Tag: ice

Mars craters are sublime

By Phil Plait | May 24, 2012 7:00 am

Someday, Mars will stop surprising me.

Today is not that day.

The image below was taken by the HiRISE camera on the Mars Reconnaissance Orbiter, which has been taking devastatingly high-res pictures of the Red Planet for many years. While passing over the edge of the Tharsis Shield — a huge uplifted region of Mars home to its four gigantic volcanoes –it saw this bizarre fieldof craters:

[Click to hephaestenate.]

First, you may think these are mounds and not craters, but that’s an illusion. Our brain uses illumination to gauge up and down in pictures like these, and assumes the sunlight is coming from above. However, these really are craters, but the illumination is coming from below — north is roughly toward the top of the picture and the crater field is at a northern latitude of about 50°. Flip the picture over if it helps (I’ll be honest, even doing that makes it hard for me to see these as other than mounds; confounded brain!). You can see more examples of this illusion here, here, and here.

But that’s not the weirdest thing about these craters. What’s really odd is they aren’t circular! Impacts are generally round unless 1) the impact is at a very shallow angle, b) the terrain suddenly goes from one kind of material to another, creating a discontinuity, or γ) something happened after the crater was formed to distort it.

A shallow-angle impact is almost certainly not the case here, since there are so many craters spread out over the region that an incoming object would’ve had to break up into a gazillion pieces, all of which came in at that angle. Not impossible, but it seems unlikely.

The changing terrain idea doesn’t work, since again the craters are spread out over the area. You might see one crater with a sudden break in its rim or change in shape, but dozens? Spread out in all directions? Nope.

That leaves after effects, and in this case we have two more clues. Read More

Huge lakes of water may exist under Europa's ice

By Phil Plait | November 17, 2011 11:52 am

We’ve known for years that Jupiter’s moon Europa almost certainly has an ocean of liquid water deep under its frozen surface. For one thing, the surface is almost all water ice. We also know that it’s covered in thousands of cracks that look very much like the type we see in ice floes floating on liquid water here on Earth. And we have a heating mechanism: tides from Jupiter as well as from the other moons flex Europa, causing its interior to warm up.

A nagging question has been how thick is the solid ice shell over that ocean: is it many kilometers thick, or much thinner? Evidence supports both arguments, which is maddening. However, that problem may now be solved: astronomers studying Europa’s terrain think the ice shell is generally very thick, but — and this is the cool part — may have vast underground lakes of water!

This picture is from observations of Europa made by the Galileo spacecraft, which orbited Jupiter for many years. It’s a combination of optical images and photoclinometry — using pictures to measure the heights of surface features. Purple and red is elevated terrain, and you can see that this looks like a depression in the surface. It’s filled with what’s called "chaotic terrain" for obvious reasons. Most of the surface of Europa has larger scale structure, and is more organized, as you might expect from a thick shell of ice. But these smaller regions are a mess, and it looks like this is from pockets of liquid water under the surface, giant lakes the size of North America’s Great Lakes, completely buried in the ice.

This artist’s view shows how this works; the lake is completely embedded in the ice shell. In general, the ice is very thick, explaining the usual look of Europa’s surface. But in some spots, just below the ice, the ice has melted. The ice above this underground lake is much thinner, perhaps only 3 km (about 2 miles) thick, explaining the chaotic surface in those localized spots.

That’s pretty nifty, but why is this so important? Read More

CATEGORIZED UNDER: Astronomy, Cool stuff

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

Fleuve avec glace de l'espace

By Phil Plait | January 20, 2010 7:21 am

It’s been weeks since I’ve seen clear ground here in Boulder; we’ve had snow and ice for a long time. You’d think I’d be sick of it and wouldn’t want to see any more, but then you either don’t know me well, or you haven’t seen this beautiful image from NASA’s Aqua satellite:


[Click to embiggen.]

This image, taken on January 17, 2010, shows thin ice forming in the St. Lawrence river in Quebec. I love the swirls of ice, forming along the eddies and flow of the water.

Aqua is an Earth-observing satellite designed to monitor our planet’s water cycle as it orbits at an altitude of 700 kilometers. The camera used in this image is the MODIS, or Moderate Resolution Imaging Spectroradiometer. It can observe in a whopping 36 different wavelengths, from visible to infrared. It has a maximum resolution of 250 meters per pixel — I find that a bit funny, given that we have probes orbiting the Moon and Mars with resolutions a thousand times higher. But each was designed to do a specific job, and for Aqua, 250 meters is good enough. Clearly, it’s enough to produce stunning images like this one.

CATEGORIZED UNDER: Pretty pictures, Space

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