Posted by
Hemos
on from the it's-like-the-earth-baby dept.
jrb writes "For the first time, a small planet (i.e. non-gas giant sized) has potentially been found outside the solar system, helped by a gravitational lensing effect that magnified it. The BBC is carrying the full story. "
Science is inductive. A theory is proposed, then grows in acceptance as a large body of data is found to agree with the theory, while none is found that contradicts it.
We've had theories of solar system evolution, planetary spacing, formation of asteroid belts, and others, for a long time. But these theories are very unsatisfying because we only have one datapoint, our own solar system.
This may not seem important, if you believe that the solar system is completely typical. By the nature of a bell curve, most likely our system is in most respects. But there is very little evidence it is yet. We were already pretty certain that gas giant planets are not uncommon. This is the very first evidence that small rocky planets may not be uncommon either.
According to my calculations the feat is very roughly equivalent to detecting a speck one micrometer in radius at a distance of two kilometers, so I'm impressed anyway.
BBC appears to have muddled the facts
by
Robert+Link
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· Score: 2
I was curious about this one, since I don't recall any mention of an earth-sized planet at the July AAS meeting on gravitational lensing. Still, I work on cosmological gravitational lensing, not microlensing, so perhaps I came down with a case of tunnel vision at the conference.
Running this one down took a little leg work, seeing as how the BBC did not elect to give the names of the researchers involved. As best I can tell the BBC has mixed up two separate lensing events. The paper that appears to have triggered the story is probably this paper on MACHO-97-BLG-41, since that is the most recent paper claiming a gravitational lensing planet detection. However, that paper is about a 3-Jupiter mass planet orbiting a binary star system, an interesting find, to be sure, but a far cry from an earth-sized planet. So, even if that is the article the BBC is responding to, it's not the one they're talking about.
The article mentions that the event was observed in 1998 and involved an earth-sized planet, so that sounds suspiciously like MACHO-98-BLG-35, but that paper came out (as a preprint) back in May, and it was announced at the January AAS meeting, so it's a little surprising to see a news article on it just now, unless it's just now appearing in the journals.
Anyhow, assuming the event is 98-BLG-35, there's more to the story. The PLANET collaboration also monitored this event, and they found no evidence of a planet in this system. As far as I know, the status of this system is still under dispute. Unless some problem has been found with PLANET's data, I think it's a little early to claim that an earthlike planet has been detected.
To get the scoop on microlensing, its application in planet searches, and the other things we can learn from it, I recommend PLANET's web page. Among other things, they talk about why microlensing is more sensitive than radial velocity studies (the technique that has produced most of the other extrasolar planet detections) to planets in star systems similar to our own solar system.
Just trying to wrap up some points that were being put out here, and maybe answer some questions in the meantime with my intermediate knowledge of astronomy.
Finding this planet, if the evidence leans towards that theory, is a big deal, as so far all we have found arround other systems are very big gas giants. One solar system is really bad for statistical analysis. We could be the fluke of the universe, so just because it happened here doesn't mean it had to happen somewhere else.
Nearly all planet observations, an really all astronomical observations, are objects infered by the bizare behavior of well lit objects. Faint changes in spectrum of a single bright object, means that it is probably a binary system... etc. The best analogy I have heard about astronomy is a goldfish trying to figure out what the world outside its pond is like. It can never go there, but can learn from indirect observations.
I assume that the gravity lensing difference between the two stars can easily be picked out because although they both throw a lot of light, they don't have the same spectrum, and probably not even the same redshift. You can then subtract out the closer star because you very carefully observed it when there was nothing significant behind it.
I don't claim to be an expert on such issues, but hopefully someone got something from my little rant here.
-- There is no silver bullet. Plus, werewolves make better
neighbors than zombies or vampires anyway.
Re:Couple of clarifications
by
DHartung
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· Score: 2
nfgaida wrote: >> We could be the fluke of the universe >How likely is that? out of the 300 billion stars or so, (give or take a few billion) that our planet would be the only one?
We don't know how likely it is. It could be as common as grass; or we may be unique. We have no information either way to make a sound judgement.
>Come on... i'm not blaming you for this view, cause many people have it.. our society has it. >It goes back to my point about religious arrogance.
Well, it is a matter of faith. I happen to agree with you, though maybe not for the same reasons. I simply believe that the evolutionary process is effective enough that once life begins on a planet, reaching intelligent life is almost a given. Now, Earth had a couple of shots; the dinosaurs were around for millions of years, but they never built a space shuttle. We've only been around a few hundred thousand years, and have accomplished a great deal in a flicker of time.
I think that is a great argument for the near-inevitability of intelligent life. On the other hand, as Larry Niven points out, there's no guarantee that we'll be intelligent at the same time as another planet's intelligent inhabitants. And that we both develop space programs, or at the very least, effective SETI. We could be a single star system away from a planet that was inhabited by intelligent life... millenia ago.
Again, though, the bottom line is that we have no data, so an intelligent determination is impossible. All we have are assumptions, and guesses, and extrapolations.
Until we found out that Jupiter, Uranus, and Neptune all have their own faint ring systems, we believed that Saturn was unique. Numerous sf stories were written where our solar system was "famous" as the one with the planet with the beautiful rings. Now, we have to assume that they're everyday things. But this, of course, is what makes astronomy exciting. We like not knowing, because that means there's more stuff to find out.
-- lake effect weblog {Network engineer in Chicago--looking for work!}
it would be really really cool if the could find out more about all these planets they are finding... right now all they can tell is mass (and from that, size) and dimensions of it's orbit...
and an even better question, is anyone pointing radio telescopes at these flying rocks?
and an even better question, is anyone pointing radio telescopes at these flying rocks?
