New Research on Planets indicates universe is full of them...

[far-trader]

We can detect very big planets and get a rough guess about their density and orbit, but there is a lot of detail missing. Worlds the size of the Earth, Mars and smaller are just too small.

We're actually detecting those smaller bodies now, for the last year or so. For various definitions of "detecting" of course, and yes, it's all very low on details. I think it's about 6 detected so far, out of over 600 of the large bodies detected. I expect small body detections to continue and increase though.

 

[BytePro]

Yeah, and it is also relevant to note that a whole lot more candidates have been detected than have been reviewed and confirmed at this point... original detection is largely being done via satellites which long since have done their multi-year sky surveys that are resulting in recent 'discoveries'.

In the last few years, instruments have confirmed that we had yet to discover most of the universe! From masses in orbit with the Earth, to super massive black holes more than 10 fold numerous than previously suspected, to many times the number of 'dark' stars and, of course, a planet rich universe...

We're still finding orbital bodies in our own solar system - and we're still blind to who knows how much of the rest of the Universe!

 

[mike wightman]

We're actually detecting those smaller bodies now, for the last year or so. For various definitions of "detecting" of course, and yes, it's all very low on details. I think it's about 6 detected so far, out of over 600 of the large bodies detected. I expect small body detections to continue and increase though.

You are completely correct - just found this:

http://www.nature.com/news/three-tiny-exoplanets-suggest-solar-system-not-so-special-1.9786

 

[aramis]

We are missing large chunks of mass in those systems. We simply do not have the ability to detect them. How often does Jupiter cross the sun?

Be very careful thinking that we know much about distant star systems - we don't.

We can detect very big planets and get a rough guess about their density and orbit, but there is a lot of detail missing. Worlds the size of the Earth, Mars and smaller are just too small.

Oh, and multi body orbital interaction based on gravitational attraction is a nightmare to solve.

By large masses, I mean things on the order of 20+ terran masses... As in, stuff bigger than what's already been discovered in some of these systems, where we have 4+ orbits that can't exist under a titus-bode relationship because there is near-linear pattern of Jovian and Superjovian bodies.

4 data points is enough to disprove Titus-Bode. Voyager at Saturn disproved titus-Bode, by confirming that it was just as bogus there as at Jupiter.

 

[mike wightman]

Not quite what I meant.

We can only detect an extra solar object when it crosses its star. From a distance of several light years that could mean a several decade even century wait. We will have to collect data for the next century or so before we can get a picture of an almost complete extra solar system.

Now add to that the fact that the density and size of such objects are best guesses and that solving the three+ body equations for gravitational attraction are nigh on impossible at the moment and you have a hard time describing anything beyond "there are a few planets in orbit and we have a rough idea which are gas giants and which aren't; plus we know the order and the rough distance and orbital periods".

And yes, I know Titus-Bode is a waste of time - but we need some sort of approximation or model to build our system design on. And at the present moment in time the scientific community has plenty of theories and models but precious little evidence and proof.

So what do we use instead?

 

[BytePro]

Dermott's law.

Tidus-Bode formula was really nothing more than a curve fitting of observed empirical data and integer number extrapolation that predicted Uranus's orbit (and Ceres, IIRC) and maybe is so wrong in the case of Neptune due to Pluto. There is some evidence that it is an initial special case of an accretion cloud that develops a power series due to resonance and certain constraining symmetries.

But, even if so, it is a generalization that is less worthwhile in terms of the reality of a dynamic universe. It certainly hasn't held true in the case of moons orbiting Jupiter and Saturn, even when modified by Dermontt, without differing constants. So, right now, it is really just a special case, at best.

For a game, simple random orbit works - and since we don't, as yet, have any formula that holds true in general, one could call it 'realistic'.

 

[aramis]

Not quite what I meant.

We can only detect an extra solar object when it crosses its star.

Wrong.

We can detect large objects by their induced wobble upon their parent star. It's how over 80% of the detected superjovians have been found.

 

[mike wightman]

Now you are wrong.

The wobble can have other explanations, until a planet is observed the wobble is a maybe it's a planet.

 

[aramis]

Now you are wrong.

The wobble can have other explanations, until a planet is observed the wobble is a maybe it's a planet.

It can have only one practical explanation - a massive object.

GO READ THE LITERATURE, Mike. Most of the "confirmed" extrasolar planets have never been imaged at all.

Go clicking on the links at http://exoplanet.eu/catalog/ - if it says "radial velocity" that means it was detected by wobble.

Radial velocity and/or astrometry are the baseline for 369 of the systems and 478 of the worlds on that list. Since it doesn't include the unconfirmed except when searching those, that's out of 624 systems, 778 planets.

Transit detections are 206 systems and 240 planets.

