October 28, 2010
Earth Sized Planets Very Common
Raising hopes that somewhere out there a planet is going thru a creative musical phase akin to the 1960s level of Rock and Roll music.
Nearly one in four stars like the sun could have Earth-size planets, according to a University of California, Berkeley, study of nearby solar-mass stars.
UC Berkeley astronomers Andrew Howard and Geoffrey Marcy chose 166 G and K stars within 80 light years of Earth and observed them with the powerful Keck telescope for five years in order to determine the number, mass and orbital distance of any of the stars' planets. The sun is the best known of the G stars, which are yellow, while K-type dwarfs are slightly smaller, orange-red stars.
The researchers found increasing numbers of smaller planets, down to the smallest size detectable today – planets called super-Earths, about three times the mass of Earth.
"Of about 100 typical sun-like stars, one or two have planets the size of Jupiter, roughly six have a planet the size of Neptune, and about 12 have super-Earths between three and 10 Earth masses," said Howard, a research astronomer in UC Berkeley's Department of Astronomy and at the Space Sciences Laboratory. "If we extrapolate down to Earth-size planets – between one-half and two times the mass of Earth – we predict that you'd find about 23 for every 100 stars."
I know, some of you are worried about the many invasion armadas sent in response to receiving 1950s TV shows. But there's upside potential: alien Elvis fans might be on their way to visit Graceland.
Any aliens that show up are either going to be robots or long-lived creatures who have long mastered the most advanced biotechnologies for rejuvenation and tissue regeneration. So if they do not want to wipe us out they might be willing to help make us all young again.
Seriously this raises the whole Fermi Paradox to a new level. According to a NASA "Ask an Astronomer" Webpage there are 14,600 stars within 100 light years of earth and the ratio given above means that there would be 634 "earth size" planets in the region. Wikipedia says, that at the low end of the estimate there are 100 BILLION stars in the Milky Way. This yields 4.3 Billion "earth size planets". The high end Milky Way estimate taken through the 23 planets to 100 star ratio yields 17.2 billion "earth sized planets".
So as Professor Fermi famously asked "Where is everybody?" Not a single unambigous visit? Not one fossilized spaceman? Not a single radio wave? Not a single big laser pulse?
Is Fred Saberhagen still alive? I am starting to REALLY study the Beserker series.
_RegisterOk so I know I am obsessing about this but if I take the Drake Equation (See Wikipedia) and assume that Drake and his buddies were too optimistic about life forming, lets say the odds aren't 100% like Drake assumed but 1/10th as great then: I still get over 63 civilizations within 100 light years of us and over 400 MILLION civilizations at the low end of the stellar population of the Milky Way. So again I ask: Not a single unambigous visit? Not one fossilized spaceman? Not a single radio wave? Not a single big laser pulse?
BUT if I change old Frank's L term the life of a civilization from his assumed 10,000 years to say 100 to 200 years then, disturbingly, I get the quantity of civlizations within our 100 lightyear sphere as close to 1. Which is the observed number, that is to say "little ol' US". How long have we been transmitting radio waves?? Is there any way to recall Voyager?
If they are out there I hope they do not find us until we are much more advanced. We have no idea whether they'll be hostile or friendly.
Based on the reasoning in the book, Rare Earth: Why Complex Life is Uncommon in the Universe, I'd say the problem isn't the frequency of life, as such, or the lifespan of civilizations. It's the frequency with which it gets blasted back to the primitive microbial state before evolving intelligence. Takes a lot longer for life to evolve intelligence, than for intelligence to evolve civilization.
The Drake equation is a bit of a joke as long as we're only guessing at the magnitude of every factor in it.
All way too optimistic. Earth-sized doesn't mean Earth-like. Mars and Venus are "Earth-sized". So what? Even Earth itself will only be "Earth-like" (by our standards) for a small percentage of its existence. There's only been breathable levels of oxygen for a billion years or so and a billion years from now our Sun's steadily increasing luminosity (a normal process for any sun-like star) will cause the oceans to boil away and turn Earth into Venus. So of Earth's 12 billion year life span -- from formation out of the primordial nebula to destruction by the Sun's red giant phase -- only for 2 billion will it be inhabitable.
There are so many factors missing from the Drake equation. For example, microbial life may be common anywhere there's liquid water, but there's reason to believe the transition from single-celled life to multi-cellular life was a very low probability event (Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane). On most planets it may never happen and life never gets past bacteria.
Another factor to consider is that it is far from a foregone conclusion that whatever single-celled life does appear will evolve photosynthesis. There are lots of chemical ways to make a living. Oxygen producing photosynthesis could well be unique to Earth, meaning this is the only planet anywhere with substantial oxygen in its atmosphere.
But even if multi-cellular life appears *and* evolves intelligence (not a guaranteed outcome by any means) consider how narrow the window must be. Depending on where you draw the line we've been around for 200,000 years and depending on whether you're an optimist or a pessimist we're either within 100 years or within 10,000 years of boosted intelligence/true AI/cyborgs, etc. which leads to who knows what. Think about what a narrow slice of the 10 or 12 billion year life span of a planet is represented by 200,000 years.
So what are the odds that two civilizations will develop on nearby planets *and* just happen to have their pre-singularity windows overlap so they can talk to each other?
American and Russian astronauts say there have been several unambigous encounters.
Why this is not front page news - or even really covered nearly at all by the news - is a mystery to me.
Also MUFON has several unambigous radar tapes showing manuevers not currently believed possible by known civilian or miltary aircraft - yet most scientists won't dare follow up on the evidence.
The perponderence of credible testimony that we ARE being currently observed is piling up!
Add to that the stacks of official papers showing that the US and UK are still actively investigating UFO cases - and clearly there seems to be more to the story.
Also - clearly - the "visiters" so not seem to want to make themselves public - likely because they are waiting for us to form a one world government - rather than dealing with the many many disorganized independent Nation States.
I personally have not seen a UFO - but the evidence has become quite compelling!
It certainly could end the paradox if civilians could get together and attempt to publicly verify this phenommena.
Let's assume that there are billions let's say Nx10exp 9 'Earthlike' planets in this galaxy, where we mean planets with acceptable biospheres over long times that allow multicellular life. Even with this large exponent #, all it takes is a few factors about which we know next to nothing to make us unique, though I hope not.
First, the probability of life arising spontaneously. Could be close to P=1 or close to P=10-exp(a significant #). This alone could wipe out any alternatives in the galaxy. We have no data. In contrast let's say life is somewhat 'common' (no need to be precise), but instead multicellular complex life has a significant small probability, say 10exp-9 or worse. Didn't happen here untill a couple billion years passed so we have no idea. Same issue for the arise of intelligences that can do computation. Only happened with one species and only after Nx10exp9 of years of evolution here. Another possible 10exp-9 or worse aliens killer.
Finally the mentioned time window for technical civilizations. If it's 'only' 10exp4 years or so, you'd need ~10exp6 civilizations during the galaxy's lifetime for us to have a good chance of having even one galactic buddy or worse yet, rival these days. We have NO idea of this # either.
The obvious answer to Fermi uses Occam's Razor and says that alien intelligences in the Milky Way are most likely rare to non-existant.
Also, if aliens capable of interstellar travel show up and want us exterminated, that's exactly what will happen, and we'll have about as much say in the matter as a wasp's nest nestled inconveniently close to your front door has. High tech battles against invading aliens make good movies, but they're fairly silly in practice. Some previously unknown stone-age tribe on some Pacific island that had just been taken over by the Japanese military in WW2 is orders of magnitude closer in technology than we would be to those aliens.