I considered it, but the problem is that the terrestrial planets are small, and they live deep in the Sun's gravity well. They aren't really big enough to toss each other out completely. So after an instability they either want to collide with each other or the Sun. The problem with an excitation that leads to a solar collision, is that you leave the remaining system in a state of instability. A collision between two proto-Venii solves this by decoupling Earth from the dynamics of the precursors. I can easily end up with solar systems that dynamically resemble our own, and I'm not sure that a solar collision would do that. But I'm still looking into it. I'm also fascinated by the apparent young, yet uniform, age of the surface of Venus.
I need you to provide an overwhelming body of evidence for this assertion, otherwise the rest of your argument it based on nothing.
First, the Faint Young Sun Paradox is not my idea. The first paper to point out the problem was written by Carl Sagan and George Mullen back in 1972, but the idea that stars steadily rise in luminosity as they age is older than that, and it is a very well established outcome of our understanding of how stars work. Basically as a main sequence star converts H->He in its core, the density of the core increases over time, which causes the core's pressure to increase in order to keep the star in hydrostatic equilibrium, and its luminosity rises as a consequence of the higher nuclear reaction rates in response.
Secondly, you need to provide some metric as to the magnitude of the "faintness" for the early sun.
An approximate functional form of the luminosity as a function of time is given by Gough (1981, Solar Physics) L=1/(1+0.4*(1-t/4.5e9))*3.9e33 erg/s (where t is given in units of years). This form, while an approximation, has been well matched by computer simulations of solar evolution, and is well matched by observations of stars on the main sequence.
And thirdly you need to show a clear (and backed by evidence) timeline for your faint early sun, the formation of the Earth, and then all of the historical data (geologic record) we have for the Earth.
Based on measurements of the partitioning of the elements Hafnium and Tungsten in rocks from the Moon mantle we can date when the giant impact that formed the Moon occurred. You can read more here. Basically Earth completed its formation in less than 100 million years after the start of the solar system, about 4.57 billion years ago. The earliest minerals on the Earth are zircon crystals that form in continental crust, which are dated to at least about 4.3 billion years ago, and seem to indicate formation on a planet with liquid water oceans on the surface. The earliest whole rocks on the surface are about 3.8 billion years ago. Plate tectonics has a tendency to recycle and destroy rocks, but nevertheless geologists have been able to identify several locations where very ancient bits of the Earth are still preserved. The Faint Young Sun Paradox is about the time from about 4.3 billion years ago to the Archean/Proterozoic boundary at about 2.5 billion years ago, or about 2 billion years after the formation of the Earth.
For the Earth to be moving away from the sun it must be gaining energy to "climb the gravitational well" from the sun. Have you done the calculations for this? Do you have a plausible source (and transfer mechanism) for this energy?
The mechanism by which Earth gets its orbit raised is by a corresponding decrease in the orbital distance of a hypothetical Venus-precursor body. Yes, I did those calculations. That was the point of the talk this article is about.
Finally, I saw a talk a couple of months ago by a world leading expert in N-body solar system simulations.
The person you describe sounds an awful lot like Jacques Laskar. Yes, I am aware of his work, and in fact it was that result that you describe that inspired me to try my hypothesis out.
Don't let my criticism get you down.
I won't
Keep going with your work, just dig deeper and be sure to always present a clear line of reasoning from what is established, to what you are claiming
Your mistake is a common one that I find in places like Slashdot and other online communities. The bulk of scientific discussion and debate takes place in the peer reviewed literature. It's what it's designed for, and for all its flaws, it works quite well. People often mistake articles written in the popular press, such as TFA, as accurately reflecting the science. Unfortunately by their nature these kinds of articles
No, the asteroid belt was never a planet. We receive pieces of the asteroid belt in the form of meteorites, and most of those meteorites basically reflect a well-mixed sample of the same kinds of things that the Sun is made out of (minus all the gas), which hints that they are samples of the solid component of the solar nebula that the Sun formed out of. If they were a part of a planet, the planet would have differentiated into a core and a mantle, so would not reflect the "primitive" composition of the solar nebula. The asteroid belt is thought of a s a place where planet formation was halted very early on (likely due to the gravitational influence of the formation of nearby Jupiter), and was cleared out of most mass before it had a chance to combine to make planets. The combined mass of the asteroid belt is quite small, only about 5% the mass of the Moon.
No, those weren't considered because their effect is so tiny. In other work I do, I consider radiation forces as they pertain to the orbits of small bodies, such as asteroids. The most important of these is the Yarkovsky effect (non-isotropic radiation of thermal photons), which can change the orbits of small asteroids, but the effect diminishes as the size of the body increase. For objects greater than about 10-20 km in diameter in the inner solar system, the Yarkovsky effect isn't important over the age of the solar system.
