What better indication of the success of our planet hunting efforts than the news out of the American Astronomical Society’s annual meeting in Honolulu. There, the California & Carnegie Planet Search team announced at least 28 new planets, with four multi-planet systems among them and two borderline cases that need further investigation. That’s a bump of 12 percent in the number of known planets over the last year. Behold:
With the exoplanet count now not that far from 250, planetary discoveries are coming fast enough that a certain ennui seems to have settled in among press and public. Sure, Gliese 581 c was big news because we thought it was potentially habitable, but finding more and more gas giants probably won’t trigger the public imagination, even if GJ 436 b did cause a ripple because of the presence of water. That ripple lasted only long enough for scientists to explain what kind of water they were talking about. Here’s Geoff Marcy (UC Berkeley) on the subject:
“From the density of two grams per cubic centimeter – twice that of water – it must be 50% rock and about 50% water, with perhaps small amounts of hydrogen and helium. So this planet has the interior structure of a hybrid super-Earth/Neptune, with a rocky core surrounded by a significant amount of water compressed into solid form at high pressures and temperatures.”
Hard, hot, high-pressure water isn’t conducive to life and researchers have been quick to note that habitability is not an issue here. But it shouldn’t be neglected that a rocky place with high water content, discovered through a transit of a ‘hot Neptune,’ is an exciting reminder that the essentials for life are likely widespread. Marcy thinks about one in ten planets in our galaxy are habitable, which by his reckoning makes for around 20 billion conceivably living worlds in the Milky Way.
Image: The interior structure of the planet, Gliese 436 b. The core is probably composed of rock, including silicates, iron, and nickel. The envelope is probably composed primarily of water under high pressure (from the weight of material above it), and of smaller amounts of methane and ammonia. The density of the planet is 2.0 grams/cc, as determined from the planet’s mass (from Doppler measurements) and the diameter (from the dimming of the starlight as the planet transits in front of the star, blocking starlight). Credit: Jason Wright/California & Carnegie Planet Search.
The news release on these findings is here, containing John Asher Johnson’s interesting discoveries around A and F stars, with masses between 1.5 and 2.5 solar mass. Coupling his observations with earlier exoplanetary discoveries around older A stars, Johnson notes that planets around massive stars seem to orbit farther from their primary. “Only one of the 9 planets is within 1 AU (astronomical unit, or 93 million miles), and none of them is within 0.8 AU, of their host stars, which is very different than the distribution around sun-like stars,” Johnson said.
So it will be interesting to see what happens as this team works through the 450 older A stars it has added to its target list. Massive A stars like these normally rotate quickly and can mask the radial-velocity ‘signal’ of accompanying planets, which is why the team focuses on older A stars that have nearly completed hydrogen burning, a short period of stability that can reveal much about planetary companions. Large planets seem to show up more often around more massive stars, a trend that, if confirmed, seems to show the core accretion model of planetary formation at work, there being more disk material available early in the process.
“Marcy thinks about one in ten planets in our galaxy are habitable, which by his reckoning makes for around 20 billion conceivably living worlds in the Milky Way”.
??? Fascinating thought and I love to endorse it. However, what is this guesstimate based on? Surely not on the discovered planets themselves. Is it a statistical thing?
Dwelling on this: through the years I have seen guesstimates varying from 6 billion to 30 billion (potentially) habitable planets in the MW galaxy, based on number of sunlike stars, fraction of stars with planets, size distribution of planets (i.e. relationship size-abundance), statistical probability of planet in habitable zone, etc.
Marcy’s figure fits nicely in this range.
(Can’t wait for TPF, Darwin).
I share your enthusiasm for those coming terrestrial planet hunter missions, Ronald. Marcy’s figure has a lot of play in it, to be sure, but I’m assuming it’s based on an extrapolation from existing planetary systems and the likelihood of finding numerous smaller, rocky worlds once we tune up the technology sufficiently to detect them. Guesswork to be sure, but if anyone’s guesstimate gets my attention, it’s a guy like Marcy’s.
20 billion stars is about the same number of stars as can be found in the arms of the Milky Way, isn’t it? And the core seems like an iffy place to look for Earthlike worlds. It seems to me that for this to be true, virtually every system outside the core would have to have a habitable world.
