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Mail Call!

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You might recall the post I wrote about the very smart Web site, Sadly, the cool project has ended, but I wanted to share some of the letters you _flossers sent me. I had promised that I'd make a contribution to your favorite charity if you sent me some snail mail. As a result, I'm making contributions to Oxfam,, Humane Society, Salvation Army and a couple others. Thanks for all the great mail! It was fun opening up some honest-to-goodness letters, some of which I've scanned and published below. Each snail mail had a completely different style, which was interesting to me. I also like how some of you shared factoids in your letters! For instance, Teresa Kane wrote to tell me something I didn't know about Ramadan. She says, "We have precise times that mark dawn and sunset, but before fancy watches, Muslims were told that it was officially daylight when 'you can plainly distinguish a white thread from a black thread. Such a lovely image, to me at least."

Agreed, Teresa! Thanks for sharing! We'll do something fun like this again, soon. Promise.

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8 Useful Facts About Uranus
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Uranus as seen by the human eye (left) and with colored filters (right).

The first planet to be discovered by telescope, Uranus is the nearest of the two "ice giants" in the solar system. Because we've not visited in over 30 years, much of the planet and its inner workings remain unknown. What scientists do know, however, suggests a mind-blowing world of diamond rain and mysterious moons. Here is what you need to know about Uranus.


Uranus is the seventh planet from the Sun, the fourth largest by size, and ranks seventh by density. (Saturn wins as least-dense.) It has 27 known moons, each named for characters from the works of William Shakespeare and Alexander Pope. It is about 1784 million miles from the Sun (we're 93 million miles away from the Sun, or 1 astronomical unit), and is four times wider than Earth. Planning a trip? Bring a jacket, as the effective temperature of its upper atmosphere is -357°F. One Uranian year last 84 Earth years, which seems pretty long, until you consider one Uranian day, which lasts 42 Earth years. Why?


Most planets, as they orbit the Sun, rotate upright, spinning like tops—some faster, some slower, but top-spinning all the same. Not Uranus! As it circles the Sun, its motion is more like a ball rolling along its orbit. This means that for each hemisphere of the planet to go from day to night, you need to complete half an orbit: 42 Earth years. (Note that this is not the length of a complete rotation, which takes about 17.25 hours.) While nobody knows for sure what caused this 98-degree tilt, the prevailing hypothesis involves a major planetary collision early in its history. And unlike Earth (but like Venus!), it rotates east to west.


You might have noticed that every non-Earth planet in the solar system is named for a Roman deity. (Earth didn't make the cut because when it was named, nobody knew it was a planet. It was just … everything.) There is an exception to the Roman-god rule: Uranus. Moving outward from Earth, Mars is (sometimes) the son of Jupiter, and Jupiter is the son of Saturn. So who is Saturn's father? Good question! In Greek mythology, it is Ouranos, who has no precise equivalent in Roman mythology (Caelus is close), though his name was on occasion Latinized by poets as—you guessed it!—Uranus. So to keep things nice and tidy, Uranus it was when finally naming this newly discovered world. Little did astronomers realize how greatly they would disrupt science classrooms evermore.

Incidentally, it is not pronounced "your anus," but rather, "urine us" … which is hardly an improvement.


Uranus and Neptune comprise the solar system's ice giants. (Other classes of planets include the terrestrial planets, the gas giants, and the dwarf planets.) Ice giants are not giant chunks of ice in space. Rather, the name refers to their formation in the interstellar medium. Hydrogen and helium, which only exist as gases in interstellar space, formed planets like Jupiter and Saturn. Silicates and irons, meanwhile, formed places like Earth. In the interstellar medium, molecules like water, methane, and ammonia comprise an in-between state, able to exist as gases or ices depending on the local conditions. When those molecules were found by Voyager to have an extensive presence in Uranus and Neptune, scientists called them "ice giants."


Planets form hot. A small planet can cool off and radiate away heat over the age of the solar system. A large planet cannot. It hasn't cooled enough entirely on the inside after formation, and thus radiates heat. Jupiter, Saturn, and Neptune all give off significantly more heat than they receive from the Sun. Puzzlingly, Uranus is different.

"Uranus is the only giant planet that is not giving off significantly more heat than it is receiving from the Sun, and we don't know why that is," says Mark Hofstadter, a planetary scientist at NASA's Jet Propulsion Laboratory. He tells Mental Floss that Uranus and Neptune are thought to be similar in terms of where and how they formed.

