Help Shape the Future of Space Exploration

Join The Planetary Society Now  arrow.png

Join our eNewsletter for updates & action alerts

    Please leave this field empty
Blogs

Headshot of Emily Lakdawalla

A brief word on Saturn's radius

Posted by Emily Lakdawalla

15-10-2009 18:44 CDT

Topics: Saturn

I've had two people write in to correct my Phoebe ring post from yesterday. In that post I said

You can measure the extent of the rings in kilometers, but astronomers and Cassini mission people both seem to find "Saturn radii" to be a handier unit that helps them have a better intuitive feel for the scale of things. One Saturn radius, abbreviated as R-subscript-s but usually written just as Rs to make things easier, is 60,330 kilometers. Beginning at Saturn's center, one radius gets you to Saturn's cloud tops.

The two readers both pointed out that 60,330 kilometers is not the accepted radius for Saturn. The value that is typically used for Saturn's equatorial radius is 60,268 ±4 kilometers; this is based on a report published in Celestial Mechanics and Dynamical Astronomy in 2007 by P. K. Seidelmann et al.: "Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006," volume 98, pp. 155-180. This is the equatorial radius of Saturn at the 1-bar level, that is, where its atmospheric pressure is about equal to Earth's at sea level.

I sent off this question to Dave Seal, and confirmed that the 60,330 radius is the one used by the Cassini mission when they speak of distances in Rs; the same number was used by the Voyager mission. It is the radius of Saturn at the 100 millibar altitude. He didn't say why they choose the 100 millibar level instead of the 1 bar level.

In any case, because the difference is only important at the fourth significant digit, it doesn't affect any of the distances I quoted in the Rs unit in my story on the Phoebe ring, which I reported to at most three (and sometimes fewer) significant digits!

 
See other posts from October 2009

 

Or read more blog entries about: Saturn

Comments:

Leave a Comment:

You must be logged in to submit a comment. Log in now.
Facebook Twitter Email RSS AddThis

Blog Search

Essential Advocacy

Our Advocacy Program provides each Society member a voice in the process.

Funding is critical. The more we have, the more effective we can be, translating into more missions, more science, and more exploration.

Donate

Featured Images

NGC 4100
The Flaming Star Nebula (IC 405)
LDN 604 and GGD 30
Schiaparelli backshell and parachute landing location from HiRISE in color
More Images

Featured Video

The Planetary Post - Carl Sagan's Pale Blue Dot

Watch Now

Space in Images

Pretty pictures and
awe-inspiring science.

See More

Join The Planetary Society

Let’s explore the cosmos together!

Become a Member

Connect With Us

Facebook, Twitter, YouTube and more…
Continue the conversation with our online community!