If you look at the picture at the top of the BBC article, you'll see that it isn't from an optical telescope. I would bet that they _did_ use radio telescopes rather than X-ray, IR, etc., particularly as the observatories are on Earth (Australia and New Zealand) rather than in orbit.
You are almost right. What you (and everbody else in the above list) are forgetting is Newton's 2nd(?) law: for every action, there is an equal and opposite reaction. Yes, the absolute accelleration of an object in a gravity field is independent of its mass, but its accelleration relative to the body creating the gravity field is not due to the object accellerating the body towards it at the same time.
The relative accelleration (ie the rate the object appears to be falling, or the rate of approach) is givven by a=G(m1+m2)/(d*d). Here's the proof:
NOTE: The directions of the two absolute accellerations are opposite to each other (unit(a1)=-unit(a2)) so as relative accellaration is a1-a2 (or a2-a1), the magnitude of the relative accelleration is mag(a1)+mag(a2) and we couldn't care less about the direction.
In conclution, the mass of an object does affect its rate of fall, but when we're talking about the moon, a hammer and a feather, the difference between the hammer and feather is insignificant and not easily measurable.
NOTE 2: I just realised that if you drop the hammer and the feather at the same time, they probably (ie I'm too lazy to prove it) fall at the same rate because they're both pulling on the moon (ie acting as a single body), but if you drop them separatly, there will be a slight difference.
--
Bill - aka taniwha -- Leave others their otherness. -- Aratak
Actually, the article stated that it's located "near the center of our galaxy". That puts it somewhere around 20,000 light years from Earth (taking our distance from the center as being around 25,000, though it does get jiggered around as new observations are made).
Since the fastest space probe we can build now would take around 60-80,000 years to reach the nearest star system, Alpha Centauri, we can infer that the quickest we could reach this newly discovered planet is around 1,200,000,000 years. By then our own sun will likely be cooling and expanding, making Earth uninhabitable. Better hurry!
Even if we assume the capability to speed up a craft near light speed, say a solar sail or a reaction drive using interstellar hydrogen as fuel, we're still looking at twice the length of written human history to reach this star.
Now, assuming a warp drive, all bets are off. But that's a bit much to assume.
As for your last question, about how Earth-like it may be, we'll probably never know. That determination would require detailed spectral analysis, and the amount of light received in these observations just couldn't have been sufficient. Whether it has an atmosphere, water, a reasonable distance from its sun... although, given the proximity to the center of the galaxy, background radiation may well be too high for life as we know it to survive.
-- lake effect weblog {Network engineer in Chicago--looking for work!}
After a report in this week's new scientist about rocky planets being formed by gamma ray bursts, I was a wee bit worried. If this is such a planet, there's no need to divide the Drake Equation by a thousand.
This would be a huge dissapointment!...but if you think about some of it, it does make good sense. I'm only an amateur astronomer/physicist (if you can even call me that) and I've always wondered how the rocky planets came together.
Having been lucky enough to do a literature review on this topic recently (as part of my 3rd year u/g course) I can clear up a couple of issues;
The method used works as follows; when gravitational field of the planet warps the space around it, any light from the star that might otherwise have 'missed' the telescope/eye/pinhole camera (!) would be 'bent' back to the aforementioned instrument.
Hence we do _not_ see the planet, rather the effect of the planet on a star which is how all extrasolar planet detection methods (except one which has failed to date) work.
We have no instruments capable of resolving a planet, but NASA & ESA both havbe projects that in 2020-2060 will be able to do so at IR frequencies. Hence the BBC picture is wrong. All it pointed out was the star.
This method is not repeatable, since it relies on a chance that a background star acts as the source and the planet in orbit around an unseen star all line up for us.
You might think, 'doesn't the planet star lens the background one?' - it does! The additional blip caused by the planet on the light curve is what gives it away.
The typical distance to the background star (usually in the galactic plane) is 100 parsecs, the planet's parent star is usually half this distance for geometric reasons.
Hence it's really far away! We can tell virtually nothing about the planet apart from it's mass (which won't help diffrentiate between tiny gas giants and big terrestrial types).
If anyone want's more info (or even <gasp> a copy of my lit review, written for an intelligent person) then email me. Dosvidania tovarish!
-- --
Thus conscience does make cowards of us all - Hamlet
People aren't being naive.. it's called arrogance. Specificly religious arrogance. The major religions have always tried to teach: 1) We are created like god(ess) therefor humans are unique 2) The universe revolves around us. We are the reason for the universe existing. 3) more that i can't think of...
At any rate, it is no suprise to me that the majority of people think of our planet as the only one to support life in the universe. and that WE are the definition of life. We meaning lifetypes here on earth. Carbon based and all that. Even science has been limited by religion, limiting our search for ETs and space exploration in general.
I always thought when i was a kid that there were millions of planets. of course most of what i read as a child was Sci-Fi, but when i started taking science classes and reading actual science litature, i relized how far we had to go yet.
nate
-- *elevator music plays*
Reaching them in our lifetimes
by
DWRM
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· Score: 2
When our parents were born (assuming your's are as old as mine) the thought of reaching space at all in our lifetimes was a faery tale. When my grandparents were born, it was doubtful that this new fangled automobile thing would ever really catch on. We should not doubt the power of science. Especially when funded properly *cough*
Like some old proverbe went, every long journey begins with just one step. (or sth like that) Discovering gigantic planets was first achieved hardly a decade ago and now we've found a small rocky planet like ours. Soon we may be able see them clearly enough to analyse its atmosphere through the light it reflects to see if it would be fit for life... One things lead to another in the world of science
The rest mass of a photon (particle of electro-magnetic radiation, which includes all frequencies of visible light) is 0 - not 0."some very small amount" but just plain 0. And, in the absence of electro-magnetic fields, a photon has speed c in all relativistic frames of reference. (hence "c" is the "speed of light", which is "invariant in a vacuum").