I wonder what he meant by habitable. If it’s just “life-bearing” (extremophiles living in frozen over iceworlds, in the seas of close orbiting ice giants or the clouds of post-boil off terrestrials), that seems at least arguable. The stronger sense, the kind of world we can live on with a minimum of technology, seems less likely.
He very likely meant at least life-bearing. Anything more
advanced at this point would be pure speculation. But I do like
the odds. Even the Rare Earthers think that many planets are
viable enough to at least have bacteria.
And with 100 billion galaxies in the rest of the Universe, plus the
idea that there may be an infinite amoutn of other universes in
the Cosmos, and I would say the odds get really good for life
beyond Earth.
My own take is that ‘terrestrial’ worlds are going to prove relatively commonplace, and so will life, but technological civilizations will be extremely rare. It’s just raw speculation, but I’d put my money on one to ten technological civilizations active at any one time in the galaxy.
Carl Sagan used to estimate that there were 1 million technological
civilizations in the Milky Way Galaxy. Even if they were of the kind
of technology and inclination to exlpore space and contact other
civilizations, on average the nearest one to us would be about
200 light years distant.
So unless they have some seriously powerful telescopes aimed at
Earth, they won’t know about us due to the speed of radio waves
for at least another century. That is one reason I like the idea of
searching for ETI signals (or sending signals) in the opposite
direction from supernovae.
See here for more on the SETI Supernova Beacon concept:
http://www.iar.unlp.edu.ar/SETI/seti-boston.htm
I still think the major factor in SETI taking a long time to succeed
not just for us but for other species is not the amount of intelligences
in the Cosmos but the vast amount of star systems and immense
distances to conquer first.
@James Nicoll: no, that must be far more, in the arms and disc I mean. The MW contains some 400 billion stars (+/- 200 billion) and Galactic Habitable Zone (GHZ) estimates vary from 5 – 50%, usually around 20% of stars (Lineweaver and others). That would be some 80 billion, but nowadays some astronomers say (almost) the entire galactic disc may be GHZ. Of course, within that GHZ there would be a further selection of suitable sunlike stars (metal-rich, not close binary, non-variable, etc.), reducing the number considerably, but still, a lot (hundreds of millions to billions).
BTW, in the Andromeda galaxy the number of metal-rich main sequence stars seems to be considerably higher.
Habitable planets: actually life-bearing or (at least) suitable for life? I mean, it is possible that conditions are potentially suitable for life (water, temperature, light, etc.), but still without life.
And keep in mind that with the relatively small sample of
exoplanets we have, astronomers have already found a
number of planets around double star systems in stable
orbits.
They used to think multiple stars in a system would
make things too unstable for planets to exist, at least
planets that could harbor life successfully.
Tatooine may be real after all.
The only things about chances of habitable terrestrial planets, that keep worrying me are: the great eccentricity of many (most?) found exoplanets and the abundance of giant planets in relatively close orbits (possibly as a result of inward migration, spoiling a lot of fun).
With regard to the first: how eccentric is allowable for a habitable planet around a sunlike star? I remember having read something about this some years ago, but forgot what and where.
With regard to the second; it would be great to know if a small planet can exist in a stable orbit with a giant planet in a smaller orbit.
Can anybody reasonably put these concerns to rest?
Hi All
First, the Milky Way has about 100 billion stars. Over the years the quoted estimate keeps going up, but astronomers have consistently said “100 billion” based on tricky estimates from light intensity and observed galactic mass.
Second, eccentricities of up to ~ 0.4 are OK for habitable planets, based on GCM studies of model earth-like planets. Parts of a planet could remain habitable in extremely eccentric orbits (~0.7) if it was a bit further out from its star. Climate modelling has changed opinions on this issue quite a bit.
Third, a number of models of planet formation with a migrating gas giant indicate that Earth-like planets could form in stable orbits outside the Hot Jupiter’s orbit. Migration happens pretty quickly (~ few myr), but terrestrial planet formation is quite slow (~+100 myr), so the two processes don’t meet in time.
Fourth, the number of civilisations depends heavily on estimates of lifetime. Sagan was an optimist and assumed an established species with interstellar travel would last for millions of years. Other estimates reduce numbers dramatically by assuming short communicative lifetimes, after which a species is either extinct or no longer interested in contact. Perhaps they “Ascend” into some other kind of presently unimagined kind of existence in higher dimensions? Or “devolve” into unintelligent forms? Or form Matrioshka brains which consider chattering newbies to be beneath their august intellects?
