Jupiter's Ice Moon Europa: Part 1

 Image of Europa taken by the Galileo spacecraft showing surface ice and cracks

The Galileo spacecraft was launched in 1989, and in the 1990's gave astronomers their first up close and personal interview with Jupiter and its moons. One of many big discoveries was that Jupiter's 2nd closest moon, Europa, is a giant ball of ice! And the best part… it's water ice! Astronomers know the surface is water ice because of two main features. One is that albedo (reflectivity) of the planet is what we would expect for a planet covered in ice. Second, spectroscopy of Europa done in the infrared from the earth shows strong water absorption lines. Now that we know what the surface of Europa is made of, the question becomes "is there liquid water underneath that icy surface?" Astronomers speculate that the answer is yes. Based on Galileo images (above), Europa has a mostly smooth surface but exhibits large surface cracks as well (brown lines in the image). This is indicative of something like plate tectonics, where the ice plates sit on top of a liquid ocean and move around due to the motion of the sub-surface ocean. The only way to know for sure if there is a liquid ocean is to send a probe there to drill through the ice. This sort of probe may be in NASA's future, but recent discoveries based on the old Galileo observations suggest that liquid water has already been discovered! Tune in next time to learn more about this amazing discovery!

Image Credit: NASA/JPL

Flowing Water On Mars!

The above image was taken back in May by the Mars Reconnaissance Orbiter, a satellite orbiting Mars that takes photos of the Martian surface. First released last Friday, the image depicts dark brown streaks  on the edge of a crater. These streaks appear during the Martian summer, then fade away during the winter months, and reappear again the next summer. It's believed that these streaks are actually flowing  liquid salt water on Mars! That's right, I said flowing liquid water! Over the past decade or so, astronomers have found much evidence that water flowed on Mars sometime in the past, but they believed that conditions on Mars today are too harsh to support liquid water. I guess they were wrong!

The main thing preventing liquid water from flowing on other planets is temperature. Planets closer to the sun than Earth are too hot; any water would evaporate. Planets farther away from the sun than earth are too cold; any water would freeze. Temperatures on Mars range from 68 F during the summer, to -124 F in the winter, with an average of -81F. So in the summer months Mars can get warm enough to have flowing liquid water! One thing that also helps is the fact that the Martian surface is very salty. This salt gets dissolved in any surface water, lowering the freezing point of water and preventing it from turning to ice. (This is why we throw salt on the roads in the winter, it lowers the waters freezing point preventing ice from forming.) Any water on Mars will be very salty, allowing it to be in liquid form at fairly cold temperatures. Water that has dissolved as much salt as it can possibly handle has a freezing point of -4 F.

This discovery  of this water on Mars has once again peaked interest in astronomers minds about searching for life on Mars. Maybe there are some microbes or bacteria that live in the water during the summer months? We will have to wait for the next round of Mars rovers to find out!

Image Credit:HiRISE, MRO, LPL (U. Arizona), NASA