Alan Stahler: A very different world
July 25, 2018
Earth is an ocean planet — over two-thirds of our world is under water.
A sink, in physics, is a low point, to which things flow. The ocean is Earth's major heat sink, where Earth stores most of the energy we get from the sun.
There are patterns to that energy storage — the ocean is warm in some places, cold in others. Some of those warm-here/cold-there energy patterns have names: El Niño and La Niña are two, very different, such patterns.
When the Pacific flips from La Niña to El Niño, the entire atmosphere feels it:
It rains in the desert, and flowers bloom.
Drought hits the rain forests, and they burn.
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Atlantic hurricanes fizzle.
Planet Mars is a desert planet. With no ocean to store the sun's energy, a major Martian heat sink is dust.
Slam one rock into another and they break. Splinters of rock become sand.
Look at a grain of sand under a hand lens, and you can tell how old it is. A young grain of sand — only recently splintered off — is shiny; its edges are sharp; it might even be pointy.
Driven by the wind, sand grains grind against one another. Their surfaces become scratched and pitted: their shininess dulls; points are ground off, edges are rounded. They grow smaller.
Salt and sugar dissolve in water. Sand … not so much. But sand does dissolve a little … just a bit. It's not noticeable, until the grains get really, really small. Then the tiny grains dissolve completely.
With lots of liquid water on Earth, there's a limit to how small sand can be ground down, before it dissolves away. But with no liquid water on Mars, sand is ground to dust, the size of the particles in cigarette smoke.
Weather on Mars
Martian winds create dust devils and dust storms. Dust storms are mostly local, but, once in a half-dozen years or so, a dust storm grows … and grows … and grows … until it covers the planet. When that much dust is lofted into the air, it becomes a major heat sink, absorbing sunlight, warming the air.
When a global dust storm struck Mars in 2001, it raised the air temperature more than fifty degrees Fahrenheit. That … is a heat wave.
A global dust storm is blowing at this moment on Mars. The sun-warmed dust is changing the atmosphere, making it thinner, raising it farther above the surface.
The InSight spacecraft launched toward Mars last May, the first interplanetary spacecraft to launch from the west coast, from California. InSight will land on Mars the Monday after Thanksgiving this year.
The light-flight time — the time it will take a radio signal to travel from Earth to Mars — will then be just under eight minutes … longer than the time it will take for InSight to enter Mars's atmosphere and make planetfall on the surface.
InSight will need to land on Mars entirely on its own.
I asked Bruce Banerdt, InSight PI (principle investigator = chief scientist) whether the craft could land in the midst of a dust storm. He felt the system could adapt to whatever conditions Mars throws at it.
This Friday night, Mars will be fully-lit by the sun. Mars will be at its brightest, and close to the full moon, as soon as the sky grows dark … although it may take a little time for it to rise above the trees.
Earth orbits closer to the sun than Mars, and so moves faster. We will catch up with Mars, and pass it, next Tuesday, July 31, at which point Earth and Mars will be closer than we've been in decades, closer than we will be for more decades. Tune in to a special edition of Soundings on KVMR next Tuesday, July 31, at noon.
Our next Sky Watch (we'll be looking at Mars, though we may see only dust) takes place at 8 p.m. Saturday, Aug. 4, at the junction of the old Downieville Highway and State Route 49 — bring a sweater.
Alan Stahler enjoys sharing his love of nature with students of all ages. His science stories can be heard on KVMR-FM (89.5 MHz), and he may be reached at email@example.com.
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