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Goodbye Jesus

The Nature Of Extrasolar Planets (Pinging Baa ;) )


Thurisaz

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Okay folks. I've taken in a load of TV documentaries over the last one or two years about the universe as far as we know and can observe it today, among these were many about extrasolar planets.

 

Cool as this shit is... one thing bothers me.

 

I see that recurring statement that "extrasolar planets are nothing like our own solar system's planets... "hot Jupiters" are extremely common, so our own solar system is the exception rather than the rule!".

 

Some of the docus mention in passing that of course the ways we have today of detecting those planets orbiting other stars almost naturally favor big worlds and/or worlds in very close orbits... but that is never really elaborated on. It's like someone saying how strange it is that she can only see sidewalk pavement at night that is close to lamps, and how thus pavements are nothing like she expected.

 

Am I right in this being a quite moronic thing to say? Or do I overlook something and even if we account for the known weaknesses of our current planet detection methods those hot Jupiters are still much more frequent than we thought?

 

Inquiring minds want to know... ;)

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Goodbye Jesus

Hey Thuriasz!

 

Be cool.

No more than 15% of all solar systems in the Milky Way galaxy are dominated by Hot Jupiters. 

I'm away from home right now, but tomorrow I'll be back and then I can pull out some info that'll help explain what the situation really is. 

 

Thanks,

 

BAA.

 

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Thankies, looking forwad to it :)

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A "funny" P. S.:

 

Watching one docu I've never seen before right now. Well "documentary" only at first glance.

 

About the topic of carbon/diamond planets...: "If such planets exist, why not planets of gold? Or uranium?"

 

Uranium, Watson? Uranium? An entire planet of it?

 

Ever heard of critical mass, Watson? Like, 52 kilograms for uranium-235? Ever heard what happens when you pile up that critical mass? A hint for you, Watson... it involves BOOM. Lots of it.

 

*head -> desk*

 

Nothing bad about sciency stuff on TV... if it's good science. But this shit... I could just as well take in babblical cretinist "science". *sigh*

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Ok Thuriasz,

 

Here's the deal on the 'Hot Jupiter' problem.

When it comes to observing any new population of objects in the skies it's inevitable that the most easily detected ones are going to be the ones that are found first.  So hot Jupiters (up to a hundred times the size of the Earth) are going to be detected long before Earth-sized planets.

 

size2.jpg

 

If we look back thru the history of astronomy, we can see this happening.

Asteroids have a number and a name.  The first discovered was 1 Ceres (590 miles across), then 2 Pallas (338 miles), 3 Juno (170 miles) and 4 Vesta (326 miles).  If you look below you'll see that nowadays were finding asteroids so small (just yards across) that they aren't even visible in this montage.

 

vestasizesup_image234_05012012.jpg

 

It was the same story with the moons of the planets in our solar system.

Galileo discovered the biggest ones, orbiting Jupiter, back in 1610.  http://en.wikipedia.org/wiki/Galilean_moons

Since then the count of moons around outer planets has been steadily rising as our scopes improve and as we've sent probes out there to take photos.   It's the same story.  The big guys get spotted first and later on, the little squirts get noticed.  So it goes with exoplanets. The biggest (and most massive) ones will be detected first and only later, when the technology improves, do we get to detect the smaller ones.  

 

Now, I must mention something about the masses of exoplanets.

A lot of them have been detected indirectly, by the gravitational pull they exert on their host stars.  The more massive a planet (like Jupter) the greater the gravitational 'wobble' it induces in it's star.  A less massive planet (like Earth) will have a much weaker effect.  Likewise, if a massive planet is orbit very close to it's star (as hot Jupiters do) then it's effect will be very much greater.  This Wiki page explains it nicely.  http://en.wikipedia.org/wiki/Doppler_spectroscopy But the same general rule-of-thumb still applies.  The bigger (more massive) you are, the earlier you're going to be detected.

 

So massive hot Jupiters were always going to be detected first - because they stand out the most.

But it'd be wrong to think that they're the most numerous kind of exoplanet!  Not so.  Since the mid to late 90's (the heyday of hot Jupiter discoveries) we've got a much better handle on the true distribution of exoplanet sizes.  Here's a fairly recent NASA release on this data.

 

 knownexoplanets_0.jpg

 

Prior to 02/26/14 the most numerous class of known exoplanet was Jupiter-size and larger.  Then Neptune-sized ones, followed by Super-Earth sized and finally Earth-sized ones.  But we now know that these samples were being biased in favor of the most easily-detected (most massive) planets - because they had the greatest gravitational effects on their host stars.

 

But everything changed with the arrival of the Kepler satellite on the scene. http://kepler.nasa.gov/

 

Now don't be fooled by the height of the blue columns in the diagram, Thuriasz!

Those results have been skewed because the most massive planets are always the ones that will be most easily detected, remember?  They aren't representative of the true numbers.  Instead, look at how the other three columns have changed.  Pay attention to the new Kepler data in orange. So, extrapolating these changes and applying them across the whole of the Milky Way gives us a far better picture of the true distribution of exoplanet sizes.

 

The Kepler data tells us that the most numerous class of exoplanets are either the Super-Earths or the Neptune-sized worlds.

Earth-sized ones are next  and after that Jupiter-sized and upwards.  Natalie Batalha, one of the lead scientists of the Kepler mission said last year that solar sytems with hot Jupiters made up no more than 15% of all the planetary systems in the Milky Way. 

 

This Wiki page has some very good information on Super Earths. http://en.wikipedia.org/wiki/Super-Earth

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I hope that explains things, Thuriasz.

 

Thanks,

 

BAA.

 

 

 

 

 

 

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Heh thanks. So I was pretty much right about my suspicions ;)

 

Makes me sad though to see how basically good stuff is bullshitized once science is put through the media wringer... in this case I had some background info and could smell that something didn't add up but who knows in how many other cases this media "science" actually dumbs people down... :vent:

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Say BAA, can you duplicate post #5 to the Cosmology thread?  Seems like it would fit nicely.  Slight editing is optional.

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Say BAA, can you duplicate post #5 to the Cosmology thread?  Seems like it would fit nicely.  Slight editing is optional.

 

Ummm... ok then, MM.

 

Things are a little stalled in that thread, btw.  I'm still writing up the next tutorial.  Please maintain a holding pattern.

 

Thanks,

 

BAA.

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I really wish i could sit down and talk to a lot of you guys face to face.

 

I am a novice when it comes to cosmology but the topic intrigues me. I live about 4 hours from meteor crator in Arizona. I went to it and found it all amazing. It really makes me wish i would have put my brain to better use when i was younger and had chosen a different profession.

 

I watched all of the universe series from all seasons and found them very educational.

 

I am thinking about heading back to college and possible getting more into that part of science.

 

Very interesting about the hot Jupiters. Learned something new today, thanks.

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