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HAT-P-2b: ‘A Really Weird Planet’

Last night I was thinking that the day would come when all the planets we’ve been discovering have proper names instead of stark designations in catalogs. Then I realized that this is unlikely. As the rate of planetary discoveries accelerates through space-borne missions and ever more precise detection methods here on Earth, it may be that we’ll keep generating new finds faster than the naming process can catch up with them. So I guess we should get used to designations like Gliese 581 c.

Of course, a planet can have multiple designations, depending on how it’s catalogued or found. The recently announced gas giant HAT-P-2b (a very strange place indeed) is called this not for its place in a catalog but its discovery method, the HAT network of automated telescopes. HAT stands for Hungarian-made Automated Telescope, but the project is headquartered at the Harvard-Smithsonian Center for Astrophysics (CfA) and works with instruments in Arizona, Hawaii and in this case, Israel. Its focus: The detection of transiting exoplanets like this one.

But HAT-P-2b is also HD 147506 b, referring to its star’s listing in the Henry Draper Catalog. You can see that designations like these lack a certainty poetry, depending on the catalog or project involved (think of TrES-1, designating the Trans-Atlantic Exoplanet Survey that found it — examples begin to multiply). We’ll have to draw our aesthetic satisfaction not from colorful names but the exotic places these designations conjure up. And HAT-P-2b by any name turns out to be exotic indeed. Gaspar Bakos (CfA) calls it “…a really weird planet.”

The parent F-class star, HD 147506, lies 440 light years away in the constellation Hercules. Larger and brighter than the Sun, it’s home to at least one planet and perhaps another. That thinking is based on the odd elliptical orbit of HAT-P-2b, which represents a marked break from the circular orbits thus far found with transiting gas giants, all of which have been ‘hot Jupiters.’ With an orbital period of a scant 5.63 days, HAT-P-2b comes into transit every five days and 15 hours. Its oval orbit moves it from periastron at 3.1 million miles to fully 9.6 million miles at apastron, an eccentricity that is probably the result of an outer planet, although at this juncture there is no hard evidence of that planet’s existence.

This one is no hot Jupiter; in fact, it’s much closer to a failed star. The co-author on the discovery paper, Dimitar Sasselov, says this: “With 50 percent more mass, it could have begun nuclear fusion for a short time.” Even so, HAT-P-2b is one dense world, eight times the density of Jupiter, but evidently packed into a ball only slightly larger than that planet. It stands out compared to previously identified transiting exoplanets.

From the discovery paper:

Its mass of 8.17 ± 0.72MJ is ~5 times greater than any of these 14 other exoplanets. Its mean density ρ = 6.6 ± 2.7 g cm−3 is ~5 times that of the densest known exoplanet (OGLE-TR-113b, ρ = 1.35 g cm−3 ) and indeed greater than that of Earth (ρ = 5.5 g cm−3) or other solar system rocky planets. Its surface gravity of 149 ± 13 m s−2 is 5 times that of any of the previously known TEPs, and 20 times that of HAT-P-1b.

A mean density greater than Earth’s, and notice that last sentence, which points out the surface gravity is five times that of any transiting exoplanets (TEPs) previously found. Expect no media buzz with this one. A massive gas giant in a peculiar orbit around a hot F-class star doesn’t offer much by way of habitability potential. But most planets aren’t going to be habitable, and every transit we find offers the chance to measure the planet’s physical size from the degree to which the star’s light is dimmed by its passage. The paper is Bakos et al., “HAT-P-2b: A Super-Massive Planet in an Eccentric Orbit Transiting a Bright Star,” submitted to the Astrophysical Journal, with abstract available.

Comments on this entry are closed.

  • ljk May 3, 2007, 14:20

    I know no mainstream astronomer would dare to suggest
    this seriously, but I wonder if this planet is actually artificial?

    See here for what I am talking about:


    We’re already finding some pretty weird exoplanets (by our
    very limited standards), so who is to say that ETI might behave
    and build in ways we expect, especially on a cosmic scale.

