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This artist's impression shows Earth alongside the super-Earth known as 55 Cancri C, which is thought to be a little more than twice as wide as our planet and 7.8 times as massive.
Two years ago, Harvard astronomer Dimitar Sasselov stunned the world when he claimed there might well be 100 million Earth-size planets in the Milky Way. To some, the number sounded shockingly high. But the torrents of data that have come in from planet-hunters since then suggest that, if anything, the estimate was almost laughably low.
Just this month, researchers reported that there are probably more planets than stars in our galaxy, which would bring the total count well past the 100 billion mark. What's more, astronomers say the planets toward the lower end of the scale — "super-Earths" that are up to 10 times as massive as our own planet — are likely to be more common than Jupiter-scale planets.
"Small planets are really much more abundant than big planets," Sasselov told me last week.
Planet-hunters have already identified more than two dozen super-Earths beyond our solar system, including a batch of 16 announced on a single day last September. A couple of weeks ago, scientists spread the news about three planets smaller than Earth, and last week the science team for NASA's Kepler space telescope mission added still more super-Earths to the list.
That kind of planetary plenitude has even had an impact on the funny pages: "I don't know why this isn't the only thing people are talking about!" one character told another last week in the Arlo & Janis comic strip.
Basic Books
"The Life of Super-Earths" focuses on how the hunt for alien worlds and artificial cells will revolutionlize life on our planet.
It's the main thing that Sasselov is talking about, for more than one reason. He's a co-investigator for the $600 million Kepler mission, the director of the Harvard Origins of Life Initiative, and the author of a new book titled "The Life of Super-Earths." In the book, he makes the case that super-Earths could be as hospitable to life as our own planet, and perhaps even more so. Super-Earths that lie in the habitable zones around their parent stars — that is, the zones where water can exist in liquid form — would be prime candidates in the search for signs of extraterrestrial life.
"Life is not rare, it seems," the Bulgarian-born astronomer says.
Sasselov talked about the Kepler mission, the plenitude of planets and its implications for the search for alien life during our wide-ranging interview. Here's an edited transcript of last week's Q&A:
Cosmic Log: Do you look back at your estimate from two years ago and just shake your head at the idea that you were guessing so low? Were people making a fuss over something that now seems obvious?
Dimitar Sasselov:I feel that I was on the right track. Basically, yes, we have on one hand an even larger number of planetary candidates than I anticipated two years ago. The numbers went up. However, there is also a result which cancels those large numbers. There is a fly in the ointment. The caveat is that as it happens, most of our planetary candidates and confirmed planets are in relatively short orbits.
That means two things. First of all, they don’t directly tell you what the exact prediction about planets in the habitable zone should be.
Second, a lot of our small-planet candidates are in compact, multi-planet systems. Planets are closely packed next to each other, and these planets usually are within the orbit of Mercury around a star which is not that different from the sun. So there must be something extraordinary about the way they formed. It's quite possible that the formation and evolution required to create such architectures in planetary orbits is different in some fundamental way from planetary formation and early evolution in our solar system.
Jon Chase / Harvard
Dimitar Sasselov is a professor of astronomy at Harvard University.
So it is still a question mark as to what these planets are telling us, and what they are made of.
For the Kepler-11 system, we have the mean density of the planets. Those little planets are very low-density planets. They’re nothing like a bigger version of Earth. They have envelopes of hydrogen, or probably hydrogen and helium. They're like mini-versions of Neptune and Uranus. There are no planets like that in our solar system, so we don't know much about them.
It’s a cautionary tale there. Yes, there may be plenty of planets that are just two to three times more massive than our own Earth. But their mean density may be very low, because they formed farther out and migrated inward, and ended up in the moderate temperature regions of their planetary systems.
What would happen if we have a very large number, maybe billions, of super-Earth-size planets in the habitable zones — but half of them, or even nine out of 10 of them, are these mini-Neptunes? Would I consider them Earthlike? Definitely not, because they don't have the same geochemistry.
So while on one hand, the numbers have gone beyond my expectations, the diversity has gone beyond my expectations, too. And that means we might have a lot of planets with something different from an Earthlike geochemistry. Looking at the physics and the geochemistry is the only way we can go to the next step — and that is the search for signatures of life.
Q: What is the next step? How do you go from Kepler and planet detection to getting at the more fundamental questions?
