Retrograde

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Turn your world upside-down and you’re looking at a very different planet. Antarctica, ringed by the vast exapse of the Southern Ocean, draws all the attention. Viewed from beneath, I think Earth might better resemble the habitable planets that are out there in the local galactic neighborhood, waiting to be found.

Speaking of upside-down planets, last week brought a curious back-to-back development. Three separate papers (one, two, three), posted to astro-ph on two successive days, presented strong Rossiter-McLaughlin-based evidence that both WASP-17b and HAT-P-7b are on severely misaligned, potentially retrograde orbits around their parent stars. Winn et al.’s data for HAT-P-7 are a near-exact inversion of the familiar sawtooth produced by well-behaved hot Jupiters such as HD 209458b or HD 189733b. It would appear that Dr. Kozai exerted a heavy hand during HAT-P-7b’s early days:

The HAT-P-7 system is alarmingly compact. The star is roughly 80% larger than the Sun, and the orbit of the transiting planet is only about four times larger than the star itself. It looks, in fact, when drawn to scale and tilted to the proper inclination, like a schematic cartoon of a transiting system.

Remarkably, HAT-P-7 lies in the Kepler field, and was the subject of a teaser-like “brevia” published in Science a few weeks ago. In the folded Kepler light curve for HAT-P-7b it’s easy to see the phase function of the orbiting planet, along with the primary transit and the secondary eclipse. The well-resolved depth of the secondary eclipse indicates that the spacecraft is performing up to spec and will be able to detect the transits of Earth-sized planets orbiting Sun-sized stars.

Interestingly, a near-perfectly inverted Rossiter-McLaughlin waveform doesn’t necessarily mean that the planetary orbit is retrograde, but rather only that the angle between the planet’s orbital angular momentum vector and the sky-projected spin axis of the star is close to 180 degrees. If the star’s polar axis is pointing nearly in our direction, then the planetary orbit is close to polar. The small vsin(i) for HAT-P-7 provides a piece of evidence that HAT-P-7b’s orbit might in fact be close to polar.

HD209458set on HD 209458b

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During my visit to the Paris Observatory earlier this summer, Alain Lecavelier showed me the work that he and David Sing and their collaborators have been doing to get a better handle on the atmospheric conditions on HD 209458b. Using the STIS spectrograph on HST, they’ve obtained both medium-resolution and low-resolution visible-wavelength absorption spectra of starlight shining through the atmosphere of the planet as it transits the parent star.

HST is sensitive enough to allow startlingly detailed portraits of “sunsets” that took place back in the mid-1850s. Here’s a reworking of Figure 1 from Sing et al. (2008):

Illustrator-editable .pdf of above with title and source.

Sing et al. manage to do a good job of matching the features in the spectrum. The big absorption spike in the orange is due to the presence of atomic sodium. Their atmospheric models also include Raleigh scattering by hydrogen molecules, a temperature inversion in the atmosphere, condensation of sodium sulfate on the planet’s night side, and the presence of titanium and vanadium oxide in the atmosphere. (Titanium oxide can be invoked to play a big role in modulating the visual appearance of hot Jupiters for much the same reason that it’s used as an opacifier in ordinary paint.)

With a detailed atmospheric model in hand, it’s possible to calculate both the color of the sky and the color of HD 209458b at various sight lines through the air column. David and Alain did exactly that, and have made an animation from the perspective of an observer in an asbestos-coated balloon drifting nightward across the terminator. The effect is reminiscent of a Turrell skyspace:



Here’s a link to their French-language press release. According to the inimitable google translator, “star at bedtime absorption is cyan”

Inside Jupiter

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Image Source: ESO

Two weeks ago, I spent a day with a team from Flight 33 productions working on an episode for the ongoing Universe series on the History Channel. Over the past several seasons I’ve appeared on occasional episodes of this show, either in connection with extrasolar planets or with regards to the ultra-distant future. The topic of the latest episode was extraterrestrial liquids, running the gamut from the (relatively) familiar and accessible — azure oceans on TPF dream planets — to the bizarre: vast expanses of liquid metallic hydrogen in the interiors of giant planets and hypothesized superfluids miles beneath the surfaces of neutron stars.

