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Podcaster: Richard Drumm
Title:
Space Scoop: The Planet with Three Suns

Organization: 365 Days Of Astronomy

Link : astrosphere.org ; http://unawe.org/kids/unawe1111/

Description: Space scoop, news for children

Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.

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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.

Today’s story is: The Planet with Three Suns

Imagine a world where each season lasts over 100 years and you have three shadows at once.

Now meet HD 131399Ab, a newly discovered exo-planet with these exact quirks!

The strange new world was discovered orbiting a star in a triple star system. It’s 320 light years away in the southern constellation Centaurus, the Centaur.

The three stars are called HD131399A, B and C, with upper case letters, in order of decreasing brightness. Since the planet orbits the brightest star, it is called HD131399Ab, with this b written in lower case.

You can see in today’s album artwork an actual image of the system with graphical overlays. The most likely or “best fit” orbit for the planet is marked. It’s the orbit that best fits the data.

Also you can see the best fit orbit for the binary pair. C, the smaller of the pair, is just a blip on the edge of the image for B.

As more data comes in the astronomers will adjust the orbit numbers to take the observations into account. The eccentricity and inclination of the orbits may be a bit different than the astronomers have determined at this early date.

The inclination of the orbit to our line of sight may be different than the 46° we show here for the planet and the 48° for the binary companion.

And the eccentricity of 0.35 for the planet and 0.13 for the binary may change as well.

By the way, A has 1.82 times the Sun’s mass, while B has 0.96 solar mass and C has 0.6 solar mass.

B & C are a tight binary pair. This makes sunrises and sunsets something special — sometimes one sun rises in the sky, then in quick succession it’s two and three!

But despite this, this planet is not entirely unique. Many planets orbit stars that come in pairs or even triples. What is special about this new world is that astronomers spotted it directly.

They didn’t have to infer it’s presence with indirect techniques like the radial velocity method. That’s where the parent star is ever so slightly pulled toward and away from us by the planet’s gravity.

More than 3,000 planets have been found orbiting distant stars, but less than 50 have been directly photographed.

However, most direct imaging surveys have traditionally excluded visual binary or multiple systems whose separations are less than a few hundred astronomical units.

This is due to the assumption that such planetary systems would either be disrupted or never form in the first place.

In addition there’s the increased technical complexity of detecting a planet amongst the scattered light of multiple stars.

As a result of this observational bias, most directly imaged exoplanets have been found around single stars, not multiples like here.

And anyway, spotting a single, tiny planet traveling around a distant star is like trying to see a mosquito flying in front of the midday sun.

Tough stuff!

The planet was discovered with telescope #3 of the VLT at the Paranal Observatory in Chile. They used SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument.

Whew! That’s a mouthfull!

This is an infrared instrument that allowed the astronomers to detect the heat signature of the young planet. SPHERE also has a coronagraph that blocks the comparatively blinding light of the host stars.

This instrument then goes further by teasing out of the unpolarized light from the star that tiny bit that is polarized.

This is the light that’s reflected from the planet and any dusty disc around the star. However, in this system the dust disk has been depleted to the point that it’s undetectable.

Unfortunately, it looks like this exotic world might not survive for long. Well, long on cosmic time scales at least. For planets to survive in a triple star system, a delicate balance must be struck.

This planet’s current orbit is roughly twice as large as Pluto’s is around our Sun, swinging it into a very unstable region of the system. It comes about a third of the way to the outer stars, just a bit too close to that binary pair.

It’s so far out there that the system is dynamically unlike any other known exoplanet system.

Because of the proximity to the binary, the planet could be doomed to one of several wretched fates.

They include burning up as it’s swallowed by one of the stars or being ejecting into deep space, destined to wander for eternity among the stars as a so-called “rogue planet”.

Hey, here’s a Cool Fact:
HD 131399Ab is four times as massive as Jupiter and as it’s about 82 times farther away from it’s star as the Earth is from the Sun, it’ll take about 550 Earth-years to complete one orbit around its star.

Thank you for listening to the 365 Days of Astronomy Podcast!
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365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by Astrosphere New Media. Audio post-production by Richard Drumm. Bandwidth donated by libsyn.com and wizzard media. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org.  This year we will celebrate more discoveries and stories from the universe. Join us and share your story. Until tomorrow! Goodbye!