A: To me, the next big step is to go from discovery and detection of planets like our Earth, to understanding their geochemistry. We have to do that to be effective in searching for biosignatures. The way we would do the first step — that is, understanding geochemistry — is by finding enough planets that are close to us. Kepler's candidates are a little bit too far for a good follow-up on characterization. So in terms of a practical approach, we should be gearing up for surveys of the nearby population of stars, and discovering those nearby planets.
There, the news from Kepler is good, because the statistics are high. If the statistics were low, then it would take more of an effort. Once we make that survey, and we can practically accomplish that in the next 10 years, we can jump onto those planetary candidates, and do atmospheric analysis, and try to understand the diversity of their atmospheres. This is a necessary step to talk about the signatures of life. Otherwise, we'd be looking blindly.
Q: Some people might say, well, let's just look for oxygen or methane, or something we associate with life on Earth.
A: That wouldn't be prudent at all. If we just look at biosignatures as we understand them on our own Earth today, they correspond to a particular moment in time in which the microbial communities on this planet have managed to change the atmosphere in a particular way. For about half of the history of life on Earth, the atmosphere wasn't anything like what it is today. It would be foolish to just assume that all life shares the same biochemistry and the same history.
Theoretically speaking, we should not assume that all planets that otherwise resemble Earth have the same geochemical cycle. There are alternatives.
Q: What sort of mission would work for this next step?
A: There are two approaches that need to be taken. The first one, when it comes to discovery, is a combination of space- and ground-based surveys. The space surveys would use smaller arrays of telescopes in orbit, and would scan the entire sky by observing the brightest stars, nearest to us, in a selective manner. But as opposed to concentrating in one direction, which was necessary due to the design of Kepler, we can select the nearest stars over the entire sky.
This can also be done from the ground for a particular subset of stars, which are the M stars. These stars are so much smaller than a sunlike star that the transits for Earth-size planets are much more prominent. You can see them using ground-based telescopes. You don't need to go to space. The trick is to do the whole sky and catch all those M dwarfs, and catch the transits.
Q: One of themes in your book is that we shouldn't limit the planet search to Earth-size planets, because the planets that are bigger than Earth — the super-Earths — might be more conducive to life than even our own planet. How can that be?
A: What we're finding out about super-Earths places them front and center as the most suitable places for life to emerge. These are planets that are only slightly bigger than Earth. In terms of size, we're talking about an average of 50 percent larger. In terms of mass, we're talking about two, three, five times as massive — maybe 10 in some cases, but overall, made of the same stuff.
Then you just compare the whole range of planets, from Mars to Earth to the largest super-Earths. In all different levels of comparison, the super-Earths end up being equal or slightly better when compared with Earth.
For example, one of the problems a planet could encounter is the ability to keep water liquid on the surface, and to have the good chemical exchange between the interior and the surface. That’s very difficult to do if you don’t have an atmosphere. An atmosphere in the habitable zone is difficult to keep, because it evaporates over the course of billions of years. If you have a small planet, made of rock but still low mass, like Mars is, eventually you lose more of your atmosphere than if you have a bigger planet. There is no negative factor, it is just more of a good thing.
Here's another example. A lot of people would say we have it good here on Earth because the moon keeps the axis of Earth's rotation more stable than it otherwise would be. It's the kind of momentum effect you get when you're on a bicycle — you can let the handlebars go and you still go straight. In a similar way, the existence of the moon out there cancels out the additional push and pull from the other planets, which could from time to time turn the axis of Earth dramatically and change the climate. This is what we think happened a few times on Mars. The more massive a planet is, the less vulnerable it would be to these effects.
Q: Is it always "the bigger, the better," until you get into a Neptune-class ice giant?
A: It's always the bigger the better. There's either no difference, or it's better. I didn’t find anything which was actually detrimental about having a big planet. Larger g-force, having more gravity on the surface, has a small effect when it comes to building biological structures, such as the membranes of cells. The list goes on and on. Everything gets better when you're slightly bigger.
Q: How long do you expect this book to stand up? I suppose that's an occupational hazard when you're writing about planet-hunting.
A: I would say it should stand up until we discover life out there on another planet, or in the lab when we manage to put it together as an artificial minimal cell. Then, of course, we'll open a whole new chapter in the history of science — and it will be so exciting that I wouldn't care. If a new book needs to be written, I will be happy to do so.
More about the planet search:
- NASA mission piles on the planets
- 160 billion planets in the Milky Way?!