The simplest way to think of what is actually happening is to think of space itself being "bent" by gravity and so the path of light through that space is not straight in the classical, Euclidean/Cartesian sense.
Another way to describe what is happening, without having to understand what is meant by space being "bent" (after all, any N-dimensional manifold can be embedded in a 2*N [-1?] - dimensional Euclidean space) is that light travels along a path in space-time with minimum seperation, where seperation is a 4-dimensional measure, somewhat akin to distance, determined by the metric tensor of the space-time traversed. In the presence of a gravitational field caused by mass (actually any gravitational field - but thats an even weirder subject), the metric tensor differs from that of Euclidean 4-space, so the path of a photon is NOT a Euclidean straight line.
(Of course, the simplest approach is just to say that gravity bends light and not try to explain why;-)
Part of the problem I see with this while thing (and with astronomy in general) is that, depending on how far away this star is (and the article never said), we're seeing this 'earth-sized' planet probably *millions* of years ago. What was Earth like millions of years ago? Even thousands of years ago? A lot can happen in the amount of time light takes to travel from a distant star to earth - species come and go, cultures rise and fall... For all we know some aliens might have already blown the place up for an interstellar highway!
Re:The only problem with looking for RF signals...
by
dentin
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· Score: 3
Actually, I think your estimate is a little low. I've been fiddling with some of these questions for a while now, and even have a sort of simulator that generates star systems. It looks (as near as I can tell) that about one in 10 star systems has a planet with liquid water, reasonable gravity, and appropriate temperature range.
Also, current thinking is that the odds of life happening on such a planet is fairly high... on the order of 10 to 50% (from various abiogenesis experiments). Of course we only have one real data point, but the evidence seems to point to the idea that life isnt that hard to make.
The probability of intelligence is significantly lower, but once they have intelligence the probability of rf technology is effectively 1, so that term vanishes as well. I don't think intelligence is that rare, and that after 5 billion years of evolution, I would put this factor around.5. You are free to use your own value of course, but given that semi-intelligent creatures abound on this rock, I don't think intelligent creatures who can use tools are that far off.
Probability of emission frequency if fairly low as well, however not quite as low as you would think: There are certain bands that are the best for transmitting in. Most of the spectrum is filled with broadband noise, and there are a few marker frequencies that would be the most efficient/effective to transmit on. Instead of 1e-6, I'd be a bit more conservative and put it at 1e-4.
Of course there is one more term you forgot to mention: the length of time an alien race might transmit such a signal. This is pretty much anyone's guess, but id place it at no more than 500 years - which is a really short period of time. This factor should be divided by the average age of the stars we will be looking at, which would be about 5 billion years. This factor alone works out to 1e-7.
So the net result is.1(star with planet)*.1(planet with life)*.5(tool/rf using life)*1e-4(proper frequency band)*1e-7(prob we will catch them transmitting)
This works out to about 5e-14 per star, which is still pretty low, but not 1e-24. Also, we can get rid of the 1e-4 factor by improving our detection technology. Additionally, the 1e-7 number may be significantly larger if electromagnetics end up being the only way to communicate across large distances. I wouldn't expect much EM radiation from the planet though, as eventually everything would go to cable/fiber optics instead of radiated waves.
So while the odds are still highly against us, they arent quite as bad as you depict and we can increase them over time.
-dentin
-- Alter Aeon Multiclass MUD - http://www.alteraeon.com
Re:Common senses - heavy objects fall faster
by
jflynn
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· Score: 2
"If you had extensive physics (any freshman college course for example) you would know that heavy objects do in fact fall faster in a vacuum."
Sorry, the gravitational force is greater on a massier object, but this increase in force balances the increase in mass precisely, so the acceleration of an object due to gravity is independent of its mass.
Assuming m1 is the object exerting gravity, and m2 is the object affected, the acceleration a2 for m2 is
a2 = F/m2 = (G*m1*m2/d*d)/m2 = G*m1/d*d
That is, acceleration, and hence velocity, is independent of the size of the mass accelerated.
A lot of people are debating the whole 'of course there are planes out there, we can't be the only one' arguement. But look at it statistically - If we assume that the universe can be represented by a bell curve (no, I'm not going to get into new-fangled 'natural' statistical curves here), then the solar system could, probability-wise, fall anywhere inside that curve (from our starting sample size of 1, we have no reference where to place ourselves).
So we start looking at the universe. We find a lot of stars, but none with obvious planets. Instead of consigning the Solar System to one of the tail ends of the bell curve, we assume we don't have equipment sensitive enough to detect planets yet (which we didn't.)
So we design better equipment. We start finding some (a few) Gas giants orbiting stars. And we go, "Ah-hah! See, we're not alone! We must fall somewhere within the center of the normal curve!" Yet still the sample size is small compared to the number of stars - which would really shove 'stars with Gas Giants' to outside one or two standard deviations, and 'stars with earth-sized planets' even further out, with a single sample we know of.
Now we find a (possible) star with another earth-type planet (Class M? Class L? When are scientists going to look up the Star Trek regs and tell us what Class Mars is?), and we say, "We are definately not unique." But look at the statistics - even with *2* systems with earth-sized planets, your sample is *miniscule* compared to the billions of stars! We could very well be in the extreme tail of the bell curve, and actually *be* unique in the universe!
