Kepler confirms its first planet in habitable zone of sun-like star

Dec 05, 2011
This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth. Kepler-22's star is a bit smaller than our sun, so its habitable zone is slightly closer in. The diagram shows an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star. It's about 2.4 times the size of Earth. Image: NASA/Ames/JPL-Caltech

(PhysOrg.com) -- NASA's Kepler mission has confirmed its first planet in the "habitable zone," the region where liquid water could exist on a planet’s surface. Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.

The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the of a star similar to our sun. The planet is about 2.4 times the radius of Earth. Scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.

Previous research hinted at the existence of near-Earth-size planets in habitable zones, but clear confirmation proved elusive. Two other small planets orbiting stars smaller and cooler than our sun recently were confirmed on the very edges of the habitable zone, with orbits more closely resembling those of Venus and Mars.

"This is a major milestone on the road to finding Earth's twin," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Kepler's results continue to demonstrate the importance of NASA's science missions, which aim to answer some of the biggest questions about our place in the universe."

Kepler discovers planets and by measuring dips in the brightness of more than 150,000 stars to search for planets that cross in front, or "transit," the stars. Kepler requires at least three transits to verify a signal as a planet.

"Fortune smiled upon us with the detection of this planet," said William Borucki, Kepler principal investigator at Ames Research Center at Moffett Field, Calif., who led the team that discovered Kepler-22b. "The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season."

The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to review observations on planet candidates the spacecraft finds. The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.

Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a sun-like star resembles that of our world. The planet's host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.

Of the 54 habitable zone planet candidates reported in February 2011, Kepler-22b is the first to be confirmed. This milestone will be published in The Astrophysical Journal.

The Kepler team is hosting its inaugural science conference at Ames Dec. 5-9, announcing 1,094 new planet candidate discoveries. Since the last catalog was released in February, the number of planet candidates identified by Kepler has increased by 89 percent and now totals 2,326. Of these, 207 are approximately Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter.

The findings, based on observations conducted May 2009 to September 2010, show a dramatic increase in the numbers of smaller-size planet candidates.

Kepler observed many large planets in small orbits early in its mission, which were reflected in the February data release. Having had more time to observe three transits of planets with longer orbital periods, the new data suggest that planets one to four times the size of Earth may be abundant in the galaxy.

The number of Earth-size and super Earth-size candidates has increased by more than 200 and 140 percent since February, respectively.

There are 48 planet candidates in their star's habitable zone. While this is a decrease from the 54 reported in February, the Kepler team has applied a stricter definition of what constitutes a habitable zone in the new catalog, to account for the warming effect of atmospheres, which would move the zone away from the star, out to longer orbital periods.

"The tremendous growth in the number of Earth-size candidates tells us that we're honing in on the planets Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable," said Natalie Batalha, Kepler deputy science team lead at San Jose State University in San Jose, Calif. "The more data we collect, the keener our eye for finding the smallest out at longer orbital periods."

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jselin
5 / 5 (2) Dec 05, 2011
Dibs!
Nanobanano
1.1 / 5 (12) Dec 05, 2011
2.4 Earth Radii is extremely massive, and probably not habitable to macroscopic life.

If it is terrestrial, it's mass is somewhere near 14 times that of Earth.

If it is some sort of "small" gas giant, or hybrid planet (rocky core, extremely dense atmosphere,) it would still be several times more massive than Earth.

Even if it was a ball of pure water and water-ice, it would be more than twice as massive as Earth.

But this is abnormal reporting the "radius" of an exoplanet, since you typically couldn't possibly know that absolutely. Normally, they report the MASS, and then you hypothesis radius based on proposed compositions.

They should clarify this statement.

Was this found with a true transit so that they could measure the radius directly?
Nanobanano
1 / 5 (8) Dec 05, 2011
"The planet is about 2.4 times the radius of Earth. Scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets."

nasa.gov/mission_pages/kepler/news/kepscicon-briefing.html

From that, I infer they must have used a true transit method, but have absolutely no idea what the composition is.

So it could literally be anything from a water world, to a super-Super earth, to a Neptune clone.

