A Piece of Mars: This 1.6×2 km (1×1.24 mi) scene mostly shows what wind will do to fine-grained, weakly-consolidated surfaces. It has created topography that further strengthens wind scour in the hollows, which even leave kilometers-long grooves reminiscent of water-carved streams. If this were Earth I’d guess they had been carved by water first. But this is Mars, where the wind is in charge. (HiRISE ESP_046504_1785, NASA/JPL/Univ. of Arizona)
A Piece of Mars: OK, you have to bring out the red/blue glasses for this one. (Or click here if you’re missing your glasses and want the black and white version.) Eberswalde crater has some lovely layered deposits, long ago laid down by running water, and since eroded steadily by the wind. The wind leaves behind the most resistant parts (mainly fluvial channels that were more cemented). The center of this image shows a tall spire: the tallest of the flat layers (top of the “wedding cake”) is 290 m (950 ft) across and casts a shadow indicating it’s 200 m (656 ft) above the next layer down. That central spike is another 70 m (230 ft) taller yet, by itself nearly rivaling the “Totem Pole” in Monument Valley. Check out the rest of the red/blue anaglyph, it’s stunning. (HiRISE, ESP_047185_1560/ESP_047119_1560, NASA/JPL/Univ. of Arizona)
A Piece of Mars: HiRISE is celebrating 10 years of success by showcasing its first high resolution image, taken back in 2006. Here is a portion of it, shown at 1/4 the full resolution (the scene is 2.5×2.5 km across). I highly recommend downloading the HiRISE image viewer and looking at the whole thing, it’s an amazing landscape. The portion shown here has many different ripple-like features, formed by a wind blowing from left to right. Notice that those in the middle and middle-left are a bit fainter: these are ripple-like features that were carved into the bedrock by the wind, and they may be much older than the sharper-edged ones nearby. (HiRISE TRA_000823_1720, NASA/JPL/Univ. of Arizona)
A Piece of Mars: This 480×270 m (0.30×0.17 mi) scene shows what are being called “ridges”. Were these ridges once dunes that have now been stabilized and eroded? They have some dune-like characteristics: nearly parallel crests, one slope is steeper than the other, that steep slope seems to have exposed layers, and sometimes the crests meet in what is called a “Y-junction” (based on the letter’s shape). But although they’re common in some areas on Mars, they’re not like any dunes or ripples I’m familiar with. I’m inclined to think they’re not ancient dunes, but it’s likely that the wind had a hand in their formation. I’m open to suggestions… (HiRISE, ESP_046998_1365 NASA/JPL/Univ. of Arizona)
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.