Until SETI produces results, or an alien shows up on Prime Time TV during the President's State of the Union address, I don't think anyone will be able to say for sure that we are not alone. I, for one, believe that we cannot be - I cannot concieve of such a lonely universe. But we really don't have any proof to the contrary. yet. So, while this is very important, don't loose perpective on what it really means about our place in the universe.
"Why the hell do you want to colonise everything? Isn't it a better idea to stop polluting our own planet? Stop wasting its resources so rapidly?"
With that attitude we'd all still be on one continent. Not that I don't agree that pollution and resource depletion are serious problems.
One good and time tested way to stop using resources here is to get them somewhere else. It doesn't look like anyone else is too interested in the asteroids at the moment, perhaps we can be permitted to use some of them? Maybe even start some space colonies to support that activity?
It's likely going to be a long time before we're capable of even near interstellar voyages, let alone colonization missions. Perhaps we'll even have better ethics about destructive exploitation by then.
Not the first Earth-sized planets, either
by
J05H
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· Score: 3
Just the first one found around a main sequence or nearly-main sequence star. In 1989, three Earth sized (well, one is Mars sized, but close enough) planets were discovered orbitting a pulsar. They are obviously dead planets, like their star, but they always fail to be mentioned, especially in the mainstream media. Anyway, check out the Extrasolar Planets Encyclopedia for more info on all of this.
The rest mass of a photon (particle of electro-magnetic radiation, which includes all frequencies of visible light) is 0 - not 0."some very small amount" but just plain 0. And, in the absence of electro-magnetic fields, a photon has speed c in all relativistic frames of reference. (hence "c" is the "speed of light", which is "invariant in a vacuum").
You've given the two important points, but failed to connect them in a useful way. The rest mass of a photon is exactly zero, but we never observe photons at rest. They always travel (through a vacuum) at c. Each photon has a energy proportional to its frequency. Dividing the energy by c^2 gives the mass of a moving photon which is a function of it's frequency.
-- I have discovered a truly marvelous sig, unfortunately the sig limit is too small to contain i
Hey wait a minute!!
by
Anonymous Coward
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· Score: 2
Maybe it's not gravity lensing, maybe it's gravity mirroring and we're looking at ourselves! The universe is curved.
The only problem with looking for RF signals....
by
mattz
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· Score: 2
...is that the statistical probability of the planets we found has life is way too low, as well as the probability of that life being intelligent, and the probability that It has found how to generate RF signals of a reasonable strength... p(find rf)= p(life) X p(intelligence) X p(rf technology) X p(emmission frequency) probably like ~1x10^-6 for each term, which gives us like p(find rf) ~ 1x10^24 for each rock. Not good odds if you ask me.
-- Remember this...no eternal reward will forgive us now
for wasting the dawn....(jim morrison)
Re:The only problem with looking for RF signals...
by
mattz
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· Score: 2
i mean p(find rf) ~ 1x10^-24.....sorry 8)
-- Remember this...no eternal reward will forgive us now
for wasting the dawn....(jim morrison)
Hmm, the 5-second explanation on CNN last night showed an animation where the detection involved the eclipsing of the star by the planet. So if this is right, they didn't detect the light reflecting off the planet, they detected the obscuring of the star as the planet orbits.
Finding planets this way is a really haphazard way of doing it. Stars rarely line up well enough to make gravitational lensing really viable as a method of detecting another planet. Another method they've been using is watching the Doppler shift of a selected star. Any star with an object revolving around it exibits a regular 'wobble' in the shift. Make a guess at the mass of the star, apply some centuries old math to it, and voila! You know how many objects are orbiting the star, how massive they are and how far away from the star!.
-- .sig: Now legally binding!
More information on microlensing
by
StupendousMan
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· Score: 2
Permit me to clear up a few questions and misconceptions. Interested readers can read the technical details for themselves in preprints on the LANL server:
A good summary: http://xxx.lanl.gov/abs/astro-ph/990819
The event MACHO-97-BLG-41 http://xxx.lanl.gov/abs/astro-ph/9908038
The event MACHO-98-BLG-35 (to which this Slashdot article refers indirectly) http://xxx.lanl.gov/abs/astro-ph/9812252
Okay, now for my comments:
1. Contrary to "cemerson"'s post (which should have been moderated to "MisInformative":-), the work _was_ done in with optical telescopes; in fact, small ones, only a meter or so in diameter (rather than the 8-meter or 10-meter behemoths like Keck). The basic method is to take pictures of the same field of stars over and over and over, and look for variations in the brightness of any star with time. The technique works best if one can point at a large number of stars at once; the two best sources for crowded fields are the Bulge of the Milky Way and our nearest neighboring galaxy, the Large Magellanic Cloud. Both are best viewed from the southern hemisphere, and the data described in the recent press releases comes from Chile, South Africa, and New Zealand.
2. The Bulge of the Milky Way is about 8,000 parsecs (about 25,000 light years) away from us. The LMC is about 50,000 parsecs away. These are the "background" stars. A star roughly halfway between us and the "background" will cause the greatest lensing effect as it passes between us and the "background" star.
3. When such an event occurs, the "background" star becomes brighter. Now, here's the key: if the "foreground" object is a lone star, then one can predict theoretically the shape of light curve: the background star brightens slowly at first, reaches a somewhat sharp peak in brightness, and then fades exactly as it brightened: the rising and falling phases look exactly the same, symmetric. And, in fact, most of the observed microlensing events (there have been over 100 followed in the past decade) follow this predicted, symmetric curve very closely.