In any case, I doubt anything more complex than bacteria or worms could ever live there...them bones and organs rupturing under continual 5.76 g-forces would tend to keep maximum size rather small...
Nerdyguy
1.4 / 5 (27) Dec 05, 2011
And again.....big deal.

So, Kepler has done what...allowed us to count how many planets we can find, and which might be in the Goldilocks zone?

To what end?

We have no visible means to do anything with this knowledge. Let's waste a little more money, a la SETI.

And, like SETI, they'll shut this nonsense down in a few years, hand this kind of thing off to amateurs (where it should be), and declare that a boatload of resources has been spent for very little return.

How about we stop it now, and put these funds and the genius intellects (literally) behind it towards building a damn rocket that can put a man in space...again.
Valentiinro
4.7 / 5 (14) Dec 05, 2011
And again.....big deal.

So, Kepler has done what...allowed us to count how many planets we can find, and which might be in the Goldilocks zone?

To what end?

We have no visible means to do anything with this knowledge. Let's waste a little more money, a la SETI.

And, like SETI, they'll shut this nonsense down in a few years, hand this kind of thing off to amateurs (where it should be), and declare that a boatload of resources has been spent for very little return.

How about we stop it now, and put these funds and the genius intellects (literally) behind it towards building a damn rocket that can put a man in space...again.


It takes inspiration for people to want to put all that effort (and of course money) in. If we know the universe is brimming with habitable planets, I think that might inspire some people (probably China) to do the research that could actually get people there. Of course what we need right now is some baby steps in the right direction.
21 second Excitation
5 / 5 (5) Dec 05, 2011
But this is abnormal reporting the "radius" of an exoplanet, since you typically couldn't possibly know that absolutely. Normally, they report the MASS, and then you hypothesis radius based on proposed compositions.

They should clarify this statement.

Was this found with a true transit so that they could measure the radius directly?


You can infer the radius of the planet by measuring the dip in the flux from the star. Since the flux is proportional to the cross section area (roughly). By measuring the decrease in the flux during the transit, you can infer the area being blocked by the planet. Thus from this decrease in flux, we can measure the radius of the planet to a good approximation. We did this is my entry level astronomy course.

I couldn't find anything on the term 'true transit' but this is how they determined the radius from what I would assume.
Nanobanano
1 / 5 (5) Dec 05, 2011
21:

I know that.

Transit happens in varying degrees. Ideally, you want to be precisely aligned with the orbital plane of the planet and the parent star.

The way many exoplanets were found is by observing the perturbed parent star over some time, infering the mass and orbital period of the planet from that, which says little or nothing about size or composition.
Nanobanano
1 / 5 (4) Dec 05, 2011
Well crap...

the way many exoplanets were found involved observing the perturbed parent star, and then calculating the mass and orbital period of the planet over and over until you got a data set that was consistent, allowing you to infer that a planet of a certain mass orbited at a certain distance.

This was quite different than the transit method, and probably can find a larger number of total planets, since transit is a special case requiring precise alignment.
0FET
4 / 5 (2) Dec 05, 2011
@Nanobanano:
correct me if I wrong, but since mass increases with radius by a power to the 3rd (assume constant density) and g ~ m/r^2, wouldn't that be 2,4 times the g-value of Earth?

"them bones and organs rupturing under continual 5.76 g-forces would tend to keep maximum size rather small...

Nerdyguy
1 / 5 (15) Dec 05, 2011
It takes inspiration for people to want to put all that effort (and of course money) in. If we know the universe is brimming with habitable planets, I think that might inspire some people (probably China) to do the research that could actually get people there. Of course what we need right now is some baby steps in the right direction.


So, was this an argument FOR or AGAINST Kepler?

From an American standpoint, you've just posited that we're wasting millions so that China can be inspired to do research that will "get us there".

In any case, your logic is faulty. We don't need to spend $500 million plus to inspire us to do anything.

Furthermore, inspiration or not, there is NO method known to man today to get to ANY of these planets. We literally have one hope - that we'll discover the Star Trek warp drive. Which most physicists consider absolute bunk.

You have made my case well. Kepler is a waste of resources.
that_guy
4.2 / 5 (9) Dec 05, 2011
"Habitable", as far as a nearly furless ape-like species is concerned. hahaha.

