[meteorite-list] Trinary system with planet

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Jul 14 01:15:21 2005
Message-ID: <42D5F4C5.5E9EEE2B_at_bhil.com>

Hi, All

    The "animation" of the three-sun sunset mentioned (with link to the .mov file) in the piece below is
truly gorgeous. It's about 2 million bytes, and due to mere dialup and wet phone wires, I had to
download it at a terribly slow 23 Kbaud, and it was worth every minute of the wait!
    Really beautifully done.

Sterling K. Webb
-------------------------------------------------------------

Darren Garrison wrote:

> http://www.msnbc.msn.com/id/8567313/
>
> Newly discovered planet has 3 suns
> Scientists puzzled at how such a planet could form
>
> By Michael Schirber
> Space.com
> Updated: 7:15 p.m. ET July 13, 2005
>
> A newly discovered planet has bountiful sunshine, with not one, not two, but three suns glowing in
> its sky.
>
> It is the first extrasolar planet found in a system with three stars. How a planet was born amidst
> these competing gravitational forces will be a challenge for planet formation theories.
>
> "The environment in which this planet exists is quite spectacular," said Maciej Konacki from the
> California Institute of Technology. "With three suns, the sky view must be out of this world --
> literally and figuratively."
>
> The triple-star system, HD 188753, is located 149 light-years away in the constellation Cygnus.
> The primary star is like our Sun, weighing 1.06 solar masses. The other two stars form a tightly
> bound pair, which is separated from the primary by approximately the Sun-Saturn distance.
>
> "The pair more or less acts as one star," Konacki told SPACE.com.
>
> The combined mass of the close pair is 1.63 solar masses.
>
> Using the 10-meter Keck I telescope in Hawaii, Konacki noticed evidence for a planet orbiting the
> primary star. This newfound gas giant is slightly larger than Jupiter and whirls around its central
> star in a 3.5-day orbit. A planet so close to its star would be very hot.
>
> Although other so-called hot Jupiters have been found in such close-in orbits, the nearby stellar
> pair in HD 188753 likely sheared off much of the planet making material in the disk that would
> likely have existed around the primary star in its youth. Since this proto-planetary disk holds the
> construction materials for planets, there does not appear to be any safe place for this far-off
> world to have been assembled.
>
> Snow line and migration
> The heat coming from a nearby star frustrates the initial stages of giant planet formation -- the
> gluing together of planetary seeds, called cores. Therefore, the typical hot Jupiter is thought to
> form farther out -- beyond a theoretical limit called the snow line.
>
> "Past about 3 AU, it is cold enough to form ices and other solid material for building cores,"
> Konacki said. An AU is the distance between the Sun and the Earth -- about 93 million miles.
>
> Once a sufficiently large core is built outside the snow line, the planet can start accreting gas
> and -- if the conditions are right -- migrate toward its sun.
>
> Although this scenario appears to work in most stellar systems, it has difficulty explaining the
> newly-discovered planet in HD 188753. Of all the planet-harboring stars known, this is the closest
> that a stellar companion has ever been found.
>
> "The problem is that the pair is a massive perturber to the system," Konacki said. "Together, these
> two stars are more massive than the main star."
>
> Moreover, the pair goes around the primary along an oblong orbit that stretches from 6 AU out to 18
> AU over a 26 year period. This eccentricity increases the instability of the disk around the
> primary. Konacki estimates that due to the gravitational perturbations from the pair, the
> proto-planetary disk was truncated down to 1.3 AU, far within the snow line.
>
> "How that planet formed in such a complicated setting is very puzzling. I believe there is yet much
> to be learned about how giant planets are formed," Konacki said.
>
> Targeting multiple stars
> Konacki hopes to find more planets around stars with companions. About 30 extrasolar planets have
> been found around double-star systems, or binaries. This is a small percentage of the total number
> of extrasolar planets, even though multi-star systems outnumber single star systems.
>
> The reason for this disparity is that the main technique for locating planets -- the radial velocity
> method -- is not well-suited for finding planets with more than one star.
>
> "Single stars are much easier to work with, since the shape of the spectrum stays the same," Konacki
> explained.
>
> By watching for wobbles in a star???s spectrum, astronomers can infer the gravitational tug from a
> nearby planet. But when there is a companion star, its light competes with that of the main star.
> Konacki has developed a method to extract the planet wobbles from this messy, combined spectrum.
>
> He found this triple-sun planet in the first 20 stars he looked at. He plans to survey about 450
> stars in the future.
>
> The discovery is reported in the July 14 issue of Nature. An animation of the system as seen from a
> hypothetical moon is available here. http://pr.caltech.edu/media/trinary_sunset-low.mov
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Received on Thu 14 Jul 2005 01:14:45 AM PDT