Ken Macleod rather pointedly speculates in his “Fall Revolution” series that uploaded software species (“Fast Folk”) will become parasitised into oblivion by members adopting strategies of optimisation for rapid growth – eliminating eventually everything but the urge to fill memory space. As a result such “Singularities” become unstable and ultimately disconnect from control of the physical world, which doesn’t respond quick enough to one’s desires unlike a VR environment. Stepping up one’s clock-speed can just create more (subjective) time to get really bored.
Thus perhaps all civilisations eventually fall victim to the equivalent of “Turing viruses” – intelligent software that edits out everything humanly worthwhile in a quest for speed.
@Adam: thanks foryour reply.
I presume the allowable eccentricity also depends on the width of the HZ, i.e. on the (spectral) type of star.
The number of stars in the MW is really probably (considerably) more than 100 billion, based on, among others, light and mass estimates. The minimum estimate is 200 billion, max. estimates much (MUCH) higher, the most common or median estimate 400 billion. See among others Wikipedia and Solstation (also for sources).
Geoff Marcy said the following from this article here:
http://www.abc.net.au/science/news/stories/2007/1936224.htm?space
“Our Milky Way galaxy has 200 billion stars. I would estimate that 10% of them, perhaps, have planets that are habitable,” Marcy says.
“There are hundreds of billions of galaxies, all of which are more or less like our Milky Way galaxy, which is tens of billions of planets like our own.”
Yes, Carl Sagan was an optimist; a rare trait these days.
With due respect to Marcy, his opinion on the # of habitable planets is just that, an opinion. We have very little factual data and the number of habitable (whatever imprecise definition that means) planets known beyond the Earth remains at 0. Opinions by allegedly authorative scientists have an excellent track record of being really wrong. Most of theses projections q.v. Sagan are really projections of wish-fullfillment.
I played around with the idea of galaxies and aliens some time ago. Looking at wiki and the Atlas of the Universe, our galaxy is the highest mass, most number of stars of all the galaxies within 20 million light-years of here. Andromeda is larger in size, but is less dense (contains fewer stars) than our own galaxy. All the other galaxies within 20-30 million light years are either smaller in dimensionality or less massive.
Now, lets say we are alone in our galaxy (which is what I believe). Since we happen to be in the biggest, most massive galaxy in the neighborhood, its likely that any aliens will be in a galaxy bigger than our own. This suggests that the nearest aliens are going to be in the Virgo supercluster, which is the closest place that has galaxies larger than our own. Virgo is 60 million light-years from here. So, I think the nearest aliens are 60 million lightyears from here.
For practical purposes, we are alone.
There really is an underlying fear of any other intelligent
beings occupying the same galaxy with humanity these
days, isn’t there? Friendly or otherwise.
This goes beyond the usual statement that we haven’t found
any aliens yet – which when you think about the fact that we
have yet to even seriously explore the worlds at the edge of the
Sol system, to say nothing of the rest of the Milky Way, makes
the previous phrase an incredibly premature statement – but
maybe that is standard for a species that still thinks it is the
Focal Point of Existence despite some nagging growing scientific
evidence to the contrary.
Humans can barely stand each other and act like the territorial
animals that we are, so perhaps something from another
world with purple tentacles instead of arms and legs or a
brain the size of Jupiter is a bit too much to deal with at our
stage of evolution.
Who was it who said that God made the stars so far apart
for a reason?
Speaking of which, and to focus on the last post in this
thread, SETI has given thought to studying the galaxies
for signals, including the Virgo Cluster.
http://www.contactincontext.org/cic/v2i1/m87.htm
These fellows think our first SETI signal will come from
that very distant cluster, of which our Local Group of
galaxies is but a small province at its edge.
http://skytonight.com/resources/seti/3304536.html
@kurt9: I presume that by ‘aliens’ you mean intelligent life and not life in general?
I notice a few flaws in your reasoning;
Your assumption that ‘we are alone in our galaxy’ is a personal believe and not based on scientific facts (nor is the opposite BTW).
