Extra-solar Planets : Mass vs. Orbital Distance

[Janus]

Th eother day while surfing I found a list of the 120 detected extra-solar planets. (Minus the 2 super giants)

Just for the heck of it I decided to take this info and plot to a graph. I decided to plot planet mass against oribtal distance. The graph is attached.

I also plotted the respective positions of Jupiter and Saturn for comparison.
The graph is plotted on a log scale.

The first thing we note is that the densest grouping is for planets between about .8 to 3AU and with masses of 1 to 10 Jupiter masses. Jupiter seem to fall just on the fringe of this group.

Also smaller massed planets tend to be closer to their primary. Saturn seems to be the exception here, being one of the least massive and the furthest. ( but this may simply be because it might be harder to detect such planets and not be due to their rarity.

It will be interesting to see, as detection methods improve, whether or not the pattern of this graph more or less holds or whether a different pattern (or no pattern emerges.

 

[russ_watters]

It will be interesting to see, as detection methods improve, whether or not the pattern of this graph more or less holds or whether a different pattern (or no pattern emerges.

I'd be real surprised (as I think you would) if the pattern holds when detection methods improve. We detect what we are capable of detecting.

 

[turbo]

too true!

We have a host of small rocky planets in our system, and they would be difficult if not impossible to detect with current technology at interstellar distances. Right now, we can detect pretty large planets, but detecting "pebbles" close to their stars is going to be tough for a very long time, especially since their brightness is greatest only when they are on the far sides of their orbits and when their angular separation from their host stars is smallest.

 

[Nereid]

I'd be real surprised (as I think you would) if the pattern holds when detection methods improve. We detect what we are capable of detecting.

Another way of saying "Saturn seems to be the exception here, being one of the least massive and the furthest" is just as Janus surmised; AFAIK, it'd be quite remarkable for something like Saturn to be detected by current methods (and Jupiter is on the edge of detection!).

Good news for younger PF members and guests! In the next 10 to 50 years there will be remarkable advances in limits of detection, and Janus' plot will likely become so thick with data points as to be a solid blob of colour; then we'd use a coding scheme like that of Hipparcos or 2MASS?

 

[Phobos]

Hey, maybe someday it will be called the Janus Plot (no, that sounds like a conspiracy...how about the Janus Diagram...or Janus' law of planetary orbits). Get your autographed copy today!

A good tautology, Russ. ;)

 

[russ_watters]

Good news for younger PF members and guests! In the next 10 to 50 years there will be remarkable advances in limits of detection, and Janus' plot will likely become so thick with data points as to be a solid blob of colour; then we'd use a coding scheme like that of Hipparcos or 2MASS?

http://origins.jpl.nasa.gov/index1.html . Man, is that ever an exciting program. IMO, we need to stop all this man-on-Mars horsesh--stuff and funnel some more money into the Origins Program.

Anyone want to place some long-term bets?

 

[Janus]

Another fun plot. This time only dealing with planets in known multi-planet systems. The planets are plotted in three series dpending on their postions relative to the other planets in the same system. Dark blue diamonds are the closest, and the yellow triangles are the furthest (there are only two systems known to have more than two planets).

There is one other difference between this plot is that instead of plotting by pure planet mass, I used its mass relative to the planet's sun mass (in solar masses). For example Jupiter would have a mass value on this chart of 1 Jupiter mass/1 solar mass = 1 A planet of .5 Jupiter mass revolving around a Sun of .5 solar mass would also have a mass value of one. Notice that this new plotting method shifts Jupiter (the black asterick) a little closer to the center of the grouping.

Note that only two of the innermost planets have mass values larger than Jupiter and only three of the next furthest have mass values of less. The two outermost planets of the three planet systems both have higher mass values.

There are no small outermost planets, but again, that is likely due to the fact that these are hard planets to detect.

If you actually look at each of the twelve systems data , 8 show increases with mass from inner to outer planets. of the remaining 4, 3 are have tow known planets that reverse this trend, one is a three planet system which follows a mass pattern of .84 , .21, 4.05 as you go from inner to outer.

Again, these are only the planets that we can detect, and these systems all most likely have other planets that fall below our detection threshold at this time. As more data comes in, we will form a better picture as to what a "typical" planet system looks like, and how our solar system fits into that picture.