Another Close Binary, Another Big Planet

Posted By Pamela on Nov 22, 2007 | 6 comments

169780main_a-330.jpgAt this point we’ve found planets in a enough places that I shouldn’t still be surprised when a neat new world is found in a neat new place. Nevertheless, I found myself awed by a new discovery of a new planet with a 3.69 year period orbiting in a close binary.

This particular discovery caught my attention for two reasons. First off, the data on this object spans ~14 years – that is a lot of data to put together. Second, this is a really close binary to have a planet! They found a planet (2.96 Jupiter masses or larger) orbiting 2.63 AU from a star that has a companion at 17.23 AU. This system is HD196885A and the announcement came in a paper with A.C.M. Correia as lead author.

Imagine the chaos involved in forming this little world. Its Sun, an F8 star, is a bit brighter (2.4 Solar Luminosities) and a bit larger (1.33 Solar Masses) than our own Sun. While this star was forming, it flared and crackled with high-energy outbursts. Meanwhile, its red dwarf companion collapses into its own violent beginning; red dwarfs also go through a terrible toddler phase of coronal mass ejections. Between these two angry youth, this planet settled into an orbit around the larger star, and pulled itself together to grow into a gasy giant. Now, 2 billion years into its evolution, the F star has settled down into a few billion years of peace and quiet. Eventually, the F star will bloat up into a red giant, go through a new round of shape shifting as it bloats and shrinks and bloats again. All the while, the planet will sit a possibly safe distance away, watching as its main source of heat and light falters and fails and eventually collapses almost completely into a white dwarf star. As the F star’s atmosphere floats away, it will form a planetary nebula that enshrodes this new found gas planet and its M-star guardian. As that white dwarf cools into ash, the dwarf planet will continue to glow, allowing the planet to experience a no onger heliocentric series of seasons, as it orbits toward and away from its secondary warmth.

What an odd fate this newly discovered planet has had and will see. What a weird place to find a planet. It really seems that alien worlds can be found in perhaps any stellar environment.

image credit: NASA/JPL-Caltech


  1. This is amazing… Quite an unlikely place to find a planet. But I thought 3-body systems are supposed to be unstable, so does that mean the orbit is likely to change over time?

  2. This red dwarf at 17AU is almost as far from its “big sister” star as Uranus is from our sun. Even though it certainly outweighs Jupiter, it clearly doesn’t prevent other planets from forming around the big sister. I’m sure it has an effect on the planetary orbits like Jupiter has here. Little sister’s orbit is probably fairly circular, if it was very eccentric it’d probably prevent any planets from forming. So it probably won’t have an opportunity to steal any atmosphere from big sister when she goes into the red giant phase.

    I wonder if little sister has any planets… Wouldn’t surprise me a bit.

  3. Kudos. We might be too myopic with our thinking. Just look how much Hubble has captured in the far reaches of space.

    Opportunities abound once craft actually able to reach the far regions of space.

    Otherwise, keep exploring…..

  4. I wonder how much the orbit of the planet would expand when the primary star loses mass during the red giant stage – far enough that it would enter the region where its orbit would be destabilised by the companion star?

  5. Thanks for that – great news article and a very interesting planetary system.

    If the exoplanet has large enough moons could they be habitable -its twice as far out round a star two-&-a-half times as bright so an intriguing prospect ..

    Seen from the planet (or its hypothetical if likely moons)the red dwarf would be relatively bright but not overpoweeringly so wouldn’t it?

    Any idea on the liklihood of other planets – maybe rocky low-mass planets orbiting it as well – possibly in the habitable zone which I think would be larger for this brighter star?

    I’m not sure how far this star is from us but it sounds like a system worth well investigating ..

  6. Thanks for the link to the actual paper too – interestingly from there :

    The star HD196885 A or HIP 101966 (& why, oh why can’t we give notable stars like this one proper rather than just ctalogue names, could I suggest Farsuntu {“far-sun-too”}, Antisoluranstar (Rivial of Sun + Uranus-distance star) or at least just Hip-101 for short!)

    – has a visual magnitude of 6.3 making it potentially just visible to the unaided eye in very dark skies.

    – Is listed as luminosity class IV or sub-giant although this is confused by llisting it later as luminosity class V or main-sequence too. This makes it a bit like Procyon the nearest F-type star which is also variously termed a main-sequence dwarf or evolving sub-giant star …

    (BTW. Luminosity classes : I = Supergiants, II & III = giants, IV = sub-giants, V = main sequence dwarfs VI = sub-dwarf, VII =white dwarfs.)

    – is located 33 parsecs away (& please for the sake of making astronomy more accessible can we please note distances in light years too?) which by my iffy calculations ( 1parsec = 3 ly aprox so 33 x 3 = 99) is about 100 light years away.

    A little far to be among the first stars visited unfortunately but still a fascinating system desrreving of more study.

    – There are a lot of calculations and jargon but it seems there wasn’t aplnate where they thought and was this planet where they didn’t think from earlier studies … So perhaps this needs a bit of followup study although clearly a considerable amount of work has been put into by the team that did find this planet & they deserve our congrats & respect. They certainly have mine.

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