Planet gets fresh look by UT astronomers

Work by a team of University of Texas at Arlington astronomers could significantly broaden astrophysicists' search for planets in other solar systems by changing the way they think about the orbiting bodies.

If correct, the findings could increase the opportunities for the discovery of new planets in candidate systems.

The paper by Manfred Cuntz, UT Arlington associate professor of physics, and Jason Eberle, a doctoral candidate from UT Arlington, is being published Oct. 1 in the American Astronomical Society's . "On the reality of the suggested planet in the ν Octantis System" is already available online. In the paper, the two scientists explore the possible existence of a proposed planet in a binary star system 69 light years, or 400 trillion miles, from Earth.

Based on six years of data, observers have suggested a planet may exist in the ν Octantis system, a star system visible only from the southern half of the globe, particularly from Antarctica. The observing technique is based on radial velocity variations or RV readings of the orbiting planet's effect on its host star - a slight wobble created by the planet's pull. Surprisingly, the planet of the system seemed to be outside of the commonly accepted zone where such an orbit could exist without disruption from the gravitational force of the second star in the binary system, Cuntz said.

Eberle and Cuntz examined the data by performing detailed time-dependent simulations of orbital stability. They concluded there is a significant chance that the planet is indeed able to exist but in a retrograde orbit. A retrograde orbit means the planet is orbiting the primary star in a different direction compared to the orbit of the secondary star. This would allow for a wider area of orbital stability, the study says.

Such an orbit is previously unheard of for a planet in an extrasolar planetary system, but this type of orbit occurs for some moons of planets in our . If confirmed, the existence of such a planet would significantly enhance the search for planets in multiple stellar systems, including the search for those that could potentially support life, according to Cuntz.

"If our theoretical studies turn out to be applicable to the ν Octantis system, they will provide evidence for the first case of a planet in a retrograde orbit in a stellar binary system," said Cuntz.

The research team's findings are likely to gain attention, according to another expert in the field.

"The results of Eberle and Cuntz are important for the big hot topic of astronomy, namely extrasolar planets, and especially interesting for the dynamics of in double ," said Rudolf Dvorak, a professor at the Institute for Astronomy at the University of Vienna. "Note that in the solar neighborhood more than 60 percent of the stars are not single."

Cuntz and Eberle's study says there is still a slim chance that the suggested planet is in a prograde orbit, traveling in the same direction as the primary star's partner star. This is highly unlikely, as it would require detailed assumptions concerning the orbital parameters of the planet.

The existence of a planet in ν Octantis was first suggested by a research team led by David Ramm of the Department of Physics and Astronomy at the University of Canterbury in New Zealand.

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Sep 29, 2010
Retrograde orbits are an enigma in the accretion disk model. I would still like to hear a plausible, logical and coherent explanation for the existence of planets with retrograde orbits - using the accretion model of planetary formation.
Maybe it's time to look at the evidence before us and either drastically revise or even totally discard that model of planetary formation. It just doesn't fit.

Sep 29, 2010
This actually contradicts statements made by physicists on various Discovery channel programs on star formation and planet formation, particularly exoplanet formation, including those made within just the past few years.

In the existing model, the only way you could explain a retrograde planet is that it must be a "rogue" planet that was ejected by another star system and then captured by the binary pair. Which would mean that the planet is probably older than the star it orbits.

Sep 29, 2010
Unless two planets in similar orbits have played 'slingshot', with the less massive turned about and the other lost to the star or long ellipse ??

Sep 29, 2010
Unless two planets in similar orbits have played 'slingshot', with the less massive turned about and the other lost to the star or long ellipse ??

No. The energy levels of say a binary planet or dwarf planet system is nowhere near high enough to get the second object moving with an orbital velocity in the retrograde direction around the star.

In order for this planet to be detectable in a binary star system, it is probably large enough to be measured in Jupiter masses.

It would have needed to obtain it's orbit from another star.

Even a larger "super jupiter" probably could not have slang it around with that much velocity, and even if it HAD done that, the second "super jupiter" would have been ejected from the system due to conservation of angular momentum because it would have accelerated to about 3 times the velocity of a stable orbit.

deltav = v - (-v) = 2v

v + 2v = 3v

Planet takes a bee-line out of the system for all eternity.

Sep 29, 2010
While its true a retrograde orbit for a planet would be difficult to explain using the standard disk model of solar system creation, that doesn't mean one or even a few exceptions disprove the theory or even require its modification. I am sure that a perfectly good explanation of this case will be discovered.

Sep 29, 2010
Yes, there are several explanations that could fit without tossing the acretion model out the window. If we could discerne which direction the star is rotating, that may tell us more. Perhaps the star and the plant are turning in the same direction, and it's the second star that is retrograde. Maybe the planet started out orbiting the other star in a highly eliptical orbit and then did a figure eight when it got stolen by its current star, leaving it in a retrograde orbit (highly unlikely). Right now it's just a computer model that is suggesting a retrograde orbit. It is far from being a confirmed fact, from the looks of it.

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