The Andromeda galaxy may have a somewhat smaller mass than our MW galaxy, however, its number of stars is probably (much) greater than that of our MW. Moreover, it seems to contain a higher proportion of main sequence and metal-rich stars and has fewer supernova explosions. So probably quite a good place to be.
And if we are indeed alone (the only intelligence) in our own galaxy, well, at least we won’t have to defend our place in the galactic pecking order. And there will be a lot (a LOT) of real estate available for us.
Ronald, your declaration that if humanity is alone in the galaxy
that we won’t have to worry about dealing with a pecking order
with other civilizations has one glaring flaw: That our descendants
won’t engage in the very behavior that we worry about with alien
societies.
When the human race finally gets off its butt and heads out into
the stars, the generations that will develop and evolve in other
star systems may eventually become as alien to each other as
a true alien species would be to us. If humanity hasn’t learned
anything by then, the pecking order scenario may come true
for our children, done by themselves.
As for ETI, if they do exist and are friendly, we have nothing to
worry about. If they are a threat, there is little to nothing we
can do at this stage. A single ship sent at relativistic velocities
aimed at Earth could wipe out the whole planet. And we might
do that to others one day.
Go to this page and scroll down halfway to where you see the
cover for the SF novel The Killing Star:
http://www.projectrho.com/rocket/rocket3aa.html
@ljk:
yes, admitted frankly, this was already nagging on my mind as I wrote the previous post: we may well be our own (and the rest of the MW’s) worst enemy! In fact the thought I had was: do I really want a race of semi-savages (us) to conquer the MW, if we haven’t achieved true civilization yet?
So, there is the dilemma: the grand mission to explore and colonize the MW and spread our species and civilization, on the one hand. The risk that we will be spreading a serious pest, on the other.
Maybe that is a reason the creator spread the stars so far apart. It’s a test, but not just a technological one.
Human migration into the galaxy and even beyond may happen
whether it is a good idea for the rest of the Cosmos or not.
There will always be some groups for one reason or another
who do not like/follow the rules of society and will head out
into space to make their own way. It has happened plenty of
times in the past and will happen again.
The shiny hero astronauts portrayed by NASA will not be
the ones to truly conquer the galaxy. It will be the rebels,
the antisocials, even the criminals. But things will change
once a few generations have passed.
Of course I also think that the first intelligences to head
out into the galaxy from Earth will not be human. They
will be better suited for existence in space and other
worlds and presumably have few or none of our issues.
Or maybe it will be a mix of the two species. It will be
interesting to see if they ignore/avoid each other, try to
co-exist, or we end up with Bear’s Great Sky River.
Hi Larry
Greg Benford’s “Great Sky River” I presume you mean – the Mechs versus the Organics. In the fullness of deep time he hints that the two sides reconcile their differences – a human and a Mech from the deep future come back in time to fight the current Mechs in one of the later books of the series.
“Shiny Hero Astronauts” sounds almost like a Japlish poster for astronaut recruiting by JAXA. And “shiny hero astronauts” might be an apt description of the intelligent machines that conquer the stars. Hopefully they will inherit our best qualities and not be heir to the failings of fleshiness.
The Age of Virtuous Machines
J. Storrs Hall
06/01/2007
In the “hard takeoff? scenario, a
psychopathic AI suddenly emerges at
a superhuman level, achieving
universal dominance. Hall suggests
an alternative: we?ve gotten better
because we?ve become smarter, so AIs
will evolve “unselfish genes” and
hyperhuman morality. More honest,
capable of deeper understanding, and
free of our animal heritage and
blindnesses, the children of our
minds will grow better and wiser
than us, and we will have a new
friend and guide–if we work hard to
earn the privilege of associating
with them.
http://www.kurzweilai.net/email/artRedirect.html?artID=708&m=25748
AI is another part of today’s unconscious technical mythos, defended as if it were a religious tenet. Despite decades of exhuberant forecasts, the AI era is always a couple decades away in the future. I’ll be we have usefull fusion power first, and I’m not optimistic.
Folks should read Taleb’s “Black Swan” for a rationalist look at forecasting the furure.
The point is, AI is possible by our hands, not waiting around
for fate or chance to make it happen.
Even if consciousness is never achieved, I am sure an AI could
be created with such sophisticated programming that no human
could tell it apart from a truly conscious being.