  • Chris Wren May 3, 2007, 21:27

    I’m all for assigning proper names to planets, and I was annoyed when Xena got shut down. We’ll eventually exhaust the world’s pantheons as source names of course, and that’s when I’d 100% in favor of immortalizing pop culture fictional characters by naming new worlds after them. I see nothing wrong with planets named Buffy, Willow, Kirk or Picard.

  • Edg Duveyoung May 3, 2007, 23:56

    The funny thing is this: by the time a human being sets first foot on an exoplanet, technology may have equally advanced in terraforming.

    Wait for it.

    Wait for it.

    Soooooo, if it “swings that way,” it might be that the first other-than-Earth-planet in the habitable zone will be the MOON! It might be a garden of delights by then, and Venus and Mars wouldn’t be that much more or less likely to be also — not to mention the moons of Jupiter, underground Mercury, inside Mar’s moons. All these, teaming with life, will be considered to be planets by the earth dwellers then, and they’ll probably think of the moon as much of another planet as today’s folks think of Gliese 581 c. — as in, “Where are you guys vacationing this year? Oh, we’re not sure; we’re favoring Ceres for the methane skiing, but the moon is so wonderful for seeing the black soot trail across the Pacific from China to L.A., but then again, Gliese 581 c is only a little more expensive, so we’re maybe going there. Who knows these days with travel being almost instantaneous!”

    Like that. Pluto will be a planet again some day — psychologically, socially.

    This concept is really just a twist on the Bradbury notion that the first Martians will be us. Historically speaking, 1,000 years from now, the smallest of orbs, like Monte Carlo today, will become worlds no matter their size, and the distinctions we have today will be long ago conceits. It won’t matter how close a globe is to its star or how far it is from earth nearly so much as whether one enjoys “gambling by the super rich” is its draw or “spectacular sunsets of Eterna’s four stars.” Like that.

    The headlines and excitement of the general population about Gliese 581 c today will be very old hat after the, say, 50th exoplanet in a habitable zone is discovered. And it could just be around the corner technologically for us to “do atmospheres cheap.” For instance, if we ever figure out how to scrub the carbon dioxide from earth’s air, that same “level of technology” might be tweakable for terraforming the moon.

    Show me regular space runs for citizens to the moon, and most talk of exoplanets will subside back down to merely us folks here jawing about them.


  • Benny Watts May 4, 2007, 2:14

    The coolest names would just be wasted on uninhabitable, and more likely than not, uninteresting hellholes. “Logan” would be some bland Uranian slushpot, “Picard” a mediocre iceball, “Serenity” just another gas giant. And then we’d discover after the fact that “Humperdinck” is a paradise world.

    As a rule, we should hold off naming things until we have some idea of whether they’re cool or not, and have some knowledge of their character. It’s kind of ridiculous if you’re naming some tiny iceball Hercules, and some roaring Wagnerian storm planet Persephone. There should be some kind of naming conventions based on the type of planet it is, its thermal environment, composition, features and companions, etc. Gas giants should draw from a different set of names than rocky and/or icy worlds, and same with (atmospheric/surface) hot planets, temperate planets, and cold planets. And within categories, there should also be conventional distinctions. I.e. certain types of names for icy, methane-rich gas planets and others for huge giants with metallic hydrogen cores. All names that imply size should have some kind of logic to them–“Gargantua,” “Humongo,” “Gigantia,” etc better be in the super-Jupiter class.

    Also, while well-recognized literary and non-deity mythic figures would be a good idea, it doesn’t make sense to name things after pop culture figures unless they’ve stood a reasonable test of time. I’d also say there should be an absolute moratorium on naming planets New Earth, Terra Nova, or anything like that, since it’s almost guaranteed to be horribly wrong.

    But aside from all that, I’d like to make a few suggestions for names of milestone planets: First exoplanet verified to have a liquid water ocean: Hydros. First verified to have an atmosphere humans can breathe: Pneuma.