- Three newfound worlds are smaller than Earth
- Flash interactive: How other worlds are found
- SETI researchers check signals in exoplanet study
- Millions of Earths? Talk causes a stir
- Cosmic Log archive on planets
Dimitar Sasselov will talk about the planet search during a book tour that takes him to Boston on Thursday and on Feb. 17, to New York on Feb. 6, San Francisco on Feb. 8 and Seattle on Feb. 10.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.
Leave a Comment:
I wonder how long it will be before one of us stands on the surface of an extrasolar planet.
Considering that the closest star system is more than 4 light years away, we need to see a revolution in space travel technology before we have even a chance of sending anyone to them. Our chemical reaction approach or even a nuclear approach just will not cut it. A more practical big question is it at all possible to send anything out to the nearest stars and have information sent back and recorded here on earth? If there is life in the universe more intelligent then then ours they will more likely discover us before we discover them.
It's fun to think about. When you consider about how people from just two centuries ago might see the world today, it really ignites the imagination about the future. I can't wait for the future! But I guess I'll have to.
when i think about these things i imagine that any significant advance in terms of putting a man in another planet with reasonable ease will only happen in about 100 years. but then again, 100 years ago, riding in the back of other animals was about the best cost/benefit mode of transportaion.
and then there is also the fact that raw material resources are quickly being depleted here or earth...im sure there is a distinct line that once crossed will ensure our species never leaves this planet to settle on another. sad days.
It depends on what you mean by "one of us". None of us reading your post will ever see it. Some human might, but very unlikely. I am not one to rule out even the remotest possibility however, because that would spoil some of my favorite science fiction!
The technology exists to travel at up to 10% the speed of light so 40 some odd years to Alpha Centauri if we could stomach exploding nukes above our planet.
Look up Project Orion, its an interesting idea that never really went where.
A super earth might be more conducive to life, but the gravitational field would greatly limit the ability of life forms to leave their planet. Similarly, it would limit our ability to "stand" on the surface of a super earth. We can barely get off of our planet without using multiple rocket stages. A super earth could (likely would) have a dense atmosphere more like Venus than earth. A life form adapted to living at the surface of a super earth would be accustomed to hundreds or thousands of atmospheres of pressure. Humans can survive at a little less than 3 psi of pure oxygen. (15 psi sea level x 0.21 oxygen = 3.15 psi oxygen pressure at sea level) That made the design of the Apollo spaceship and spacesuits relatively easy. The inhabitants of a super earth would need a massively strong space capsule (heavy) and a lot more rocket (than us) to reach space.
Sasselov argues that the higher g would not be that big of a factor for the development of life, because the cellular structures would evolve to accommodate that environment. I left a bit of that discussion out of the Q&A transcript, will have to review the recording to see if I can glean anything else. That's a good point that it may be harder to reach escape velocity if the super-Earthers want to be spacefarers.
@ dale
you are confused about how to calculate pressures I see what you are trying to illustrate but that's not how it work's ,for instance if you removed all the other gases from a room full of air the remaining presser would not be 3.15 psi even if you warmed it back up to room temp ,further more it would kill you immediately.
the % of o2 required depends on the presser and mix of gases there in , ask any professional diver.
and you seem to have not understood that a planet that is 2x bigger has only a slightly bigger G force do to the fact the surface is father from the center of the mass.
so in conclusion the statement " surface of a super earth would be accustomed to hundreds or thousands of atmospheres of pressure." is completely incorrect.
We know life that can exist under hundreds of thousands of atmospheres of pressures - we have oceans, these oceans have that much pressure (water is heavy), and we have life very deep down there.
It's not necessary that if a planet is larger in mass then Earth, its gravity will also be greater. That's because gravitational acceleration also depends on a planet's radius. So:-
A planet with 2 times the mass of Earth and twice Earth's radius, will have 1/2 Earth's gravity
A planet with 4 times the mass of Earth and twice Earth's radius, will have Earth's gravity
A planet with 8 times the mass of Earth and twice Earth's radius, will have two times Earth's gravity
In general, the higher the density of a planet (or a star), the higher is it's gravity.
Not going to happen... the distances are too great
The guy didn't even mention the role of a suitable magnetic field. There isn't any way of detecting magnetic fields around planets so distant.
Sasselov is quoted as mentioning magnetic fields in this article about the recent AAS meeting, but only in a theoretical sense. I think folks generally have to assume that a planet of a certain heft is going to have a core dynamo and a protective magnetic field. I think you're right that it would be hard to check exoplanetary magnetic fields.
Larger planets would also likely retain their internal heat for a longer period, even if their cores aren't as Uranium rich as we believe ours to be. Which leads to the core dynamo effect, etc. Mars is again a good planet to contrast to.