Hi, good questions. The time period relevant to this is the Archean. The interior of the Earth was warmer back in the Archean than it is now, and there may have been more volcanic activity, but it's difficult to know what style of tectonics was operating at the surface. Very few rocks survive from that time period. Now one proposed solution to the Faint Young Sun problem was just that there was a lot more CO2 in the atmosphere. The subject of a few talks at this workshop a couple weeks ago was constraining the abundance of atmospheric CO2 from looking at the chemistry of the few rocks we have from that epoch. There were some presentation suggesting that the atmosphere contained no more than about 20x the present abundance of CO2, but you may need more like 100-1000x in order to completely solve the problem. So people have suggested things like more CH4, NH3, and also that perhaps the Earth was somewhat darker due to different styles of cloud-making and fewer continental land masses (oceans are quite dark), meaning that the surface did not reflect back as much radiation as it does now. All of these ideas are being actively debated.
Now as to the question of meteor bombardment: that was the topic of the last 1/3 of my talk at the workshop, but was not mentioned in TFA. I am on a paper coming out in a couple of weeks that is showing that the so-called Late Heavy Bombardment persisted on the Earth all throughout the Archean, rather than ending abruptly at the end of the Hadean, as was thought from looking at lunar samples. The bombardment rate, while much higher than present-day, was not so high as to likely have had any major direct effect on the climate over geologically interesting timescales (say an impact creating a 1000 km wide basin occurring every 200-500 million year during the Archean). However, there may have been indirect effects of impact bombardment that have yet to be explored, and we find that it is an interesting coincidence that bombardment rate pretty much drops off completely by the early Proterozoic, just as Earth began to show signs of having some oxygen in the atmosphere, and the first real evidence for any kind of major glaciation events (the Huronian snowball). Could somewhat elevated impact bombardment rate be a controlling factor in the warm and anoxic Archean? I don't know the answer to that, but were studying it.
The problem is not Earth's stability, it's Mercury's. Mercury is close to a so-called secular resonance, and it's eccentricity varies more chaotically than Earth or Venus. So yes, Earth would remain bounded indefinitely as long as Mercury never attains a high enough eccentricity that it begins crossing into Venus's orbit. Once close encounters take place with Mercury, the whole inner solar system can rapidly destabilize.
That was the subject of my 2007 paper. The problem is that the present-day mass loss rate of e Sun due to solar wind and coronal mass ejections is tiny. The Sun loses more mass do to the conversion of mass to energy in the core, and it's not enough to appreciably change the mass of the Sun over the age of the solar system. Young Sun-like stars appear to have stronger stellar winds, correlated with their higher rotation rate. But the Sun would have had to sustain orders of magnitude higher mass loss than present-day winds for its first 2 1/2 billion years on the main sequence, and this does not appear to match measured mass loss rates of nearby Sun-like stars of those ages.
During the Archean, the time period relavant to this study, tidal heating was not terribly important. The larger internal heat from radioactive decay was higher, yet still dwarfed by the energy input from the Sun in setting the surface temperature of the Earth.
Ah, so here's the deal. I'm the person that this article is talking about (David Minton, professor at Purdue University). I've been reading Slashdot for a fair number of years now, though it took me a long time to sign up and comment for the first time (I've always been a lurker at heart). Because I have a soft spot for all you basement dwellers (I kid!), I'm going to give you a bit of behind the scenes regarding this article, which kind of took me by surprise, actually. This is a bit long, so TL;DR: Science sometimes happens during panicked last minute coding sessions in hotel rooms prior to delivering invited talks that were procrastinated about.
So about five years ago my graduate school advisor and I wrote what was my very first peer-reviewed paper, which was on the subject of the Faint Young Sun Paradox. The paradox goes something like this: The early Sun was fainter than it is today, so all things being equal the Earth should have spend the first half of its life frozen over. Geologists tell us it wasn't, so something wasn't equal. What was it? We investigated the idea that the Sun may have been slightly more massive (something like 2-7% more massive), and that it had to lose most of that excess mass over a few billion years, which is at odds with measurements of mass loss of Sun-like stars. So we published it, and I went on to do other things in grad school, mostly involving trying to figure out the early impact bombardment history of the solar system, which we think may have been influenced by an early period of migration of the gas giant planets.
Fast forward to a few months ago, and a fellow at the Space Telescope Science Institute (the place they run the Hubble from) contacted me to ask if I'd like to give a talk about my old mass-losing Sun paper at a workshop that was planned to bring together astrophysicists, geologists, climate scientists, and planetary dynamicists to talk about the Faint Young Sun problem. They wanted me to also talk about planet migration and how that might fit in to the problem. Sure, why not? Revisiting the problem would be fun! The thing is, I've just started a new faculty job, and part of my job is helping get a new planetary science group built up at Purdue, so I've been extremely busy. And, well, I procrastinated. Big time. There was always some pressing thing to do that took time away from getting ready for the workshop. So the next thing I know, it's a few days before the meeting and I still haven't really thought about the faint Sun in about five years. So I dust off my old files, start futzing around with a talk, and the next thing I know I'm on a plane to Baltimore.
