Comments on: A New Planet and Its Implications

By: ljk

ljk — Tue, 22 Jan 2008 18:32:07 +0000

Extrasolar Planet Interactions

Authors: Rory Barnes (Arizona), Richard Greenberg (Arizona)

(Submitted on 21 Jan 2008)

Abstract: The dynamical interactions of planetary systems may be a clue to their formation histories. Therefore, the distribution of these interactions provides important constraints on models of planet formation. We focus on each system’s apsidal motion and proximity to dynamical instability.

Although only ~25 multiple planet systems have been discovered to date, our analyses in these terms have revealed several important features of planetary interactions. 1) Many systems interact such that they are near the boundary between stability and instability. 2) Planets tend to form such that at least one planet’s eccentricity periodically drops to near zero. 3) Mean-motion resonant pairs would be unstable if not for the resonance. 4) Scattering of approximately equal mass planets is unlikely to produce the observed distribution of apsidal behavior. 5) Resonant interactions may be identified through calculating a system’s proximity to instability, regardless of knowledge of angles such as mean longitude and longitude of periastron (e.g. GJ 317 b and c are probably in a 4:1 resonance).

These properties of planetary systems have been identified through calculation of two parameters that describe the interaction. The apsidal interaction can be quantified by determining how close a planet is to an apsidal separatrix (a boundary between qualitatively different types of apsidal oscillations, e.g. libration or circulation of the major axes). The proximity to instability can be measured by comparing the observed orbital elements to an analytic boundary that describes a type of stability known as Hill stability. We have set up a website dedicated to presenting the most up-to-date information on dynamical interactions: this http URL

Comments: 10 pages, 3 figures, 1 table. To appear in the proceedings of IAU Symposium 249: Exoplanets: Detection, Formation and Dynamics, held in Suzhou, China, Oct 22-26 2007. A version with full resolution figures is available at this http URL

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0801.3226v1 [astro-ph]

Submission history

From: Rory Barnes [view email]

[v1] Mon, 21 Jan 2008 16:55:05 GMT (90kb)

http://arxiv.org/abs/0801.3226

By: ljk

ljk — Tue, 07 Aug 2007 14:34:50 +0000

arXiv:0708.0822

Date: Mon, 6 Aug 2007 19:04:32 GMT (56kb)

Title: Thermal Emission from Transiting Very-Hot Jupiters: Prospects for
Ground-based Detection at Optical Wavelengths

Authors: Mercedes Lopez-Morales and Sara Seager

Categories: astro-ph

Comments: accepted for publication on ApJL

Very hot Jupiters (VHJs) are defined as Jupiter-mass extrasolar planets with
orbital periods shorter than three days. For low albedos the effective
temperatures of irradiated VHJs can reach 2500-3000 K. Thermal emission from
VHJs is therefore potentially strong at optical wavelengths. We explore the
prospects of detecting optical-wavelength thermal emission during secondary
eclipse with existing ground-based telescopes. We show that OGLE-TR-56b and
OGLE-TR-132b are the best suited candidates for detection, and that the
prospects are highest around z’-band (~0.9 microns). We also speculate that any
newly discovered VHJs with the right combination of orbital separation and host
star parameters could be thermally detected in the optical. The lack of
detections would still provide constraints on the planetary albedos and
re-radiation factors.

http://arxiv.org/abs/0708.0822 , 56kb

By: andy

andy — Thu, 26 Jul 2007 00:35:55 +0000

While the HZ of a red dwarf star is narrower in real space, consider that Gliese 581 has two planets (c and d) located close to the habitable zone. Same also goes for Gliese 876 (planets b and c).

Formation of two habitable planets around a G star is probably possible (I’ve seen a paper about terrestrial planet accretion that ends up with such a configuration, both planets just on the edge of the HZ), but the planets would probably interact quite significantly: in the configuration produced by the accretion simulation, the two planets traded orbital eccentricity back and forth.

By: Ronald

Ronald — Wed, 25 Jul 2007 23:48:59 +0000

@andy:
does this then confirm the ‘window of opportunity’ of the solar type stars (late F – early K), the hotter A and F stars having a too narrow CHZ and the cooler (late K, M) stars having a very narrow HZ anyway.

But is seems hard to fit 2 or more terrestrial planets into the CHZ of a solar type star. E.g. a ‘typical’ G star with a CHZ from 0.9 – 1.2 AU orso (maybe a bit more), if you try to fit more than one planet in, it becomes rather crowded for long-term stable orbits. Or not?