4. But, if the "foreground" object is not a lone star, but a binary star, or a star with a planet, the light curve will depart from its theoretical, symmetric shape. If there's a planet around the foreground star, and it passes in front of the background star, it can cause a distinctive "spike" in the light curve: a short, sudden, very brief rise and fall. The event MACHO-98-BLG-35 shows a LITTLE bit of evidence for such a spike: see Figure 9 in the paper by Yock: http://xxx.lanl.gov/abs/astro-ph/9908198
5. There are several efforts underway to detect planets around other stars by searching for the tiny 'eclipses' caused as a planet passes in front of its star in its orbit, but no solid detections yet. This is very difficult, because even a big planet like Jupiter causes only a (roughly) one-percent dip in the light of its star -- and many stars vary by more than one percent. Planets like the earth decrease the light by even smaller amounts, maybe one-hundredth of one percent. At that level, _most_ stars are variable. So, one must disentangle the intrinsic variation of the star from the brief dip caused by the planet -- and that means waiting months/years for the planet to come around in its orbit again. You can find information on one such search, Kepler, at this site: http://web99.arc.nasa.gov/~mars/vulcan/
-- Michael Richmond "This is the heart that broke my finger." mwrsps@rit.edu http://stupendous.rit.edu
Astronomy is a science where you can not repeat your experiment (the universe). Whenever you get a result, in this case the result is that we live on a planet, you have to spend a long time considering any possible biases. The fact that we'd be dead if we weren't on a planet is a pretty big bias towards finding ourselves on one, even if it's the only planet in the universe.
As for it being pretty obvious that there are other planets out there, 1000 years ago it was pretty obvious that the earth was flat.
Lensing occurs with any mass of object. The size of the effect depends on the mass of the lens, and on its position. Lensing has been observed around the sun, which is not very massive.
In this case, they were looking for the distinctive brightening of the light from a star which would occur if some object like a dead star or jupiter sized planet passed exactly infront of a background star. From studying the number of such events, you can calculate the amount of mass in our galaxy made up of such `dark' objects.
What they found is that one of their light curves didn't match the theoretical curve. Unfortunately the experiment is essentially not repeatable, as you'd have to wait for something else to pass in front of that star, which could be thousands of years.
Slashdot Mirror
Science is inductive. A theory is proposed, then grows in acceptance as a large body of data is found to agree with the theory, while none is found that contradicts it.
We've had theories of solar system evolution, planetary spacing, formation of asteroid belts, and others, for a long time. But these theories are very unsatisfying because we only have one datapoint, our own solar system.
This may not seem important, if you believe that the solar system is completely typical. By the nature of a bell curve, most likely our system is in most respects. But there is very little evidence it is yet. We were already pretty certain that gas giant planets are not uncommon. This is the very first evidence that small rocky planets may not be uncommon either.
According to my calculations the feat is very roughly equivalent to detecting a speck one micrometer in radius at a distance of two kilometers, so I'm impressed anyway.
Running this one down took a little leg work, seeing as how the BBC did not elect to give the names of the researchers involved. As best I can tell the BBC has mixed up two separate lensing events. The paper that appears to have triggered the story is probably this paper on MACHO-97-BLG-41, since that is the most recent paper claiming a gravitational lensing planet detection. However, that paper is about a 3-Jupiter mass planet orbiting a binary star system, an interesting find, to be sure, but a far cry from an earth-sized planet. So, even if that is the article the BBC is responding to, it's not the one they're talking about.
The article mentions that the event was observed in 1998 and involved an earth-sized planet, so that sounds suspiciously like MACHO-98-BLG-35, but that paper came out (as a preprint) back in May, and it was announced at the January AAS meeting, so it's a little surprising to see a news article on it just now, unless it's just now appearing in the journals.
Anyhow, assuming the event is 98-BLG-35, there's more to the story. The PLANET collaboration also monitored this event, and they found no evidence of a planet in this system. As far as I know, the status of this system is still under dispute. Unless some problem has been found with PLANET's data, I think it's a little early to claim that an earthlike planet has been detected.
To get the scoop on microlensing, its application in planet searches, and the other things we can learn from it, I recommend PLANET's web page. Among other things, they talk about why microlensing is more sensitive than radial velocity studies (the technique that has produced most of the other extrasolar planet detections) to planets in star systems similar to our own solar system.
-r
Just trying to wrap up some points that were being put out here, and maybe answer some questions in the meantime with my intermediate knowledge of astronomy.
I don't claim to be an expert on such issues, but hopefully someone got something from my little rant here.
There is no silver bullet. Plus, werewolves make better neighbors than zombies or vampires anyway.
Come on, everybody knows the earth is flat and travels through space on the back of a giant turtle (Great A'Tuin), carried by four giant elephants.
pffffff.
-- It's always darker before it goes pitch black.
it would be really really cool if the could find out more about all these planets they are finding...
right now all they can tell is mass (and from that, size) and dimensions of it's orbit...
and an even better question, is anyone pointing radio telescopes at these flying rocks?
I post links to stuff here
The relative accelleration (ie the rate the object appears to be falling, or the rate of approach) is givven by a=G(m1+m2)/(d*d). Here's the proof:
f1=G*m1*m2/(d*d) -> a1=f1/m1=G*m2/(d*d)
f2=G*m1*m2/(d*d) -> a2=f2/m2=G*m1/(d*d)
a=a1+a2 = G*m2/(d*d) + G*m1/(d*d) = G*(m1+m2)/(d*d)
NOTE: The directions of the two absolute accellerations are opposite to each other (unit(a1)=-unit(a2)) so as relative accellaration is a1-a2 (or a2-a1), the magnitude of the relative accelleration is mag(a1)+mag(a2) and we couldn't care less about the direction.
In conclution, the mass of an object does affect its rate of fall, but when we're talking about the moon, a hammer and a feather, the difference between the hammer and feather is insignificant and not easily measurable.
