Evening moon, popular planets and extreme sports on Mars

Face west-northwest tonight to see the moon near the star Regulus as well as a tight group of four bright sky objects – two stars an two planets. Created with Stellarium

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.

A recent image from the Mars Odyssey spacecraft showing dark-bordered streaks caused by winds blowing around the dual craters’ walls. The dark areas are scoured of surface dust; the light zones are where the winds deposited their load of dust after being braked by the craters’ walls. Credit: NASA/JPL/ASU

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.

Mars Reconnaissance Orbiter photo of “linear gullies,” which may be explained by slabs of dry ice gliding down the slopes of sand dunes.  Different in form from other streaks and gullies on Mars, they can extend up to a mile (2 km) and end abruptly in pits.  Scale in meters at left. Click to enlarge. Credit: NASA/JPL-Caltech/Univ. of Arizona

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.

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

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