OK, so it's not terribly unique, but I thought it was a bit of fun. The background (and the explanation of some odd bits) is at my personal blog. I wrote this because I was curious about my weight on the new Earth which was discovered. The program takes your current weight (in any units) as an argument. Defaults to my weight :)

#!/usr/bin/perl

use strict;
use warnings;

my $weight = shift || 189;  # you can manually change the weight here,
+ if you prefer

# for simplicity's sake, we assume Audrey and Johnny are spherical
my @data = (

    # body                mass in kg         radius in km
    [ 'Mercury',          3.302 * 10**23,    2439.7    ],
    [ 'Venus',            4.8685 * 10**24,   6051.9    ],
    [ 'Earth',            5.9736 * 10**24,   6378.137  ],
    [ 'Moon',             7.3477 * 10**22,   1748.14   ],
    [ 'Mars',             6.4185 * 10**23,   3402.5    ],
    [ 'Ceres',            9.46 * 10**20,     950       ],   # rough es
+timates
    [ 'Jupiter',          1.8986 * 10**27,   71492     ],
    [ 'Saturn',           5.6846 * 10**26,   60286     ],
    [ 'Uranus',           8.6832 * 10**25,   25559     ],
    [ 'Neptune',          10.243 * 10**25,   24764     ],
    [ 'Pluto',            1.305 * 10**22,    1195      ],   # rough es
+timates
    [ 'Eris',             1.6 * 10**22,      1200      ],   # rough es
+timates
    [ 'Audrey Hepburn',   49.8951607,        0.0017018 ],
    [ 'Johnny Depp',      70.3068174,        0.001778  ],
);

my ( %mass_of, %radius_of );
foreach my $data (@data) {
    my $body = $data->[0];
    $mass_of{$body}   = $data->[1];
    $radius_of{$body} = $data->[2];
}

$mass_of{Hope}   = 5 * $mass_of{Earth};
$radius_of{Hope} = 1.5 * $radius_of{Earth};

$mass_of{'Heavy Earth'}   = 2 * $mass_of{Earth};
$radius_of{'Heavy Earth'} = $radius_of{Earth};

$mass_of{'Fat Earth'}   = $mass_of{Earth};
$radius_of{'Fat Earth'} = 2 * $radius_of{Earth};

print "If you weighed $weight units ...\n";
foreach my $body ( map( { $_->[0] } @data ), 'Hope', 'Heavy Earth', 'F
+at Earth' ) {
    printf "... you would weigh %.2f units on '$body'\n" => weight_on(
+$body);
}

sub weight_on {
    my $body = shift;
    return $weight * ( gravity($body) / gravity('Earth') );
}

sub gravity {
    my $body = shift;
    return density($body) * $radius_of{$body};
}

sub density {
    my $body = shift;
    return $mass_of{$body} / $radius_of{$body}**3;
}
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