December 12, 2003
Earthlike Planets May Be Common In The Universe

Either we are not alone or there are some prime planets waiting to be colonized.

Astrobiologists disagree about whether advanced life is common or rare in our universe. But new research suggests that one thing is pretty certain if an Earthlike world with significant water is needed for advanced life to evolve, there could be many candidates.

In 44 computer simulations of planet formation near a sun, astronomers found that each simulation produced one to four Earthlike planets, including 11 so-called "habitable" planets about the same distance from their stars as Earth is from our sun.

"Our simulations show a tremendous variety of planets. You can have planets that are half the size of Earth and are very dry, like Mars, or you can have planets like Earth, or you can have planets three times bigger than Earth, with perhaps 10 times more water," said Sean Raymond, a University of Washington doctoral student in astronomy.

Raymond is the lead author of a paper detailing the simulation results that has been accepted for publication in Icarus, the journal of the American Astronomical Society's Division for Planetary Sciences. Co-authors are Thomas R. Quinn, a UW associate astronomy professor, and Jonathan Lunine, a professor of planetary science and physics at the University of Arizona.

The simulations show that the amount of water on terrestrial, or Earthlike, planets could be greatly influenced by outer gas giant planets like Jupiter.

"The more eccentric giant planet orbits result in drier terrestrial planets," Raymond said. "Conversely, more circular giant planet orbits mean wetter terrestrial planets."

In the case of our solar system, Jupiter's orbit is slightly elliptical, which could explain why Earth is 80 percent covered by oceans rather than being bone dry or completely covered in water miles deep.

The findings are significant because of the discovery in recent years of a large number of giant planets such as Jupiter and Saturn orbiting other suns. The presence, and orbits, of those planets can be inferred from their gravitational interaction with their parent stars and their affect on light from those stars as seen from Earth.

It currently is impossible to detect Earthlike planets around other stars. However, if results from the models are correct, there could be planets such as ours around a number of other suns relatively close to our solar system. A significant number of those planets are likely to be in the "habitable zone," the distance from a star at which the planet's temperature will maintain liquid water on the surface. Liquid water is thought to be a requirement for life, so planets in a star's habitable zone are ideal candidates for life. It is unclear, however, whether those planets could harbor more than simple microbial life.

Suppose there are a lot of planets which are similar to Earth in size and in the amount of radiation they receive from their own suns. Even if some of them do not contain sentient lifeforms they still may have native life forms and those life forms may be incompatible with human life. Imagine pathogens that human immune systems couldn't even recognize let alone effectively fight. Or all native plant matter might be poisonous not only to humans but to any plants humans would bring to grow on such a planet.

It is incredibly common in science fiction movies and television shows for humans to mate and reproduce with aliens and to find edible food on distant planets. But if there is life on other planets both of these possibiliities are very unlikely. Other lifeforms will probably use different combinations of compounds for genetic encoding and for building tissues. Species on other planets may use amino acids to build proteins but probably not the exact same set of amino acids humans use. Ditto for sugars and other biological compounds.

The real tragedy is that even if humans and sentient species from other planets could get along and even if other sentient species lived under similar levels of gravity and atmospheric pressure and also were oxygen breathing it would probably be necessary to never have direct physical contact due to fears that pathogens would jump from one species to another with deadly results.

Share |      Randall Parker, 2003 December 12 01:24 AM  Space Exploration

Reptoid said at December 12, 2003 3:11 AM:

I'm probably wrong, but I suspect the likelihood of an extraterra species being brought down by terrestrial pathogens is remote and vice-versa. Pathogenic organisms tend to evolve to best thrive in certain hosts which is why trees don't catch SARS and lobsters don't come down with AIDS. The biochemistry and cell structure that lobsters share with humans is probably much closer than that between human and alien. If we are ever technologically advanced enough to meet up with an extraterra species outside of our solar system, I imagine at least one side will be able to counteract most threats of communicable disease.

