[ExI] fun fact

[spike at rainier66.com]

From: extropy-chat <extropy-chat-bounces at lists.extropy.org> On Behalf Of Adrian Tymes via extropy-chat
Sent: Tuesday, 2 May, 2023 11:13 AM



 

>…Also, Luna is not a planet.  ;)

 

 

That would depend on how the term planet is defined.  Years before the big debate over whether Pluto qualifies as a planet, there was a big debate over whether the moon would qualify.  It has long been considered a satellite of Earth, but its orbit about the sun is concave everywhere.  At no point in its orbit is the earth’s gravity stronger than the sun’s.  So… it is correct to say that the moon and Earth are two co-orbiting planets which are gravitationally locked together.

 

Most stars are gravitationally locked to at least one other star, and the pair (or trio (or gravitationally-locked group)) co-orbits about the barycenter of the galaxy.  Each of those stars is considered a star.

 

I agree with those who argued 20 years ago that the term planet should apply to those bodies with sufficient gravity to shape them into a sphere and are gravitationally dominated by the sun.  This excludes the satellites of Mars because they are dominated by Mars gravity and are non-spherical.  It excludes the spherical moons of Jupiter because they are gravity locked to that big dude.  It brings in Pluto because it is spherical, even though we know it is a Kuiper belt object.

 

So… we have ten planets in the solar system now.

 

spike

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.extropy.org/pipermail/extropy-chat/attachments/20230502/de1846ea/attachment.htm>