Tag: carbon dioxide

Frosty blue dunes on Mars

By Phil Plait | February 27, 2012 7:00 am

It’s been a while since I’ve posted a jaw-dropping high-res picture from Mars, so how about this one: a gorgeous shot of frost coating dunes on the surface of the Red Planet?

[Oh yes, you want to click that to enaresenate.]

This picture was taken by the HiRISE camera on board the Mars Reconnaissance Orbiter, which takes extremely detailed images of the surface of the planet. It shows wind-driven sand dunes on Mars, rippling in a similar way as on Earth. The sunlight is coming from the upper left direction, and where the light hits the surface you can see the familiar reddish cast; that’s actually from very fine-grain dust laden with iron oxide — rust!

But the shadows, where the Sun doesn’t reach, it’s cold enough that carbon dioxide in the Martian air freezes out, forming a thin layer of dry ice on the surface. In this image — where the colors have been enhanced so you can see the effects better — this shades the dunes blue. You can see the frost not just covering the dunes in general, but hiding in the troughs of the ripples too (which I think is why the sunward facing parts of the dunes can look blue; that’s from the ripple shadows). The non-color-enhanced version showing the entire dune region can be found here — and is stunning in its own right.

These dunes fascinate me. The sand on Mars is actually basaltic, making it look grey to the eye. Those grains are big enough that they don’t move as easily as the finer dust, and they pile up to form the big dunes, with the redder dust coating them. The color can change when frost forms, as in the picture above, but you also get incredibly dramatic and simply stunning patterns when dust devils — tornado-like vortices that form when wind blows over warm air rising off the surface — lift up the red dust and expose the grey basalt underneath. The swirling patterns are intricate and incredible, as you can see in this picture here (click to embiggen and get more details).

Pictures like this remind me viscerally that these objects we see in the sky are not just some distant lights, they are whole worlds. They have fantastic details and are as diverse and have complex interactive systems as any we find on Earth. This makes their study important, fascinating… and of course, astonishingly beautiful.

Image credit: NASA/JPL/University of Arizona. Tip o’ the heat shield to HiRISE on Twitter.

Related posts:

- The artwork of the Martian landscape
- Martian dunes under the microscope
- The Devil is in the details
- Happy first day of spring… Mars!

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Happy first day of spring… Mars!

By Phil Plait | September 14, 2011 6:53 am

Today, September 14, 2011, is the vernal equinox for the northern hemisphere of Mars!

If you want to be technical, it’s the time when the axis of Martian rotation is perpendicular to the direction of the Sun, and the northern hemisphere is headed into summer (making it the autumnal equinox for the southern hemisphere). When this happens here on Earth, it’s called the first day of spring (here in the US at least, in other countries it’s considered the middle of the season — a tradition with which I agree).

Mars, like Earth, is tilted with respect to its orbit around the Sun; Earth is canted at an angle of roughly 23°, while Mars is at 25°. That’s why we (and Mars) have seasons! Over the course of the year, the angle of sunlight hitting the surface of the planet changes, heating it more efficiently in the summer and less in the winter. Boom! Seasons.

On Earth, that’s most dramatically seen as polar ice shrinks and grows over the year. Same with Mars! The picture above is from the European Space Agency’s Mars Express orbiter, and shows the northern polar cap in May 2010, during the last summer. The north pole of Mars is icy, but it’s actually two kinds of ice: water, and frozen carbon dioxide. CO2 turns directly from a solid into a gas (a process called sublimation), and does so at much lower temperature than water ice melts. This means the CO2 goes away first as temperatures rise in the northern hemisphere, leaving the water ice behind. In that picture, the ice is essentially all water.

In other words: the north pole of Mars is sublime*.

Where does the CO2 go? Into the atmosphere! So much of it adds to the air there that the atmospheric pressure on the planet increases measurably, by about 30%. That much extra carbon dioxide adds a small but significant greenhouse effect to the planet as well, warming the surface. Estimates vary, but I’ve seen quotes of a few degrees Celsius for the effect.

The change of seasons also kicks up winds on Mars, and that can cause everything from dust devils which leave incredibly beautiful scrollwork on the surface to planet-wide dust storms.

I’ll note that the year on Mars is about twice the length of an Earth year, so all the seasons are about twice as long as well. May 2010 is when summer started on Mars (in the northern hemisphere), and here we are 17 months later with the start of spring. The Planetary Society has a page listing the next few seasonal dates on Mars if you’re curious.

So anyway, happy first day of spring, Martians! Don’t forget to try to stand up malagor eggs today.