NOTE 2: I just realised that if you drop the hammer and the feather at the same time, they probably (ie I'm too lazy to prove it) fall at the same rate because they're both pulling on the moon (ie acting as a single body), but if you drop them separatly, there will be a slight difference.
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
Actually, the article stated that it's located "near the center of our galaxy". That puts it somewhere around 20,000 light years from Earth (taking our distance from the center as being around 25,000, though it does get jiggered around as new observations are made).
... although, given the proximity to the center of the galaxy, background radiation may well be too high for life as we know it to survive.
Since the fastest space probe we can build now would take around 60-80,000 years to reach the nearest star system, Alpha Centauri, we can infer that the quickest we could reach this newly discovered planet is around 1,200,000,000 years. By then our own sun will likely be cooling and expanding, making Earth uninhabitable. Better hurry!
Even if we assume the capability to speed up a craft near light speed, say a solar sail or a reaction drive using interstellar hydrogen as fuel, we're still looking at twice the length of written human history to reach this star.
Now, assuming a warp drive, all bets are off. But that's a bit much to assume.
As for your last question, about how Earth-like it may be, we'll probably never know. That determination would require detailed spectral analysis, and the amount of light received in these observations just couldn't have been sufficient. Whether it has an atmosphere, water, a reasonable distance from its sun
lake effect weblog
{Network engineer in Chicago--looking for work!}
After a report in this week's new scientist about rocky planets being formed by gamma ray bursts, I was a wee bit worried. If this is such a planet, there's no need to divide the Drake Equation by a thousand.
The method used works as follows; when gravitational field of the planet warps the space around it, any light from the star that might otherwise have 'missed' the telescope/eye/pinhole camera (!) would be 'bent' back to the aforementioned instrument.
Hence we do _not_ see the planet, rather the effect of the planet on a star which is how all extrasolar planet detection methods (except one which has failed to date) work.
We have no instruments capable of resolving a planet, but NASA & ESA both havbe projects that in 2020-2060 will be able to do so at IR frequencies. Hence the BBC picture is wrong. All it pointed out was the star.
This method is not repeatable, since it relies on a chance that a background star acts as the source and the planet in orbit around an unseen star all line up for us.
You might think, 'doesn't the planet star lens the background one?' - it does! The additional blip caused by the planet on the light curve is what gives it away.
The typical distance to the background star (usually in the galactic plane) is 100 parsecs, the planet's parent star is usually half this distance for geometric reasons.
Hence it's really far away! We can tell virtually nothing about the planet apart from it's mass (which won't help diffrentiate between tiny gas giants and big terrestrial types).
If anyone want's more info (or even <gasp> a copy of my lit review, written for an intelligent person) then email me. Dosvidania tovarish!
-- Thus conscience does make cowards of us all - Hamlet
This is the first _Earth-sized_ planet discovered. Not the first planet. Other Jupiter-sized planets have already been discovered, IIRC.
1) We are created like god(ess) therefor humans are unique 2) The universe revolves around us. We are the reason for the universe existing. 3) more that i can't think of...
At any rate, it is no suprise to me that the majority of people think of our planet as the only one to support life in the universe. and that WE are the definition of life. We meaning lifetypes here on earth. Carbon based and all that. Even science has been limited by religion, limiting our search for ETs and space exploration in general.
I always thought when i was a kid that there were millions of planets. of course most of what i read as a child was Sci-Fi, but when i started taking science classes and reading actual science litature, i relized how far we had to go yet.
nate
*elevator music plays*
When our parents were born (assuming your's are as old as mine) the thought of reaching space at all in our lifetimes was a faery tale. When my grandparents were born, it was doubtful that this new fangled automobile thing would ever really catch on. We should not doubt the power of science. Especially when funded properly *cough*
DWRM
http://www.freebsd.org
Like some old proverbe went, every long journey begins with just one step. (or sth like that) Discovering gigantic planets was first achieved hardly a decade ago and now we've found a small rocky planet like ours. Soon we may be able see them clearly enough to analyse its atmosphere through the light it reflects to see if it would be fit for life... One things lead to another in the world of science
Well, uh, no.
;-)
The rest mass of a photon (particle of electro-magnetic radiation, which includes all frequencies of visible light) is 0 - not 0."some very small amount" but just plain 0. And, in the absence of electro-magnetic fields, a photon has speed c in all relativistic frames of reference. (hence "c" is the "speed of light", which is "invariant in a vacuum").
The simplest way to think of what is actually happening is to think of space itself being "bent" by gravity and so the path of light through that space is not straight in the classical, Euclidean/Cartesian sense.
Another way to describe what is happening, without having to understand what is meant by space being "bent" (after all, any N-dimensional manifold can be embedded in a 2*N [-1?] - dimensional Euclidean space) is that light travels along a path in space-time with minimum seperation, where seperation is a 4-dimensional measure, somewhat akin to distance, determined by the metric tensor of the space-time traversed. In the presence of a gravitational field caused by mass (actually any gravitational field - but thats an even weirder subject), the metric tensor differs from that of Euclidean 4-space, so the path of a photon is NOT a Euclidean straight line.
(Of course, the simplest approach is just to say that gravity bends light and not try to explain why
Part of the problem I see with this while thing (and with astronomy in general) is that, depending on how far away this star is (and the article never said), we're seeing this 'earth-sized' planet probably *millions* of years ago. What was Earth like millions of years ago? Even thousands of years ago? A lot can happen in the amount of time light takes to travel from a distant star to earth - species come and go, cultures rise and fall... For all we know some aliens might have already blown the place up for an interstellar highway!