Late the night before the workshop is about to start, I'm racking my brain trying to come up with something new to say. You see, I've been thinking about early solar system history, and planet formation. Migration is a big deal in those early days. It's easy to get planets to move around in young solar systems. But the Faint Young Sun problem is a problem for the Earth's mid-life, not it's adolescence. Then I remembered a paper I really liked that came out a couple of years ago by Jaques Laskar and Mickaël Gastineau. They showed that our own solar system could potentially destabilize after a few billion years of seeming-stability due to Mercury's proximity to a chaotic region. It's described briefly here: http://en.wikipedia.org/wiki/Stability_of_the_Solar_System#Laskar_.26_Gastineau
What if something like that had happened *already?* So I futzed around with an N-body gravitational dynamics code remotely from my hotel room, in my pajamas, playing around with plausible initial solar systems where Earth stared just a tad closer to the Sun, but close enough to solve the problem of being frozen over, and Venus started out as two separate planets and then went unstable after many billions of years, scattering Earth to its present location in the process. And, when I checke
Actually, more than a dozen "Hubble space telescopes" were built and launched into orbit. The biggest differences are that they point at the Earth instead of away from it, and they are called KH-11 instead of HST. Oh, and their imagery data is mostly classified.
Considering that out of the 150,000 stars, there are 1200 planetary systems that are both oriented such that the planets pass directly in front of their stars as seen from our solar system, and did so over a period of about 4 months, that's a *very* good ratio.
The whole point of Kepler is to gather statistics on planetary systems. There's no need to wait 20 years. Trend lines are being plotted now.
I would guess that some of the data is submitted monthly and the tracts show when the data was submitted, not necessarily observed. there's also a lot of big pulses early on, far larger than the overall rate would see to indicate as within the normal deviation of observation rate at that point. hence, the thought that it's mapping based on submission date and some are submitting bulk results on a monthly or quarterly basis.
Well, to an astrophysicist "roughly 12 times" is equivalent to 13 times, but your point is taken. I've sat in with the Catalina guys (on a nearly full moon night, so they didn't discover anything while I was there), and they don't wait to submit data. They send candidate objects to a followup telescope to confirm the discovery, then publish any object with the Minor Planet Center as soon as they are confirmed. They need to act quickly, because orbit refinements often rely on followup observations (often by amateur astronomers), and many objects, especially Near Earth Asteroids, could be lost if they are not followed up quickly. The big pulses in the discovery rates at early times are because objects were only discovered in sensitive surveys that were not run very frequently (and before the mid 1990s usually relied on photographic plates). After about 1997 once LINEAR got going (and later Catalina and a couple others) asteroid surveys have more or less been continuous, with lulls arising due to full moon nights and the weather patterns of southern Arizona and New Mexcio.
You'll also notice that the discovery rate seems to "pulsate" with a period of about 12 times per year (this is most obvious in the 2000s when the discovery rate was mostly uniform throughout the year). I'll leave it as an exercise to the reader to explain why that is (hint, skies need to be very dark to observe faint asteroids).
That comes from the WISE mission: http://wise.ssl.berkeley.edu/mission.html
WISE is a whole sky infrared survey that happens to pick up asteroids. The spacecraft spins to survey a complete arc of sky roughly perpendicular to the Sun direction.
You'll also notice that during much of the 2000s, there is a gap in discoveries at about the 5 o'clock position. This corresponds to monsoon season in the southwest U.S. (roughly July to mid September). Most of the discovered asteroids in the past decade were made by the Catalina Sky Survey, based just outside of Tucson, AZ, and they generally don't bother observing during monsoon season because of the increase in cloud cover.
Ugh. Every time one of these stories comes up, someone has to bring up Velikovsky. As someone who studies early solar system evolution, I've had the "pleasure" of talking with Velikovsky supporters on numerous occasions. What Velikovsky wrote about was wide-scale rearrangements of the architecture solar system WITHIN HISTORICAL TIMES, based on nutty interpretations of classical mythology. What the article here discusses is a hypothesis for the formation of Triton during an event called the Nice model that is thought to have happened about 3.9 billion years ago (based on dating of large lunar basins from Apollo samples). During this time, a much more massive precursor to the Kuiper belt fueled the migration of the outer four giant planets, disrupting stable reservoirs of small bodies throughout the solar system. Once the ancient Kuiper belt was depleted of mass, the migration stopped (so the "fuel" is gone, and therefore this process can only occur once in the lifetime of the solar system). Had planetary migration occurred within historical times, then we would currently be in the midst of a massive bombardment of comets and asteroids, and the Earth's oceans would currently reside in the atmosphere (along with perhaps some rock vapor clouds).