How can one get liquid metallic hydrogen’s essence across during a brief segment of commercial television? By comparison, conveying the atmosphere of a Jovian planet is quite easy. Towering sunlit clouds. The chilly deluge of the Jovian rainstorms. The awful smell. Liquid metallic hydrogen, on the other hand, couldn’t be any more alien. It exists at typical pressures of ten million atmospheres. In Jupiter, there are hundreds of Earth masses of the stuff, all at temperatures several times hotter than the surface of the Sun. A handful of the deep Jovian interior, materialized somehow on the surface of the Earth for the sake of demonstration, would instantly explode with fully counterproductive newsworthy effect.

The analogy I came up with is provided at a heavily congested bumper car rink in which the bumper car drivers are free to jump between cars. In this model, the cars represent the heavy protons and the drivers represent the much lighter electrons. Arrangements were made to utilize the Santa Cruz Beach Boardwalk for the filming of this mock-up of the Jovian interior. The logistics of the event drew together a rather diverse range of participants, and the event snowballed to make the front page of the Santa Cruz Sentinel (link to the article).

It’ll be interesting to see how things turned out when the episode airs.

the pause that refreshes

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The systemic backend will be offline for a period of time starting on Monday Aug. 03. We’re pulling our server from its current rack space. When it comes back on line, it be on the UCSC network. The database has been fully backed up, so despite the temporary unavailability, there’ll be no loss of data. The oklo.org web log will continue uninterrupted.

When we return, we have several goals in mind for the backend. First, there will be support. Several UCSC physics and computer engineering undergrads will be joining the systemic team, and will be focused on improving the backend and keeping it running smoothly. Due to time constraints, and despite best efforts, we just weren’t able to keep up with this ourselves. Second, the backend will maintain improved integration with the console as the console develops, and will be more focused on scientific tools rather than the web 2.0 social network aspect. Third, we’ll be introducing features geared toward the use of the console as an instructional tool in astronomy, physics and astrobiology classes.

Latest ‘606 news

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An unsung advantage of long-period transiting planets is that the occultations occur on a civilized timescale. An interval of 111.4357 days is long enough not to feel pressured, rushed, or in constant danger of getting scooped. This is in stark contrast, to, say, managing your affairs with a fixed 2.2185733 day turn-around time.

Earlier this summer, there were two papers, one by Pont et al. and one by Gillon which presented complete, leisurely analyses that combine all of the available photometric and RV data for the HD 80606 system taken through the Valentine’s Day 2009 transit. These papers adopted a fully Bayesian approach to analyzing the heterogeneous data sets, and were able to improve the system’s vital stats: The planet has a radius very similar to Jupiter. The full duration of the transit is close to 12 hours (and uncertain to a bit more than an hour). With high confidence, the planet’s orbit is badly misaligned with the stellar equator — just as expected from the Kozai migration hypothesis.

Last night, Josh Winn sent me a new preprint that reports results from an extensive campaign that he spearheaded to observe the June 4th/5th 2009 transit. June, to put it mildly, is not exactly an ideal time to observe HD 80606 from Earth. The nights in the Northern Hemisphere are short, and the star sets early. At any given spot, you can get at best a few hours of uninterrupted data. Nevertheless, it was of great interest to bag the transit. The ingress was weathered out during the February event, and so the analyses of Pont et al. and Gillon had to lean rather heavily on the Good Reverend Bayes.

Josh’s strategy was to recruit an East-to-West swath of observers in Massachusetts, New Jersey, Florida, Indiana, Texas, Arizona, California, and Hawaii. The idea was that 168 electoral votes would be enough to tilt the contest in favor of the good guys.

The multi-state strategy paid off. By stringing together the individual photometric blocks, the first half of the transit was nicely resolved. At the finish line, on the summit of Mauna Kea, the Keck telescope stepped up to the podium to obtain a series of mid-transit spectroscopic measurements that further confirmed the severe spin-orbit misalignment.

.ppt-ready higher resolution version

This is just the sort of project that underscores the great value of ad-hoc collaborations. The Florida ingress observations, for example, were made using the University of Florida’s recently refurbished Rosemary Hill Observatory, 30 miles from Gainesville. The DeKalb observations, made by Indiana amateur Donn Starkey, produced reduced data that were among the best in the entire aggregate. Mount Laguna Observatory, run by San Diego State University, has generated many cutting-edge exoplanet observations, including critical photometry in the Fall 2007 HD 17156b campaign. The University of Hawaii 2.2m telescope turned out photometry with astonishing rms=0.00031 precision. And as the cherry on top, the simultaneous commandeering of not one but two major telescopes on Mauna Kea? It seems that perhaps someone has made a Faustian bargain.