@Nano - you're an idiot. Please go back and learn how to calculate gravity.
@OFET - You are closer, but it is not directly proportional to mass.

The surface gravity of an object is related to the distance from the center of mass. As you get farther from the center of mass, gravity goes down. What this means generally, is that for planets, as the planet gets bigger, the surface gravity to mass ratio goes down.

For example, the moon is 1/81 the mass of the earth, but it has a gravity a quarter as much as our own. Jupiter has a mass many thousands of times more than the earth, but it's surface gravity is only 2.5 times more than earth.

If this planet has a similar or slightly higher density to earth, you're only looking at maybe a gravity of 1.5 gees...probably less...
0FET
5 / 5 (3) Dec 05, 2011
@that_guy:
that's why I wrote g ~ m/r^2, so the radius is in the equation; g would decrease with the radius squared if the mass were constant. Since the mass itself increases with the radius cubed, g should increase with r^3/r^2 = r.
Judgeking
5 / 5 (4) Dec 05, 2011
Nerdyguy, a nuclear thermal rocket could get us (or a probe) there, but it would probably take 1000 years. I still think it'd be worth it because I find the knowledge that there may be intelligent life there incredibly inspiring.
nanotech_republika_pl
3 / 5 (1) Dec 05, 2011
In the article they said that the mass of this planet would be similar to Earth mass, not the same density. Which means that if the radius increases the gravity would go down. So the gravity force would be only 20% of the Earth gravity. Here is how I calculate this:

gravity on a planet, Fp = G * m1* mp / rp^2
gravity on Earth, Fe = G * m1 * me / re^2
Fp/Fe = re^2 / rp^2 = 1 / 2.4^2 = ~0.17
TheGhostofOtto1923
4.3 / 5 (6) Dec 05, 2011
In any case, I doubt anything more complex than bacteria or worms could ever live there...them bones and organs rupturing under continual 5.76 g-forces would tend to keep maximum size rather small...
Because - after all - you ARE an accomplished exobiologist in addition to being a celestial mechanic and prodigious calculationist, and are thus able to offer informed opinions on all these things. Arent you?
infering the mass and orbital period of the planet from that, which says little or nothing about size or composition.
How would you know? Please I must ask for a reference. If you dont mind.
javjav
4.7 / 5 (7) Dec 05, 2011
Nerdyguy, a nuclear thermal rocket could get us (or a probe) there, but it would probably take 1000 years. I still think it'd be worth it

No, it does not worth it. There is a much easier way to see this planet, even with today technology, which is to build a 100m or even a 1000m telescope. Theoretical projects already exist. It would be really difficult and very expensive, but technically it is not impossible. In any case, the idea of building a huge telescope here or in the moon makes much more sense than sending a very small telescope in a probe to other star systems. And it would permit to see thousands of other planets, not just one star system.
nanotech_republika_pl
5 / 5 (1) Dec 05, 2011
Oh shoot, the Sun and the other star is about the same mass, but we don't know what the masses of the planet and the Earth are. Then, the gravity is unknown till we know what the density of the planet is, right?
that_guy
4.4 / 5 (5) Dec 05, 2011
In the article they said that the mass of this planet would be similar to Earth mass, not the same density. Which means that if the radius increases the gravity would go down. So the gravity force would be only 20% of the Earth gravity. Here is how I calculate this:

gravity on a planet, Fp = G * m1* mp / rp^2
gravity on Earth, Fe = G * m1 * me / re^2
Fp/Fe = re^2 / rp^2 = 1 / 2.4^2 = ~0.17

The article does not state the planet's mass or density.
scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.

Therefore we cannot accurately calculate the gravity. We can only assume that the density for a rocky planet would be slightly higher than earth, or for a mostly gaseas planet, it would be likely substantially lower density than earth.
Nerdyguy
1.7 / 5 (9) Dec 05, 2011
Nerdyguy, a nuclear thermal rocket could get us (or a probe) there, but it would probably take 1000 years. I still think it'd be worth it because I find the knowledge that there may be intelligent life there incredibly inspiring.


Random Thoughts:

1) There are NO nuclear rockets. So, now you are perhaps proposing we spend more money.