The Nice model and Late Heavy Bombardment is backed up by observations of the structure of the Kuiper belt, observations of other solar systems around other stars, radioisotope dating of lunar rocks (in a variety of isotope systems, but most especially K-Ar, and U-Pb), observations of the structure of the asteroid belt, dynamical models based on plausible initial conditions for the early solar system (constrained by aforementioned observations), observations of zircon crystals found in ancient Earth rocks, cratering chronologies of the rocky planets, the Moon, and icy satellites. Basically it's a preponderance of evidence pointing toward plausible models for the early history of the solar system. Velikovsky has tortured interpretations of ancient literature. Who do you think is more likely to be closer to describing reality?
Wow, an astounding amount of ignorance is on display in this post.
Near Earth Asteroids (NEAs, or NEOs if you prefer) may indeed be easier to visit than the Moon, and they are quite a bit easier to visit than Mars. Mainly this is due to the lack of appreciable gravity, so that the escape velocity from the surface adds only a negligible delta V to the total delta V budget required (for both landing and taking off again).
You're not going to find yourself on a 100+ year orbit on an NEA. If you did find yourself on a 100+ year orbit and on on your way out of the inner solar system, then, by definition, you would have landed on a Halley-type comet (or perhaps even a long-period comet if you were *really* on your way out).
Take as a typical NEA 433 Eros. The NEAR spacecraft successfully landed on it, despite the fact that the spacecraft was designed to be an orbiter (which, I think, succinctly illustrates how easy it is to land on an asteroid). Its perihelion distance (closest approach to the Sun) is 1.13 AU (1 AU is the Earth-Sun distance) and has a period of a bit less than 2 years.
Once nice thing about asteroids is that they basically represent remnants of the original solar nebula from which planets were formed, and most of them never differentiated (melted and formed iron cores and rocky mantles). That means that they are relatively rich in many raw materials compared to the surfaces of planet-sized bodies. A carbonaceous asteroid contains valuable metals (often as little blobs of pure metal), water (up to 30% by weight in many cases), and organics (kerogen). Some other asteroids are nothing but metal, and would require very minimal processing to make them useful (unlike many ores found on Earth).
Going to asteroids makes a lot of sense. The main difficulty with an asteroid vs. a lunar mission is that the mission length to an asteroid would be longer than one to the Moon (although depending on the asteroid, it could be much shorter than a Mars trip).
It is actually quite possible that Charon formed in exactly the same way as the Earth-Moon system. See this abstract.
Most modern planet formation simulations show that the end stage of formation involves collisions between large proto-planets. Whether or not any particular giant collision results in a satellite or not depends on the details such as impact velocities and angles. Double bodies such as Earth-Moon and Pluto-Charon are likely to be relatively common outcomes given what we know of planet formation.
OK, I could ben wring about it being a captured object. But does giant planet migration address the orbit of Eris being 44 degrees tilted compared to the other planets and the like? It isn't entirely understood how Kuiper Belt objects were given high inclinations. Simulations of giant planet migration generally fail to pump up the inclinations of enough objects high enough to match the observations. One idea is that the Kozai mechanism is able to trade off eccentricity for inclination, but it is not clear why this wouldn't show up in the numerical simulations. There also seems to a correlation between KBO inclination and size. Big KBOs like Pluto and Eris seem to have higher inclinations on average than smaller ones. It is not at all clear why there would be such a correlation. This is an active area of research in planetary dynamics.
Pluto is nothing if not very different from every other planet or that matter all the known bodies in the solar system. Except for the Plutinos, which are similar to Pluto in that they are all in 3:2 mean motion resonance with Neptune. Plutinos are themselves just one of several collections of resonant Kuiper Belt objects (the "Twotinos" at the 2:1 resonance being another). The resonant population is just a subclass of the Kuiper Belt, which itself contains other large objects like Eris, Sedna, and many more.
Pluto the 2nd largest of the as yet discovered Kuiper Belt objects. It is also the largest Plutino. In addition it is the 2nd largest known dwarf planet. I'm not sure why Pluto needs yet another classification category. It is certainly not justified on grounds of uniqueness.
IIRC it is a kuiper belt object that actually isn't on the same plane as the other planets.
I think I actually recall it being found by accident because it isn't where we would expected it to be, most likely it is a captured object not formed by our suns accretion disk. It is unlikely that any of the Kuiper Belt objects were captured from somewhere else. The Kuiper Belt is thought to have formed from the same accretion disk that formed the planets. However, it is thought that the original Kuiper Belt contained far more material than it does today, and that the objects were in more circular and coplanar orbits than we find them today. Due to an episode of giant planet migration, this original disk was scattered and depleted.
