Slashdot Mirror

Terrible headline aside

Since there may be others that feel this way, in the case of exoplanets here is "the one", all-inclusive resource that even the professionals in the field make use of and cite.

(For the click-lazy:) "The Exoplanet Data Explorer is an interactive table and plotter for exploring and displaying data from the Exoplanet Orbit Database. The Exoplanet Orbit Database is a carefully constructed compilation of quality, spectroscopic orbital parameters of exoplanets orbiting normal stars from the peer-reviewed literature, and updates the Catalog of nearby exoplanets."

Access is granted to all data, and I (hopefully along with other slashdotters) am willing to "translate" from the scientific jargon if something sounds too specialized.

Perhaps we've stumbled across this planet during the last million years of its billion year life-cycle. Sounds like a one in a thousand chance that we'd do that. But the summary says that over 370 exo-planets[1] have been found ... so (waves hands as if doing actual math) its about a 1 in 3 chance that one of the planets we've found so far will be in some one in a thousand situation.

Wait until Kepler starts kicking in a few thousand more exo-planets to the database. Then we'll see even more "impossible" situations.

[1] http://exoplanets.org/ says the current tally is just 358

From what I've read here: http://exoplanets.org/aasjune07s/pr_280507.htm there have been some 236 exoplanets detected to date. I believe that they have the ability to see if these exoplanets are in highly eliptical orbits or not - so how does this simulation tie with the observed reality?
The description of Gliese 436 for example seems to also be an exception to this simulation model - so if out of 236 finds we are already finding systems similar to sol - then this simulation model must be at fault or?

The interesting data is not how many hot Jupiters are found, but how many stars do not have hot Jupiters.

Here's a list of extrasolar planets (last updated in January); and another list. Note the large number of stars that have planets found with mass less than Mj. The converse of that is that those stars do not have planets of mass greater than Mj. The problem, of course, is that negative results are much less published than positive results. However, here is a list of three published papers that listed stars with no planets found (that is, no planets large enough to detect-- which is to say, no hot Jupiters. This list is somewhat out of date, as of 2006.)

So the story is a little incomplete. Some solar systems have hot Jupiters, which in their migration inward disrupt smaller, earthlink planets... but by no means all.

In the first 8 years of the 21st century I have witnessed an almost feverish acceleration of astronomer attention on the discovery of "exoplanets" - planets around stars other than our own Sun. Already some solar systems very similar to our own have been discovered and some tentative measurements of the atmospheric content of these planets is underway. I believe it is only a matter of months or years before an oxygen-rich "earth-like" planet is discovered. Prognosticator of prognosticators that I am, I'll even go so far as to suggest a date: before the end of 2012.

But who cares when it happens, if it does happen, what then? What next? Will there be any debate that the concentration of oxygen implies that life is present on this newly discovered world? Will it take the imaging of an exoplanet to "prove" that life exists elsewhere in the universe? Will it take more?

And finally, will anyone care? Not the geeks. Not the astronomers or the scientists or the science fiction writers, but the average person on the street. At the time of writing, each exoplanet discovery is treated to an orgy of poorly understood journalism. It seems the idea of "planets around other stars" is something the mainstream audience can understand just enough and goes well to fill that slot in the news between the sports and the weather. Will this fad wear off by the time the startling discovery of exoplanet life is made? Or worse yet, will such an amazing discovery get exactly the same amount of coverage as the average exoplanet discovery gets now?

Ultimately the whole thing could be a terrible disappointment. Imagine, for a moment, that not only do astronomers discover life on an exoplanet but they actually discover intelligent life on an exoplanet. Pretty little pictures of roads and factories, ships at sea, planes and rockets in flight. Some serious questions would need to be directed towards the SETI program.. as it seems highly unlikely that a modern society could exist without emanating some signals that SETI should have picked up. Maybe a thorough search of the archives will reveal that many possible signals from that part of the sky were ignored accidentally.

In any case, now that we know they're there, how do we go about contacting them? Should we? Who gets to decide? Is that a pointless question as there's just no way to stop someone from sending a signal if they want to? And then there's the long long wait for the signal to get there and maybe no-one is listening or maybe the signal is too corrupted or just not decipherable by an alien mind. Decades may pass with no message returned. The general public will lose interest. Can you imagine?