  • Dennis May 4, 2007, 5:02

    We have some very good news from Corot mission…

  • Jyril May 4, 2007, 5:51

    Apparently everyone (including me) have forgotten SWEEPS-11, the transiting planet near the center of the Galaxy. Its mass is 9.7 MJ which makes it more massive than HAT-2-b.

    There is another, yet to be announced very massive and somewhat eccentric planet XO-3b. However, with the mass of ~12 MJ it lies at the minimum mass border of brown dwarfs. In addition, its host star is metal-poor, which suggests it may be a very low-mass brown dwarf instead.

  • Matt Robare May 4, 2007, 22:28

    There’s the joke about how Canada was named: All the people got together to name their country and agreed to pull letters out of a hat.

    The Governor-General pulled out the first letter and announced to the masses: “C!”

    Said the masses: “Eh!”

    The second letter: “N!”




    I think that in the future names will likely be restricted to planets in inhabited systems and of course, ET’s will surely have their own names and pantheons. I mean, the little, green, furry things from Alpha Centauri B c aren’t going to call their world Alpha Centauri B c.

  • Benny Watts May 4, 2007, 23:25

    Even if ETs had their own names for worlds, it’s unlikely to be in any communications format humans could duplicate. We couldn’t translate chemical scents, temperature oscillations, color patterns, or electrical signals representing pronouns into our phonemes or alphabets without being totally arbitrary, so ET isn’t really a reason not to name something. Even if they communicate with sound, the likelihood of those sounds being human-pronounceable or even approachable is very small. Mandarin is hard enough–try Anglicizing dolphin speech. We couldn’t very well call a planet chirp-squawk-fart-fart-rumble-click.

  • Adam May 5, 2007, 7:56

    I think we should call the planets after Fire-Gods considering how incandescent these “Hot SuperJovians” probably are. Anything else just doesn’t seem appropriate.

  • dog May 23, 2007, 14:41

    As quickly as we are finding extrasolar planet, it makes it important to have unique identities for each. And, using coded numbers and letters is no problem for the scientific society.
    On the same hand, humanity is being challenged to find new places that may have life on them. We are on a great adventure but the ordinary person, if he was stopped on the street and asked if he knew where PSR B 1620-26c was located would probably guess his computer progam.
    The question is how do we get this humanity interested in finding these places and the only way is to make it exciting for them. Make it simple. Give these places ordinary names.
    Leave behind all the ancient history names and get with the real people on the street. It was funny to read that we can not name a planet “chirp-squawk……..” but ten thousand years from today that may be normal and so would “Joan N Dallas” or “Bill N Hawaii” or just plain “Jane.” Make it simple for the layman, so that he can understand and relate to these far away places.
    You know, mythical names were just as familiar to the ancient Greeks as the word “email” is to us. Giving these places tangible names simplifies, not confuses us.
    Soooo, you could say “I am going to visit the star “Joan N Dallas” and stop off and ski on her second planet ‘BJoan”and then visit her fourth planet “DJoan! where they make the best pizza!” ::) ::)

  • ljk November 15, 2007, 13:25

    Hydrodynamic Simulations of Unevenly Irradiated Jovian Planets

    Authors: Jonathan Langton, Gregory Laughlin

    (Submitted on 14 Nov 2007)

