OMG Mercury has water ice and organics. But what does that really mean?

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Has Curiosity detected organics on Mars? Not yet, said NASA in a press conference held earlier today. But last week, the Agency presented some of the most compelling evidence to date that Sun-scorched Mercury not only hosts impressive quantities of water ice, but organic (i.e. carbon-containing) molecules. But why is this such an exciting discovery?

Mercury circles the Sun in a tighter orbit than any other planet in our Solar System, and surface temperatures on the Swift Planet can exceed 800 degrees Fahrenheit (430 °C) — that's well beyond the boiling point (let alone the freezing point) of good ol' H2O.

But Mercury's surface is also riddled with craters. Some of them are deep enough that large swaths of their interiors remain perpetually hidden from the light and heat of the Sun's rays. These permanently shadowed regions are more common in craters localized near the planet's poles, and are estimated to reach temperatures as frigid as minus 370 degrees Fahrenheit (-223 °C).


Decades-old data, collected by radio telescopes here on Earth, have long suggested that these cold spots may, in fact, harbor water ice. Nevertheless, opportunities for close-range observations have been almost nonexistent; NASA's MESSENGER spacecraft, the first to ever orbit the planet, has only been circling Mercury since March 2011 — but last week's announcement goes a long way in corroborating the hypothesis of a watery Mercury. To quote Sean Solomon, principal investigator of the MESSENGER mission: "For more than 20 years the jury has been deliberating on whether the planet closest to the Sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict." Here's what that verdict looks like:


Pictured here is an image that superimposes permanently shadowed regions of Mercury's surface as seen by MESSENGER (depicted in red) over regions that radar data suggest could be covered in ice (depicted in yellow). Notice how the yellow (ICE!) regions are localized to craters.

"The more we examine the solar system, the more we realize it's a soggy place," said Jim Green, director of NASA's Planetary Science Division, in a press conference last Thursday. How soggy? Here's a map of all the water in our solar system. Surprise: it's everywhere, not nearly as rare as once believed. That's exciting, says Green, because it means the water we have here on Earth was probably brought here and that "other volatiles" were likely distributed throughout the solar system as well. What kind of volatiles? How about carbon-containing organic compounds? Oh yeah — Mercury has those, too! Bad Astronomy's Phil Plait Explains:

Further observation indicates that some regions in [Mercury's craters] are intrinsically dark, and others bright. The best explanation of this is the presence of organic, that is carbon-based, molecules on the surface. This does not mean life! But carbon molecules are very interesting because we know comets (and some asteroids) have lots of organic compounds like that, as well as water ice. And this is starting to give us a complete picture of what's going on.


According to MESSENGER scientist David Paige, the organic materials detected in Mercury's cold craters "may be the same type of organic material that ultimately gave rise to life on Earth." Does that mean scientists are hopeful about finding life on Mercury? Not exactly — but these are still important findings. Speaking at last week's press conference, Solomon had this to say:

Mercury is becoming an object of astrobiological interest, where it wasn't much of one before...That's not say to say that we expect to find any lifeforms - I don't think anybody on this table does - but in terms of the book of life, there are some early chapters, and Mercury may indeed inform us about what's in those chapters.


Does that mean we'll be sending more satellites — or even landers — to the scientifically neglected Mercury? Again: not exactly. Remember, these findings add to a growing body of evidence that water and other elements may exist in a lot more places than we originally thought. The whole solar system is ripe for exploration. So where to? Mercury? Nah. Our vote's with Titan. Or Europa! Yeah. Let's go to Europa, already. Hell, there's more water there than there is on Earth: