# Newfound planet orbits backward

by Evo
Tags: backward, newfound, orbits, planet
Mentor
P: 26,527

 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.
http://www.msnbc.msn.com/id/32391095...science-space/
 PF Gold P: 302 I was just about to post this... Very interesting.
 P: 105 That's nothing. Kapteyn's Star orbits the galaxy retrograde.
 P: 606 Newfound planet orbits backward What happens when they flush their toilets?
P: 81
 Quote by Huckleberry What happens when they flush their toilets?
They invert :O.
Mentor
P: 11,749
 Quote by Huckleberry What happens when they flush their toilets?
They get wet!
 P: 504 How does one measure the axis of rotation of a distant star?
P: 948
 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.
i wonder if they made a small mistake. i think venus orbits backwards also
P: 1,070
 Quote by flatmaster How does one measure the axis of rotation of a distant star?
red/blue shift maybe?
P: 15,319
 Quote by fourier jr i wonder if they made a small mistake. i think venus orbits backwards also
No, Venus rotates backwards. It orbits forwards, like the rest of us.
 P: 3,408 What is the chance that a planet-sized object may be captured exclusively by a star's gravitation, to orbit against the rotation of a the star? Perhaps smaller planetoids (like Pluto), difficult to see outside out own solar system, would be much more likely to be captured in the first place. Can a planet in a binary system have a oscillating trajectory? My guess is that it would be more likely ripped apart or fall into a star.
 Mentor P: 40,957 I deleted a 2012 doom post by a regular member and the responses. Please check your references before posting obvious stupid stuff. Snopes.com is a good place to start for obvious stuff. Thanks.
P: 948
 Quote by DaveC426913 No, Venus rotates backwards. It orbits forwards, like the rest of us.
thx for clearing that up. does that have anything to do with why a day on venus is longer than a year?
P: 15,319
 Quote by fourier jr thx for clearing that up. does that have anything to do with why a day on venus is longer than a year?
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.
Emeritus
PF Gold
P: 2,361
 Quote by DaveC426913 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.
Venus has an actual physical retrograde sidereal rotation. As a result, its solar day is 116.5 days long.
Mentor
P: 12,069
 Quote by DaveC426913 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.
 Quote by Janus Venus has an actual physical retrograde sidereal rotation. As a result, its solar day is 116.5 days long.
Interesting. I wonder how long before it is tidally locked to the sun. Anybody know if there is an estimate of this?
 Sci Advisor HW Helper P: 1,326 I read about this too on Wednesday, It was listed on BBC Science News. So the planet's name WASP-17 has to do with the 'Wide Area Search for Planets' consortium of UK universities Very interesting that we are able to deduce this kind of information for planets orbiting other stars.
Emeritus
PF Gold
P: 2,361
 Quote by Redbelly98 Interesting. I wonder how long before it is tidally locked to the sun. Anybody know if there is an estimate of this?
Hard to tell.
We don't know yet if there is a cause for a particular resonance between the Earth and Venus or whether it is just a coincidence. Venus' rotation and orbit are such that whenever Earth and Venus are in inferior conjunction (when they are at their closest to each other) Venus always presents the same side to the Earth.

There is a formula to calculate tidal locking times. it is

$$t= \frac{\omega a^6 I Q}{3GM^2 K_2 R^5}$$

$\omega$ 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
$K_2$ is the Love number
R is the radius of the planet.

However, Q and K2 are not well known except for the case of the Earth and moon.

 Related Discussions Cosmology 6 Introductory Physics Homework 2 Astronomy & Astrophysics 3 Astronomy & Astrophysics 1