The article is pretty vague about it's findings. It found 2 to 4 systems that look like a collision like the one that is thought to have created our moon took place. They don't say exactly why it must be at that time and not sooner. The ones they found are at 100 million and 400 million years after the star formed, when I think most of the planetary formation and therefore dust should have been gone (50 million years is what they say). I assume they looked at 40 stars, that gives the 5% and 10% figures. Did they take into account how long it would take for that dust to be cleared by the planets? If planet formation and the dust should be done by 50 million years, there could be many more that have already happened. They looked at a 400 million year old star that seems to have had it happen, what if they looked at another 400 million year old star that had it happen at 30 million years like our system. All the dust would have been gone by 370 million years later.

It's 5-10% of planetary systems? What's the ratio? It may seem like stars are very spread out, we usually only hear about our nearest neighbor that is less than 5 light-years away. If you pull back to 20 light-years though, you'll see 109 stars! Considering about 30% of stars have planetary systems, and 5% of those would have a collision that could produce a moon like ours, that's 1.5%. IF you take into account that our galaxy alone has between 200 and 400 billion starts, that's 3-6 billion moons like ours in our galaxy alone. If you take into account the middle numbers for star count and the percentages here, you get 6 billion. That's one moon like ours in our galaxy for nearly every man, woman and child on earth.

Seconded. The actual Exoplanets site here has a lot more real data, it actually links to the abstracts of the papers where the discoveries were actually published, and has zero ads:

http://exoplanets.org/planets.shtml

There are two stable possibilities: where the two stars orbit each other fairly closely (ie, 0-4 AU from the article, IIRC), and planets then orbit the common center of gravity formed by these two stars...or where one star has a very distant orbit, which is so far that it doesn't disrupt planets close in to the bigger primary.

If the second binary star is in a medium-sized orbit (ie, somewhere between where Jupiter and Pluto are in our system), it seems to be the case that this disrupts the planet-forming disk of gas so much that no planets are likely to form.

If you want to see a full list of all known exoplanets, go here: http://exoplanets.org/planets.shtml
The column marked "a (AU)" is orbital radius, where 1 AU is the earth's distance from the sun.

Unless there are aliens within a few hundred light years of us (which at this point is a vanishing probability given that we've found under 200 exoplanets within 200 parsecs) we won't find any aliens -- and they won't find us, either.

I tend to agree. Think about it this way: how much of *our* resources are we currently using to explore the entire galaxy? And how much are we likely to in the future? The answer is, not much. It's a vanishingly small return on a huge investment to explore the galaxy, especially when we've got bigger problems at home and so much raw material in our own solar system. The costs of sending crap into deep space will probably outweigh the benefits of mineral riches for far into the future, despite Ridley Scott's imagination. Unless there are aliens within a few hundred light years of us (which at this point is a vanishing probability given that we've found under 200 exoplanets within 200 parsecs) we won't find any aliens -- and they won't find us, either.

That's completely opposed to my experience.

The more and more we learn about space, the more amazing I find it. We always knew it was mostly empty, so that's not news. But here is some news,

Frankly, our own ideas of space aliens, and perhaps our expectations of finding them as we expect are boring. If we find Klingons tomorrow.. yawn..

for summary of discovered extrasolar planets (exoplanets) check
    www.exoplanets.org

(it's not updated as frequently as news sites, but it IS maintained by astronomers, not someone making a quick buck...)

I don't totally agree. Definitely, the extrasolar planets found by the radial velocity planet searches are largely close to their stars, but that's another observational bias. Not only do closer-in planets tug on their stars more (v ~ 1/r^1/2), but it takes longer for a large-separation planet to complete an orbit, and radial velocity teams don't report a planet until they've seen one orbit. Which means the time baseline of the surveys becomes important. The longest target stars have been monitered is 15 years or so. This is, not coincidentally, the orbital period of the largest-separation extrasolar planet known to date, 55 Cnc d (14.7 years, 6 AU). Also, the star 55 Cnc was being carefully monitered all this time in large part because it was known to already harbor a planet (55 Cnc b, has just a 15 day period, and was one of the first half-dozen extrasolar planets discovered).