 

[mike wightman]

I have read it, and you are the one obstinately refusing to accept the fact that science can not say for certain that it is planets causing the wobble.

A likely explanation yes, but not the only explanation.

You are falling into the science is faith category.

The presence of mass indicates that planetary bodies are probably present - but that is not the same as confirming a planet.

Unless you can say how big it is and how many there are all you are saying is that other stars have planets around them.

Which is why once wobbles are detected the systems are looked at by other methods.

 

[BytePro]

Aramis only stated detection - not confirmation - by wobble.

Technically, detection by "radial velocity" generally refers to via Doppler spectroscopy - indirectly inferring wobble. Detection by wobble directly is via astrometry. But the net effect is the same - most confirmed, by Astronomers' definition - exoplanets have been detected via doppler spectroscopy (via the Keck ground based telescope pair, last I recall). Keck has also used radial velocity technique directly on an exoplanet earlier this year, IIRC.

Kepler (space based) uses a Transit method, and it has generated several thousand candidates that are waiting confirmation before they can be declared 'detected'. So, right now, the largest number of detections is by radial velocity.

There are a lot of other methods with lesser track records - IIRC, the first actual exoplanet detection goes to a Pulsar based technique! Microlensing has also been used successfully in limited number.

Direct imaging is, unfortunately, very rare and quite difficult - for earth based observatories especially. Hopefully new extremely large telescopes (20+ m) come online in the coming years to address that. Unfortunately, most (all?) of the space based aperture synthesis interferometry proposals have been canned over the last few years.

 

[BytePro]

I was gonna make some mention of the fact it is a shame 'obsolete' military space based assets aren't being used...

Just yesterday NASA was to have sent out a solicitation letter regarding two Hubble-class* optical telescopes that are being transferred to NASA!

A team is being established to determine how they may be used re:
* for 2010 Decadal Survey for a Wide Field Infrared Survey Telescope
* “as is” plus a coronagraph for 2010 Decadal Survey for the detection and study of exoplanets.

*Some details: http://science.nasa.gov/media/medialibrary/2012/07/30/Moore.pdf

 

[mike wightman]

Oh I'm not doubting that there are planets around other stars, or that we know something is there by dint of the wobble etc.

But it is very bad science to claim more than the evidence supports. It could be due to dark matter (yeh right - I don't believe that either), it could be the presence of a dim companion, there could even be a black hole. Planetary presence is the most likely and sensible explanation in most cases, but there is not really sufficient evidence yet.

I'll be more trusting of astronomers' claims when they are able to catalogue all the major planets around the stars closest to our Solar system.

 

[Dragoner]

An elephant is like a rope!

Face it, we just really NEED to go there to figure it all out, be sure to tell your politicians that next election...

 

[BytePro]

Ha - who claims we've even cataloged all the major planets around our Solar system, yet?! :rofl:

All we can do presently is detect evidence - even 'direct imaging' can be in error... Astronomers call it a win (confirmed) with collaborating evidence.

 

[aramis]

Science works by preponderance of the evidence... the same standard as most US civil law...

It is more likely true than not true.​

This is coupled to...

We have failed to disprove that this is true.​

99% of the new science done in the last 30 years has been by complex inference ...

People can't see atoms... but most accept they exist.
People can't see brain chemistry... but alter it, and its effects can be detected.
We can't see gravity, only its effects. But we accept that it exists as a property of matter.

We can't see most worlds with current technology... but we can detect the motion to within ±1m/s accuracy (and ±0.05m/s granularity or better). If a jupiter class world were orbiting Alpha Centauri at jupiter's ~8 AU, we'd be hard pressed to detect it by any means other than direct interferometry while in a particular two 60-70° wide chunks of its orbit... It's too small to generate the radial V we're able to accurately detect at those distances.

Many of the candidates are cases where we see the wobble effects, and when we add them up, we come up with multi-jovian subsolar masses being the singular most reasonable explanation. By preponderance of the evidence at that point, the community generally will accept them as proven.

One of them, Jeff Marci commented about. It took his team months to realize that the complex wobble was 3 superjovians... they finally worked out the math, and found that only one solution fit the data... and it wasn't simple measurement error.

 

[Frankymole]

May I ask details of your tweak?

Sorry for not getting back on this, I haven't seen the thread again until just now.

I've got about 10 A4 pages of notes from just after WBH came out, on system and world generation (though much of it is social not physical). I don't have them to hand but they can't be far away. As with the Book 6 corrections (home-made errata from the 1980s!) it must've been done from working back from a known result - especially in the case of Earth's mean temperature, solar luminosity and Earth's (best-guessed) albedo; the result for Book 6 was different to the one given in the text, and so the WBH munged-down formula was different too.

I'm still in the market for a Kepler-style system generator, though I did turn up a document about brown dwarfs and other gas giants placement.