2) "may be intelligent life there incredibly inspiring". You say that like there's someone who WOULDN'T find it inspiring. However, it doesn't change the facts. Waste of time, money, and other resources.

3) Do you really believe the U.S. government has $500 million to waste on something that, by your own estimate, might transpire in 1,000 years?

Bottom line: "inspiring" you does not constitute a valid reason to spend $500 million.
Burnerjack
1.4 / 5 (10) Dec 05, 2011
While probing our surroundings is endemic to human nature, Making plans and budgets to go somewhere 600 lightyears away is just silly. No better word for it. I suggest ANY tax revenue to be spent on this (if any) be done with a checkbox on our tax return forms. We can't even feed our elderly but instead head off to planet 600 lightyears away? Hey, pass that thing this way you Bogartin' mothe....
FrankHerbert
1.3 / 5 (58) Dec 05, 2011
We can't even feed our elderly but instead head off to planet 600 lightyears away?


Uhh, what? Under our system the elderly have had plenty of time to amass enough wealth to secure their diets into their old age.

Nah, I don't actually believe that shit. However, I do believe the elderly are much more responsible for their conditions (absolute AND political) than children. I just find it odd that the starving elderly is the sticking point for you.

I don't believe in making people lie in the bed they made, but if we are forced to do such, wouldn't the elderly be more deserving of such treatment? They did create the world we live in after all.
Nerdyguy
1.7 / 5 (6) Dec 05, 2011
We can't even feed our elderly but instead head off to planet 600 lightyears away?


Uhh, what? Under our system the elderly have had plenty of time to amass enough wealth to secure their diets into their old age.

Nah, I don't actually believe that shit. However, I do believe the elderly are much more responsible for their conditions (absolute AND political) than children. I just find it odd that the starving elderly is the sticking point for you.

I don't believe in making people lie in the bed they made, but if we are forced to do such, wouldn't the elderly be more deserving of such treatment? They did create the world we live in after all.


A) It's a pretty damn good world actually. Crybabies, liberals, and Henny Penny types aside.

B) So, by your dubious logic, every person of retirement age is individually accountable for anything on the planet that you don't like?

FrankHerbert
0.9 / 5 (51) Dec 05, 2011
I'm parodying conservatives if it isn't obvious.

Conservatives believe in the "make your bed and lie in it" mentality.

If living to retirement doesn't qualify as "making your bed" what does?

I never said the elderly should starve or anyone for that matter. I never said every individual elderly person is responsible for the world we live in. Obviously the ones in poverty (the starving ones) aren't.

However you are naive or a sophist if you can really put in print that you don't think the elderly affect the world more than other groups. Can you really claim that?

And since that is the case, if we are going to talk about sacrificing one groups comfort for another, isn't it fair to take from the people responsible for the mess and give to the people that could not have possibly been responsible?

This is the dichotomy between the elderly and children with regards to starvation. Get over it or support a responsible economic system.
Nerdyguy
1 / 5 (3) Dec 05, 2011
Conservatives believe in the "make your bed and lie in it" mentality.


Really? Very deep man, very deep. Groovy even. Do you read liberal minds as well? How about moderates/centrists? Only conservatives in the U.S., or internationally? Just checking.

I never said every individual elderly person is responsible for the world we live in.


Wrong. You said the elderly are responsible. Your words:

"They did create the world we live in after all."

Obviously the ones in poverty (the starving ones) aren't.


So, the level of food in one's belly is the prime indicator for one's responsibility level for all things? Okey dokey.
Nerdyguy
1 / 5 (3) Dec 05, 2011
However you are naive or a sophist if you can really put in print that you don't think the elderly affect the world more than other groups. Can you really claim that?


Who the hell are you referring to? You're the only one yapping on about the elderly on an article about Kepler, ffs.

And since that is the case, if we are going to talk about sacrificing one groups comfort for another, isn't it fair to take from the people responsible for the mess and give to the people that could not have possibly been responsible?


Mess? What mess? The drool oozing from your mouth? WTH are you going on about?

This is the dichotomy between the elderly and children with regards to starvation. Get over it or support a responsible economic system.


lmfao, but you've taken mental retardation to new heights. I do believe you are in an argument with more than one person, and haven't figured that out. In any case, wtf does this have to do with Kepler?
FrankHerbert
0.8 / 5 (49) Dec 05, 2011
So, the level of food in one's belly is the prime indicator for one's responsibility level for all things? Okey dokey.