My point is that while the results of the radial velocity surveys are pretty complete within 3 or 4 AU or so, beyond this the results are heavily driven by observational bias. Not only do you need 15 years of data to close an orbit, you need enough data points to see a much fainter radial velocity signature. For comparison, the next furthest-out extrasolar planet is at 4.5 AU, and of the 136 extrasolar planets found by the radial velocity method, only 5 are beyond 4 AU (see the California and Carnegie planet almanac for details).

Jupiter is in an orbit of 5.2 AU, taking 12 years to go around the sun. So I would submit we've found no planets of Jupiter-like mass at Jupiter-like orbits (closest would be 55 Cnc d, 6 AU, but--at least--4 times the mass of Jupier, or HD 50499, 1.84 Jupiter masses at 4.4 AU). And I'd say further that current observational techniques would really need to stretch to hit such a planet, so I don't think we're not finding them because they aren't there. (Plus, it's widely suspected that radial velocity teams know about a lot of these long-period planets, but are waiting to announce them until the orbits have been confirmed. All the rest of us can do is wait and see).

As to the basic question of this thread, whether you can get other stellar systems similar to our solar system (namely, a rocky planet in a stable orbit in the habitable zone), I think that issue is nowhere near solved. Recent papers have shown that of nearby, sun-like stars, about 10-20% have a planet that can be detected with the radial velocity method (the exact percentage depends on the metallicty of the star). What that means is that we know between a tenth and a fifth of stars have a planet more massive than Jupiter within the inner 3 or 4 AU. That says absolutely nothing about the other 80-90% of stars. What fraction of these have a Jupiter-like planet in a Jupiter-like orbit is very much up for grabs. We know that it's unlikely for an earth to form in most of the planetary systems we've been seeing (migrating giant planets, or planets in eccentric orbits, would almost certainly disrupt the earth-wannabe). But again, that's only 10 or 20% of stars. So, it could very well be that 80-90% of stars have a rocky planet in the habitable zone. We don't know how common our solar system is yet, and it'll likely take future missions (Kepler, TPF, next-generation adaptive optics systems on ground based telescopes) to really find out.

The radius is indeed a guess (it has not been measured), but it's an educated guess based on the planet's mass. The current, best model for planet formation involves rocky material forming a large core early in a stellar system's life. These rocky cores, once they reach a critical mass of 15-20 Earth masses, begin to accrete gas and grow to form giant gas planets like Jupiter and Saturn. As evidence, Uranus and Neptune have around 2 Earth masses of gas and 15 Earth masses of rock. According to this model, GL 876 d is so small (only around 7 Earth masses) that it could not have accumulated significant amounts of gas, so it must be rocky.

From the press release:

Though the team has no direct proof that the planet is rocky, its low mass precludes it from retaining gas like Jupiter.

and

"The planet's mass could easily hold onto an atmosphere," noted Laughlin, an assistant professor of astronomy at UC Santa Cruz. "It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that's intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune."

Mercury orbits in 88 days. There are planetary
fact sheets at http://nssdc.gsfc.nasa.gov/planetary/planetfact.ht ml
that are useful for finding solar system data quickly. For extrasolar planets, go to http://exoplanets.org/

Well, found a link to the NSF Press release.

The new planet whips around the star in a mere two days, and is so close to the star's surface that its temperature probably tops 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius) oven-like temperatures far too hot for life as we know it.

The nice thing is, if it's size is twice the size of earth and its mass is about 8.0 times the mass of earth - then it has the same density as Earth does. So, probably it's inner structure and composition is similar to our own planet.

Now, if only we find another one of those which took a little longer to go around it's local sun, we could start worrying about carrying our towel with us wherever we go.

Yup, by Mayor and Queloz, see the abstract of the paper. There has been some argument as to whether it's a planet or not, but as far as I can tell it's now mostly agreed that it is- in fact, the site tmacd himself referenced lists it as entry #10 in its (non-chronologically ordered) list.