Saros 136

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My UCSC Astronomy Dept. colleague Enrico Ramirez-Ruiz sent me a cool graph the other day. It amounts to a photometric transit observation of an R~1700 Km satellite of a habitable terrestrial planet.

Enrico writes:

The attached figure shows the main power voltage to LAT (Large Area Telescope instrument on the Fermi Satellite). There is a regular pattern of increasing voltage when the battery is being charged, a plateau when charging is complete but we are still in sunlight, and discharge when Fermi moves out of sun. You can see a sudden dip in voltage at 3:30 UT when the sun is blocked.

Last week’s total solar eclipse prompted me to think back to the last millennium, to July 11, 1991, when the previous eclipse of Saros series 136 occurred. My fellow graduate students and I drove down to the center line near the tip of the Baja Peninsula. I wrote down my recollections, which we later adapted for one of the chapter vignettes in The Five Ages.

The partial eclipse phases lasted for more than an hour. Even as an ever-larger fraction of the Sun was obscured, the change was so gradual that eyes adjusted continuously. The slackening of the daylight went unnoticed until about fifteen minutes before totality, as more than 90 percent of the Sun’s face was obscured. Due to the reduced sunshine over a swatch of the Earth as large as the diameter of the Moon, the morning was unusually cool for a Mexican July. By 10:00 A.M., the temperature was only in the seventies. The thermometer dropped slightly as the eclipse progressed, and when the daylight finally began to visibly dim, the air seemed almost chilly. The surface of the ocean looked dull and flat, but without the slate gray color of a cloudy day. Cumulus clouds billowed over the distant spine of mountains like an accelerated film.

All at once, the dunes were awash in subtle shadowy ripples, like caustics at the bottom of a midday swimming pool. The ripples drifted slowly across the sand, their contrast flickering. The bands persisted for less than a minute, and then seemed to evaporate. The wind seemed to grow stronger.

With only a minute left, the sky grew darker every second. The air was alive with flapping fruit bats that had been fooled into emerging by the unnatural dusk. A dangerous stray glance at the sun gave a moment’s impression of a starlike point. With five seconds left, the black shadow of totality swept toward us across the water at nearly two thousand miles an hour.

The starlike impression of the Sun was superseded by the disk of the Moon easing into place. A final, fleeting, brilliant burst of light flashed out as the Sun shone through a valley on the limb of the Moon. Totality descended, the stars leapt out, and the nebulous electric blue corona arced away from the black disk.

A look inside an extrasolar planet

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Image Source.

Cranking out a paper invariably takes longer than one expects. Last week, I was confident that Konstantin and Peter and I would have our HAT-P-13 paper out in “a day or so”, and then it ended up taking the whole week. As of ten minutes ago, however, it’s been shipped off to the Astrophysical Journal Letters. It’s also been submitted to astro-ph, hopefully in time to make tomorrow’s mailing.

In the meantime, here’s a link to (1) the .pdf of our text, and (2) the two figures (one, two) both in .gif format. The two figures are 800 pixels across, all the better for dropping in to presentations.

Put briefly, HAT-P-13 is an absolutely remarkable set-up. The presence of the outer perturbing body in its well-defined orbit allowed us to show that the system has undergone long-term evolution to a “tidal fixed point”. In this state of affairs, secular variations in the orbital elements of the two planets have been damped out by tidal dissipation, the apsidal lines of the orbits have been brought into alignment, and most importantly, the two orbits precess at the same rate. The paper shows how the eccentricity of the inner planet is a sensitive function of the planet’s interior structure, and in particular, the degree of central concentration (parameterized by the “Tidal Love Number”, k_2).

Here’s a schematic that shows what’s going on:

Right now, the eccentricity of the inner planet is determined to rather modest precision e=0.021 +/- 0.009. The system is transiting, however, and so when Warm Spitzer measures the secondary eclipse time, the error on the eccentricity measurement will drop dramatically. The situation will also benefit from an improved measurement of the planet’s radius. When improved measurements come in, it’ll be possible to literally read off the planet’s core mass and, in addition, the value of the much-discussed tidal quality factor Q.

