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Eugenio has finished combing through this summer’s literature, and has added twenty newly published radial velocity data sets to both the systemic backend and to the current version of the downloadable systemic console. As a result of his efforts, new or augmented data is now available for the following stars: Cha Ha 8, GJ 317, HD3651, HD5319, HD11506, HD17156, HD37605, HD43691, HD75898, HD80606, HD89744, HD125612, HD132406, HD170469, HD171028, HD231701, NGC2423, NGC4349, HAT-P-3, and TrES-4. As always, the published literature citations for the velocities are contained in the “vels_list.txt” file that comes bundled with the systemic console download. The vels_list.txt file can be indispensible if you want to publish results that use the systemic package as a research tool — indeed, we’re quite excited that researchers are starting to adopt the console in the course of carrying out state-of-the-art research (see, e.g. here.)

There’s quite a bit to explore with these new data sets. Eugenio has had a first look, and included in his recommendations are:

GJ 317: This system (discovered by John Johnson and the California-Carnegie planet search team, preprint here) is only the third red dwarf that’s been found to harbor a Jovian-mass companion. The data shows clear evidence for one planet “b”, with at least 1.2 Jupiter masses and a 693-day orbit, and there’s a strong hint of a second planet in the radial velocity variations. Check it out with the console!

HD 17156: This data comes from a recent paper by the California-Carnegie team. There are radial velocities from both the Keck and the Subaru telescopes, and the signal-to-noise of the orbit is very high.

The data show a ~3 Jupiter-mass planet on a 21.2 day orbit. The orbit is remarkably eccentric for a planet on such a short period, leading to a 25-fold variation in the amount of light received during each trip around the star.

It’ll be interesting to get a weather forecast for this world, and it’s also important to point out that the orientation of the orbit is very well suited for the possibility of observing transits. Periastron is reasonably close to being aligned with the line of sight to Earth, leading to an a-priori transit probability of more than 10%. In the discovery paper, a preliminary transit search is reported, but only about 1/4th of the transit window was ruled out. With a Dec of +71 degrees and a nice situation in the winter sky, this is definitely one for Transitesearch.org’s Finland contingent.

Countdown

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August 1st marked the most recent ‘606 day, which came and went without wide remark. Perhaps this was because in late Summer, HD 80606 rises and sets in near-synch the Sun, and is thus lost from the Earth’s night skies.

At the moment, HD 80606b is headed back out toward apastron.

The global storms and shockwaves that were unleashed at the beginning of August are dissipating rapidly, and the flux of heat from the planet is likely fading back down to the sullen baseline glow that arises from tidal heating.

HD 80606’s next periastron passage occurs on November 20th, and the Spitzer Space Telescope is scheduled to observe the whole event (details here). It’s going to be a big deal. Spitzer can only observe HD 80606 during two three-week windows each year, and fortunately, the Nov. 20th Periastron passage occurs during one of these windows. It’s literally the only opportunity to catch HD 80606 b’s big swing before Spitzer’s cryogen runs out in 2009.

The orbital geometry of the periastron passage looks like this:

Each marker of the orbit is separated by one hour. The prediction for the pseudo-synchronous rotation of the planet is also indicated. The planet should be spinning with a period of 36.8 hours. Jonathan Langton’s hydrodynamics code predicts what the temperature distribution on the planet should look like at each moment from Spitzer’s viewpoint in our solar system:

Transitsearch.org observers have covered a number of the HD 80606 b transit opportunities, and it seems pretty certain that the planet doesn’t transit. This isn’t surprising. The geometry of the orbit is such that when the planet crosses the plane containing the line of sight to the Earth, it’s quite a distance away from the star. Not so, however, for the secondary transit. There’s a very respectable 15% chance that Spitzer will detect a secondary transit centered two hours prior to the periastron passage.

Even if the planet doesn’t transit, we should be able to get a good sense of the orbital inclination from the shape of the light curve. If the orbit is nearly in the plane of the sky, then we should see a steady rise followed by a plateau in the 8-micron flux coming from the planet. For more nearly edge-on configurations, the flux peak should be clearly discernable. The observations are scheduled to start 20 hours prior to periastron and end 10 hours after.