A sufficiently dense atmosphere also has a strong mitigating effect on inbound radiation. A magnetic field is certainly helpful, but again, if the conditions on the surface have the right chemistry, it's very likely local life will adapt to resist the radiation, or even accommodate it. Depending on how things work, all that bombardment might be a potential energy source that local lifeforms could thrive on. Unless it's being blasted by its primary, a super-earth is going to have a far denser atmosphere than here, and retain it far longer.
James...
with out a magnetic field even a thick atmosphere will not last long as the solar wind will strip it away.
given this fact it is absolutely imperative a planet with life potential has a magnetic field.
I would think it wouldn't be THAT hard to detect a planet's magnetosphere--wouldn't there be detectable interactions between it and the surrounding heliospheric magnetic field? Signatures of charged particles, etc?
Or life might use the inbound radiation as a power source. It's not hard to imagine a system where the ionization of atmosphere that would otherwise eventually strip away the atmosphere be used by life as energy, thereby both keeping the atmosphere from leaving and providing a power source for life.
@ Quiet P
the problem with mag.field detection is in the distance.
let say seeing the aurora of a planet 10 light years from hear would require the detection of heat or (electromagnetic radiation) that is probably 1 millionth or billionth of a degree above the back ground.not imposable but darn hard
Wade,
Tell that to the Venusians...
James
I see what you are saying but Venus has extreme volcanism that maintains the atmosphere with out which would slowly be eroded .
so I stand by my statement. that is not to say a form of life so different from are expectations couldn't take advantage of that, as in who would have predicted hot smokers in the ocean.
Thanks Alan for your response. I hope they pay you well for what you do ! Sasselov makes constant reference to the geochemistry of a planet. I find that to be a nebulous concept and he probably only uses the word loosely... The only thing that allows a magnetosphere is an iron core and the interaction with fluid material that allows a flow of electrons to make a magnet. Iron and ferromagnetic minerals are good conductors. I guess his theory is that a large rockey planet with an iron core and a circulating mantle is the only way to make a magnetosphere. To have life to take hold as we understand it, it is essential to have a magnetosphere that operates over billons of years. That to me makes the search even more difficult and maybe not answerable as there is no way to know that.
The Aliens will be back on Earth this year to take some of us to new worlds to inhabit. You can sign up at alienadventure.com if you want to be a candidate to go.
So we know they are there, now regardless human trip there or not , time to start sending out devices to get closer pictures without having to wait forever for results.
Lets put the idea of "we are the only beings in the universe" to rest. Its completely absurd to think that there's no life on any other planet in the trillion other Galaxies that hold billions of solar systems which have 1 to 20 planets in each system. im not a mathmetician but if there are at least 1,000,000,000,000 galaxies that the Hubble telescope has identified, which hold 1,000,000,000's of solar systems... which means there is waaaayyyyyyy more then 1,000,000,000,000,000,000,000 (sextillion <1*10^(21)>) other solar system, that can hold 1 to 20 planets
I wonder if the super-earthers would just be blobs. Not that there's anything wrong with that.
What a cr@p!!! Professor Doc Senile!!! Study??? What Study??? "There are more small planets, than big planets" Right On!!! There are more small thieves, than big thieves; more hungry, than well fed; more small endowed men and women, than large endowed men and women; more bad coffee than great coffee; more chinese, than jews and arabs combined!!! No free love, only, wine dine couldshe
Remember though, it's not size that matters the most, but whether you have the right chemistry to keep things interesting.
Doug, you're still talking about planets, right? ;-0
Michael, yes, planets of course. I like them nice and round :D
What is this? I don't even..
Oh, my, science. Betelgeuse, look at that planet.
It's so big. It looks like...
one of those black dwarfs' castoffs.
But, you know, who understands hypothetical star remnants?
They only let it orbit, because,
it looks like a total supergiant, 'kay?
I mean, the planet, its just so big!
I can't believe it's just so round, it's like
out there, I mean - huge. Look!
It's just so... super!
I like big planets and I cannot lie,
and you other brothers can't deny...
(With apologies to Sir Mix-A-Lot...)
I realize the number of planets discovered is still very small but I wonder if there is any correlation surfacing between the characteristics of the discovered solar systems and there locations on the specific galactic arms and their position on each of the galactic arm?
After all: Er = [(Mo*c^2)^2 + (P*c)^2]^-1/2
I'm ready and bags are packed. Let's go.
