Tuesday, February 28, 2023

WATER ON PLANETS - is there life there?

 -  3893  -  WATER  ON  PLANETS  -  is there life there?    This research adds another link in the chemical chain reaching from the Big Bang to life.  How do organic molecules in space gain nitrogen atoms, which are critical components to amino acids, DNA, and life?    This work shows how the materials for life are wrapped up in the formation of stars, solar systems, and planets.


--------------  3893  -   WATER  ON  PLANETS  -  is there life there?

-    Among other discoveries made by the “Curiosity rover” exploring Mars is rippled rock textures suggesting lakes existed in a region of ancient Mars that scientists expected to be drier. 

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-    When NASA’s “Curiosity rover” arrived at the “sulfate-bearing unit” last fall, scientists thought they’d seen the last evidence that lakes once covered this region of Mars. That’s because the rock layers here formed in drier settings than regions explored earlier in the mission. The area’s sulfates, salty minerals, are thought to have been left behind when water was drying to a trickle.

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-   Curiosity’s team was surprised to discover the mission’s clearest evidence yet of ancient water ripples that formed within lakes. Billions of years ago, waves on the surface of a shallow lake stirred up sediment at the lake bottom, over time creating rippled textures left in rock.

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-    Curiosity rover climbed through thousands of feet of lake deposits and never saw evidence like this and now we found it in a place we expected to be dry.  Since 2014, the rover has been ascending the foothills of “Mount Sharp”, a 3-mile-tall mountain that was once laced with lakes and streams that would have provided a rich environment for microbial life, if any ever formed on the Red Planet.

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-    Billions of years ago, waves on the surface of a shallow lake stirred up sediment at the lake bottom. Over time, the sediment formed into rocks with rippled textures that are the clearest evidence of waves and water that NASA’s Curiosity Mars rover has ever found.

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-    “Mount Sharp” is made up of layers, with the oldest at the bottom of the mountain and the youngest at the top. As the rover ascends, it progresses along a Martian timeline, allowing scientists to study how Mars evolved from a planet that was more Earth-like in its ancient past, with a warmer climate and plentiful water, to the freezing desert it is today.

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-    This rock layer is so hard that Curiosity hasn’t been able to drill a sample from it despite several attempts.  Lower down the mountain, on “Vera Rubin Ridge,” Curiosity had to try three times before finding a spot soft enough to drill.

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-   At the bottom of this valley, called “Gediz Vallis”, is a mound of boulders and debris that are believed to have been swept there by wet landslides billions of years ago.

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-    Wind carved the valley, but a channel running through it that starts higher up on Mount Sharp is thought to have been eroded by a small river. Scientists suspect wet landslides also occurred here, sending car-size boulders and debris to the bottom of the valley.

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-    Because the resulting debris pile sits on top of all the other layers in the valley, it’s clearly one of the youngest features on Mount Sharp. Curiosity got a glimpse of this debris at Gediz Vallis Ridge twice last year but could only survey it from a distance.

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-    Curiosity used its “ChemCam instrument” to view Gediz Vallis Ridge, spotting boulders that are thought to have been washed down in an ancient debris flow. One reason scientists are interested in this ridge is because it includes boulders which originated much higher up on Mount Sharp, where Curiosity won’t be able to reach.

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-   One more clue within the Marker Band that has fascinated the team is an unusual rock texture likely caused by some sort of regular cycle in the weather or climate, such as dust storms. Not far from the rippled textures are rocks made of layers that are regular in their spacing and thickness.

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-    This kind of rhythmic pattern in rock layers on Earth often stems from atmospheric events happening at periodic intervals. It’s possible the rhythmic patterns in these Martian rocks resulted from similar events, hinting at changes in the Red Planet’s ancient climate.

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-    The wave ripples, debris flows, and rhythmic layers all tell us that the story of wet-to-dry on Mars wasn’t simple.    Mars’ ancient climate had a wonderful complexity to it, much like Earth’s.

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-    After Mars,  astronomers are also searching for water in exoplanets. There is a population of ocean-world exoplanets, “water-worlds”, around   M-dwarf stars. Water-worlds, also known as ocean worlds, are planets that possess bodies of liquid water either directly on its surface, such as Earth, or somewhere beneath it, such as Jupiter’s moon, Europa and Saturn’s moon, Enceladus.

