View Full Version : Discussion: How Many Habitable Planets Could ...

2005-Apr-05, 04:34 PM
SUMMARY: The chances of finding life somewhere else in the Universe depends on how many planets are capable of supporting life. Well, according to new calculations by astronomers at Open University, as many as half of all star systems could contain habitable planets. The team created mathematical models of known exoplanetary systems, and then added Earth-sized planets into the mix. They found that in half of all planetary systems they simulated, the gravity of the gas giants won't catastrophically affect the orbits of these smaller planets, giving life a chance to evolve.

View full article (http://www.universetoday.com/am/publish/how_many_habitable_planets.html)

What do you think about this story? Post your comments below.

2005-Apr-06, 02:30 AM
Planets in the habitable zone may have stable orbits but could they have formed there? There are plenty of asteroids in what I assume to be stable orbits but they never coalesced into a larger object.

Mr. Smartypants gamer guy
2005-Apr-07, 01:46 AM
ok, now here's the download if it is even posible for life to be our there..."which there inesplicebly is", we havent, sadly, found it :angry: so as with all things we should endevor to find it. but as a posibility for another earth... well lets just say the odds are "out there" :) sry couldent help myself :) and i mean what would it look like if there was???

2005-Apr-07, 03:05 AM
In regard to the asteroids forming planets, maybe they are like the chicken and the egg. Which came first? Asteroids forming planets or planets being destroyed by large impacts and forming asteroids.

2005-Apr-07, 08:15 AM
:huh: Around, and around we go. The same old doughting tomasess.
Stick to the 'Facts'. We know of many star systems that have largish gas giant type planets, thats not unreasonable to draw the conclousion that they may suport smaller planets in the habital range. As we have in this solar system. Why are so many so quick to dought this possabilaty? The most common element in the universe Hydrogen. And a note to all you chemistry types. For every molicule of Carbon Dioxide theres two otoms of oxygen. All we gota do is free it up.
We are going to find an abundance of life across the universe.
Or it will find us, . I know which I would choose.

2005-Apr-07, 08:33 AM
This new report on the possible existence of "earth-like" planets is very encouraging. Now we can expect solid rock planets of a size comparable with our world may be much more common than was previously thought! It's even more exciting that the possibility of them forming within the "Goldilocks" zone is higher than astronomers had previously thought. Now we need to develop the means of detecting such worlds !

2005-Apr-09, 05:45 PM
In regard to the asteroids forming planets, maybe they are like the chicken and the egg. Which came first? Asteroids forming planets or planets being destroyed by large impacts and forming asteroids.

I elect Asteroids --> Planets, since planets had to coalesce first before asteroids could destroy them.

As regards to other matters, I agree that just because the distribution of gas giants is such that it allows a planet of any kind to form in the habitable zone does not MEAN one will, in fact, form there (although I find it fairly likely that a planet of some sort WILL actually be there, but that's just my unprovable opinion). Furthermore, let's consider the three things about rocky-metallic (RM) worlds (including Earth-size RM moons of gas giants):

(1) the mass of the worlds
(2) the positions of earth-like worlds in exoplanetary systems

For a star closely related to the sun that has planetary systems with reasonably circular orbits, let's use our own solar system as an example (however risky that may be)

Number of RM worlds in the inner solar system: 4 (Mercury through Mars)

How many such worlds' mass is at least 0.5 Earths (the theoretical minimum necessary for meaningful plate tectonics lasting for billions of years): 2 (Earth and Venus, although Venus almost certainly has vulcanism, it just as certainly does not have tectonics)

How many worlds are in the Continuous Habitable Zone (HZ): 1 (Earth)

So using our solar system as a model (risky I know, but it's the best we have), the probability of having a planet meeting ALL THREE of these characteristics is
0.5 (for sufficient mass) X 0.25 (for continuous habitable zone) = 0.125, or 1/8.

Multiply this number by the total number of RM worlds in the inner part of the system and you get 4 X 0.125 = 0.5 truly Earth-like planets (at least potentially).

This means that, on average, about 1/2 of all solar systems whose gas giant locations permit the formation of living planets where the presence of life lasts for several billion years WILL, in fact, have living planets where life is present for several billion years.

Another way to look at this is to determine the width of the location of the continuous habitable zone, then divide that by the width of the space between the star itself and the outer edge of the star's habitable zone at the time just befor it begins its red giant phase (when the star begins to transform into a red giant).

Here, I'll go out on a limb by speculating about the width of these zones over time.
Let's say the outer edge of our star's habitable zone just before it turns red giant is 2 AU (twice the sun-earth distance), while the continuous habitable zone is, say 0.5 AU wide. That means the continuous habitable zone will cover 1/4 of the width of that space between the sun's surface and its outermost habitable zone just before it starts its red giant phase. This means that at any given time, in a 4 inner-world system, there is going to be at least one that is in the continuous habitable zone (assuming the worlds are more or less evenly spaced apart). But note well we still have the masses of the worlds to contend with, given that plate tectonics, a magnetic field, and suitable atmospheres depend on having a certain minimum mass.

So overall, I expect we will almost certainly find a non-living world in a continuous HZ. It's also fairly probable we will even find Earth-sized planets within HZ's after Kepler goes into service (though whether we find actual tell-tale signs of life on those worlds is another matter)

2005-Apr-14, 05:52 PM
The thinking is that the asteroid belt would have coalesced into a small planet at the same time all of the other planets formed had it not been for the unfortunate proximity of Jupiter. The effect of the nearby giant's gravity would have prevented or distrupted the formation of a planet sized body. The reason the process was distrupted at a later phase after some medium sized objects had formed likely had to do with a brief inward migration of Jupiter from where it originally formed.