Many (but not all) of the observed dynamical features of the Kuiper Belt can be explained by giant planet migration.
Eris, which measures about 70 miles wider than Pluto, is the farthest known object in the solar system at 9 billion miles away from sun. Eris is not the farthest known object in the solar system. It is a member of the "scattered disk," a subclass of Kuiper Belt objects (KBOs). It is the largest scattered disk object (SDO) discovered so far, but by no means the farthest away. This article has some nice diagrams that show the location of Eris relative to other known SDOs. There is another subclass of KBOs, called the "detached" objects, that are even further away. Sedna is a member of this family.
Slashdot Mirror
I considered it, but the problem is that the terrestrial planets are small, and they live deep in the Sun's gravity well. They aren't really big enough to toss each other out completely. So after an instability they either want to collide with each other or the Sun. The problem with an excitation that leads to a solar collision, is that you leave the remaining system in a state of instability. A collision between two proto-Venii solves this by decoupling Earth from the dynamics of the precursors. I can easily end up with solar systems that dynamically resemble our own, and I'm not sure that a solar collision would do that. But I'm still looking into it. I'm also fascinated by the apparent young, yet uniform, age of the surface of Venus.
I need you to provide an overwhelming body of evidence for this assertion, otherwise the rest of your argument it based on nothing.
First, the Faint Young Sun Paradox is not my idea. The first paper to point out the problem was written by Carl Sagan and George Mullen back in 1972, but the idea that stars steadily rise in luminosity as they age is older than that, and it is a very well established outcome of our understanding of how stars work. Basically as a main sequence star converts H->He in its core, the density of the core increases over time, which causes the core's pressure to increase in order to keep the star in hydrostatic equilibrium, and its luminosity rises as a consequence of the higher nuclear reaction rates in response.
Secondly, you need to provide some metric as to the magnitude of the "faintness" for the early sun.
An approximate functional form of the luminosity as a function of time is given by Gough (1981, Solar Physics) L=1/(1+0.4*(1-t/4.5e9))*3.9e33 erg/s (where t is given in units of years). This form, while an approximation, has been well matched by computer simulations of solar evolution, and is well matched by observations of stars on the main sequence.
And thirdly you need to show a clear (and backed by evidence) timeline for your faint early sun, the formation of the Earth, and then all of the historical data (geologic record) we have for the Earth.
Based on measurements of the partitioning of the elements Hafnium and Tungsten in rocks from the Moon mantle we can date when the giant impact that formed the Moon occurred. You can read more here. Basically Earth completed its formation in less than 100 million years after the start of the solar system, about 4.57 billion years ago. The earliest minerals on the Earth are zircon crystals that form in continental crust, which are dated to at least about 4.3 billion years ago, and seem to indicate formation on a planet with liquid water oceans on the surface. The earliest whole rocks on the surface are about 3.8 billion years ago. Plate tectonics has a tendency to recycle and destroy rocks, but nevertheless geologists have been able to identify several locations where very ancient bits of the Earth are still preserved. The Faint Young Sun Paradox is about the time from about 4.3 billion years ago to the Archean/Proterozoic boundary at about 2.5 billion years ago, or about 2 billion years after the formation of the Earth.
For the Earth to be moving away from the sun it must be gaining energy to "climb the gravitational well" from the sun. Have you done the calculations for this? Do you have a plausible source (and transfer mechanism) for this energy?
The mechanism by which Earth gets its orbit raised is by a corresponding decrease in the orbital distance of a hypothetical Venus-precursor body. Yes, I did those calculations. That was the point of the talk this article is about.
Finally, I saw a talk a couple of months ago by a world leading expert in N-body solar system simulations.
The person you describe sounds an awful lot like Jacques Laskar. Yes, I am aware of his work, and in fact it was that result that you describe that inspired me to try my hypothesis out.
Don't let my criticism get you down.
I won't
Keep going with your work, just dig deeper and be sure to always present a clear line of reasoning from what is established, to what you are claiming
Your mistake is a common one that I find in places like Slashdot and other online communities. The bulk of scientific discussion and debate takes place in the peer reviewed literature. It's what it's designed for, and for all its flaws, it works quite well. People often mistake articles written in the popular press, such as TFA, as accurately reflecting the science. Unfortunately by their nature these kinds of articles
No, the asteroid belt was never a planet. We receive pieces of the asteroid belt in the form of meteorites, and most of those meteorites basically reflect a well-mixed sample of the same kinds of things that the Sun is made out of (minus all the gas), which hints that they are samples of the solid component of the solar nebula that the Sun formed out of. If they were a part of a planet, the planet would have differentiated into a core and a mantle, so would not reflect the "primitive" composition of the solar nebula. The asteroid belt is thought of a s a place where planet formation was halted very early on (likely due to the gravitational influence of the formation of nearby Jupiter), and was cleared out of most mass before it had a chance to combine to make planets. The combined mass of the asteroid belt is quite small, only about 5% the mass of the Moon.