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-   Super-Earths and sub-Neptunes with hydrogen (H) / helium (He) atmospheres were searched for close-in exoplanets orbiting M-dwarf stars in an attempt to calculate their total water mass.

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-    Those planets containing a significant fraction of their total mass         (10-50%) in water might be extremely rare or nonexistent.  This would imply planet formation is fairly uniform across a wide range of stellar masses, producing the same type of planets: terrestrial worlds that acquired a few percent by mass of hydrogen gas from the accretion disc around the young star.

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-    James Webb Space Telescope observations of sub-Neptunes  may suggest that large mass fractions of water in their atmosphere ( steam atmospheres)  that the planets are indeed water-worlds.   However, if the atmospheres are consistent with being dominated by H/He, then it suggests that they are not water-worlds.

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-  The raw materials for life form early on in “Stellar Nurseries” doesn’t appear from nothing. Its origins are wrapped up in the same long, arduous process that creates the elements, then stars, then planets. Then, if everything lines up just right, after billions of years, a simple, single-celled organism can appear, maybe in a puddle of water on a hospitable planet somewhere.  You think?

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-    Stars form in Giant Molecular Clouds, vast stellar nurseries that can be hundreds of light-years across and contain millions of solar masses of gas and dust. These nurseries contain mostly hydrogen, the stuff of star formation. But they also contain carbon, and the carbon, hydrogen, and some other atoms combine to form complex molecules that are the rudiments of life.

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-    Some important organic molecules can form in these stellar nurseries. Life requires organic chemistry, and all the life we know of is carbon-based. That means carbon and its ability to form large, complex and durable molecules that can branch off into rings and chains is at the heart of life.

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-   Each carbon atom can form chemical bonds with four other atoms, and that means that carbon-based molecules can contain thousands of atoms. Unsurprisingly, carbon is present in all organic matter.

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-     In nature, chemistry evolved over time. The Universe began with only hydrogen and helium (and a little lithium.)  Over time, more elements formed and that allowed more complex chemicals to form. Once carbon was synthesized in stars and spread out into the Universe, the stage was set for truly complex chemistry.

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-   In the present-day Universe, all of the elements that can occur naturally already occur. The stage is set for chemistry to work its magic, creating all kinds of organic compounds, even in gas clouds.

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-     That’s what a team of researchers sees happening in the Taurus Molecular Cloud,  a stellar nursery about 440 light-years away. It’s called a molecular cloud because the hydrogen atoms are paired together into molecules (H2.) Scientists observe the Cloud in detail because it’s a stellar nursery.

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-   It’s probably the closest star-forming region to Earth, and astronomers study it extensively. Telescopes like the Herschel Space Observatory have taken its portrait many times.

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-   There are surprisingly large amounts of “five-membered ring compounds.” Each of these compounds is built on a pentagon of carbon atoms.  Finding complex chemicals in a very cold environments, around -263 degrees Celsius is unexzpected.   That’s only 10 degrees above absolute zero. The cold temperatures are what allow the clouds to collapse and form stars. If they were warmer, there would be outward pressure that inhibited the collapse. But chemical reactions normally require energy, so finding so many of them in frigid TMC-1 is puzzling.

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-    In 2021, researchers found another chemical that helps explain the presence of the pentagon-shaped compounds without any energy source. It’s called ortho-benzene, and it’s a small molecule based on six carbon atoms instead of five. It also has four hydrogen atoms. Its key property is that it can easily react with other molecules without needing a lot of heat.

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-   But just because ortho-benzene has the potential to create the pentagon-shaped compounds in TMC-1 doesn’t mean that it is creating them.  Researchers used UV light from the synchrotron in lab experiments to identify chemical compounds that might be created in stellar nurseries.

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-   They saw that ortho-benzene, the same chemical found in the starless core TMC-1, combined with another type of chemical called methyl radicals to form more complex molecules.   It’s a good hint, but it didn’t yet explain the presence of the pentagon-shaped molecules they found in TMC-1.

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-    Next, the researchers turned to computer models of stellar nurseries spanning several light-years in space. Those models produced the same mix of organic molecules that astronomers observed in TMC-1 using telescopes. It appears that ortho-benzene is capable of driving the production of the pentagon-shaped fulvenallene and 1- and 2-ethynylcyclopentadiene.         This compound will be on your next spelling test. 

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            February 28, 2023       WATER  ON  PLANETS  -  is there life there?            3893                                                                                                                         

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