Superearth=Bigger battlefields
Well then, alien "tourists" have an awful lot of destinations from which to choose. We should stop concerning ourselves too much with talk of "contact", etc. Our Earth is probably not worth anyone's trouble....
Oxygen deprivation... Now there's a killer for human and most life as we know it here on earth life. That doesn't necessarily mean that life can not exist on super earths. There are other forms of life right here on earth than do not require oxygen.
Whether there is intelligent life on those plants depends on which side of the argument you agree with... Here's a little food for thought though. A one time or another we have all spoken to the ants... They did not answer did they?
Is that because they did not hear/understand us? or because we did not hear/understand the response.
I wonder how many politicians we can shove into a space capsule and send them anywhere else. Lord knows their of no use to us here on earth. SCUM SUCKING MAGGOT POLITICIAN's. Yes i am talking to you Newt the man who should be known as Newt the parasite, sucker of life's freedoms. At least in my view.
Were you married to Newt at some point?
@ Alan Boyle
I see one of your methods is to make logical extents to new discoveries. In that case, what follows from the dichotomy of the high probability of alien life to certain knowledge of alien life? If, for example, we estimate 100 billion super Earths or some very large number of them with corresponding high probability of life in one form or another (or many other life forms to be exact), and if we are (most likely) widely separated in space and time from any really interesting life form(s), why should we care so much and spend so much to discover actual alien life forms? Put another way, if we DO care a great deal to discover distant alien life forms, why are we so reckless with regard to other life forms here on Earth?
You know, rhino horns for quack medicinal cures, deforesting the Amazon Basin, etc.
Should our scientific curiosity about alien life be coherent to our relations to life on Earth, including other human beings?
What logical extents do you see to this burgeoning search for alien life forms? Where are we going, and why?
Maybe that is precisely why we haven't "found" alien life. They don't want a darn thing to do with us animals that kill our own kind.
This is a very good point!
Dubina .... you said
"if we DO care a great deal to discover distant alien life forms, why are we so reckless with regard to other life forms here on Earth?"
I think your forgetting that is a very small % of people that do things like poaching and as for deforestation we (man kind) needs to survive long enough to solve the energy problems we now face.
we most probably would have solved them already if it where not for the dark ages(500 years of wasted time do to RELIGION)
its likely the same for all advanced life so they would understand and maby help us
Wade: those 500 "wasted" years were actually the period of more scientific advancements than the Renaissance. The reference to "dark ages" is due to the fall of Rome, and it's a total misnomer otherwise.
You could also consider that the fall of Rome was due to... technology (roads, lead cups, the civilization of barbaric peoples) and not religon. Futher, the eastern empire (Byzantium) survived until nearly 1500 and was considered a center of learning and science.
The "Dark Ages' is in reference to the fact that the amount of written script took a huge dive during that time.
Also, the fall of Rome was due to wine being sold by weight, instead of volume ;-)
Mitchell
WOW you guys are so far off
the dark ages are 1200 -1600 and are only a reference to the face that any one doing science was burned at the stake ....come on learn history not the F.N Bibles lies
Um, wade. What I said was correct, it's considered dark ages because we actually don't know a lot about those times. This is because there was a dramatic drop in writings during that time.
Some of that was due to the Catholic Church, but a good part of it was because it was a volatile time. A lot of fighting and war ravaged throughout Europe, there wasn't a stability that was found that could compared to say...Greece or Rome of old.
Mitchell
Mitchell
you sound like a 17 year old that has been programed by some sort of "RELIGIOUS FREAK" go get help before its to late.
regardless of what you call it RELIGION has screwed us all .if man kind fails it is RELIGIONS fault.
Or, perhaps I sound like a person you actually had several history courses in college which has covered this topic and knows what he is talking about. I suggest you spend a bit more time reading history books, instead of being as ignorant as you sound.
Then again, your reading comprehension is very suspect since I did specifically state that part of the blame actually did fall on the Rome Catholic Church, so history books may not do you much good.
Ah well, children these days,
Mitchell
Tell you what, I'll help you out a little.
The term "Dark Ages" was first used by a person named Petrarca. He was an Italian scholar who lived in the 14th century and he was rather disgusted with Latin literature at the point in history. It was of his view that very little was being contributed to it and that what was being written, mostly had no quality to it. So, from the very start, it was about lack of literature.
Throughout the centuries, it's definition has been modified some. Early on, it was used to describe the "barbarian uprisings" that followed after the fall of Rome. Later used to describe the oppression that the Rome Catholic Church instilled upon Europe.