No, those weren't considered because their effect is so tiny. In other work I do, I consider radiation forces as they pertain to the orbits of small bodies, such as asteroids. The most important of these is the Yarkovsky effect (non-isotropic radiation of thermal photons), which can change the orbits of small asteroids, but the effect diminishes as the size of the body increase. For objects greater than about 10-20 km in diameter in the inner solar system, the Yarkovsky effect isn't important over the age of the solar system.
Hi, good questions. The time period relevant to this is the Archean. The interior of the Earth was warmer back in the Archean than it is now, and there may have been more volcanic activity, but it's difficult to know what style of tectonics was operating at the surface. Very few rocks survive from that time period. Now one proposed solution to the Faint Young Sun problem was just that there was a lot more CO2 in the atmosphere. The subject of a few talks at this workshop a couple weeks ago was constraining the abundance of atmospheric CO2 from looking at the chemistry of the few rocks we have from that epoch. There were some presentation suggesting that the atmosphere contained no more than about 20x the present abundance of CO2, but you may need more like 100-1000x in order to completely solve the problem. So people have suggested things like more CH4, NH3, and also that perhaps the Earth was somewhat darker due to different styles of cloud-making and fewer continental land masses (oceans are quite dark), meaning that the surface did not reflect back as much radiation as it does now. All of these ideas are being actively debated.
Now as to the question of meteor bombardment: that was the topic of the last 1/3 of my talk at the workshop, but was not mentioned in TFA. I am on a paper coming out in a couple of weeks that is showing that the so-called Late Heavy Bombardment persisted on the Earth all throughout the Archean, rather than ending abruptly at the end of the Hadean, as was thought from looking at lunar samples. The bombardment rate, while much higher than present-day, was not so high as to likely have had any major direct effect on the climate over geologically interesting timescales (say an impact creating a 1000 km wide basin occurring every 200-500 million year during the Archean). However, there may have been indirect effects of impact bombardment that have yet to be explored, and we find that it is an interesting coincidence that bombardment rate pretty much drops off completely by the early Proterozoic, just as Earth began to show signs of having some oxygen in the atmosphere, and the first real evidence for any kind of major glaciation events (the Huronian snowball). Could somewhat elevated impact bombardment rate be a controlling factor in the warm and anoxic Archean? I don't know the answer to that, but were studying it.
The problem is not Earth's stability, it's Mercury's. Mercury is close to a so-called secular resonance, and it's eccentricity varies more chaotically than Earth or Venus. So yes, Earth would remain bounded indefinitely as long as Mercury never attains a high enough eccentricity that it begins crossing into Venus's orbit. Once close encounters take place with Mercury, the whole inner solar system can rapidly destabilize.
That was the subject of my 2007 paper. The problem is that the present-day mass loss rate of e Sun due to solar wind and coronal mass ejections is tiny. The Sun loses more mass do to the conversion of mass to energy in the core, and it's not enough to appreciably change the mass of the Sun over the age of the solar system. Young Sun-like stars appear to have stronger stellar winds, correlated with their higher rotation rate. But the Sun would have had to sustain orders of magnitude higher mass loss than present-day winds for its first 2 1/2 billion years on the main sequence, and this does not appear to match measured mass loss rates of nearby Sun-like stars of those ages.
This work bears only a superficial resemblance to the ideas of Velikovsky (and I'm being generous here).
During the Archean, the time period relavant to this study, tidal heating was not terribly important. The larger internal heat from radioactive decay was higher, yet still dwarfed by the energy input from the Sun in setting the surface temperature of the Earth.
Ah, so here's the deal. I'm the person that this article is talking about (David Minton, professor at Purdue University). I've been reading Slashdot for a fair number of years now, though it took me a long time to sign up and comment for the first time (I've always been a lurker at heart). Because I have a soft spot for all you basement dwellers (I kid!), I'm going to give you a bit of behind the scenes regarding this article, which kind of took me by surprise, actually. This is a bit long, so TL;DR: Science sometimes happens during panicked last minute coding sessions in hotel rooms prior to delivering invited talks that were procrastinated about.