The "level of food in one's belly" is highly correlated with one's wealth which is highly correlated with "one's responsibility for [many] things."

Wrong. You said the elderly are responsible. Your words:

"They did create the world we live in after all."

Obviously the ones in poverty (the starving ones) aren't.


You have an uncanny knack for exposing your own lies immediately after you commit them. Just in case anyone doesn't understand what's going on in the above quot, Nerdyguy claims I said one thing then immediately quotes me as saying the opposite. I don't think he even realized this because he was so eager to jump on the second point without realizing it corrected the first.

In any case, wtf does this have to do with Kepler?


I dunno, what does feeding the elderly have to do with Kepler?
AdamCC
5 / 5 (3) Dec 05, 2011
So the gravity force would be only 20% of the Earth gravity. Here is how I calculate this:

gravity on a planet, Fp = G * m1* mp / rp^2
gravity on Earth, Fe = G * m1 * me / re^2
Fp/Fe = re^2 / rp^2 = 1 / 2.4^2 = ~0.17

The article does not state the planet's mass or density.
scientists don't yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.

Therefore we cannot accurately calculate the gravity. We can only assume that the density for a rocky planet would be slightly higher than earth, or for a mostly gaseas planet, it would be likely substantially lower density than earth.


True. The ratio of the gravities (since G is constant and m1, the mass on the surface, is constant) is actually (rp*dp)/(re*de). d is rho, the density. If dp=de, then .17 is a correct ratio. But we don't know the density, so we have no clue on the ratio of gravities.
AdamCC
5 / 5 (3) Dec 05, 2011
Clarification/further explanation. Mass is volume*density. Volume is 4/3*pi*r^3. 4/3 and pi cancel out in the ratio. Since force of gravity is Gm1m2/r^2, that is Gm1Vd/r2 (again, d is density, since I can't type a rho). r^3/r^2 is simply r. Thus the ratio simplifies to (rp*dp)/(re*de) (p is the planet, e is earth, if that wasn't obvious).
monger
5 / 5 (6) Dec 05, 2011
"In any case, I doubt anything more complex than bacteria or worms could ever live there...them bones and organs rupturing under continual 5.76 g-forces would tend to keep maximum size rather small..."

Nonsense, on earth life most likely evolved in water, and therefore the actual force due to gravity on a water-based lifeform would be... just about zero. Balanced out by buoyancy.

And it doesn't matter what fluid life evolves in, the same principle would apply. Complex life should be able to evolve even under very extreme gravitational forces provided fluid is present.
AdamCC
not rated yet Dec 06, 2011
And it doesn't matter what fluid life evolves in, the same principle would apply. Complex life should be able to evolve even under very extreme gravitational forces provided fluid is present.


A very good point, one I didn't think of. The buoyant force is equal to the *weight* of the displaced fluid - so matter how high the gravity, life can evolve in fluid. The life-form just has to be at least a little less dense than the fluid (or even a little more, though that would require either a lot of energy spent or relatively shallow waters).

Also, regarding my math earlier. It was all right. But I wasn't thinking about the conclusion, since the squared drops out (thanks to the r^3 in the volume), .17 is NOT the correct answer. Assuming exactly equal density, the ratio is actually .42 - about half our gravity. Not bad at all. In fact, *extremely* friendly to life, I'd say (as we know it). If the density is a little higher due to less water, e.g., it gets even better. :)
AdamCC
not rated yet Dec 06, 2011
Once again clarifying my post, when I say life "as we know it" above, I'm referring to land life. As Monger pointed out and I elaborated, life in water (even large life) is quite possible regardless - and in my opinion quite *probable* given the presumed average temperature (which assumes proper atmosphere; if it's tidally locked, that also decreases the chances but does not make them zero).
ShotmanMaslo
3 / 5 (2) Dec 06, 2011
Knowledge itself, without any direct practical applications, is well worth the money spent in this case.
infiniteMadness
not rated yet Dec 06, 2011
did this thread just derail into american politics? youre fucking pathetic.

some people are so easily trolled.
AdamCC
not rated yet Dec 06, 2011
Another thought regarding density/buoyancy/etc. While everything we said is true, the higher radius indicates (statistically and perhaps almost certainly due to physical processes I don't know/understand) that this planet is very probably gaseous. So regardless of the density and thus (in combination with radius) surface gravity, it may not be viable anyway.