I believe the first exoplanet was discovered in 1996, by Marcy and Butler, around 70 Virginis

The up to date list (minus these recent 100) can be found at exoplanets.org

7% of the exoplanets listed at this table are greater than 10 Jupiter masses. Deuterium burning occurs at 10-12 Jupiter masses and greater, but doesn't help us categorize objects that have burned up their deuterium. 2-3 Jupiter masses might be a good dividing line, as it marks the transition from the object's radius increasing with mass to the radius actually decreasing with mass (which I won't go into as it leads to discussions of things like electron degeneracy pressure). Other definitions of planets and brown dwarfs make a distinction between the method of formation of the object, but this makes the mass much less important than the object's history, which is much harder to deduce. For instance, Jupiter was long regarded as having formed from runaway accretion starting with a small rocky core, but recent computer models suggest it (and the other gas giants) formed directly from gravitational collapse, just like a star. Also consider the 55-78 Jupiter mass object found orbiting at a distance roughly equivalent to Saturn's orbit around a sun-like star, a distance much too close for many astronomers' comfort.

A limitation of this technique is that if a planet orbits its star in the plane of the sky, there will be no radial component to the star's reflex velocity, so we won't detect it. Further, unless the planet orbits with an inclination such that it passes nearly in front of the star, we will measure only a fraction of the total reflex motion.

This means that when we detect a planet, we can only put lower limits on the mass of the planet, since the signal could be from a massive planet in a nearly face-on orbit, or a tiny planet in an edge-on orbit. This ambiguity is proportional to the sine of the inclination (the "tilt"), so what we measure to be the mass of the planet is actually M*sin(i), where M is the true mass of the planet.

What these folks have done is use an instrument on HST to make extremely accurate measurements of the position on the sky of a star known to have planets, and used these measurements to measue the path of the star in the plane of the sky as it wobbles under the influence of the orbiting planet. This measures the missing tangential component of the reflex velocity, resolving the sin(i) ambiguity, and determining M itself. This is only the second time anyone has precisely determined the inclination of one of these planets.

A limitation of this technique is that if a planet orbits its star in the plane of the sky, there will be no radial component to the star's reflex velocity, so we won't detect it. Further, unless the planet orbits with an inclination such that it passes nearly in front of the star, we will measure only a fraction of the total reflex motion.

This means that when we detect a planet, we can only put lower limits on the mass of the planet, since the signal could be from a massive planet in a nearly face-on orbit, or a tiny planet in an edge-on orbit. This ambiguity is proportional to the sine of the inclination (the "tilt"), so what we measure to be the mass of the planet is actually M*sin(i), where M is the true mass of the planet.

What these folks have done is use an instrument on HST to make extremely accurate measurements of the position on the sky of a star known to have planets, and used these measurements to measue the path of the star in the plane of the sky as it wobbles under the influence of the orbiting planet. This measures the missing tangential component of the reflex velocity, resolving the sin(i) ambiguity, and determining M itself. This is only the second time anyone has precisely determined the inclination of one of these planets.

You believe wrongly.

HD28185 b and IotaHor b both could support moons with liquid water, year-round.

HD27442 b (aka Epsilon Reticulum) could also do it.

Other planets visit their star's habitable zones, too. Even though most of these other planets have eccentric orbits which would take them in and out periodically, they still "come close to matching those criteria".

Also a much better link to details of the Gamma Cephei system can be found here.

Lalande 21185: No paper reporting a planet around this star has yet been published, although there was a "SORTA KINDA" statement made about 5 years ago.

Eps Eri: Is a maybe planet. See here

The planets around Upsilon Andromedae are however not in question. But it is not clear from the article that they are detecting masers on each (or any) of the planets. They should be able to detect clear periodic doppler signals as each of the planets orbits.

If photemetry or "S" value measurements continue to show periodicities similar to the observed Doppler velocity period, this would suggest that the source of variation is intrinsic to the star rather than an orbiting planet.... We are not yet completely convinced of the planet-companion interpretation for the velocity variations of HD 19622

Though how this relates to a 100 light year sphere around earth confuses me:
The article is pretty clear that the 100th planet is "symbolic". It's in really big font in a colored box -- you can't miss it! Anyway, it's not this 100th planet that leads to the 30 billion number. It's just a lead in for the article.

