A Piece of Mars: This 0.96×0.54 km (0.6×0.34 mi) late winter scene is a study in contrast. The dark top half is uniformly rippled. This is the shady surface of the main windward side of one of Mars’ biggest dunes, in Kaiser crater. On the bottom is the sunlit side of the dune, strewn with gullies colored by CO2 frost (white), dark basaltic sand (black), and what may be oxidized fines (orange). (HiRISE ESP_045614_1330, NASA/JPL/Univ. of Arizona)
A Piece of Mars: This 480×270 m (0.3×0.17 mi) scene shows the contact between two very different terrains. On the left is a bright surface with polygonal cracks (characteristic of periglacial terrain – this is at a high latitude). On the right is a dark rippled sand sheet that superposes the polygonally-cracked surface. The long meandering furrows might be the beginnings of polygonal cracking in the sand, which might expand if wind doesn’t erase them. (HiRISE PSP_006473_1125, NASA/JPL/Univ. of Arizona)
A Piece of Mars: Barchan dunes on Mars have a characteristic crescent shape, with a steep slope (“slip face”) on the inside of the sharpest curve (see examples like this, this, these, or this). This image (873×491 m, or 0.54×0.31 mi) shows an example of a dune that probably looked a bit like those other dunes did once, but it’s been highly eroded so that the characteristic curved slip face is no longer the steepest slope. This dune is located pretty far north, so I’m betting it’s been stabilized by ice, so that the wind can no longer easily reshape it into a typical barchan. (HiRISE ESP_036404_2590, NASA/JPL/Univ. of Arizona)
August 31: See update at the end of this post
Several readers have contacted me recently about reports that a group of international astronomers have detected a strong signal coming from a distant star that could be a sign of a high-technology civilization. Here’s my reaction: it’s interesting, but it’s definitely not the sign of an alien civilization—at least not yet.
Here’s why: (more…)
A Piece of Mars: How far do windblown materials move on Mars? This scene (0.9×1.2 km, 0.56×0.75 mi) shows a bright layer of bedrock (top right) that is eroding, exposing a darker, bluish rock (bottom left). Ripples 5-20 m wide have slowly moved towards the lower right, with some migrating into the darker terrain. Those near the interface show that they’re made of stuff from the brighter terrain, as they are still brighter than the dark, bluish bedrock. But those at the bottom are much more blue. This means that this type of ripple incorporates material from nearby rocks: unlike other kinds of windblown material, they don’t travel far from their source. (HiRISE, ESP_017262_1560, NASA/JPL/Univ. of Arizona)
What began as a tantalizing rumor has just become an astonishing fact. Today a group of thirty-one scientists, led by Guillem Anglada-Escude at the Queen Mary University of London, UK, announced the discovery of a terrestrial exoplanet orbiting Proxima Centauri. The discovery of this planet, Proxima Centauri b, is a huge breakthrough not just for astronomers but for all of us. Here’s why.
A Piece of Mars: The erosionally-streamlined bright areas are on high ground. They are remnants of a vast dusty mantle that once covered this whole area – the rest of it has been blown away. The surrounding regions (check out the whole image) are still covered by that mantle, but here you can see through to the underlying, dark surface made of dark, cratered lava flows. (HiRISE ESP_017914_1685, NASA/JPL/Univ. of Arizona)
A Piece of Mars: Potential signs of wind activity are everywhere on Mars. Take this 0.96×0.54 km (0.6×0.34 mi) scene, which is on bedrock dated to be several billion years old. There’s a fabric of ridges trending from the upper right to lower left. The smaller and smoother ones are clearly windblown bedforms. The larger, bright ones are shedding boulders, so if they’re old bedforms then they’ve been lithified. How old are they? Billions of years old? Or did they form sometime in the intervening years? (HiRISE ESP_046389_1695, NASA/JPL/Univ. of Arizona)
A Piece of Mars: This 1.92×1.08 km (1.19x 0.67 mi) scene shows eroded ridges that are, in fact, lithified dunes. They are so old that you might not recognize them as dunes without more context. This doesn’t happen much on Earth, where inactive dunes are quickly eroded, buried, and/or destroyed by other geologic processes, so enjoy this uniquely martian wonder! (HiRISE ESP_046597_1670, NASA/JPL/Univ. of Arizona)
A Piece of Mars: Ten years ago I participated in a global survey of martian dunes. But we missed a few dune fields, like these beauties. They’re small, low, and in rugged terrain, which made them difficult to spot in the lower resolution data set we used. I keep a list of dune fields we’ll have to add if we get a chance to update the database. This scene is 0.96.0.54 km (0.6×0.34 mi) wide. (HiRISE ESP_043582_1555, NASA/JPL/Univ. of Arizona)