Vorticity

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Vorticity can be thought of as the tendency of a paddlewheel to spin if placed in the flow. High vorticity is a large counter-clockwise spin, zero vorticity is no spin, and a large negative vorticity is a tendency to spin clockwise. The climate models of short-period extrasolar planets that Jonathan Langton and I have developed show a remarkable variety of vorticity patterns on their surfaces, in keeping with the incredibly stormy and complex nature of their atmospheres. Here’s a gallery of Mercator-projection vorticity maps for the known strongly irradiated Jovian planets that have significant eccentricities. The red arrows indicate the wind speeds and directions across the planetary surfaces. These figures are all from a paper that’s currently under review at the Astrophysical Journal (see here for an overview of the numerical method that we’re using). Also, a shout-out is due to Edward Tufte for advocating the strong graphic-design effect of small spots of saturated color on a gray-scaled backdrop.


HAT-P-2b:

Here are 1.1 MB North Pole, South Pole and Mercator Projection animations of the HAT-P2b vorticity evolution.

HD 80606 b:

1.1 MB Mercator animation here.

HD 185269 b:

1.1 MB Mercator animation here.

HD 108147 b

1.1 MB Mercator animation here.

HD 118203 b:

1.1 MB Mercator animation here. The animations above are hosted on the Oklo Corporation’s servers.

It’s interesting to compare the vorticity maps with the temperature distributions on the planetary surfaces (shown in the same order as above):

Gigantic

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The TrES survey announced the discovery of a new transiting planet today, raising the number of known transits to twenty (including Mercury and Venus). The new planet, “TrES-4”, has a mass of order 84% that of Jupiter, and with a radius of 1.67 Rjup, it’s pumped to nearly five times Jupiter’s volume:

The false color image of Jupiter was produced from near-infrared data obtained with the Gemini telescope. The even more luridly false-color representation of TrES-4 is based on a vorticity map from one of Jonathan Langton’s recent simulations.

In order for TrES-4 to be swollen to its current size, it needs to be experiencing heating of order 6×10^27 ergs per second. One way to do this is to have a significant perturbing companion which drives large time-averaged variations in TrES-4’s orbital eccentricity. So far, there are only four published radial velocities for TrES-4, so the orbit could easily be non-circular. More provocatively, if strong orbital forcing is indeed occurring, then there’s a reasonable chance that the perturber might also be observable in transit. I recommend that Transitsearch.org observers keep this bad boy under constant supervision.

Whorls

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HAT-P-2b. The name doesn’t exactly ring of grandeur, but this planet — a product of Gáspár Bakos’ HAT Net transit survey — is poised to give the Spitzer Space Telescope its most dramatic glimpse to date of a hot Jupiter.

HAT-P-2b’s orbit is remarkably eccentric for a planet with an orbital period of only 5.6 days, and by a stroke of luck, periastron is located almost exactly midway between the primary and the secondary transits (as viewed from Earth). The strength of the stellar insolation at periastron is nine times as strong as at apastron, which more than guarantees that the planet will have disaster-movie-ready weather.

On June 6th, Josh Winn and his collaborators used the Keck telescope to obtain 97 radial velocities for HAT-P-2. The observations were timed to occur before, during, and after primary transit, and the Rossiter-McLaughlin effect is clearly visible in their data (preprint here):

The symmetry of the Rossitered points indicates that the angular momentum vector of the planetary orbit is aligned with the spin pole of the star:

schematic diagram showing rossiter effect

This state of affairs also holds true for the other transiting planets — HD 209458b, HD 149026b, HD 189733b — for which the effect has been measured. The observed alignments are evidence in favor of disk migration as the mechanism for producing hot Jupiters.

With its apparent magnitude of V=8.7, the HAT-P-2b parent star is roughly ten times brighter than the average planet-bearing star discovered in a wide-field transit survey. The star is bright enough, in fact, to have earned an entry in both the Henry Draper Catalog (HD 147506) and the Hipparcos Database (HIP 80076), but with its surface temperature of 6300K (F8 spectral type) it was too hot to have been a sure-fire “add” to the ongoing radial velocity surveys. Prior to this May, it had been entirely ignored in the astronomical literature (save a brief mention in this paper from 1969).

HAT-P-2’s intrisic brightness and its planet’s orbital geometry mean that in a relatively compact 34-hour observation, Spitzer can collect on the most interesting features of the orbit with high signal-to-noise. In particular, there is an excellent opportunity to measure the rate at which the day-side atmosphere heats up during the close approach to the star. The planet, in fact, presents such a remarkable situation that a block of Director’s Discretionary time was awarded so that the observations can be made during the current GO-4 cycle. They’ll be occurring soon.