So about five years ago my graduate school advisor and I wrote what was my very first peer-reviewed paper, which was on the subject of the Faint Young Sun Paradox. The paradox goes something like this: The early Sun was fainter than it is today, so all things being equal the Earth should have spend the first half of its life frozen over. Geologists tell us it wasn't, so something wasn't equal. What was it? We investigated the idea that the Sun may have been slightly more massive (something like 2-7% more massive), and that it had to lose most of that excess mass over a few billion years, which is at odds with measurements of mass loss of Sun-like stars. So we published it, and I went on to do other things in grad school, mostly involving trying to figure out the early impact bombardment history of the solar system, which we think may have been influenced by an early period of migration of the gas giant planets.
Fast forward to a few months ago, and a fellow at the Space Telescope Science Institute (the place they run the Hubble from) contacted me to ask if I'd like to give a talk about my old mass-losing Sun paper at a workshop that was planned to bring together astrophysicists, geologists, climate scientists, and planetary dynamicists to talk about the Faint Young Sun problem. They wanted me to also talk about planet migration and how that might fit in to the problem. Sure, why not? Revisiting the problem would be fun! The thing is, I've just started a new faculty job, and part of my job is helping get a new planetary science group built up at Purdue, so I've been extremely busy. And, well, I procrastinated. Big time. There was always some pressing thing to do that took time away from getting ready for the workshop. So the next thing I know, it's a few days before the meeting and I still haven't really thought about the faint Sun in about five years. So I dust off my old files, start futzing around with a talk, and the next thing I know I'm on a plane to Baltimore.
Late the night before the workshop is about to start, I'm racking my brain trying to come up with something new to say. You see, I've been thinking about early solar system history, and planet formation. Migration is a big deal in those early days. It's easy to get planets to move around in young solar systems. But the Faint Young Sun problem is a problem for the Earth's mid-life, not it's adolescence. Then I remembered a paper I really liked that came out a couple of years ago by Jaques Laskar and Mickaël Gastineau. They showed that our own solar system could potentially destabilize after a few billion years of seeming-stability due to Mercury's proximity to a chaotic region. It's described briefly here: http://en.wikipedia.org/wiki/Stability_of_the_Solar_System#Laskar_.26_Gastineau
What if something like that had happened *already?* So I futzed around with an N-body gravitational dynamics code remotely from my hotel room, in my pajamas, playing around with plausible initial solar systems where Earth stared just a tad closer to the Sun, but close enough to solve the problem of being frozen over, and Venus started out as two separate planets and then went unstable after many billions of years, scattering Earth to its present location in the process. And, when I checke
http://en.wikipedia.org/wiki/KH-11_Kennan
Actually, more than a dozen "Hubble space telescopes" were built and launched into orbit. The biggest differences are that they point at the Earth instead of away from it, and they are called KH-11 instead of HST. Oh, and their imagery data is mostly classified.
And only 1200 so far may look reasonable.
Still a good ratio.
Considering that out of the 150,000 stars, there are 1200 planetary systems that are both oriented such that the planets pass directly in front of their stars as seen from our solar system, and did so over a period of about 4 months, that's a *very* good ratio. The whole point of Kepler is to gather statistics on planetary systems. There's no need to wait 20 years. Trend lines are being plotted now.
then why wouldn't it be 13 times per year?
I would guess that some of the data is submitted monthly and the tracts show when the data was submitted, not necessarily observed. there's also a lot of big pulses early on, far larger than the overall rate would see to indicate as within the normal deviation of observation rate at that point. hence, the thought that it's mapping based on submission date and some are submitting bulk results on a monthly or quarterly basis.
Well, to an astrophysicist "roughly 12 times" is equivalent to 13 times, but your point is taken. I've sat in with the Catalina guys (on a nearly full moon night, so they didn't discover anything while I was there), and they don't wait to submit data. They send candidate objects to a followup telescope to confirm the discovery, then publish any object with the Minor Planet Center as soon as they are confirmed. They need to act quickly, because orbit refinements often rely on followup observations (often by amateur astronomers), and many objects, especially Near Earth Asteroids, could be lost if they are not followed up quickly. The big pulses in the discovery rates at early times are because objects were only discovered in sensitive surveys that were not run very frequently (and before the mid 1990s usually relied on photographic plates). After about 1997 once LINEAR got going (and later Catalina and a couple others) asteroid surveys have more or less been continuous, with lulls arising due to full moon nights and the weather patterns of southern Arizona and New Mexcio.
You'll also notice that the discovery rate seems to "pulsate" with a period of about 12 times per year (this is most obvious in the 2000s when the discovery rate was mostly uniform throughout the year). I'll leave it as an exercise to the reader to explain why that is (hint, skies need to be very dark to observe faint asteroids).
That comes from the WISE mission: http://wise.ssl.berkeley.edu/mission.html WISE is a whole sky infrared survey that happens to pick up asteroids. The spacecraft spins to survey a complete arc of sky roughly perpendicular to the Sun direction.
