# How does 67P rotate?

What can be said about 67P/Churyumov-Gerasimenko axial tilt?

Is it fixed (if so, at what value), only changing with precession (at what rate?) or does 67P "tumble" with axial tilt changing over time? (and if so, at what rate?)

I'm interested in estimating the 'polar night' area of the comet, and how it changes over time - but without knowing the rotation properties this is quite hard to do.

Looking at this site, there is a table, which has some information.

Rotation period: 12.4043 ± 0.0007 * hours

It also rotates around a fixed axis

recent observations suggest that the axis is tilted about 40 degrees

There are actually only two objects known to rotate chaotically in the solar system - one is Saturn's moon Hyperion, and the other is a small asteroid called 4179 Toutatis (source: this link from Guinness World Records)

• 40 degrees - that suggests a pretty big "polar night" area. Now if we could get direction of the tilt relative to orbital semi-major axis (at what distance from the Sun equinox happens?)...
– SF.
Nov 20 '14 at 23:40

Some useful sources:

"Ancient", preliminary data from ros_67pcg_v00.tpc:

• BODY1000012_POLE_RA = ( 270.0 0.0 0.0 )
• BODY1000012_POLE_DEC = ( 66.560709 0.0 0.0 )
• BODY1000012_PM = ( 0.0 720.0 0.0 )
• BODY1000012_RADII = ( 2.5 1.5 1.5 ) (ellipsoid, kilometers)

2012 data from ROS_CGS_RSOC_V03.TPC:

• BODY1000012_POLE_RA = ( 220.0 0.0 0.0 )
• BODY1000012_POLE_DEC = ( -70.0 0.0 0.0 )
• BODY1000012_PM = ( -86.369364827 679.245283019 0.0 )
• BODY1000012_RADII = ( 2.398 1.887 1.532 )

"679.245283019" should define rotation period in terms of degrees: 24*360/679.245283019 gives 12.72 (hours?) Don't know about the "-86.369364827", anyway "PM" should stay for "Prime Meridian". Anyway the xxx_PM row corresponds to this definition (from pck00010.tpc ):

• W = -86.369364827 + 679.245283019 d

No nutation/precession data available.

For xxx_RADII: "The first number is the largest equatorial radius (the length of the semi-axis containing the prime meridian), the second number is the smaller equatorial radius, and the third is the polar radius."

• Retrieving orbital data: ssd.jpl.nasa.gov/horizons.cgi#top Nov 25 '14 at 14:45
• More recent 3d model: ssols01.esac.esa.int/pub/data/SPICE/ROSETTA/LSSP (CSHP files) Nov 25 '14 at 14:46