming again ^_^)...

---

Auxin is a plant hormone (actually a class of hormones, but mostly when people say auxin, they mean indole-3-acetic acid) which promotes cell elongation and division. The basic principle which allows auxin to act in the organising way it does is that auxin is produced inside cells, and proteins which export auxin from a cell develop on the side of the cell which has the highest auxin concentration (see figure below).

So auxin gets transported up the concentration gradient of auxin! Thus if you get an area of high auxin concentration developing somehow, more auxin is then transported towards that area. An area of high auxin concentration relative to the surrounding tissue is called an auxin maximum (plural 'maxima').

For most of the life of the plant, auxin is produced pretty much equally in most cells. However, at the very early stages of embryo development, it gets produced preferentially along the embryonic axis (see figure below, part 1). That creates a meristem - a group of cells where cell division is taking place - at the auxin maximum at each end of the embryo. Since this particular meristem is at the apex of the plant, it is called the apical meristem, and it is usually the strongest one in the plant.

So by having a meristem at each end, the embryo then elongates as cell division is only taking place at those points. This leads to part 2 of the image above, where the two meristems get so far apart that the auxin gradient is so weak as to no longer have its organising effect (area in the red square). When that happens, the auxin produced in cells in that area concentrates in a chaotic way for a short time until another center of transport is created. This happens, as the first one did, when a particular area of the tissue has a slightly higher concentration of auxin, and so auxin in the surrounding tissue is transported towards it. This leads to part 3 of the figure, in which two new meristems are created on the sides of the plant (called lateral meristems).

Lateral meristems are where branches occur on plants. If you then imagine this process continuing to iterate over and over, you will see that the branches, as they elongate, will develop meristems at the tips and along the sides. The main stem will also continue elongating, and develop more lateral stems. The root will begin to branch, and those branches will branch, etc. If you can understand how this elegant system works, you understand how plants grow, and why they grow in repeating units as opposed to in a body plan like animals.

It also explains why, if you cut off the tip of a stem, it promotes branching. By removing the apical meristem, you get rid of the auxin gradient and enable the creating of multiple smaller meristems which each develop into branches.

So far I've explained regular branching, but the same system causes the radial symmetry which makes trees (usually) grow in all directions equally...

Imagine taking a cross section through a stem and looking down all the way through it (as depicted crudely above). Just as auxin gradients act to coordinate growth along the length of the plant, they also coordinate it radially, as the maxima will tend to space themselves out as far from one another as possible. That leads to branches growing in all directions equally (on average).

I welcome comments on this answer, as I think its so important to understanding plant growth that I'd like to hone my answer to make it as good as possible.

Mini black holes, a possible result of the LHC experiment at CERN

Mini black holes are thought not to exist, so it's an unlikely idea anyway, and Hawking Radiation is largely accepted (but I think, not proven) . . . so maybe, "what if" concerns very unlikely but slightly valid, but there's also this:

We get particle collisions faster than Cern can produce in our upper atmosphere every day. If there was any danger of high energy collisions, We'd have likely observed it already either in our atmosphere or by Hubble. The fact that high energy collisions happen every day on every planet, every good sized moon and every star in the galaxy suggests that high energy collisions don't form into matter eating strangelets or tiny but hungry black holes. If they did, we'd have seen some evidence of that.

So we have both very strong observational evidence as well as theoretical evidence. CERN isn't playing with particle energy that doesn't happen - it happens all the time in space.

Just for fun - the Oh-my-god particle, way more energy energy than anything that happens in CERN: http://en.wikipedia.org/wiki/Oh-My-God_particle

rotation - Earth-Centered Earth-Fixed coordinates with respect to heliocentric coordinate system at vernal equinox

I am trying to calculate the position of a point on the Earth's surface with respect to the Sun's center at certain date at time.
For what I am trying to do it is OK to ignore precession of Earth's orbit and precession, nutation and polar motion of the rotating Earth.

Lets say that I have coordinate system centered at the Sun $X,Y,Z$, where the $X$ axis points at the point of vernal equinox, the $XY$ plane is the plane of Earth's orbit around the Sun, the $Z$ axis pointing toward the ecliptic north pole and then $Y$ completes the right-handed system.

So far I've been able to find the following orbital elements at the epoch J2000:

$a=1AU$ - major radius

$bar{lambda_0}=100.47^circ$ - mean longitude at epoch

$e=0.01673$ -eccentricity

$I=0^circ$ - inclination to the ecliptic

$bar{omega}=102.93^circ$ - longitude of perihelion

$T=1yr$ - orbital period

$frac{m}{M}=3.039times 10^{-6}$ - planetary-solar mass ratio

Now knowing this I could determine the orbit of the Earth at certain date, however I am unable to determine Earth's orientation.
Lets say that we have ECEF coordinate $x,y,z$ system centered at Earth's center of mass with the $z$ axis pointing toward the north pole (we can assume that it coincides with Earth's rotational axis), the $x$ axis pointing toward the intersection of the prime meridian and the equator and then $y$ completing the right-handed system.