After the industrial revolution was well underway, the term came back to describe both the uprisings and the oppression of the Church that followed Rome's fall. It was now that the term also started to include the idea of repression of the sciences by the Church. That idea continued until the roughly the mid 1900's.
It was at this time there was a shift back to the idea that it donated a time where literature of the era saw a rather sharp decline. The term 'dark' now referred to the idea that the era between the fall and the Renaissance had little written record, therefore was 'dark' because we couldn't see what was happening at the time. The wars that followed the Fall and the Roman Catholic Church were now used to describe why we saw this decline.
Of course at this point in time the term "Dark Ages" is even slowly losing that definition. From an academic point of view, it's simply becoming a term that simply denotes the time between the Fall and the Middle Ages/Renaissance. Over the past 20-30 years we've uncovered quite a bit of writings from that era so we are learning quite a bit about the time. And Because of this, we are also realizing that the sciences we not repressed as much as was previously thought with significant strides being made in chemistry and mathematics.
There, you have a very very condensed history lesson.
Mitchell
Wade,
Again, you're making an arguement based on a fallacy. The Dark Ages started at 1200? No. Historians put it at the fall of Rome (500 AD) and culminated with the Renaissance, which started in the 1300s and went into the 1600s. So right there we have overlapping eras (part of the Renaissance was during the Middle Ages/Dark Ages).
Yet by your definition, (1200-1600) were bad years, yet they contained the greatest technological and scientific advancements Europe had seen since Rome. Ancient manuscripts were recovered from from Moorish Spain, trade blossomed from Italy and other parts of Europe all around the globe, Marco Polo, and the advent of regular trans-Atlantic travel and the rise of colonialism all bear this out. Never mind little things like you're discouting the effect of the Black Death (losing 1/3rd of your population in 1350 will cause problems!).
Further, if you want to put the blame on religion, why haven't areligious states ever flourished? The Soviet Union was a failure. So is Castro's Cuba, four generations after the revolution. North Korea? Cambodia? Spain under Franco? Nazi Germany? Fascist Italy? Why didn't the Mongols under Ghengis consolidate their great empire (that went from Krakow to Korea!)? There are many reasons why human advancement slows or speeds up, and you can't just blame one thing.
Religion has aided science over the years as much as it has hindered it. It's not different from (say) money or sport or any other influence.
Let's stay on topic, boys.
I haven't found or read an article that discusses the relationship of earth's life compared to those of possible habitable planets. Also, couldn't that factored into the search for intelligent life?
@Alan Boyle
Many of the comments talk about the magnetosphere, chemical analysis of the atmosphere, solid inner cores with resulting magma but no one seems to say anything about the gravity of the planet. The larger the super earth the larger effect of gravity on the surface. Unless the life is like the Incredible Hulk would life similar to ours be able to exist in the crushing gravity?
In this context, larger simply means larger diameter. When it comes to gravity, density matters just as much. So if a body is twice as big, but half as dense, you would actually experience a gravity that's less than Earth's.
Certainly some of then will be less dense than Earth, some about the same, and some that are more dense depending on the composition.
Also, keep in mind that gravity follows the inverse square law. That means the further from the center, the less pull there is. For a planet that's 2 and large, given the same density, I believe you only experience 1.3g's (if I remember correctly) simply because you'd be standing that much further away from the center. This is why I said 'less than Earth's' in my first paragraph.
One other thing to consider is rotational speed. The faster it spins, the more angular velocity you have (assuming you're not in the polar regions) which means there's a less "perceived" effect gravity has on you.
Hope this helps out, any other questions feel free to ask.
Mitchell
See post 2.4
Maybe all those unexpected planets and maybe unexpected asteroids and unexpected...what else, will explain all that "Missing Matter" in the univers and Dark Matter will not be needed to explain anything.
There was a story in Analog Science Fiction Oct 1974 called "A Matter of Gravity." If I'm remembering correctly, it takes place on a very high gravity world with intelligent life. Because of the gravity, these beings superficially resemble flatworms, and have a severe fear of height. Humans have landed and are able to communicate, but are forced to live in a liquid-filled tank lest they be crushed. I can't find the story on-line, just references to it. Perhaps someone here has a copy.
When are the prawns coming back to save wikus?
People who pretend to be the expert on things not proven. That is a job i need....
It is really quite easy. All you need is a PhD in astrophysics.
Go for it. :-)
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