    Abstract: We employ a two-dimensional grid-based hydrodynamic model to simulate upper atmospheric dynamics on extrasolar giant planets. Our model is well-suited to simulate the dynamics of the atmospheres of planets with high orbital eccentricity that are subject to widely-varying irradiation conditions. We identify six such planets, with eccentricities between $e=0.28$ and $e=0.93$ and semimajor axes ranging from $a=0.0508$ A.U. to $a=0.432$ A.U., as particularly interesting objects for study. For each of these planets, we determine the temperature profile and resulting infrared light curves in the 8-$\mu$m Spitzer bands. Especially notable are the results for HD 80606b, which has the largest eccentricity ($e=0.9321$) of any known planet, and HAT-P-2b, which transits its parent star, so that its physical properties are well-constrained. Despite the variety of orbital parameters, the atmospheric dynamics of these eccentric planets display a number of interesting common properties. In all cases, the atmospheric response is primarily driven by the intense irradiation at periastron. The resulting expansion of heated air produces high-velocity turbulent flow, including long-lived circumpolar vortices. Additionally, a superrotating acoustic front develops on some planets; the strength of this disturbance depends on both the eccentricity and the temperature gradient resulting from uneven heating. The specifics of the resulting infrared light curves depend strongly on the orbital geometry. We show, however, that the variations on HD 80606 b and HAT-P-2b should be readily detectable at 4.5 and 8 $\mu$m using the Spitzer Space Telescope. Indeed, these two objects present the most attractive observational targets of all known high-$e$ exoplanets.

    Comments: 24 pages, 5 figures, 3 tables

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0711.2106v1 [astro-ph]

    Submission history

    From: Jonathan Langton [view email]

    [v1] Wed, 14 Nov 2007 04:31:18 GMT (366kb,D)


  • ljk August 13, 2009, 10:46

    Refined stellar, orbital and planetary parameters of the eccentric HAT-P-2 planetary system

    Authors: András Pál (1,2,3), Gáspár Á. Bakos (1), Guillermo Torres (1), Robert W. Noyes (1), Debra A. Fischer (4), John A. Johnson (5), Gregory W. Henry (6), R. Paul Butler (7), Geoffrey W. Marcy (8), Andrew W. Howard (8), Brigitta Sipőcz (1,3), David W. Latham (1), Gilbert A. Esquerdo (1) ((1) Harvard-Smithsonian Center for Astrophysics, (2) Konkoly Observatory, (3) Department of Astronomy, Loránd Eötvös University, (4) Department of Physics and Astronomy, San Francisco State University, (5) Institute for Astronomy, University of Hawaii, (6) Center of Excellence in Information Systems, Tennessee State University, (7) Department of Terrestrial Magnetism, Carnegie Institute of Washington, (8) Department of Astronomy, University of California, Berkeley)

    (Submitted on 12 Aug 2009)

    Abstract: We present refined parameters for the HAT-P-2(b) extrasolar planetary system (also known as HD 147506(b)), based on new radial velocity and photometric data. HAT-P-2(b) is a transiting extrasolar planet (TEP) that exhibits an eccentric orbit.

    We present detailed analysis of the planetary and stellar parameters, yielding consistent results of the mass and radius of the star, better constraints on the orbital eccentricity and refined planetary parameters.

    Namely, the refined stellar parameters are M_star = 1.36 +/- 0.04 M_sun and R_star = 1.64 +0.09 -0.08 R_sun, while the planet has a mass of M_p = 9.09 +/- 0.24 M_Jup and radius of R_p = 1.157 +0.073 -0.092 R_Jup. The refined ephemeris for the planet are E = 2,454,387.49375 +/- 0.00074 (BJD) and P = 5.6334729 +/- 0.0000061 (days) while the newly obtained orbital eccentricity and argument of pericenter are e = 0.5171 +/- 0.0033 and omega = 185.22 +/- 0.95 degs. These orbital elements allow us to predict the timings of secondary eclipses with a reasonable accuracy.

    We also discuss effects of this significant eccentricity, such as the time-lag between the radial velocity and photometry based transit centers, or the asymmetry in the transit light curve. Simple formulae are presented for the above, and these, in turn, can be used to constrain the orbital eccentricity using purely photometric data. These will be particularly useful for very high precision, space-borne observations of TEPs.

    Comments: Submitted to MNRAS, 11 pages, 6 figures

    Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

    Cite as: arXiv:0908.1705v1 [astro-ph.EP]

    Submission history

    From: Andras Pal Mr. [view email]

    [v1] Wed, 12 Aug 2009 13:10:57 GMT (136kb)