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

Earth from the ISS

Many pictures have been published on the web of Earth from outer space. Astronauts often take images of Earth from the International Space Station (ISS). The ISS is a satellite in low Earth orbit that houses up to 15 astronauts at one time. It is used to conduct low gravity experiments, monitor Earth's weather and learn how humans and plant life survive in outer space. Using onboard cameras and other instrumentation, astronauts can image every inch of Earth as they fly by. Below is a video compilation of  many images taken from the ISS from August-October of 2011. Note the beautiful aurora which forms at the top of Earth's atmosphere (defined by what looks like a thin yellow shell around Earth). You can also see city lights across all countries, and flashes of lightening within clouds.

Video credits are listed  here: http://vimeo.com/32001208

Earth | Time Lapse View from Space, Fly Over | NASA, ISS from Michael König on Vimeo.

Did the Moon Form From Earth?

Artists impression of the impact which formed our moon

There are many theories out there as to how Earth's moon formed. Some think the moon formed right with the earth out of the circumstellar disk of material around our young sun, others think that it is a captured object that got caught up in Earth's gravity and became our moon. The leading theory is that a Mars sized object crashed into Earth during the Late Heavy Bombardment, and broke off a chunk of earth that formed into the moon. But why do we think this is the case? Well first of all, measurements of  the amount of Tungsten-182 (decay product  of Halfnium-182) in returned moon rocks suggest that the moon appears to be ~100 million years younger than the Earth. I know that sounds like a long time, but it's really fairly short, considering the Earth is 4.6 billion years old. The age of the moon suggests that after the Earth was hit, the moon formed in a short period of time, but it took an extra 100Myrs for Earth to recuperate and reform back into a spherical planet. So this rules out the "same time formation" theory (the moon is younger). So what about the "captured rock" theory? Well, based on analysis of moon rocks and the lunar composition via satellite missions to the moon, we know that the moon is made almost solely of molecules that consist of oxygen (silica, alumina, iron oxide, sodium oxide, etc.). Measurements of the oxygen isotope ratios in rocks tell us that this ratio is almost exactly the same as that on Earth. It's very unlikely that a random captured rock would have exactly the same oxygen isotope ratios as we do on Earth, so the moon probably formed from a piece of the Earth!

Image Credit: Fahad Sulehria