Both HAT-P-2b and HD 80606 b will provide a crucial ground truth for extrasolar planetary climate simulations. Jonathan Langton’s current model, for example, predicts that that the temperatures on HAT-P-2b will range over more than 1000K. At the four times shown in the above orbital diagram, the hemisphere facing Earth is predicted to show the following appearances:

Spitzer, of course, can’t resolve the planetary disk. It measures the total amount of light coming from the planet in chosen passband. At 8-microns, the planet’s light curve should look like this:

The temperature maps only hint at the complex dynamics of the surface flow. A better indication is given by the distribution of vorticity,

which we’ll pick up in the next post…

Showing Mercury the Door (Part 1).

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The long-term stability of the planetary orbits has been a marquee-level question in astronomy for more than three centuries. Newton saw the ordered structure of the solar system as proof positive of a benign deity. In the late 1700s, the apparent clockwork regularity of interaction between Jupiter and Saturn helped to establish the long-standing concept of Laplacian determinism. In the late Nineteenth Century, Poincaré’s work on orbital dynamics provided the first major results in the study of chaotic systems and nonlinear dynamics, and began the tilt of the scientific worldview away from determinism and toward a probabalistic interpretation.

In the past ten years, it has become fairly clear that the Solar System is dynamically unstable, in the sense that if one waits long enough (and ignores drastic overall changes such as those wrought by the Sun’s evolution or by close encounters with passing stars) the planets will eventually find themselves on crossing orbits, leading to close encounters, ejections and collisions. The question has shifted more to the following: What (if any) chance is there that the planets will experience orbit crossings within the next 5 billion years?

It’s clear that the probability of the planets going haywire prior to the Sun’s red giant phase is pretty small. Computers are now fast enough to integrate the eight planets forward for time scales of ten billion years or more. Konstantin Batygin, a UCSC physics undergrad who has been collaborating with me, has been running a suite of very long term solar system integrations, and he’s been getting some nice results.

It’s well known that over the long term, the planetary orbits are chaotic. The Lyapunov timescales for the planetary orbits in both the inner and the outer solar system are of order a few million years, which means that for durations longer than ~50 Myr into the future, it becomes impossible to make a deterministic prediction for exactly where the planets will be. . We have no idea whether January 1, 100,000,000 AD will occur in the winter or in the summer. We can’t even say with complete certainty that Earth will be orbiting the Sun at all on that date.

We can, however, carry out numerical integrations of the planetary motions. If the integration is carried out to sufficient numerical accuracy, and starts with the current orbital configuration of the planets, then we have a possible future trajectory for the solar system. An ensemble of integrations, in which each instance is carried out with an unobservably tiny perturbation to the initial conditions, can give a statistical distribution of possible long-term outcomes.

Here’s a time series showing the variation in Earth’s eccentricity during a 20 billion year integration. In this simulation, the Earth experiences a seemingly endless series of secular variations between e=0 and e=0.07 (with a very slight change in behavior at a time about 10 billion years from now). The boring, mildly chaotic variations in Earth’s orbit are mostly dictated by interactions with Venus.

Mercury, on the other hand, is a little more high-strung.

These two plots suggest that the Solar System is “good to go” for the foreseeable future. Indeed, work by Norm Murray and Matt Holman suggests that the four outer planets have a dynamical lifetime of order one hundred quadrillion years. Work by Jaques Laskar, however, suggests that the inner solar system might be on far less stable footing. Konstantin has obtained some very interesting new results on this particular point, which we’ll be sharing in an upcoming post…

HAT-P-3b

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The HATNet survey’s latest single, “3b” landed on the charts last week at #12. This hot (Teff~1053K) new disk shows a definite metal influence, which makes sense, given that [Fe/H] for the parent star is an Ozzy-esque +0.27. You can get a free download of the paper from the Extrasolar Planets Encyclopaedia.

The past twelve months has seen the inventory of known transiting planets more than double, as wide-field surveys such as TrES, Exo, and HATnet start to reach the full production end of their observational pipelines. As the number of planets reaches the threshold for statistical comparisons, interesting trends (or possible trends) have started to emerge.

By far the most remarkable correlation, however, has been with respect to sky location. Among the fourteen fully announced transiting planets orbiting stars with V<14, every single one is located north of the celestial equator.

