Opportunity rover gets a free car wash / Mars back up, almost hits Porrima

A self-portrait of NASA’s Mars Exploration Rover Opportunity taken in late March 2014 (right) shows how fortuitous winds in late March cleaned much of the accumulated dust off the rover’s solar panels. Compare to a similar portrait from January 2014 (left). Click to enlarge. NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

What a difference a windy day can make. Before and after self-portraits dramatically show how gusty Martian winds swept away months of dust that had accumulated on the Opportunity rover’s solar panels.

Photo taken by the Opportunity rover looking east over the rim of the 14-mile-wide Endeavour Crater in March 2012. Winds blowing up over the crater’s rim in March removed much of the Mars grime coating the robot. Credit: NASA

Strong winds blowing over the rim of Endeavour Crater in mid-March removed almost all of the accumulated dust, increasing the power available from 375 watt-hours in January to more than 620 watt-hours per day by mid-April or about 80% of maximum. In fact, the rover now has cleaner solar arrays than in any Martian winter since it first landed on the Red Planet in 2005.

In a similar move, rains recently removed the accumulated road salt from my car deposited during the long winter. It’s now about 70% back to its original appearance. Opportunity ‘cleaning events’, as they’re called, happen periodically, and have played a significant role in the rovers’ longevity. Mars’ winds typically blow 20 mph with maximum speeds recorded by the 1970s Viking landers of 60 mph.

With extra juice to power its instruments, Opportunity can continue exploring Murray Ridge on the western rim of Endeavor Crater. Can you believe the rover’s been rolling around the Red Planet for more than 10 years now?

During Opportunity’s first decade on Mars and the 2004-2010 career of its twin, Spirit, the hardy robots have shown that Mars was once wet with both acidic waters and milder, more neutral ones conducive to supporting life.

Mars is still in retrograde motion, moving to the west directly underneath the beautiful double star Porrima (Gamma Virginis) in Virgo. Beginning in mid-May, the planet resumes its normal movement to the east. Created with Chris Marriott’s SkyMap program

While we’re on the topic of Mars, you may have noticed that the planet has been moving in the wrong direction since early March. The outer planets normally track east across the sky as they orbit the sun, but around the time of opposition, when they’re closest to Earth, they reverse gears and travel west in retrograde motion.

As Earth speeds past Mars, the planet appears to ‘drop behind’ or move westward for a time before resuming its normal motion. Credit: NASA

Of course, Mars didn’t really stop and change directions. It only appears that way as the faster Earth laps the slower-moving planet. Like passing a slower car, Mars appears for a time to travel backwards from our perspective. Once Earth moves far enough ahead of Mars – rounding the corner of our orbit as it were – the Red Planet resumes its normal eastward movement.

All the outer planets move more slowly around the sun than Earth and show retrograde motion, but the farther the planet, the smaller the loop. Mars scrawls a bigger loop because it’s closest.

This year’s retrograde amble takes Mars only a degree from Porrima, an attractive, closely paired double star in Virgo.

They’ll be closest later this week on May 2-3. Small telescope owners can use Mars to find Porrima. At low magnification, it looks like a single star, but increase the power to 100x and higher and you’ll see twin pearls of starlight.

Porrima is a true double star where each member orbits a common center of gravity. Diagram at right shows the orbit of the secondary companion around the primary star. The two were too close together to split in any but the largest telescopes in 2005. Since then they’ve been opening up. Credit: Damian Peach (left), www.dibonsmith.com (right)

Porrima’s stellar twins are similar to the sun but hotter and nearly identical in size. They go around each other every 169 years in an elliptical orbit that makes their separation narrow and widen as seen from Earth. The stars were closest in 2005 when they were separated by about 500 million miles, equal to Jupiter’s distance from the sun. They’ll be over 7 billion miles apart around the year 2080.

Mars and Porrima – also known as Gamma Virginis – tonight April 27 around 10 o’clock local time. Mars also passed the star on Dec. 29, 2013 moving east. Stellarium

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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.

4 thoughts on “Opportunity rover gets a free car wash / Mars back up, almost hits Porrima

  1. Bob,
    Thanks for the mention of Porrima – it takes me back a ways. Back to 1959, when I got my first telescope (an Edmund Scientific 3-inch reflector), the accompanying star guides featured Porrima as a nice easy-to-split double in a small scope. And indeed it was. But eventually the two stars merged as seen in the 3-inch. It appears it’s nearly time to split the double once again after several decades. Some things, like eclipses and meteors, happen in seconds; watching Porrima’s orbital loop takes a good chunk of a lifetime. When I spot it again with the 3-inch (which I still have) it will be one of those “circle of life”, or more properly, “ellipse of life” moments!

    • Richard,
      “Ellipse of life” sure has a nice ring to it. I often share similar astronomical touchstones with my class. One of my favorites is seeing Saturn go ’round the ecliptic – a journey from childhood to adulthood. I’m hoping to put in at least one Uranian year before departing this life.

      • Bob, a Uranian year plus some would be real nice! When I first saw Uranus it was approaching Regulus for a close conjunction in 1962. It would be fun to watch the planet slide by Regulus again in 2046. A side benefit would be catching lots of eclipses and other neat events in the meantime. We can do it if we eat lots of oatmeal, have one beer a day, and keep our scopes collimated.

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