Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site lsuc.UUCP
Path: utzoo!lsuc!msb
From: msb@lsuc.UUCP (Mark Brader)
Newsgroups: net.sci
Subject: Re: Pluto surface gravity?
Message-ID: <1080@lsuc.UUCP>
Date: Wed, 29-Jan-86 01:07:10 EST
Article-I.D.: lsuc.1080
Posted: Wed Jan 29 01:07:10 1986
Date-Received: Wed, 29-Jan-86 02:52:53 EST
References: <26500005@inmet.UUCP> <112@dg_rtp.UUCP>
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 40
Summary: 0.04 earth, not 0.225

To the question:

> > Does anyone have a reasonable estimate of the surface gravity of Pluto?
> > It would be most useful relative to Earth = 1.0.

Wayne Throop replies with a plug ...
> I always get my estimates from The Handbook of Chemistry and Physics.
> ... Pluto has a mean value of 221.0 (+- 207.0) [cm/sec**2]
> ... not too damn accurate, is it?
> ...so the ratio is .225 or so.

Note that huge uncertainty.  The reason is that until recently the
mass of Pluto, and hence the surface gravity, was very much unknown.
Wayne did say:

> (I suspect that more recent books should have more accurate estimates...
> you might check out your nearby friendly college library for the latest
> edition of the HofC&P (mine is 52nd edition))

Well, I'm putting this here to remind people not to neglect the World
Almanac.  To cite one more instance, you can find the orbital elements
of the planets in there, and they aren't in my Van Nostrand's Scientific
Encyclopedia (6th edition)/y.  What follows is the letter I mailed to the
original poster, which, in view of the above, I have decided is worth
posting to the net after all.  The last sentence is not from the almanac,
but follows from Newton's law of gravitation.

To: utzoo!ihnp4!inmet!tower
Subject: Pluto surface gravity?

This one is found, appropriately, in the World Almanac.

Page 728 of my 1985 edition gives Pluto's surface gravity as 0.04 of Earth's.
This is fairly reliable since it is derived from measurements made since
Pluto's satellite Charon was discovered: planet diameter 1,860 miles,
mass 0.0025 of Earth's.  Surface gravity is proportional to m/r^2 (planet
mass over square of planet radius).

Mark Brader