Planet

Mass

Mjup

Period

days

 Dec V
Gl 436b 0.07 2.64385 +26 42 10.68
HAT-P-1 b 0.53 4.46529 +38 40 10.4
HAT-P-3 b 0.61 2.8999 +48 02 11.86
HAT-P-2 b 8.64 5.63341 +41 03 8.71
HD 149026 b 0.36 2.8766 +38 21 8.15
HD 189733 b 1.15 2.21857 +22 43 7.67
HD 209458 b 0.69 3.52475 +18 53 7.65
TrES-1 0.61 3.03007 +36 38 11.79
TrES-2 1.98 2.4703 +49 19 11.41
TrES-3 1.92 1.30619 +37 33 12.4
WASP-1 b 0.89 2.51997 +31 59 11.79
WASP-2 b 0.88 2.152226 +06 26 11.98
XO-1 b 0.9 3.941534 +28 10 11.3
XO-2 b 0.57 2.615838 +50 13 11.18

Looks like there’s some opportunity down under…

Barred Spiral

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I’d never really seen the Milky Way until I saw it on a perfectly clear and moonless July night from a spot just below the Arc Dome in central Nevada. It spills a swath of patchy luminosity that seems to split the sky in half; a barred spiral galaxy, seen edge-on, and from within. One hundred billion intensely glowing stars, like sand grain jewels, each separated by miles. The photo above (taken by Steve Jurvetson last weekend from the Black Rock Desert in Nevada) reminded me of that experience.

The dark sky applet shows that the interior of Nevada (away from Las Vegas!) contains many of the least light-polluted areas of the United States.

Under a totally dark sky, you can distinctly see the star clouds in the foreground of the galactic center. It’s eerie to think that the 3-million solar mass black hole lurking in the center of the galaxy is just to the right of the bright luminosity of Baade’s Window near the boundary between Sagittarius and Scorpius.

The photo also shows Jupiter within a few degrees of Antares — a nice illustration of the fact that Jupiter appears slightly brighter than the brightest stars.

Newton used this similarity in apparent brightness to get the first real estimate of the staggering distances to the stars. He assumed that the stars are similar in absolute brightness to the sun, and he assumed that Jupiter (whose distance and angular size were known to him) is a perfect reflector of sunlight. This method underestimates the distance to Sirius by more than a factor of five, but it does a fairly reasonable job for Alpha Centauri.

A hot hot Neptune

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Regular oklo readers will recall Gillon et al.’s discovery that the Neptune-mass planet orbiting the red dwarf star Gl 436 can be observed in transit. Transitsearch got scooped, and the whole eposide got me all worked up enough to neglect the exigencies of everyday academic life and reel off three straight posts on the detection and its consequences (see here, here, here, and also here). The transits of Gl 436 b are a big deal because they indicate that the planet is possibly composed largely of water. It’s not a bare rock and it’s not a Jupiter-like gas giant. Rather, it’s consistent with being a fully Neptune-like object, hauled in for inspection on a 2.64385 day orbit.

Following Gillon et al.’s announcement, it became clear that Gl 436 transits would fit into a window of observability during the June 24th – July 04 IRAC campaign on the Spitzer Space Telescope. The red dwarf parent star, furthermore, because of its proximity, is bright enough for Spitzer to achieve good photometric signal-to-noise at 8-microns. As a result, Joe Harrington’s Spitzer Target of Opportunity GO-4 proposal was triggered, and the Deep Space Network radioed instructions to the spacecraft to observe the primary transit on June 29th, as well as the secondary eclipse (when the planet passes behind the star) on June 30th, a bit more than half an orbit later. Joe, along with his students Sarah Navarro and William Bowman, and collaborators Drake Deming, Sara Seager, and Karen Horning asked me if I wanted to participate in the analysis. After watching all the ‘436 action from the sidelines in May, I was more than happy to sign up!

One of the most exciting aspects of being a scientist is the round-the-clock push to get a time-sensitive result in shape for publication. There’s a fantastic sense of camaraderie as e-mails, calculations, figures and drafts fly back and forth. On Monday afternoon PDT (shortly after midnight GMT) when Mike Valdez sent out his daily astro-ph summary, it was suddenly clear that we were under tremendous pressure to get our results analyzed and submitted. The Geneva team had swooped in and downloaded the data for the primary transit the moment it was released to the community! They had cranked out a reduction, an analysis, and a paper, all within 48 hours. Their light curve confirmed the ground-based observations. Spitzer’s high-quality photometry indicates that the planet is slightly larger than had been indicated by the ground-based transit observations. Drake submitted our paper yesterday afternoon.

