So what is the "Mars mystery" NASA has solved? Flowing water on Mars.
This is indeed a major discovery. Where there's water, there may be life.
But in this case I wouldn't hold your breath. NASA hyping this finding is a bit like throwing a party over a patch of wet sand in a desert when - right around the celestial corner - at least two vast, inhabitable oceans remain unexplored.
The news we'll hear about today (watch the live stream here) dates back to 2011, when an undergraduate named Lujendra Ojha discovered dark streaks on the slope of a crater near the Martian equator.
Back then, Ojha, planetary scientist Alfred McEwan, and other researchers announced in the journal Science that these streaks, called "slope lineae," appeared during warmer periods on Mars. (McEwen also led a 2013 followup study in the journal Nature.) They suggested that water in the soil is melting, leaking down the crater wall, and showing up in Mars Reconnaissance Orbiter satellite images.
NASA told the world back in August 2011 that "salt water may flow on Mars."
First, both Ojha and McEwen are in NASA's announcement. Second, Keith Cowing at NASAWatch.com learned that both Ojha and McEwen authored a recent scientific abstract about the same slope lineae titled "Recurring Slope Lineae on Mars: Atmospheric Origin?" at the 2015 European Planetary Science Congress. Third, that conference is happening now, from Sept. 27 - Oct. 2.
The new abstract suggests that salts in Martian soil are absorbing traces of water in the planet's thin atmosphere, then periodically melting. This is similar to the process that makes table salt, brown sugar, and other compounds in your cupboard soak up humid air. Except on Mars it's blisteringly cold - so the water freezes until it gets warmer, at which time it melts into salty liquid.
It's possible something else is causing the streaks, perhaps an underground aquifer or a reserve of ice beneath the soil. Wherever the water comes from, it's not looking promising for life.
"If [recurring slope lineae] form via atmospheric deliquescence, then they are likely eutectic brines with temperatures and water activities too low to support terrestrial life," the new abstract concludes.
And this doesn't mean Mars isn't a worthy or interesting target for exploration, robotic or human. Elon Musk and others believe we can terraform the planet (with nuclear weapons!) and send humans there to colonize it. Also, Mars may have been habitable at one point. Many studies showed it had vast, 450-foot-deep oceans covering 19% of the planet.
But something went wrong. Mars' internal dynamo stopped, shutting down its magnetic shield that once helped protect the surface from solar radiation - which, in turn, blasted away the Martian atmosphere and almost all of its water over the millennia.
NASA/JPL
A vast ocean probably lies beneath Enceladus' icy shell.
Given NASA's growing mission to search for signs of alien life in the Solar System, it's high time the US government seriously commit resources to exploring much more promising if difficult-to-reach locations, such as Jupiter's moon Europa and Saturn's moon Enceladus. Scientists suspect both of these worlds hide warm, habitable oceans beneath their icy shells.
If we could orbit or land on one of these ice moons - or even send a submersible into the waters below - we stand to quickly advance two of the greatest questions ever posed by humankind: Are we alone? And if we find some microbial life, the follow-up question: Why haven't we heard from intelligent alien races yet?
This artist's rendering shows a concept for a future NASA mission to Europa in which a spacecraft would make multiple close flybys of the icy Jovian moon, thought to contain a global subsurface ocean.
Stretch the cost over years, however, and those billions should be relatively easy for the US government to find.
It's also crucial that the government commit to helping NASA increase its dwindling supply of plutonium-238: A rare, unique, and red-hot material that can power spacecraft for decades - and could help a submersible robot melt through a miles-thick ice shell with relative ease.
The problem is that the entire world is running out. It hasn't been made in earnest since the end of the Cold War, and a $50-million-a-year effort by NASA and the US Department of Energy to reboot production has stalled over and over again, according to Scientific American.
NASA planned to use plutonium-238 to power the Europa mission, but it required more material than the space agency has available. So it opted for a more limited, solar-powered version of the mission.
Jupiter, Saturn, and their moons are very far away, requiring years of space travel to get there. It also takes scientists and engineers years to design, build, and test the spacecraft they want to send. This means a mission can take more than a decade to pull off.
A recent feature story about Europa in Popular Science summed up the problem well (emphasis added):
"We understand how special Europa is. It's worth the investment. It's worth the risk," says Louise Prockter, a planetary scientist at Johns Hopkins University's Applied Physics Laboratory. Prockter has already made that investment herself, having spent half her career studying Europa's unique, frosty terrain. "I just hope we can get something there while I'm alive."
If we're ever going to answer "are we alone?" within our lifetimes, let alone those of the scientists most capable of attacking the question, it's time for NASA and the US government to seriously commit to looking somewhere other than Mars. And right now, Europa and Enceladus are our best shots.