[meteorite-list] 53 planets, soon to be 80

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Thu Aug 17 04:13:57 2006
Message-ID: <20060817081354.80604.qmail_at_web50905.mail.yahoo.com>

80. Crikey! I don't fancy trying to write a mnemonic
for that one!
Kids will graduate from school simply by being able to
remember the first 75, I'm sure.

Rob McC

> ----- Original Message -----
> From: "Darren Garrison" <cynapse_at_charter.net>
> To: <meteorite-list_at_meteoritecentral.com>
> Sent: Wednesday, August 16, 2006 6:59 PM
> Subject: [meteorite-list] 53 planets, soon to be 80
>
>
> By the "if it is round, and not orbiting another
> planet, it's a planet"
> definition, our solar system now has 53 planets,
> with the number soon to
> jump to
> 80. I feel a great disturbance in the Force, as if
> millions of voices of
> schoolchildren suddenly crying out in terror.
>
> (see the site to see the charts)
>
>
http://www.gps.caltech.edu/~mbrown/whatsaplanet/howmanplanets.html
>
> How many planets are there?
> While most people would answer that there are 9 or
> perhaps 10 planets, a
> proposal by the International Astronomical Union
> that will be voted on soon
> would significantly increase the number of objects
> that astronomers call
> planets. The proposal is to call any object that is
> large enough to make
> gravity
> cause it to become round a planet.
>
> How many planets would this make? The nine planets
> that everyone knows are
> all
> round, so they are clearly planets. Ceres, the
> largest asteroid, is also
> round
> and would become a planet (the fifth). The big
> question, then, is how many
> new
> planets are there in the Kuiper belt, a region of
> rocky/icy bodies beyond
> Neptune, and the home of Pluto and 2003 UB313 ("the
> 10th planet").
>
> While we can't see most of the objects in the Kuiper
> belt well enough to
> determine whether they are round or not, we can
> estimate how big an object
> has
> to be before it becomes round and therefore how many
> objects in the Kuiper
> belt
> are likely round. In the asteroid belt Ceres, with a
> diameter of 900 km, is
> the
> only object large enough to be round, so somewhere
> around 900 km is a good
> cutoff for rocky bodies like asteroids. Kuiper belt
> objects have a lot of
> ice in
> their interiors, though. Ice is not as hard as rock,
> so it less easily
> withstands the force of gravity, and it takes less
> force to make an ice ball
> round. The best estimate for how big an icy body
> needs to be to become round
> comes from looking at icy satellites of the giant
> planets. The smallest body
> that is generally round is Saturn's satellite Mimas,
> which has a diameter of
> about 400 km. Several satellites which have
> diameters around 200 km are not
> round. So somewhere between 200 and 400 km an icy
> body becomes round.
> Objects
> with more ice will become round at smaller sizes
> while those with less rock
> might be bigger. We will take 400 km as a reasonable
> lower limit and assume
> that
> anything larger than 400 km in the Kuiper belt is
> round, and thus a planet.
>
> How many objects larger than 400 km are there in the
> Kuiper belt? We can't
> answer this question precisely, because we don't
> know the sizes of more than
> a
> handful of Kuiper belt objects (for an explanation
> why, see the discussion
> on
> the size of 2003 UB313), but, again, we can make a
> reasonable guess. If we
> assume that the typical small Kuiper belt object
> reflects 10% of the
> sunlight
> that hits its surface we know how bright a 400 km
> object would be in the
> Kuiper
> belt. As of late August 2006, 44 objects this size
> or larger in the Kuiper
> belt
> (including, of course, 2003 UB313 and Pluto), and
> one (Sedna) in the region
> beyond the Kuiper belt. In addition our large
> ongoing Palomar survey has
> detected approximately 30 more objects of this size
> which are currently
> undergoing detailed study.
>
> We have not yet completed our survey of the Kuiper
> belt. Our best estimate
> is
> that a complete survey of the Kuiper belt would more
> than triple this
> number.
>
> For now, the number of known objects in the solar
> system which are likely to
> be
> round is 53, with the number jumping to 80 when the
> objects from our survey
> are
> announced, and to more than 200 when the Kuiper belt
> is fully surveyed.
>
> The large number of new planets in the solar system
> are very different from
> the
> previous 9 planets. Most are so small that they are
> smaller across than the
> distance from Los Angeles to San Francisco. They are
> so small that about
> 30,000
> of them could fit inside the earth.
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Received on Thu 17 Aug 2006 04:13:54 AM PDT