True consciousness may not even be necessary, especially if
such an AI is used for interstellar missions. A quick understanding
and action of the various environments such a probe is likely to
encounter would be of prime value for such missions. A true and
deep understanding of what is found/going on at Alpha Centauri
could be left up to the humans back on Earth.
But I still think Artilects will happen one day, so there.
ronald that last point you made above about why the stars may be so far apart etc is a good one i appreciated reading it! thank you your friend george
Thank you for your encouragement, george!
And encouraged by george’s kind words, I cannot help bringing up a thought that I had in this connection and with ref. to my previous post (about the great distances between stars):
As a biologist I strongly favour the principle of natural selection and adaptation, as an explanation for many observed facts. Perhaps this principle, in some way, also applies to entire galaxies.
This is to say: maybe galaxies where technologically advanced civilization can thrive, persist and spread are those where stars and in particular habitable planets are quite far apart, so that the civilizations that manage to cross the gaps are those that have truly stood the tests of time, survival and ‘true civilization’, including a fundamental respect for life in general.
In other words, violent barbarians will probably either destroy themselves before they reach any serious level of technology, or at least blow themselves up before they manage to cross over to other planetary systems. In even in the worst case that they manage to do that, they will probably not get very far across the galaxy. So, in order to make it to other planetary systems a civilizaton must survive long enough and therefore be inherently peaceful and ‘inwardly civilized’. Just a hopeful thought.
Just a little elaboration on the previous: this may to some seem in contradiction with the principle of ‘survival of the fittest’, which often seems to favor and select the aggressive and violent. Not necessarily so, this is actually a too simplistic and rather outdated view: survival of an entire society and civilization entails a lot more and higher skills than simple aggression and violence.
ronald thank you very much for the kind words above! and… i fear that by the standard you mention then,we of earth are as of yet a long way from “civilization” and the ability to cross the interstellar distances! hope we arrive long before we destroy ourselves!and yes “survival of the fittest” is a catch phrase frequently used for the wrong or even crass reasons! hope we can talk again soon. your friend george
As David S. F. Portree points out in a very recent article of
the Earth & Sky blog, only 5 new exoplanets were found, not
28.
http://blogs.earthsky.org/dsfportree/astronomy-outreach/053013/28-new-worlds/
To quote:
The headlines should have read, “Team Announces Five New Planets.” Of course, if the news media knew that “only” five new planets had been found, we might not have seen any headlines.
I think that this goof is an indictment not only of press release writers and science reporters, but also of the way astronomers refer to the planets they find orbiting other stars. Few people can recognize the arcane alphanumeric designations they use. We need to start giving these worlds real names. If we did, these planets would become distinct, recognizable worlds, not mere interchangable sets of letters and numbers.
i think that milk way has by less 1 trillion planets because if the milk way has 400 billions star and astronomers discovery planet around metal pool stars. planet like PSRb 1620-26b in globular cluster M4 around neutron star like PSR1257+12 and dust disk around star type O 70 sun mass by Spitzer Space Telescope dusk disk around every kind of star like in many brown dwarf star and planet around every kind of star it’s show that planets can survive at stellar evolution and born around heavy mass star so i believe that the galaxy has not just billions but trillions of planets
Stability constraints in modeling of multi-planet extrasolar systems
Authors: K. Gozdziewski, C. Migaszewski, A. Musielinski
(Submitted on 2 Feb 2008)
Abstract: We present an analysis of high precision radial velocity (RV) observations of stars hosting multi-planet systems with Jovian companions.
We use dynamical stability constraints and quasi-global methods of optimization. As an illustration, we present new results derived for the RV data of the Sun-like dwarfs HD 155358 and $\tau^1$ Gruis.
Comments: 13 pages, to appear in the Proceedings of IAU Symposium 249, Suzhou (China) “Exoplanets: Detection, Formation and Dynamics”, eds. Y.-S. Sun, S. Ferraz-Mello, J.-L. Zhou. Please download pdf for acceptable quality of figures (see also this http URL)
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.0254v1 [astro-ph]
Submission history
From: Krzysztof Gozdziewski [view email]
[v1] Sat, 2 Feb 2008 15:49:51 GMT (2589kb,D)
http://arxiv.org/abs/0802.0254