Venus 2 billion years ago.

[thor_001]

I was watching a documentary on the planets. During the show, it was brought up that there might have been life on Venus before the run away greenhouse effect turned it into what it is today. <br /><br />There is always a point that these shows never bring up however, and that is the position of the planets and their distance from the sun millions of years ago. Was Venus once in the "habitable zone" where life could have emerged? If this is the case, then maybe life on Venus may have been more possible than life on Mars. My logic is that Mars was probably much colder millions of years ago than it is today since it was farther away from the sun in the solar system than it is today.<br /><br />My other question would be, how much closer do planets get to the sun each year generally?

 

[nikshliker]

Theoretically, planets should not move closer to the sun at all. The celestial masses in our system will reach an equilibrium in which the centripetal force is enough to counteract the force of gravity pulling it in. as the mass gets closer to the rotation point it will speed up and would therefore have more centripetal force to make the vector pointing away from the sun greater which would make the radius larger. Should just stay the same distance away. however, if i am wrong and objects do gt closer every year then it would be because the sun itself would be moving and acting as a dampener. as far as my physics background goes we have only lookd at the situation in which the center mass does not move. <br /><br />This is a horrible answer to your question because it is kinda shady, but if anyone else can give a better answer i love learning something knew and would apreciate if you explained y this phenominon would happen.<br />

 

[Leovinus]

Isn't the sun constantly losing mass? Through solar wind and coronal mass ejections and even losing mass through nuclear fusion. You'd think that if the mass would become less, then gravity would weaken and the planets orbits would get larger. But I'm just guessing... <div class="Discussion_UserSignature"> </div>

 

[newtonian]

Leovinus - I will research it. Meanwhile, off the top of my head: <br /><br />The standard model has the sun losing mass. Exactly how much is the variable. The solar wind stops most accretion, if not all. <br /><br />My doubt would be when the sun passes through a dense (relatively) gas and dust cloud in Milky Way.<br /><br />Or merges with a sub-brown dwarf, etc. <br /><br />Especially in the future during the Andromeda-Milky Way merger.<br /><br />Also, there are widely variant models as to how far earth will move away from the sun by red giant phase - again according to the standard model.<br /><br />Some have earth swallowed up by the sun, while others have earth well beyond the sun's surface in a more distant orbit.<br /><br />Geological evidence has early earth hotter, then milder but more uniform. Astronomy indicates it should have been colder. Perhaps early earth was slightly closer to the sun. Certainly, the greenhouse effect was much stronger than today. Here is just one line of evidence for this:<br /><br />The vast carbonate deposits on earth indicate a very extensive geologic carbon cycle, whereby atmospheric carbon dioxide (CO2) combines with water (H2O) in the oceans: H2O + CO2 yields H2CO3. The CO3 separates as a dissolved negative ion (Co3-), and combines with 'metal' ions dissolved in ocean water, such as sodium (Na+) in salt (NaCl) or Potassium (K) in Potassium salt (KCl) [also Calcium ions, Ca+) to form carbonates, or limestone, which precipitates out to form these vast carbonate deposits.<br /><br />Calculating mathematically, the vast carbonate deposits in earth’s crust indicates a vast CO2 atmosphere in early earth - comparable to Venus at present. <br /><br />And that, in turn, caused a powerful greenhouse effect. <br /><br />Earth has been fine tuned for life in many ways. One way was the change from venus-like to the present life sustaining environment. <br /><br />BTW - one should not ignore tidal interactions. Earth's moon is receding slightl

 

[heyscottie]

Leovinus:<br /><br />I calculated the loss of mass of the sun once, (I don't feel like doing it again at this instant) and found that the overall loss of mass was MINISCULE.<br /><br />It was something like .01 percent of the sun's mass lost over 4 billion years. Not enough to move orbits any appreciable amount.

 

[newtonian]

heyscottie- That just doesn’t sound right, since the standard model has the sun running out Hydrogen fuel in 10 billion years, and the solar wind sending out 1 million tons per second of electrons and protons.<br /><br />How did you calculate that?<br /><br />Alas, all of this was on the old SDC - links and all. Sad its gone.

 

[newtonian]

Alas, all of this was on the old SDC - links and all. Sad its gone. Or, perhaps good, since now I am going to calculate somewhat independently.<br /><br />Let’s see. Fusion of 2 hydrogens with a mass of 1.0078 each into 1 Helium with a mass of 4.0026 gives us a mass reduction of .0294 which is converted to 6.8 million electron-volts (MeV) of energy, such as gamma rays. - Britannica 2003 CD under Sun, Energy generation and transport.<br /><br />That would be about 1.5% (roughly) of the hydrogen mass of the sun lost if all the hydrogen was fused, and the sun is currently 90%+ hydrogen?<br /><br />OK, that would be about .7% in 4 billion years assuming a steady rate and a life-span of 10 billion years. If the actual answer is .01%, then it would logically follow that only about 1%+ of the sun’s hydrogen would be fused before it ran out of hydrogen.<br /><br />And that is ignoring the actual mass loss from 1 million tons of electrons and protons expelled in the solar wind every second!<br /><br />OK, correction, but I don’t know why. Britannica states .7% of the mass of hydrogen would be converted into energy in the sun’s entire life if all hydrogen was converted into energy (e=mc^2).

 

[j_rankin]

The Sun won't completely run out of hydrogen fuel for several billions of years. But it will have significantly less (0.7%), which is why the rate of fusion will decrease, causing the star to expand.

 

[nexium]

I believe Newtonian is correct the moon is moving away from Earth by a tiny, but measureable amount. Billions of years ago, the Moon rotated faster, was not tidelocked and was thus moving closer to Earth. If so, the planets should be moving closer to the sun for the same reasons (not tide locked) but much slower. The solar wind tends to push the planets away, so these two (and other) effects approximently cancel for Earth and Venus. <br /> Galactic wanderers, asteroids and comets do fall into the sun rarely, but it could happen lots more often at some time in the future, such as the likely Androndoma merger with our galaxy. This will offset some (all?) of the current mass loss due to fusion and solar wind. If the core is disturbed sufficiently by very massive impactors, I think the shrinking of the sun's core could be much slowed, allowing the heat of contraction to escape to the surface of the sun. Thus the core of the sun would not get hot enough to fuse helium to oxygen except in a very small portion of the core. This could delay the red giant expansion for several billion years, perhaps never. This would likely require very fine tuning, such as only God can do. Neil

 

[nexium]

My guess is many (most?) of the other moons will become tide locked before they crash into their planet and thereafter they will move away very slowly.

 

[Maddad]

nexium<br />I'm going to add just a bit to eddie's remarks. Stars are counterintuitive in one way because they live shorter lives if they are more massive. Your giant impactors, if they occured, would cause our Sun to burn hotter and faster, not cooler and longer. In burning up its fuel faster, it would reach the red giant stage sooner, not later.<br /><br />The next comment involves hydrostatic equilibrium. A star exists in a balance between gravity trying to squeeze it smaller, and nuclear fusion pushing it apart. If the star shrinks from gravity, the fusion process increases greatly, pushing the star back out to its optimum dimension. If the star expands, then the fusion process slows and gravity takes over, again returning the star to it's optimum size. The Sun would be very resistant to any change in output.

 

[nexium]

Hi crazyedie: I do get things backwards sometimes. Are you saying The moon was not getting closer until it was tide locked, and has since been moving farther away? Perhaps it will reverse direction again when both Earth and Moon are tide locked at 47 days? Neil