Intermediate Period Planet Desert

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Intermediate Period Planet Desert

Post by exoplanet on 14th January 2010, 7:09 pm

Hi,

could someone point out a reference where the apparent "Intermediate Period Planet Desert" (IPPD) is discussed ?
Where exactly is the desert region ? Looking at the current known planets you have *many* hot jupiters in < 10 day orbits.
Would the desert extend outwards all the way to the ice-line distance ?

There is some speculation that high metalicity stars/ protoplanetary disks favor migration of giant planets, whereas for lower metalicities giants usually form and stay beyond the ice-line. The "intermediate period planet desert" might make some sense if the migration of giant planets would in almost all cases stop only very near the host star (thus producing the observed population of "hot jupiters" for the higher metalicities) and thus leaving few giants at intermediate distances/periods.

I this line of thought I would think that the IPPD would not extend to lower mass (Neptune, super-Earth) planets, since these may have a harder time migrating through the disk. Then again it could be related to the type of migration.

Sorry for all the "thinking out loud" but I'm trying to make sense of this in my head Rolling Eyes

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Re: Intermediate Period Planet Desert

Post by Sirius_Alpha on 14th January 2010, 8:09 pm

Maybe this will help you out.
http://online.itp.ucsb.edu/online/planetf_c04/ida/pdf/Ida1.pdf

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Re: Intermediate Period Planet Desert

Post by Lazarus on 14th January 2010, 8:20 pm

If you take a look at the plot of log(mass) against log(period) for the known extrasolar planets there are two fairly obvious clumps.

http://exoplanet.eu/graph_correl.php?Global_Language=en&catPlanet[]=1&catPlanet[]=7&catPlanet[]=8&obs1=plPeriod&obs2=plMass&scalex=log&scaley=log&minx=&miny=&maxx=&maxy=&resol=700&grille=on

There's a short period population at periods roughly 1-5 days (the hot Jupiters), and a second group of planets with periods above 100 days or so (the eccentric Jupiters).

The region between these two clumps appears to be quite underpopulated in giant planets, especially given the biases inherent in radial velocity surveys. This is the intermediate-period planet desert.

This shouldn't be taken too far though. The distribution of planets in multi-planet systems appears to be quite different from single-planet systems. For example, the multi-planet systems mostly are devoid of hot Jupiters: the ~3-day pileup is not observed in such systems.

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Re: Intermediate Period Planet Desert

Post by exoplanet on 14th January 2010, 9:20 pm

Hi,

Lazarus wrote:
If you take a look at the plot of log(mass) against log(period) for the known extrasolar planets there are two fairly obvious clumps.

http://exoplanet.eu/graph_correl.php?Global_Language=en&catPlanet[]=1&catPlanet[]=7&catPlanet[]=8&obs1=plPeriod&obs2=plMass&scalex=log&scaley=log&minx=&miny=&maxx=&maxy=&resol=700&grille=on

There's a short period population at periods roughly 1-5 days (the hot Jupiters), and a second group of planets with periods above 100 days or so (the eccentric Jupiters).

The region between these two clumps appears to be quite underpopulated in giant planets, especially given the biases inherent in radial velocity surveys. This is the intermediate-period planet desert.


Yes, I had seen these graphics at exoplanet.eu and the deficit of planets in that period interval is obvious. My point was whether this is just an observational pattern for which no explanation exists so far (as you say it cannot be a selection effect given the nature of the radial velocity method) or if this was predicted to exist by models of planetary system formation.

Sirius_Alpha, thanks for the slides. I have to read them carefully but they do model the planet desert in their work.

BTW, you refer to the second clump as the eccentric Jupiters. Currently, many Jupiter analogs are being found in there, so what exactly do you mean by "eccentric" ?

Lazarus wrote:
This shouldn't be taken too far though. The distribution of planets in multi-planet systems appears to be quite different from single-planet systems. For example, the multi-planet systems mostly are devoid of hot Jupiters: the ~3-day pileup is not observed in such systems.

Do we have a big enough sample of multiplanet systems to have meaningful statistics ? Even if we do have a deficit of hot jupiters in those systems, do we still see a desert until de 100 day period ? Is there some reference for this ?

Thank you both for the feedback !

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Re: Intermediate Period Planet Desert

Post by Sirius_Alpha on 14th January 2010, 9:42 pm

exoplanet wrote:BTW, you refer to the second clump as the eccentric Jupiters. Currently, many Jupiter analogs are being found in there, so what exactly do you mean by "eccentric" ? !
Many of the long period gas giants have eccentric orbits. While in multiple-planet systems, they eccentricities are not as severe.

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Re: Intermediate Period Planet Desert

Post by TheoA on 15th January 2010, 7:35 pm

Could at least some of this be a detection bias.

It is known for instance that the S/N Ratio for eccentric planets further out is better than that for circular planets with e < 0.1.

As we get further out ~ to 2/3 au, more observations might might be required to fill out some of this desert.

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Re: Intermediate Period Planet Desert

Post by Sirius_Alpha on 16th January 2010, 12:36 am

The radial velocity amplitude is indeed higher for an eccentric planet, but not by much. I don't see how it could be a detection bias. (It may be that many of the eccentric planets are actually resonant planets in desguise though, but I've no idea how common this would be.)

Here is the radial velocity chart of a planet in a circular orbit, compared to the same planet in an eccentric orbit (Made with Systemic).

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Re: Intermediate Period Planet Desert

Post by Lazarus on 16th January 2010, 5:30 am

Regarding eccentricity bias... On the Eccentricity Distribution of Exoplanets from Radial Velocity Surveys. Seems that for various reasons (e.g. the shorter timescale over which rapid velocity changes occur) the detection efficiency decreases as eccentricity increases, but is fairly uniform up to quite high eccentricities.

Again though, it is quite difficult to come up with an observational bias that would knock out this period range while leaving the populations at shorter and longer periods... it seems likely that there is a real lack of giant planets in this region. Incidentally the median period of the RV planets listed on EPE is about 200 days. Roughly half of the known extrasolar planets are eccentric Jupiters, despite the strong bias of RV and especially transit surveys towards close-in planets.

There isn't much known about the low mass planetary population at these periods though. Various predictions suggest that the population of "failed cores" and terrestrial planets should be fairly uniform and not exhibit the intermediate period planet desert.

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