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: