Sand dunes are found in many places on Mars. At most of these places the dunes are slowly moving, blown by the wind, just like on Earth. However, in this location in south Melas Chasma they appear to have turned to stone. The large dunes are slowly being eroded and disappearing, replaced by smaller structures of scalloped sand. source : uahirise.org

As the waning crescent moon rises in the small hours of the morning of Tuesday, Feb. 18, skywatchers will be preparing for an unusual event. That morning the moon glides in front of orange, starlike planet Mars for viewers in much of central and eastern North America, in what is known as an occultation. Parts of the western and central U.S. and Canada will be able to view both the disappearance and reappearance of the Red Planet in a dark or twilight sky. However, from western Canada, the Pacific Northwest and northern portions of California and Nevada, only the end of the occultation will be seen, since Mars will already be behind the moon when it rises around 3:30 a.m. local time. On the other hand, across the Eastern U.S., the planet will both disappear and emerge after sunup. Under reasonably dark skies, this event can be watched over western locations with the naked eye or binoculars, although a telescope will provide the best views. Over the Desert Southwest and parts of the Rocky Mountain States along and east of the Continental Divide, the entire event will occur under a dark sky, but will take place very low in the east-southeast; an open view of the horizon is required. Right now, Mars is relatively faint at magnitude +1.2 and will be dimmed further by its low altitude, but it should not be hard to spot. Near and immediately east (right) of a line extending roughly from Santa Barbara, California to Idaho Falls, Idaho to Havre, Montana, the bright limb of the moon occults the planet when it is still too low to view. But Mars' reappearance from behind the moon's dark limb will be much more observable, because the moon will be higher above the horizon and the planet won't be washed out by the crescent's bright glare. Unlike the pinpoint image of a star, which upon interaction with the moon appears to vanish or reappear as if you've clicked a switch, the larger apparent size of Mars causes it to disappear or emerge more gradually. About 15 seconds should elapse for the moon to fully cover (or uncover) the tiny disk of Mars after the edges of the two bodies appear to make contact. But the duration will be slightly longer for locations well to the north or south, where the occultation is not nearly central. Mars currently shows a gibbous disk with an apparent diameter of 5.1 arc seconds. The first speck of light from the Red Planet when it reappears from behind the moon will be at the moon's dark limb and can be spotted by an observer looking in the right place with a small telescope. Mars will emerge into view as a tiny, brilliant fiery blob — seemingly like a burst of lava from some great lunar volcano. In order to help observers anticipate where Mars will disappear (behind the moon's bright limb) and reappear (from behind the moon's dark limb), the accompanying diagram shows the apparent path of Mars as seen from various cities. The numbers specify the cities as given in this list. For some locations (such as San Francisco, #17), the disappearance will occur before moonrise, so its track on the left is not shown. More difficult farther east As one heads east, the occultation will take place after the break of dawn and the advance of morning twilight. Across the northern and central Great Plains, as well as the western half of Oklahoma and Texas, Mars will disappear in a dark sky, but twilight will be well advanced when it reappears. Binoculars or a telescope will be needed to see the emergence from behind the moon's dark limb. From the Great Lakes, Greater Ohio Valley and the Deep South, Mars will disappear in a twilight sky and reappear after sunrise. And for New England, upstate New York, Toronto and Montreal, the greater New York City area and New Jersey, Middle Atlantic Coast, Piedmont and Southeast Coast including Florida, the entire occultation will be a daytime affair. Trying to see the occultation from these regions will prove to be quite a challenge to say the least! Prior to sunrise, you'll see Mars sitting less than a couple of degrees to the left of the 24% illuminated lunar crescent. Moving at roughly its own apparent diameter per hour, the moon will appear to gradually creep closer to Mars as they slowly ascend and the background sky turns progressively brighter. With the naked eye alone, you'll probably lose sight of Mars about a half hour before sunrise, though it still should be readily visible through binoculars and small telescopes. To continue seeing it after sunrise however, will require a very clear (haze-free) day. The surface brightness of Mars (amount of light per square arc second) is about equal to that of the moon. In the accompanying table, predicted times at 28 cities are given for this "Mars eclipse." Also included is whether the event in question takes place in a dark sky, at mid-twilight (30 to 60 minutes before sunrise), bright twilight (30 minutes to just a few minutes before sunrise), near sunrise (within a couple of minutes of sunup) and daytime (after sunrise). For San Francisco and Seattle, where no time is listed under disappearance, that event occurs before moonrise.

MARS’ WATER WAS MINERAL-RICH AND SALTYCategories:Alien Life Also In News Comparative Planetology Habitable Worlds Mars MissionsJan 21, 2020 Presently, Earth is the only known location where life exists in the Universe. This year the Nobel Prize in physics was awarded to three astronomers who proved, almost 20 years ago, that planets are common around stars beyond the solar system. Life comes in various forms, from cell-phone-toting organisms like humans to the ubiquitous micro-organisms that inhabit almost every square inch of the planet Earth, affecting almost everything that happens on it. It will likely be some time before it is possible to measure or detect life beyond the solar system, but the solar system offers a host of sites that might get a handle on how hard it is for life to start. Mars is at the top of this list for two reasons. First, it is relatively close to Earth compared to the moons of Saturn and Jupiter (which are also considered good candidates for discovering life beyond Earth in the solar system, and are targeted for exploration in the coming decade). Second, Mars is extremely observable because it lacks a thick atmosphere like Venus, and so far, there are pretty good evidence that Mars’ surface temperature and pressure hovers around the point liquid water–considered essential for life–can exist. Further, there is good evidence in the form of observable river deltas, and more recent measurements made on Mars’ surface, that liquid water did in fact flow on Mars billions of years ago. Scientists are becoming increasingly convinced that billions of years Mars was habitable. Whether it was in fact inhabited, or is still inhabited, remains hotly debated. To better constrain these questions, scientists are trying to understand the kinds of water chemistry that could have generated the minerals observed on Mars today, which were produced billions of years ago. Salinity (how much salt was present), pH (a measure of how acidic the water was), and redox state (roughly a measure of the abundance of gases such as hydrogen [H2, which are termed reducing environments] or oxygen [O2, which are termed oxidising environments; the two types are generally mutually incompatible]) are fundamental properties of natural waters. As an example, Earth’s modern atmosphere is highly oxygenated (containing large amounts of O2), but one need only dig a few inches into the bottom of a beach or lake today on Earth to find environments which are highly reduced. Recent remote measurements on Mars suggest its ancient environments may provide clues about Mars’ early habitability. Specifically, the properties of pore water within sediments apparently deposited in lakes in Gale Crater on Mars suggest these sediments formed in the presence of liquid water which was of a pH close to that of Earth’s modern oceans. Earth’s oceans are of course host to myriad forms of life, thus it seems compelling that Mars’ early surface environment was a place contemporary Earth life could have lived, but it remains a mystery as to why evidence of life on Mars is so hard to find. source: astrobio.net/alien-life/mars-water-was-mineral-rich-and-salty/

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