The three big factors of habitability are:
- temperature (water or perhaps something else being in a liquid state)
- density (not being gas, possible presence of water, etc.)
- surface gravity (less of a factor thanks to liquid-only life as discussed, but still relevant)
btb101
1 / 5 (2) Dec 06, 2011
why has there been no search for the source of the wow signal?
now that should have been at the top or near top of any telescope's mission.
but after 20 yrs there is still nothing mentioned...

was it hoax or cover up?
that_guy
not rated yet Dec 06, 2011
Another thought regarding density/buoyancy/etc. While everything we said is true, the higher radius indicates (statistically and perhaps almost certainly due to physical processes I don't know/understand) that this planet is very probably gaseous. So regardless of the density and thus (in combination with radius) surface gravity, it may not be viable anyway.

If the planet is mostly gaseus, that would make it a gas giant half the size of uranus or neptune, but much warmer than them due to proximity to the star. These are all factors that we have not seen/studied in depth.

From what we DO know, IF it IS a gas planet, at that range, it would be less dense than earth, have a mass at only 2-3 times more than earth, and have a 'surface' gravity lower than earth.

@BTB - the wow signal was inconclusive. Also, they've been trying to follow it up for the last 20 years, and found nothing. It is neither hoax nor cover up. Just coincidence 1000 monkeys typing a single word
ED__269_
1 / 5 (1) Dec 06, 2011
... As you get farther from the center of mass, gravity goes down. What this means generally, is that for planets, as the planet gets bigger, the surface gravity to mass ratio goes down.

thats wrong

The vectorial sum of force is 0. since the center of mass is vectorially neutral, it's sum is 0.
(vector sum)mg = 0 -> (vector)g=0/m.

you could ask the question what happens given a constant density and arrive at the conclusion -> mass is proportional to gravity.

you could consider the case of changes density... concluding that gravity is proportional to both mass an its density.

this also means that surface gravity increases as r increases given a constant density.
that_guy
not rated yet Dec 06, 2011
ok...so as you get farther from the surface, gravity goes down.

Since the gravitational force of matter affects you less as you go farther away from it (Inverse square), the matter on the other side of a planet influences you less than the matter directly under your feet.

So, for a planet of a given density, the increase in gravity at the surface of a planet does not scale linearly with the circumference or mass of the planet.
ED__269_
1 / 5 (1) Dec 06, 2011
... for a planet of a given density, the increase in gravity at the surface of a planet does not scale linearly with the circumference or mass of the planet.


to me, it reads as confused.
use the following to enable your own derivation.

Consider a point mass m on the surface of a planet with known gravity g of mass Earth E of known radius R to the center of Earths mass; and G is the gravitational constant. The force acting on that point mass is F = mg.

F = GmE/(RR)-> mg = GmE/(RR) --> g = GE/(RR)

You know from the vector sum at the center g goes to 0 at the center of mass.

it doesn't take much more to realize that as mass decreases, so does the radius, and so does surface gravity (given a constant density). therefore, sure as mass increases, so does the radius.
ED__269_
1 / 5 (1) Dec 06, 2011
Just in case...
you should have arrived at g = 4/3G(pi)pR.

where density = p ; therefore g is linearly dependent upon the radius and directly proportional.

I'll leave it to you to verify and relate it to the circumference.
andyrdj
not rated yet Dec 10, 2011
Nanoblanco said "Even if it was a ball of pure water and water-ice, it would be more than twice as massive as Earth."

With a radius of 2.4 times that of earth, the mass for the same surface gravity would need to 5.76 times that of earth, due to the usual inverse square law.

If its densisty were identical to that of earth's, then its mass would increase by a factor of 2.4 cubed = 13.824

So its surface gravity would be 13.824/5.76 that of earths = 2.4g.

That doesn't seem immediately impossible for life.

Knowing what it's actually made of seems crucial, however.