By: andy

andy — Wed, 25 Jul 2007 00:36:08 +0000

Interestingly enough, according to Kasting et al. 1993, "Habitable Zones around Main Sequence Stars", the continuously habitable zones around A and F stars of a given duration of habitability are narrower when measured on a logarithmic scale than the comparable zones around G stars, due to faster stellar evolution. The reason given for using a log scale is that the planets in our solar system are logarithmically-spaced. A quick check of some 3 and 4 planet extrasolar systems suggests that they too seem to have planets spaced in a logarithmic pattern (if you allow for unfilled gaps which may perhaps host additional low mass planets or asteroid belts: fitting our solar system to a logarithmic spacing requires inclusion of the asteroids), so perhaps, paradoxically enough, it is low mass stars which are more likely to have multiple habitable planets.

By: djlactin

djlactin — Wed, 25 Jul 2007 00:13:09 +0000

note that the “habitable zone” is currently defined in “our” terms. a life form based on liquid ammonia or liquid methane would have a very different idea…

By: Ronald

Ronald — Tue, 24 Jul 2007 23:13:23 +0000

@philw: great ideas. But since A and F stars are relatively scarce in the MW galaxy, and short-lived and emitting rather aggressive radiation, I would still prefer to go for the more solar (spectral) type stars: roughly from F5 to K2. And as we are learning now, the smaller, cooler stars probably show a scarcity of planets combined with a very narrow HZ.
Maybe the solar stars really constitute a window of opportunity for (suitable) planets, in several ways: insolation and temperature, lifespan, stability, metallicity (well, at least part of them), mass, HZ, …

By: philw

philw — Tue, 24 Jul 2007 17:37:33 +0000

Ronald, you expressed my A and F terraforming idea well. Yes the stars are short lived and yes, early A star planets would not last long enough to cool down geologically as Adam suggested. But plenty of possibly late A and certainly F stars with luminosities 1.5 to several suns would have habitable zones that would be ‘stable’ for human horizon purposes of terraforming. Were the planets to have oceans and land. Nanotech (i.e. advanced biotek) technology could seed O2 producing organisms, create soil, etc. The hardest part from today’s horizon is the seemingly impossible task of geting there.

And yes, the width of the HZ is a function of the luminosity. Multiple Earth type planets ‘could’ exist within a wide HZ. And yes it moves fast, but not fast on a thousands of years timescale.

By: Ronald

Ronald — Tue, 24 Jul 2007 08:27:50 +0000

@djlactin: agree, but what may be tentatively possible is what the California & Carnegie Planet Search team did a few years ago: extrapolating the planetary abundance to planetary mass ratio (see their web site exoplanets.org), finding, even despite the bias towards giant planets, that the smaller the planetary mass the more abundant.

Very promising.

@Adam: agree on the short lifetimes of A and F stars, but that is probably why philw speaks about the “need to accelerate the life complexity process seeding them with Earth based complex life forms which could thrive for millions or tens of millions of years”.
Kind of terraforming or at least propagating life on lifeless but potentially habitable planets.

@philw: are the *continuously* habitable zones of A and F stars wide enough for 3 or even 2 habitable planets? In other words: are they really that wide and isn’t it so that they move outward relatively fast?

By: Ronald

Ronald — Tue, 24 Jul 2007 08:14:37 +0000

Yes! This is in line with what I mentioned in an earlier post Exoplanet Prediction by Stellar Elements (ref. Lineweaver’s work on this), June 9th:

“I always thought that stellar characteristics would determine planetary system composition, in particular metallicity and stellar mass. ‘Knowing the mother is knowing the children’ “.

From the article itself:

“We find a positive correlation between stellar mass and the occurrence rate of Jovian planets within 2.5 AU; (…). Our analysis shows that the correlation between Jovian planet occurrence and stellar mass remains even after accounting for the effects of stellar metallicity”.

I already noticed a few years ago (OK, as an amateur, looking at data from the Extrasolar Planet Encyclopedia), when the California & Carnegie Planet Search team published about the correllation between stellar metallicity and planet occurrence, that the correllation becomes (a bit) stronger when both metallicity ánd stellar mass together (for instance metallicity * mass, expressed as x times solar) are related to (total) planetary mass.

The correllation was still rather weak though, possibly because not all giant planets had been discovered for those stars yet (i.e. not yet the ones in greater orbits).

(With regard to metallicity: as Lineweaver suggested, the correllation may become clearer and stronger as we learn to distinguish between various elements, in stead of just overall metallicity).