The ambling moon is one day shy of first quarter phase tonight and lights up the sky near the star Regulus in Leo the Lion. Closer to the horizon, Venus and Mercury couple up with Gemini’s brightest stars Pollux and Castor, with bright Capella glimmering alone in the north.
Mercury and Venus join up for a conjunction (close pairing) on the 19th and 20th, while the moon passes near Saturn on June 18-19. Mars and Jupiter are both too close to the sun to see, but will soon return to morning twilight in the next several weeks.
Speaking of Mars, I came across some great images recently of wind streaks and dry ice “snowboard” trails on the Red Planet. Wind streaks can appear either dark or light-colored on Mars. When strong winds converge around craters and cliffs they can sweep away the lighter surface dust exposing the darker lava plains beneath. Craters can also slow down the winds, causing them to drop their loads of dust as light-colored streaks on the obstacle’s lee side. Sometimes both happen at the same time as in the photo above.
While wind streaks make sense because of their earthly analogs, dry ice chunks gliding down the slopes of sand dunes on cushions of their own vaporizing gas sounds distinctly more alien. Yet that’s what NASA researchers believe is happening to create the zillions of narrow furrows seen along the slopes of some Martian sand dunes.
“I have always dreamed of going to Mars,” said Serina Diniega, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and lead author of a report published online by the journal Icarus. “Now I dream of snowboarding down a Martian sand dune on a block of dry ice.”
Dry ice gliding on sand dunes
Carbon dioxide frost coats the dunes during the Martian winter which lasts about twice as long one on Earth. Over time, the ice accumulates and gets compressed into slabs which can break off and glide downhill during the spring season. As frozen carbon dioxide (dry ice) changes directly from a solid to a gas on contact with the warmer sand, the gas pushes against the surface to create a cushion of air. The block rides the cushion all the way to the bottom where it continues to vaporize, forming a little pit at the end of the gully. Be sure to watch the short video – I think you’ll be delighted at the experiment using dry ice on sand dunes here on Earth.