Lucky 13

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In reviewing grant proposals and observing proposals that seek to study extrasolar planets, one notices that two cliches turn up with alarm-clock regularity. Number one is Rosetta Stone, as in this or that planetary system is a Rosetta Stone that will enable astronomers to obtain a better understanding of the formation and evolution of planetary systems. Number two is ideal laboratory, as in this or that system is an ideal laboratory for studying the processes that guide the formation and evolution of planetary systems.

A terse unsolicited e-mail from Gaspar Bakos always means that a big discovery is in the offing, and today was no exception:

Hello Greg,

You may like this.
http://xxx.lanl.gov/abs/0907.3525

Best wishes
Gaspar

Indeed! HAT-P-13b and c constitute a really exciting discovery. For a number of reasons, this system is a Rosetta Stone among extrasolar planets, and in large part, this is because the system is an ideal laboratory for studying processes such as tidal dissipation and orbital evolution.

HAT-P-13 harbors the first transiting planet that has a well-characterized companion planet. In this case, the outer companion has a P=428 day orbit, an Msin(i) of 15 Jupiter masses, and an eccentricity, e=0.7. In the following diagram, the orbits and the star are shown to scale; the small filled circles that delineate the outer orbit show the position of the outer planet at 4.28 day intervals.

Illustrator-editable PDF of the above

Of obvious interest is the question of whether planet c can be observed in transit. The a-priori probability is seemingly enhanced by the transit of the inner planet. (Give that one to the good Reverend Bayes). The next opporunity rolls around in April 2010, with the opportunity to observe secondary transit following a bit more than two months later.

It’ll be quite something if planet “c” does transit. A sense of the wide open spaces in the system can be obtained by plotting the star and the two planets to scale with their respective separations at the moment of inferior conjunction. Given the width restriction of the blog post format, one needs to present this plot vertically:

There’s a lot more to say about the HAT-P-13 system — so much in fact, that Peter Bodenheimer, Konstantin Batygin and I are furiously writing an ApJ letter. Should have it out the door in a day or so, with a roundup to follow here on oklo.org immediately thereafter…

Panthéon

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The opportunity to see Paris was a real high point of my recent trip to Europe. I have to admit, arriving from small-town California, speaking no French, I felt every bit Mr. Country Mouse. As the midwestern saying goes, it’s hard to keep the boy down on the farm once he’s seen Paree.

Travelogue slideshows get real old real fast, but nevertheless, I’ll indulge in a couple of posts that touch on my Paris visit. On my first day there, I visited the Paris Observatory (more on that later in the week). The next two days were taken up with walking all over the city.

The Panthéon probably left the biggest impression. It was a chilly, rather gloomy day. The soaring interior was a somber chamber of echoes. I’ve always been interested in the events surrounding the French Revolution — the ideal of a Republic seems to find no better expression than in a secular cathedral. Foucault’s pendulum is the centerpiece. Its slow precession silently, subtly underscores the ascendancy of a rational world view. Chills down the spine.

A stone spiral staircase leads down to the crypt.

Where I found the grave of Joseph Louis, comte Lagrange, its stone inscription just visible among the shadows.

reintroduction

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i-Phone snapshot of Difference Engine #2.

The systemic console started life over five years ago as a web-based applet for analyzing radial velocity data. The original version was a collaboration between Aaron Wolf (then a UCSC Undergraduate, now a Caltech Grad Student) and myself, and the Java was coded in its entirety by Aaron. Our goal was to clarify the analysis of radial velocity data — the “fitting” of extrasolar planets — by providing an interactive graphical interface. The look and feel were inspired by sound-mixing boards, in particular, the ICON Digital Console built by Digidesign:

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Over the intervening years, the console has expanded greatly in scope. Stefano Meschiari has taken over as lead software developer, and has directed the long-running evolution with considerable skill. The console has been adopted by planet-hunting groups world-wide, as well as by classroom instructors and by a large community of users from the public.

Tuesday’s post pointed to our new peer-reviewed article (Meschiari et al. 2009) that describes the algorithms under the console’s hood, and now that the code base has matured, we’re developing documentation that can serve the widely varying needs of our users. We also intend to return the systemic backend collaboration to the forefront of relevance. A great deal of very interesting work has been done by the backend users, and it can be leveraged.

As the first step, we’re updating and expanding the tutorials, which have been largely gathering dust since November 2005. Following the page break, the remainder of this post updates tutorial #1. If you’ve ever had interest in using the console, now’s the time to start…

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