Actually, I think your estimate is a little low. I've been fiddling with some of these questions for a while now, and even have a sort of simulator that generates star systems. It looks (as near as I can tell) that about one in 10 star systems has a planet with liquid water, reasonable gravity, and appropriate temperature range.
.5. You are free to use your own value of course, but given that semi-intelligent creatures abound on this rock, I don't think intelligent creatures who can use tools are that far off.
.1(star with planet)*.1(planet with life)*.5(tool/rf using life)*1e-4(proper frequency band)*1e-7(prob we will catch them transmitting)
Also, current thinking is that the odds of life happening on such a planet is fairly high... on the order of 10 to 50% (from various abiogenesis experiments). Of course we only have one real data point, but the evidence seems to point to the idea that life isnt that hard to make.
The probability of intelligence is significantly lower, but once they have intelligence the probability of rf technology is effectively 1, so that term vanishes as well. I don't think intelligence is that rare, and that after 5 billion years of evolution, I would put this factor around
Probability of emission frequency if fairly low as well, however not quite as low as you would think: There are certain bands that are the best for transmitting in. Most of the spectrum is filled with broadband noise, and there are a few marker frequencies that would be the most efficient/effective to transmit on. Instead of 1e-6, I'd be a bit more conservative and put it at 1e-4.
Of course there is one more term you forgot to mention: the length of time an alien race might transmit such a signal. This is pretty much anyone's guess, but id place it at no more than 500 years - which is a really short period of time. This factor should be divided by the average age of the stars we will be looking at, which would be about 5 billion years. This factor alone works out to 1e-7.
So the net result is
This works out to about 5e-14 per star, which is still pretty low, but not 1e-24. Also, we can get rid of the 1e-4 factor by improving our detection technology. Additionally, the 1e-7 number may be significantly larger if electromagnetics end up being the only way to communicate across large distances. I wouldn't expect much EM radiation from the planet though, as eventually everything would go to cable/fiber optics instead of radiated waves.
So while the odds are still highly against us, they arent quite as bad as you depict and we can increase them over time.
-dentin
Alter Aeon Multiclass MUD - http://www.alteraeon.com
"If you had extensive physics (any freshman college course for example) you would know that heavy objects do in fact fall
faster in a vacuum."
Sorry, the gravitational force is greater on a massier object, but this increase in force balances the increase in mass precisely, so the acceleration of an object due to gravity is independent of its mass.
Assuming m1 is the object exerting gravity, and m2 is the object affected, the acceleration a2 for m2 is
a2 = F/m2 = (G*m1*m2/d*d)/m2 = G*m1/d*d
That is, acceleration, and hence velocity, is independent of the size of the mass accelerated.
A lot of people are debating the whole 'of course there are planes out there, we can't be the only one' arguement. But look at it statistically - If we assume that the universe can be represented by a bell curve (no, I'm not going to get into new-fangled 'natural' statistical curves here), then the solar system could, probability-wise, fall anywhere inside that curve (from our starting sample size of 1, we have no reference where to place ourselves).
So we start looking at the universe. We find a lot of stars, but none with obvious planets. Instead of consigning the Solar System to one of the tail ends of the bell curve, we assume we don't have equipment sensitive enough to detect planets yet (which we didn't.)
So we design better equipment. We start finding some (a few) Gas giants orbiting stars. And we go, "Ah-hah! See, we're not alone! We must fall somewhere within the center of the normal curve!" Yet still the sample size is small compared to the number of stars - which would really shove 'stars with Gas Giants' to outside one or two standard deviations, and 'stars with earth-sized planets' even further out, with a single sample we know of.
Now we find a (possible) star with another earth-type planet (Class M? Class L? When are scientists going to look up the Star Trek regs and tell us what Class Mars is?), and we say, "We are definately not unique." But look at the statistics - even with *2* systems with earth-sized planets, your sample is *miniscule* compared to the billions of stars! We could very well be in the extreme tail of the bell curve, and actually *be* unique in the universe!
Until SETI produces results, or an alien shows up on Prime Time TV during the President's State of the Union address, I don't think anyone will be able to say for sure that we are not alone. I, for one, believe that we cannot be - I cannot concieve of such a lonely universe. But we really don't have any proof to the contrary. yet. So, while this is very important, don't loose perpective on what it really means about our place in the universe.
"Why the hell do you want to colonise everything? Isn't it a better idea to stop polluting our own planet? Stop wasting its resources so rapidly?"
With that attitude we'd all still be on one continent. Not that I don't agree that pollution and resource depletion are serious problems.
One good and time tested way to stop using resources here is to get them somewhere else. It doesn't look like anyone else is too interested in the asteroids at the moment, perhaps we can be permitted to use some of them? Maybe even start some space colonies to support that activity?
It's likely going to be a long time before we're capable of even near interstellar voyages, let alone colonization missions. Perhaps we'll even have better ethics about destructive exploitation by then.
Just the first one found around a main sequence or nearly-main sequence star.
In 1989, three Earth sized (well, one is Mars sized, but close enough) planets were discovered
orbitting a pulsar. They are obviously dead planets, like their star, but they always fail
to be mentioned, especially in the mainstream media. Anyway, check out the Extrasolar Planets Encyclopedia for more info on all of this.
gigantino.tv - Heavy but weighs nothing.
The rest mass of a photon (particle of electro-magnetic radiation, which includes all frequencies of visible light) is 0 - not 0."some very small amount" but just plain 0. And, in the absence of electro-magnetic fields, a photon has speed c in all relativistic frames of reference. (hence "c" is the "speed of light", which is "invariant in a vacuum").
