The discussion centers on the peculiar retrograde orbit of the newly discovered planet WASP-17, which orbits its host star in the opposite direction of the star's rotation. Participants explore potential explanations for this phenomenon, including the possibility of a near-collision, and draw comparisons to other celestial bodies with unusual orbital characteristics.
Participants express a mix of agreement and disagreement on various points, particularly regarding the nature of Venus's orbit and rotation, as well as the implications of tidal locking. The discussion remains unresolved on several technical aspects and hypotheses presented.
Some assumptions about the definitions of retrograde motion and the conditions under which planets can be captured by a star's gravity are not fully explored. The discussion also highlights the complexity of measuring distant stellar properties and the uncertainties surrounding tidal locking parameters.
Newfound planet orbits backward
Planets orbit stars in the same direction that the stars rotate. They all do. Except one.
A newfound planet orbits the wrong way, backward compared to the rotation of its host star. Its discoverers think a near-collision may have created the retrograde orbit, as it is called.
The star and its planet, WASP-17, are about 1,000 light-years away. The setup was found by the UK's Wide Area Search for Planets (WASP) project in collaboration with Geneva Observatory.
Huckleberry said:What happens when they flush their toilets?
Huckleberry said:What happens when they flush their toilets?
Planets orbit stars in the same direction that the stars rotate. They all do. Except one.
A newfound planet orbits the wrong way, backward compared to the rotation of its host star. Its discoverers think a near-collision may have created the retrograde orbit, as it is called.
flatmaster said:How does one measure the axis of rotation of a distant star?
No, Venus rotates backwards. It orbits forwards, like the rest of us.fourier jr said:i wonder if they made a small mistake. i think venus orbits backwards also
DaveC426913 said:No, Venus rotates backwards. It orbits forwards, like the rest of us.
fourier jr said:thx for clearing that up. does that have anything to do with why a day on venus is longer than a year?
DaveC426913 said:Yes.
It orbits the sun (definition of a year) every 224 days, but it rotates on its own axis (definition of a day) every 243 days. The fact that the axial rotation is slower than the orbit is tantamount to a retrograde rotation.
DaveC426913 said:Yes.
It orbits the sun (definition of a year) every 224 days, but it rotates on its own axis (definition of a day) every 243 days. The fact that the axial rotation is slower than the orbit is tantamount to a retrograde rotation.
Janus said:Venus has an actual physical retrograde sidereal rotation. As a result, its solar day is 116.5 days long.
Redbelly98 said:Interesting. I wonder how long before it is tidally locked to the sun. Anybody know if there is an estimate of this?
Love number?Janus said:There is a formula to calculate tidal locking times. it is
[tex]t= \frac{\omega a^6 I Q}{3GM^2 K_2 R^5}[/tex]
[itex]\omega[/itex] is the initial spin rate (radians/sec)
a is the semi-major axis of the orbit
I is the moment of inertia of the planet
Q is the dissipation factor
G is the gravitational constant
M is the mass of the sun
[itex]K_2[/itex] is the Love number
R is the radius of the planet.
DaveC426913 said:Love number?