You'll also notice that during much of the 2000s, there is a gap in discoveries at about the 5 o'clock position. This corresponds to monsoon season in the southwest U.S. (roughly July to mid September). Most of the discovered asteroids in the past decade were made by the Catalina Sky Survey, based just outside of Tucson, AZ, and they generally don't bother observing during monsoon season because of the increase in cloud cover.
It's an optical telescope and it's designed for wavelengths from 450 nm to 1050 nm.
Ugh. Every time one of these stories comes up, someone has to bring up Velikovsky. As someone who studies early solar system evolution, I've had the "pleasure" of talking with Velikovsky supporters on numerous occasions. What Velikovsky wrote about was wide-scale rearrangements of the architecture solar system WITHIN HISTORICAL TIMES, based on nutty interpretations of classical mythology. What the article here discusses is a hypothesis for the formation of Triton during an event called the Nice model that is thought to have happened about 3.9 billion years ago (based on dating of large lunar basins from Apollo samples). During this time, a much more massive precursor to the Kuiper belt fueled the migration of the outer four giant planets, disrupting stable reservoirs of small bodies throughout the solar system. Once the ancient Kuiper belt was depleted of mass, the migration stopped (so the "fuel" is gone, and therefore this process can only occur once in the lifetime of the solar system). Had planetary migration occurred within historical times, then we would currently be in the midst of a massive bombardment of comets and asteroids, and the Earth's oceans would currently reside in the atmosphere (along with perhaps some rock vapor clouds). The Nice model and Late Heavy Bombardment is backed up by observations of the structure of the Kuiper belt, observations of other solar systems around other stars, radioisotope dating of lunar rocks (in a variety of isotope systems, but most especially K-Ar, and U-Pb), observations of the structure of the asteroid belt, dynamical models based on plausible initial conditions for the early solar system (constrained by aforementioned observations), observations of zircon crystals found in ancient Earth rocks, cratering chronologies of the rocky planets, the Moon, and icy satellites. Basically it's a preponderance of evidence pointing toward plausible models for the early history of the solar system. Velikovsky has tortured interpretations of ancient literature. Who do you think is more likely to be closer to describing reality?
According to Ciclops it's 480 km inward of the outer edge of the B ring, which puts it at a radial distance of 117,100 km
Wow, an astounding amount of ignorance is on display in this post. Near Earth Asteroids (NEAs, or NEOs if you prefer) may indeed be easier to visit than the Moon, and they are quite a bit easier to visit than Mars. Mainly this is due to the lack of appreciable gravity, so that the escape velocity from the surface adds only a negligible delta V to the total delta V budget required (for both landing and taking off again). You're not going to find yourself on a 100+ year orbit on an NEA. If you did find yourself on a 100+ year orbit and on on your way out of the inner solar system, then, by definition, you would have landed on a Halley-type comet (or perhaps even a long-period comet if you were *really* on your way out). Take as a typical NEA 433 Eros. The NEAR spacecraft successfully landed on it, despite the fact that the spacecraft was designed to be an orbiter (which, I think, succinctly illustrates how easy it is to land on an asteroid). Its perihelion distance (closest approach to the Sun) is 1.13 AU (1 AU is the Earth-Sun distance) and has a period of a bit less than 2 years. Once nice thing about asteroids is that they basically represent remnants of the original solar nebula from which planets were formed, and most of them never differentiated (melted and formed iron cores and rocky mantles). That means that they are relatively rich in many raw materials compared to the surfaces of planet-sized bodies. A carbonaceous asteroid contains valuable metals (often as little blobs of pure metal), water (up to 30% by weight in many cases), and organics (kerogen). Some other asteroids are nothing but metal, and would require very minimal processing to make them useful (unlike many ores found on Earth). Going to asteroids makes a lot of sense. The main difficulty with an asteroid vs. a lunar mission is that the mission length to an asteroid would be longer than one to the Moon (although depending on the asteroid, it could be much shorter than a Mars trip).
Pluto and Charon aren't formed the same way.
It is actually quite possible that Charon formed in exactly the same way as the Earth-Moon system. See this abstract. Most modern planet formation simulations show that the end stage of formation involves collisions between large proto-planets. Whether or not any particular giant collision results in a satellite or not depends on the details such as impact velocities and angles. Double bodies such as Earth-Moon and Pluto-Charon are likely to be relatively common outcomes given what we know of planet formation.Pluto the 2nd largest of the as yet discovered Kuiper Belt objects. It is also the largest Plutino. In addition it is the 2nd largest known dwarf planet. I'm not sure why Pluto needs yet another classification category. It is certainly not justified on grounds of uniqueness.
Many (but not all) of the observed dynamical features of the Kuiper Belt can be explained by giant planet migration.