In any case, these discoveries of exo-planets really jog the imagination, I can't wait until telescopes like the terrestrial planet finder are operational ( We might be able to find strong evidence of extraterra life by just analyzing the spectrum of these worlds for oxygen and other tell tale signs. The possibility of more Earth's being out there then there are people on Earth is somehow a comforting thought.

jb said at December 12, 2003 4:49 AM:

Yeah, I'm with Reptoid on the pathogens - I mean, if you assume we can't digest their food because its structure and sugar bases are very different, it seems very unlikely that they would have germs that could digest us. I think either Gould or Dawkins raises this very point in one of their books. (I think it was Gould, and I think it was in reference to the movie E.T.) Our viruses and bacteria are very tightly adapted to Terra 3's cells, structures and acids - unless the aliens were amazingly similar, genetically (which is possible, I suppose) - but then we could probably digest their food, etc.

Bob Hawkins said at December 12, 2003 8:40 AM:

If the alien life is protein-based, severe allergic reactions would probably kill everything involved in a physical First Contact. If the alien life is silicon-based or something like that, environmental factors like temperature and atmosphere would probably rule out unprotected contact.

Blogging will be the primary method of galactic intercourse.

ExtreemUK said at December 12, 2003 10:51 AM:

Why is it not possible that we will be perfect matches.

Afterall we were made as we are now, and assuming an infinite number of planets or whatever number you so desire, there is a chance that there are others out there that are 100% identical to us!

But i understand what every says and i agree with them.

Also just looking at the news header.

The Professors made an astounding message of "planets could be smaller than the earth and be dry or larger than the earth and be wet"
Well it didn't take me 4 years of a phd and a simulation program to realise that!

David Weisman said at December 12, 2003 4:55 PM:

If we can't eat the flora and fauna, why assume they can eat us? Many bacteria which flourish in the human body (some causing diseases, others not) have trouble surviving in an environment even slightly different. Why should our innards necessarily provide the right environment and nutrients? I read somewhere they might be entirely unable to deal with our amino acids and proteins :-)

Either condition might well be common or even universal, that we are unable to eat alien food or that we are very vulnerable to their parasites. It would be surprising to find both commonly true at the same time.

David Weisman said at December 12, 2003 4:56 PM:

Great post though! I'm glad to see someone is thinking about alien life. Best to be ready if it's thinking about us.

Bob Badour said at December 13, 2003 9:32 AM:


Neither need eat the other for mutual toxicity. Transpiration, exhalation, urination and defecation introduce numerous organic products into the environment, and any of these might prove toxic on contact, inhalation, consumption or wound exposure.

heet said at December 16, 2003 8:24 AM:

I agree w/ Badour that there could be some toxic compounds the other ecosphere makes, though they may have completely benign uses on the foreign planet. I don't think there is any chance of a "super pathogen" that can somehow infect anything on our planet. Many, many choices were made by evolution regarding things like the handedness of proteins and amino acid structure. I believe some of these choices were random though I would love to hear the opinion of an expert. I would be interested to know if some of the physical conformations (especially enantiomers) are energetically preferred. Regarding other planets having silicone based lifeforms -- I thought carbon's great property is it is the lightest element that can form 4 pi bonds?? I would think silicone bonds would be more unstable due to it's extra electron orbitals. Wouldn't this make reactions less predictable plus the extra weight would show up on a macro scale in heavier structures. What about solubility in water? Maybe a hotter environment would be less sensitive to these problems.

Sweet Mandie said at March 28, 2004 1:40 PM:

Thank u for this info. im a high school student and i am writing about aliens.... everyone thinks im crazy :) have a nice day! BYE!

Grant Johnson said at October 4, 2005 9:00 AM:


I believe there is other life out there but to say that if there is infinite number of planets, there is also a chance there will be life 100% identical to us is very unlikely. Many things have determined how we have evolved, this leads me to believe we are unique. The same as any other life form that exists in the universe. There might be similar life forms to us but not 100%. The odds of there being the exact same life forms as us is probably the same as winning the National Lottery 3 or 4 a row.

Myles said at January 16, 2008 4:23 AM:

Grant, you have just come up with some random numbers there based on your own thoughts.

Extreem said there was a chance that if there were infinite planets there is a chance that there are some beings 100% identical to us is a very valid assumption.

It doesn't negate the fact there is also a greater chance that there isn't.