Image credits: Earth/Mars tilts: from Calvin J. Hamilton’s fantastic Solar views website; Mars polar cap: ESA/DLR/FU Berlin (G. Neukum.)

* Hahahahahaha! Man, that’s funny. Also, <McBain>ice to see you.</McBain>

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

As arctic ice shrinks, so does a denier claim

By Phil Plait | June 22, 2011 11:00 am

It’s been known for some time that the ice sheet in the arctic is thinning. And now, a new study (PDF) by the Arctic Monitoring and Assessment Program lays this out in grim detail.

The report lists 15 key findings about the changes at the Earth’s northern regions. Fifteen. Here are four that alarmed me particularly:

1) The past six years (2005–2010) have been the warmest period ever recorded in the Arctic. Higher surface air temperatures are driving changes in the cryosphere.

3) The extent and duration of snow cover and sea ice have decreased across the Arctic. Temperatures in the permafrost have risen by up to 2 °C. The southern limit of permafrost has moved northward in Russia and Canada.

7) The Arctic Ocean is projected to become nearly ice-free in summer within this century, likely within the next thirty to forty years.

12) Loss of ice and snow in the Arctic enhances climate warming by increasing absorption of the sun’s energy at the surface of the planet. It could also dramatically increase emissions of carbon dioxide and methane and change large-scale ocean currents. The combined outcome of these effects is not yet known.

That last sentence is — pardon the expression — chilling. The real truth of this is we don’t know how this will affect the planet. We know what’s happening (sea levels are rising as the Earth warms, for example), and we have a good idea why it’s happening (despite deniers’ claims), but we don’t know the long-term effects. All we can say for sure is, they won’t be fun.

And speaking of deniers, a claim I’ve heard bandied about is that a single volcano eruption pours more carbon dioxide into the air than humans do over the course of a year (the time scale may vary depending on the claimant, but as you’ll see it doesn’t matter).

Read More

Dana Rohrabacher (R-CA): on climate change, makes wrong even wronger

By Phil Plait | May 31, 2011 9:30 am

Sadly, I am not surprised when I hear a Republican congressman make some sort of grotesquely antiscience statement. It’s all too common now, and seems hardly worth noting except to throw it on the ever-growing pile of political distortions of reality the GOP is now known for.

But sometimes, one comes along that is so outrageous and ridiculous it must be noted. Enter Dana Rohrabacher.

He is a far-right Republican in California, and toes the GOP stance of climate change denial. Recently, he made a statement that’s pretty bizarre, and it’s making the rounds on the internet. There was a hearing of the House Foreign Affairs subcommittee (which he chairs) about UN climate policies and the US contributions to it. On the stand as a witness was the "top U.S. climate diplomat" Todd Stern… and Rohrabacher asked him this:

"Is there some thought being given to subsidizing the clearing of rainforests in order for some countries to eliminate that production of greenhouse gases? … Or would people be supportive of cutting down older trees in order to plant younger trees as a means to prevent this disaster from happening?"

Say WHAT? The idea here is that decaying matter in rainforests is emitting a lot of carbon dioxide, contributing to global warming. Rohrabacher seems to be saying that if we cut down old trees in rain forests there will be less decay, and therefore less CO2 emission.

This is such a bizarre statement it’s hard to know where to start. Read More

Ancient ice, wet and dry, from deep inside a comet

By Phil Plait | November 15, 2010 7:00 am

The comet Hartley 2 has come and gone, and the NASA mission EPOXI is also moving on after an exceedingly close flyby of the comet’s solid nucleus. The pictures we got were fantastic and beautiful… but their real power comes from coupling them with spectra.


In the picture above — an enhanced version of one of the images taken during the space probe’s flyby — you can see fan-like emission coming from the comet’s nucleus. These are jets; sprays of material coming out of the nucleus. Comets are made of rock and ice, and when the comet nears the Sun, the heat can turn that ice directly from a solid to a gas. This gas then shoots out from pockets on the nucleus, creating these jets. The EPOXI team (including my old boss, Don Lindler!) made a fantastic animation from a series of observations showing these jets in action.

But what are these ices made of? Lots of things we normally think of as liquids or gas (water, ammonia, carbon dioxide, and so on) exist in comets. In many comets, we see lots of water, and in fact the Swedish satellite Odin detected about 200 kg/sec (440 pounds per sec) of water coming off Hartley 2! So is water powering these jets?

hartley2_irplotWe can find out… using spectra. By breaking up the light from an object into its component colors, we can learn all manners of things including what it’s made of. EPOXI did just that with the jets streaming from Hartley 2, and while it did find water, amazingly, it found a lot more carbon dioxide!
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