Fortunately for us, the real prize from Spitzer is the secondary eclipse. Its timing is capable of independently confirming that the orbit is eccentric, and the depth gives an indication of the surface temperature on the planet itself.

The upper panel of the following figure shows the raw Spitzer photometry during the secondary eclipse window. IRAC photometry at 8 μm is known to exhibit a gradually increasing ramp-up in sensitivity, due to filling of charge traps in the detectors, but even before this effect is modeled and subtracted, the secondary transit is visible to the eye. The bottom panel shows the secondary transit in detail.

The secondary transit occurs 58.7% of an orbit later than the primary transit, which proves that the orbit is eccentric. A detailed fit to the transit times and to the radial velocities indicates that the orbital eccentricity is e=0.15 — halfway between that of Mars (e=0.1) and Mercury (e=0.2). The orbital geometry can be drawn to scale in a diagram that’s 440 pixels across:

The depth of the secondary eclipse is 0.057%, which allowed us to estimate a 712 ± 36K temperature for the planetary surface.

A temperature of 700+ K is hotter than expected. If we assume that the planet absorbs all the energy that it gets from the star and re-radiates its heat uniformly from the entire planetary surface, then the temperature should be T = 642 K. The higher temperature implied by the secondary eclipse depth could arise from inefficient transport of heat to the night side of the planet, from a non-“blackbody” planetary emission spectrum, from tidal heating, or from a combination of the three. If the excess heat is all coming from tidal dissipation, then the Q-value for the planet is 7000, suggesting that it’s a bit more dissipative inside than Uranus and Neptune.

What would Gl 436 b look like if we could go there? To dark adapted eyes, the night side is just barely hot enough to produce a faint reddish glow (as is the case on the surface of Venus, which has a similar temperature). The atmosphere is too hot for water clouds, and is likely transparent down to a fairly high atmospheric pressure level. The day-side probably reflects a #E0B0FF-colored hue that contrasts with the orange-yellow light of the star. The planet spins with a period of 2.32 days so that it can be as spin-synchronous as possible during the sector of its orbit closest to periastron. At a fixed longitude on the planet, the day drags on for 456 hours from high noon to high noon.

Jonathan Langton has been running atmospheric simulations with the latest parameters. On the phone, just a bit ago, he would only say that the preliminary results were “interesting”…

Second quarter earnings report

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On Thursday and Friday of last week, the Dow Jones Industrial Average jumped nearly 2%. Given the soaring price of oil and the subprime mortgage crisis, many students of the financial markets were puzzled by this seeming burst of irrational exuberance.

A visit to exoplanet.eu, however, suggests that investors and speculators were placing buy orders in response to the rapid recent increase in the number of known planets. During the first two quarters of ’07, the extrasolar planet detection rate has been running more that 100% above the rate reported for the most recent full fiscal year.

When asked about the impact of the new discoveries, one metals trader was quoted, “Well, Mate, the Marketplace has been pricing in the core-accretion theory for several years now. That means we’re looking at a Z of ~0.1 for each one of these planets coming in, so that’s roughly 30 Earth masses of ore per extrasolar planet. If we use the solar gold assay, that works out to one quintillion ounces of new proven reserves for each discovery. With gold at $660, we’re starting to talk real money.”

Jocularity aside, the raft of new planet discoveries is having a noticeable impact on the correlation diagrams that can be explored at the exoplanets.eu site. One (likely statistically insignificant) curiosity is the lack of Saturn-mass planets in this year’s crop to date. At the low-mass end, Neptunes such as Gl 674b are turning up with increasing frequency, and the detection-rate for Jupiter-mass planets and above also remains strong. This dichotomy is very much in line with a key prediction of core-accretion in its simplest form. The rapid gas accretion that occurs once the planet mass reaches ~30 Earth masses should tend to make Saturn-mass planets relatively rare.

Another interesting diagram results when one plots the masses and eccentricities of the known RV-detected planets. A glance at the resulting diagram indicates that low-mass planets tend to be on more circular orbits. Could this be hinting at two populations of planets and (perhaps) two different formation mechanisms? It’s hard to tell. Much of the effect comes from the fact that low-mass planets need to have short periods in order to be detectable. Short-period planets, in turn, are far more affected by tidal circularization of the orbits. The plot is also reflecting the still-mysterious (but well known) shortage of high-mass hot Jupiters.