Monthly Archives: March 2009

california academy of sciences, equinox, space weather

Living With a Star: Equinoxes and Space Weather

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When Day and Night are Equal Length

The equinox terminator satellite view. Courtesy miss_braceys photostream at http://www.flickr.com/photos/30086332@N06/
The equinox terminator GOES satellite view. Click to embiggen. Courtesy miss_bracey's photostream at http://www.flickr.com/photos/30086332@N06/

On this auspicious occasion I’d like to wish you a happy March Equinox.  It’s an astronomically derived “holiday” of sorts, and what it means is that the Sun’s apparent path in the sky throughout the year crosses from the southern celestial hemisphere into the northern one.

People often think of this as the first day of spring (for northern hemisphere dwellers) or the first day of autumn (for folks south of the equator), although as Phil Plait points out, that’s not quite correct. (Read here for why he says that.)

People also often — and wrongly — say that this is the only time that you can do something you wouldn’t normally do: balance an egg on its end.  I ran into this bit of conventional weirdness (the opposite of conventional wisdom) back when I worked at a newspaper.  I came in to work one day in early March (well before the equinox) and all the copy desk editors were engrossed in a conversation about how you could balance an egg on its end only on the equinox.  I asked them that could be and they didn’t know, but thought it make a cool “weird science” story. I told them it was weird, but it wasn’t science, and that set off another discussion that ended with me buying a dozen eggs and bringing them back up to the office and showing them that you could balance them on any day, not just the equinox or the first day of autumn or any other conveniently interesting date.

Imagine if you will the messy desks of a newsroom, each one with an egg balanced on it. And NOT on the equinox. and a bunch of smart-aleck copy desk editors scratching their heads because what they thought they knew was wrong. Another beautiful theory bit the dust as reality proved it wrong.

Phil Plait (his BadAstronomy-ness himself) made a great movie showing how the egg thing works throughout the year. Check it out here.

Living With a Star

Equinoxes and solstices are some of the things we live with because we live near a star. So are the seasons. And so is space weather. Speaking of which, in all the excitement yesterday, I forgot to post an entry here directing you to 365 Days of Astronomy (which you should be listening to every day anyway, right?).  I had an entry about space weather, so go check it out.

Are They Really That Ignorant?

Speaking of the change of seasons and calendrical things, there’s a fascinating bit of data out there about how only 53% of adults in the U.S. in a survey conducted by the California Academy of Sciences know how long it takes for the Earth to go once around the Sun. That’s pretty bad.  What’s even worse is that nearly 40% of those same people thought that humans and dinosaurs lived at the same time.  That IS also something that the earliest humans knew as they trod the plains of Africa only 160,000 or so years ago.  The earliest primate ancestors of humans didn’t even exist when dinosaurs did. That’s because dinosaurs were thriving some 65 MILLION years ago (before a combination of factors, including a killer asteroid of some kind, started them down the road to extinction).  At that time, only the most primitive mammal ancestors of humans existed. (There’s a nice explanation of when primates did show up at this site.) Nary a human nor primate of any kind was to be found. The first hominid (a form of primate that was the immediate predecessor to us) didn’t show up until about 4.4 million years ago.  That’s a LONG time after the dinosaurs bit the dust. And, there’s fossil evidence aplenty to prove it. Hard, cold data.

But, that doesn’t stop some folks from making up faux science out of whole cloth (and some kind of curious shame over evolution) to make money on dinosaur-human theories.  And, apparently it doesn’t stop others from believing what these charlatans say instead of checking it out for themselves.  The whole thing kind of begs the question about the quality of science education these people got. If they got any.

Anyway, see how you stack up against the rest of the folks who took the test — surf on over to CalAcademy (link above) and take their mini quiz on science — it comprises six questions on their front page.  I did, and I only got one wrong (and it wasn’t the one about the year or the dinosaurs).  See if you can beat my score!

astronomy, Mars, Mars Phoenix Lander

Sweatin’ Mars

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Liquid Saltwater Likely Present on Mars

What happens when you have salt water on a surface in cold weather?  On a human body, it comes out of pores as sweat and if the conditions are right, it condenses on the skin as droplets of salty water.  The saltiness means that they probably wouldn’t freeze to your skin until it gets very, very cold — which is why if you exercise outside in the winter, sweat droplets don’t turn into ice blobs right away, even if they land somewhere other than on your warm skin.

Droplets of salty water on the legs of the Mars Phoenix Lander. (Click to emibiggen.)
Droplets of salty water on the legs of the Mars Phoenix Lander. (Click to embiggen.)

It turns out that this tendency of salt water to freeze more slowly in cold weather is behind the discovery of water droplets on the legs of the Mars Phoenix Lander which is sitting silent in the Martian north polar region.

Scientists at the University of Michigan have analyzed an an image taken during the mission and say that this is proof of liquid water on Mars.  This is the first time liquid water has been detected and photographed anywhere but Earth.

So, how could this be?

The common wisdom is that water exists on Mars only as ice or vapor. This is because of the planet’s low temperature and atmospheric pressure. Any water ice that did get exposed would probably vaporize in the low pressure and dry conditions, but it wasn’t likely to just simply melt.  At least, that was the thinking before the Mars Phoenix mission landed.

It came to rest in a place where an interesting confluence of conditions exist to make the droplets of salt water found on the Phoenix lander leg possible. First, temperature fluctuation in the arctic region of Mars where Phoenix landed and salts in the soil could create pockets of water too salty to freeze in the climate of the landing site.

The droplets you see on the leg in the image grew during the polar summer. Based on the temperature of the leg and the presence of large amounts of “perchlorate” salts detected in the soil, scientists think that the droplets were most likely salty liquid water and mud that splashed on the spacecraft when it touched down. The lander was guided down by rockets whose exhaust melted the top layer of ice below a thin sheet of soil.

Some of the mud droplets that splashed on the lander’s leg appear to have grown by absorbing water from the atmosphere, Images suggest that some of the droplets darkened, then moved and merged—physical evidence that they were liquid.

So, where did the salt water come from?  The wet chemistry lab on Phoenix found evidence of perchlorate salts, which likely include magnesium and calcium perchlorate hydrates. Mix these with water vapor released during landing and you have compounds with freezing temperatures of about -90 and -105 Fahrenheit respectively. The temperature at the landing site ranged from approximately -5 to -140 Fahrenheit, with a median temperature around -75 Fahrenheit. Temperatures at the landing site were mostly warmer than this during the first months of the mission.

The Michigan team did thermodynamic calculations, which provide additional evidence that salty liquid water can exist where Phoenix landed and — this is important — elsewhere on Mars.And the fact that the droplets seem to grow as time went by implies more salty water available than the amount melted when the lander came to rest on the surface.

Now, this is quite interesting of course because water is one of those things that we’re pretty sure that life needs to survive in the long term. And, we know that life can exist in pretty salty environments (the so-called halophiles). So, the discovery that liquid salty water can exist on Mars is a big boost for the search for places where life could exist on Mars (now or in the present).  Looking at it another way, knowing that such conditions exist on Mars widens the number of places where we know conditions are suitable for life.