While the 300 billion stars is correct, a vast majority of them are on the galatic disk or in the galatic core, where the gravity of the densely packed stars would prevent planet formation according to any currently held theory.:
Wow -- that's news to astronomers. We're in the disk, and our sun formed planets, so it can't be that hard!

most of the exo-solar planets that have been found so far are multiple Jupiter-sized and orbiting so close to the star that it doesn't resemble our solar system, the only one we really know about, making any inferences about the existence of other planets useless and pointless :
Oh, so knowing how commonly planets form has nothing to do with how many planets are in the galaxy?!? Knowing that 10 percent of stars near us have detectable planets is astonishing: we can only regularly detect these weird "hot Jupiters" right now. This implies that, unless these systems are for some reason much more common than other planetary systems, a substantial fraction of all stars bear planets. In that case, 30 billion is a reasonable guess -- maybe on the low side!

The final link in the logical chain is provided in the article itself:

But even in this "biased" survey of giants, the smaller worlds predominate - which makes astronomers think that Earth-like worlds do exist. They may even be as common as Jupiter-sized exoplanets.

In other words, if you make a histogram of exoplanets sorted by mass, you see that the least-massive ones are the most common. Go to exoplanets.org and see for yourself. So the above caveat that "hot Jupiters" might be more common than other kinds of planets seems unlikely.

Yes, the author has dumbed down the science to the point where it can be hard to figure out what he's writing about, but that per se doesn't boggle the mind of anyone who reads the science section of any major paper.

The closest thing that has been discovered is the two gas giants around 47 Ursa Majoris. This is the planetary system that so far looks most like our own. The two giants have less extreme (more circular) orbits than most of the ca 70 planets found, which also contributes to make it look a lot like ours. Gas giants can be an important contributor for life to appear on a smaller planet, since they act like magnets for asteroids and other debris, sheltering the smaller planets and giving life a chance to evolve.

To the original post: Most of the extrasolar planets found so far have orbits that are far more elliptical than any planets in our system. And many of the detections are well above the limits of our abilities (depends on the mass and size of the orbit). Check out these radial velocity diagrams. (Click on the star name to see its plot)

Take a look at Geoff Marcy's website at exoplanets.org. Marcy is a professor here at Berkeley who leads one of the two teams which has done most of the planet finding thus far. This most recent announcement is by Michel Mayor, a Swiss astronomer who leads the other major extrasolar planet hunt. I think the two teams have a fairly friendly rivalry going on, and often both end up observing/discovering the same planets. One of Geoff's graduate students (who I think reads /.; Jason, you reading this?) told me that this latest batch was all discovered by using southern hemisphere telescopes, so none of these were discovered by Marcy et al's search, since that is conducted solely with Northern hemisphere telescopes.

Right now, we're finding Jupiter-sized planets around roughly 5% of the stars we've looked at - 60-ish planets around about a thousand stars. It's expected that the actual numbers of stars with planets is much higher than that, potentially as much as 50% or so, but smaller planets or ones further from their parent star are much harder to detect, so we have not yet identified any.

No, the goal of future pie-in-the-sky NASA missions like the TPF (Terrestrial Planet Finder) is to directly image other planets by nulling the light from the star. This is not the indirect wobble detection that Marcy and Butler are doing so successfully on the ground now: rather, you image the planet, maybe as a dot, get a spectrum, and - holy smoke - there's free oxygen in the spectrum!! Life! Little green men! More funding! :)

The Keck interferometer, OTOH - it's not going to resolve small earth-like planets. But its a step in the right direction, and should resolve brown-dwarf companions and maybe giant planets too...

(Yes, IAAAstronomer)

Yahoo article

NASA Ames Research center Click on NEWS or here

And finally pictures, well, actually graphs which illustrate the dance can been seen at exoplanets.org

Ticks me off, really, I bust my knuckles to do research for article submissions and some twit only puts up a link to NY Times and /. puts it up.

--

Whoops, wrong paper. Sorry. Well, here are just the radial velocity curves.

The story was generated based on several presentations given at the General Assembly of the International Astronomical Union (IAU). The total number of new planets discovered is 10, including the double planet system of twin Saturn-sized planets.

The information was actually released to the various news agencies last week, but was under strict embargo until early this morning.

This brings the total number of extrasolar planets to 50.

Here're the original source links to this story:

• Geneva Extrasolar Planet Search
• Extrasolar Planet Search

And then coverage by news sources around the Internet:

• ABC News
• BBC News
• CNN Space
• Discovery.com
• Fox News
• MSNBC
• Space Chronicle

And of course, my own coverage on Universe Today.
Planet Discoveries Coming Fast and Furious - August 7, 2000

Fraser Cain