You've given the two important points, but failed to connect them in a useful way. The rest mass of a photon is exactly zero, but we never observe photons at rest. They always travel (through a vacuum) at c. Each photon has a energy proportional to its frequency. Dividing the energy by c^2 gives the mass of a moving photon which is a function of it's frequency.
I have discovered a truly marvelous sig, unfortunately the sig limit is too small to contain i
Maybe it's not gravity lensing, maybe it's gravity mirroring and we're looking at ourselves! The universe is curved.
...is that the statistical probability of the planets we found has life is way too low, as well as the probability of that life being intelligent, and the probability that It has found how to generate RF signals of a reasonable strength...
p(find rf)= p(life) X p(intelligence) X p(rf technology) X p(emmission frequency)
probably like ~1x10^-6 for each term, which gives us like p(find rf) ~ 1x10^24 for each rock. Not good odds if you ask me.
Remember this...no eternal reward will forgive us now for wasting the dawn....(jim morrison)
i mean p(find rf) ~ 1x10^-24.....sorry 8)
Remember this...no eternal reward will forgive us now for wasting the dawn....(jim morrison)
Hmm, the 5-second explanation on CNN last night showed an animation where the detection involved the eclipsing of the star by the planet. So if this is right, they didn't detect the light reflecting off the planet, they detected the obscuring of the star as the planet orbits.
Finding planets this way is a really haphazard way of doing it. Stars rarely line up well enough to make gravitational lensing really viable as a method of detecting another planet. Another method they've been using is watching the Doppler shift of a selected star. Any star with an object revolving around it exibits a regular 'wobble' in the shift. Make a guess at the mass of the star, apply some centuries old math to it, and voila! You know how many objects are orbiting the star, how massive they are and how far away from the star!.
.sig: Now legally binding!
Permit me to clear up a few questions and misconceptions. Interested readers can read the technical details for themselves in preprints on the LANL server:
:-), the work _was_ done in with optical telescopes; in fact, small ones, only a meter or so in diameter (rather than the 8-meter or 10-meter behemoths like Keck). The basic method is to take pictures of the same field of stars over and over and over, and look for variations in the brightness of any star with time. The technique works best if one can point at a large number of stars at once; the two best sources for crowded fields are the Bulge of the Milky Way and our nearest neighboring galaxy, the Large Magellanic Cloud. Both are best viewed from the southern hemisphere, and the data described in the recent press releases comes from Chile, South Africa, and New Zealand.
A good summary:
http://xxx.lanl.gov/abs/astro-ph/990819
The event MACHO-97-BLG-41
http://xxx.lanl.gov/abs/astro-ph/9908038
The event MACHO-98-BLG-35 (to which this Slashdot article refers indirectly)
http://xxx.lanl.gov/abs/astro-ph/9812252
Okay, now for my comments:
1. Contrary to "cemerson"'s post (which should have been moderated to "MisInformative"
2. The Bulge of the Milky Way is about 8,000 parsecs (about 25,000 light years) away from us. The LMC is about 50,000 parsecs away. These are the "background" stars. A star roughly halfway between us and the "background" will cause the greatest lensing effect as it passes between us and the "background" star.
3. When such an event occurs, the "background" star becomes brighter. Now, here's the key: if the "foreground" object is a lone star, then one can predict theoretically the shape of light curve: the background star brightens slowly at first, reaches a somewhat sharp peak in brightness, and then fades exactly as it brightened: the rising and falling phases look exactly the same, symmetric. And, in fact, most of the observed microlensing events (there have been over 100 followed in the past decade) follow this predicted, symmetric curve very closely.
4. But, if the "foreground" object is not a lone star, but a binary star, or a star with a planet, the light curve will depart from its theoretical, symmetric shape. If there's a planet around the foreground star, and it passes in front of the background star, it can cause a distinctive "spike" in the light curve: a short, sudden, very brief rise and fall. The event MACHO-98-BLG-35 shows a LITTLE bit of evidence for such a spike: see Figure 9 in the paper by Yock:
http://xxx.lanl.gov/abs/astro-ph/9908198
5. There are several efforts underway to detect planets around other stars by searching for the tiny 'eclipses' caused as a planet passes in front of its star in its orbit, but no solid detections yet. This is very difficult, because even a big planet like Jupiter causes only a (roughly) one-percent dip in the light of its star -- and many stars vary by more than one percent. Planets like the earth decrease the light by even smaller amounts, maybe one-hundredth of one percent. At that level, _most_ stars are variable. So, one must disentangle the intrinsic variation of the star from the brief dip caused by the planet -- and that means waiting months/years for the planet to come around in its orbit again. You can find information on one such search, Kepler, at this site:
http://web99.arc.nasa.gov/~mars/vulcan/
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
It's not silly. It's a perfectly valid point.
Astronomy is a science where you can not repeat
your experiment (the universe). Whenever you
get a result, in this case the result is that
we live on a planet, you have to spend a long
time considering any possible biases. The fact
that we'd be dead if we weren't on a planet is
a pretty big bias towards finding ourselves on
one, even if it's the only planet in the universe.
As for it being pretty obvious that there are
other planets out there, 1000 years ago it was
pretty obvious that the earth was flat.
Ale.
Lensing occurs with any mass of object. The size
of the effect depends on the mass of the lens, and
on its position. Lensing has been observed around
the sun, which is not very massive.
In this case, they were looking for the
distinctive brightening of the light from a star
which would occur if some object like a dead star
or jupiter sized planet passed exactly infront
of a background star. From studying the number
of such events, you can calculate the amount of
mass in our galaxy made up of such `dark' objects.
What they found is that one of their light curves
didn't match the theoretical curve. Unfortunately
the experiment is essentially not repeatable, as
you'd have to wait for something else to pass
in front of that star, which could be thousands of years.
Ale.