At the point of vernal equinox by definition the equatorial plane crosses the center of the sun.Knowing this and the axial tilt of $~23.44^circ$ of the Earth's rotational axis I can determine the $z$ axis and $xy$ plane with respect to $X,Y,Z$ coordinates but I cannot determine the exact positions of $x$ and $y$ axes which I need.

I searched a lot for data showing me the orbital elements at certain epoch AND the exact orientation of the Earth ($x,y,z$ coordinates expressed as $X,Y,Z$ at the vernal equinox) so that I can use it for my calculations but I didn't succeed. From all the things that I found I am still unable to tell what the orientation of the Earth is at certain point so I can't really determine the position of certain point on its surface at certain time with respect to the Sun.

I assume that I am missing something or that I have some fault in my approach since I am complete noob at astronomy and I've never dealt with this before I had to find a way to perform this calculation. I will take any suggestions if there is a better way to solve the initial problem that I am trying to solve or if there is a place where I can find the data that I need.

general relativity - Understanding gravity

The magnitude of the force of gravity between two bodies is proportional to the product of their masses:
$$F=Gfrac{m_1m_2}{r^2}$$
This doesn't change depending on which body you're applying the force to, i.e. if you interchange the masses. The magnitude is the same.

What does change is the direction of the force. Force is a vector quantity, denoted as $vec{F}$ or $mathbf{F}$. If we write the equation for gravity using proper vector notation, we have
$$mathbf{F}=Gfrac{m_1m_2}{|mathbf{r}_1-mathbf{r_2}|^2}frac{mathbf{r_1}-mathbf{r_2}}{|mathbf{r_1}-mathbf{r_2}|}$$
Here, the positions of the objects are represented by vectors, $mathbf{r}_1$ and $mathbf{r_2}$. Additionally, $|mathbf{x}|$ denotes the norm of a vector $mathbf{x}$ - its magnitude.

Now, if you interchange the masses, the direction of the force changes, although $|mathbf{r_1}-mathbf{r_2}|=|mathbf{r_2}-mathbf{r_1}|$, because this refers to the magnitude of the vectors. So the force applied on one object is the opposite of the force applied on the other object. This is Newton's third law.

The acceleration is more interesting. The force on object $1$ due to gravity is
$$F_1=m_1g_1$$
Here,
$$g_1=frac{Gm_2}{r^2}$$
where $m_2$ is the other mass. This should tell you that $g_1neq g_2$, except when $m_1=m_2$.

I'm not an expert in general relativity, but I do know that it describes how spacetime curves due to the presence of one body. The solution to the Einstein Field Equations, the metric, is different for different bodies, because one piece of it, the stress-energy tensor, is different for objects of different mass/energy/etc.

evolution - Homologies to insect wings

Insects and vertebrates are extremely distantly related: they're on opposite sides of the oldest split among bilaterally symmetric animals. Their most recent common ancestor lived in the pre-cambrian and was almost certainly worm-shaped with no limbs at all. There's no way that insect wings are homologous to any body parts of vertebrates.

The evolution of insect wings is a somewhat difficult topic, because it happened 350 million years ago in animals that do not fossilize well. Wikipedia discusses several possible theories for what parts of non-winged insects are homologs of insect wings. Currently the situation does not seem to be resolved.

tidal forces - Terminology: Is there a name for the points on the surfaces of tidally locked parent/satellite bodies that always face each other?

For tidally locked binary stars, the two points in question are known as the substellar points.

For a tidally locked exoplanet, the point closest to the star would also be known as the substellar point. If the star was also tidally locked to the planet, then there would be a subplanetary point.

For a moon locked to a planet, the point on the moon would also be the subplanetary point. If the planet was mutually locked, it would have a sublunar point (not sure whether this latter only applies to the Earth's moon).

genetics - How is eye color in humans inherited?

In high school we studied the inheritance of eye color, as it was explained to us in the most simple way: blue eye color is a recessive, monogenic, autosomal trait. Now I know that it is a bit more complicated than that; there are several genes which determine the inheritance of eye color. That's as far as I my knowledge goes.

Which are these genes and what do they encode for? How is the eye color trait inherited? Provided that a man with blue eyes and a woman with brown eyes have a child, can the probability of their child to have blue eyes be calculated?

planet - Where is Mars in the night sky

At that time (20:50), and that location (Houston, Tx), Mars was closer to the horizon.
You can see that in the sky-chart provided by heavens-above.com (attached below).

I cannot tell what's the other object you describe, but if you are not sure whether something is a planet or a star, the planets doesn't twinkle whether the star does.