We have not yet emerged from mourning

I've still got the ninth planet galaxy's most famous iceball on the brain today, partially because I can't stop thinking about our fabulous commemorative t-shirt (have you pre-ordered yours yet? email us at tips-at-mentalfloss-com or leave a comment with your email address), and partially because of all the crazy things I learned last week while reporting this article on the solar system. Here are some assorted tidbits I found that didn't end up in the final story:

• Europa, a moon of Jupiter, has a saltwater ocean which is probably 100 km deep, much deeper than the Pacific. There may also be volcanoes, which could be heating up the water at the bottom of the ocean -- providing similar conditions to those that support life in deep-water ocean vents here.
• Scientists first figured out that the moon must have been a chip off the Earthly block by comparing the types of oxygen found in lunar rocks with the types found here at home. The oxygen istotope ratios (how much O16 there is compared to O18) are identical.
• The Earth has its axis tipped by 23.5 degrees, probably because of the same impact that broke off the Moon. Mars is also tipped by about the same amount. Uranus is tipped by a whopping 90 degrees, and no one knows why.

Also, here's a great new mnemonic for the planets, courtesy of our latest contest winner, Wendell Wittler:

Many very easy mnemonics just seem unnecessarily nonsensical.