So why is Uranus the only planet not giving off heat? "The big question is whether that heat is trapped on the inside, and so the interior is much hotter than we expect, right now," Hofstadter says. "Or did something happen in its history that let all the internal heat get released much more quickly than expected?"

The planet's extreme tilt might be related. If it were caused by an impact event, it is possible that the collision overturned the innards of the planet and helped it cool more rapidly. "The bottom line," says Hofstadter, "is that we don't know."


Although it's really cold in the Uranian upper atmosphere, it gets really hot, really fast as you reach deeper. Couple that with the tremendous pressure in the Uranian interior, and you get the conditions for literal diamond rain. And not just little rain diamondlets, either, but diamonds that are millions of carats each—bigger than your average grizzly bear. Note also that this heat means the ice giants contain relatively little ice. Surrounding a rocky core is what is thought to be a massive ocean—though one unlike you might find on Earth. Down there, the heat and pressure keep the ocean in an "in between" state that is highly reactive and ionic.


Unlike Saturn's preening hoops, the 13 rings of Uranus are dark and foreboding, likely comprised of ice and radiation-processed organic material. The rings are made more of chunks than of dust, and are probably very young indeed: something on the order of 600 million years old. (For comparison, the oldest known dinosaurs roamed the Earth 240 million years ago.)


The only spacecraft to ever visit Uranus was NASA's Voyager 2 in 1986, which discovered 10 new moons and two new rings during its single pass from 50,000 miles up. Because of the sheer weirdness and wonder of the planet, scientists have been itching to return ever since. Some questions can only be answered with a new spacecraft mission. Key among them: What is the composition of the planet? What are the interactions of the solar wind with the magnetic field? (That's important for understanding various processes such as the heating of the upper atmosphere and the planet's energy deposition.) What are the geological details of its satellites, and the structure of the rings?

The Voyager spacecraft gave scientists a peek at the two ice giants, and now it's time to study them up close and in depth. Hofstadter compares the need for an ice-giants mission to what happened after the Voyagers visited Jupiter and Saturn. NASA launched Galileo to Jupiter in 1989 and Cassini to Saturn in 1997. (Cassini was recently sent on a suicide mission into Saturn.) Those missions arrived at their respective systems and proved transformative to the field of planetary science.

"Just as we had to get a closer look at Europa and Enceladus to realize that there are potentially habitable oceans there, the Uranus and Neptune systems can have similar things," says Hofstadter. "We'd like to go there and see them up close. We need to go into the system." 

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Christie's Images Ltd. 2017
Abraham Lincoln Letter About Slavery Could Fetch $700,000 at Auction
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Christie's Images Ltd. 2017

The Lincoln-Douglas debates of 1858, in which future president Abraham Lincoln spent seven debates discussing the issue of slavery with incumbent U.S. senator Stephen Douglas, paved the way for Lincoln’s eventual ascent to the presidency. Now part of that history can be yours, as the AP reports.

A signed letter from Lincoln to his friend Henry Asbury dated July 31, 1858 explores the “Freeport Question” he would later pose to Douglas during the debates, forcing the senator to publicly choose between two contrasting views related to slavery’s expansion in U.S. territories: whether it should be up to the people or the courts to decide where slavery was legal. (Douglas supported the popular choice argument, but that position was directly counter to the Supreme Court's Dred Scott decision.)

The first page of a letter from Abraham Lincoln to Henry Asbury
Christie's Images Ltd. 2017

In the letter, Lincoln was responding to advice Asbury had sent him on preparing for his next debate with Douglas. Asbury essentially framed the Freeport Question for the politician. In his reply, Lincoln wrote that it was a great question, but would be difficult to get Douglas to answer:

"You shall have hard work to get him directly to the point whether a territorial Legislature has or has not the power to exclude slavery. But if you succeed in bringing him to it, though he will be compelled to say it possesses no such power; he will instantly take ground that slavery can not actually exist in the territories, unless the people desire it, and so give it protective territorial legislation."

Asbury's influence didn't end with the debates. A founder of Illinois's Republican Party, he was the first to suggest that Lincoln should run for president in 1860, and secured him the support of the local party.

The letter, valued at $500,000 to $700,000, is up for sale as part of a books and manuscripts auction that Christie’s will hold on December 5.

[h/t Associated Press]


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