Read before posting rubbish.

pyxsius said at January 17, 2009 10:45 PM:

The biological reality is that life, all forms within an ecosystem, evolve in relativity. Meaning, nothing 'evolves' on it's own in a vacuum, unaffected by external input. By this functionality, every life form on this planet has affected the evolution of the proximate life forms it interacts with. Pathogens; microbial, viral, chemical, seem to be a resultant product of the life they can affect.

Which refutes the notion that extraterrestrial life forms, in their complete spectrum, could be affective on our life here. Now it is feasible that different forms of energy synthesis could produce differing proteins and sugars that could be unrecognizable to the enzymes we have evolved and thereby be unusable to our biology.

The deeper, developing reality we are beginning to understand is that most life processes on this planet are effected by a viral antecedent or enabler. The implications of which are profound. It is now known that embryos will not implant in the placental lining in the absence of a specific viral symbiont.

How far down does the rabbit hole go? It is even more wildly believed that many of the viral strains on this planet are themselves extraterrestrial ...having hitched a ride here on a cometary vehicle.

Want even more food for thought? It is further speculated that viruses aren't even alive! I.e. a life form themselves!

kingbarney said at November 7, 2010 4:18 AM:

After reading some of the comments most good it just came to me why there are not aliens every where ?. What i mean is even with technoligy a bit better than ours given enough time you would conquer the galaxy but we do not see this. But maybe there is a problem that you cant go on most planets or eat alien life forms so any race that has made it into space ends up staying on there own planet or living in structures they built this would slow down exploration. at least they wouldn't eat us they probably would just find us interesting.

b.gupta said at April 10, 2012 3:54 PM:

in india ,tamilnadu ,human souls are taken under earth ,under rocks ,even to several thousnds kilometers under rocks,taking old revenges ,vengenes ,conspirancies ,polatics and given different shapes .in sevrages and made like aliens .taking under earth and beating and burning .
even to center of the earth, where no body can be able to find out , under rocks .even converting souls (atamas) to pieces the size of molecules even to newtron, proton size so that no one can search .buring alive .beating , cutting parts of boby of (souls) atama , sending to hell the place like toilt severages where no body sees , making aliens and like aliens from human .joining different souls atamas giveing unnatural shapes .breaking soul cutting hands , legs .stomach ,toungs,seprating layers of body and souls . spoil of budies brains , spoiling souls , kundlanies shakties ,nurves systems ,spoiling humans ,beating souls ,human micro soul powers .

request ------souls ,grand souls, microsouls or any molecules of human or any creatures should not be taken under earth or any hell for any punishment ,any kind of torturings ,sufferings .and requests, what ever punishment ,what ever punishment is should be given on the earth only infront of all .

every one was not born with the god'good grace and nature's good grace of good qualities and the good fate and luck to have good inteligence ,good wisdom ,good qualities ,and circuimstances not to commit ever any mistakes or sins .
request and pray ---every human every soul either good or bad ,angle or evil ,sinner,demon , god or devil every creature ,every one want to live as a good humanbeing --please save
request----instead of killing ,spoiling lives,destroying ,sending under earth ,hells ,if some place is given far away from india .and some thing are done for better to improve the qualities of humans and souls .so that every one can live .
whatever punishment for anyone .please given on the earth only , what ever it may be human,souls ,grand souls or any molecules infront of every one. not by taking under earth or hell-
REQUEST to request to give DEATH for ME ,MOTHER ,and FATHER ,and even to my TWO BROTHERS,and ONE SISTER to soul,grand soul ,kundaliy ,by giving or injecting POSION (which science & scientits can produce) and shown in the "DASAVATARAM "tamil & hindi india movie.BURN infront of ALL ON THE EARTH ONLY

Ladies souls are being made to rape and even souls 's souls are brought and some thing is given in stomach and it is happening under under and the stomachs, happening for revenges . in my eyes was seen a human body was pushed into holes , under groung in earth , how humans are born same way sending back . is it not shame full even for great humans are doing like such kind of things for revenges . please requests you to request and pray to stop ans save every soul .what ever punishment is should be given on the earth only infront of all.

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