- 3329 - LIFE - on Mars and other planets? Exoplanets exceed the compositional spread of >4,000 nearby main sequence stars and their unique silicate compositions are unlikely to reflect variations in parent star compositions. These polluted white dwarfs reveal greater planetary variety in our solar neighborhood with consequently unique planetary accretion and differentiation paths that have no direct counterparts in our Solar System.
--------------------- 3329 - LIFE - on Mars and other planets?
- As of November , 2021, “1,909 MARTIAN SOLS (days)” on Mars a lot has happened. The robot’s drill stopped working while Curiosity was on Mars’ Vera Rubin ridge at the base of Mount Sharp.
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- The rover had collected a sample of Martian dirt. Instead of dropping the sample into one of the cups in the sample carousel, they dropped it into a cup pre-filled with a chemical mixture. The molecules released from the cup were then trapped and analyzed, revealing organic molecules on Mars that no space agency had previously detected.
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- Curiosity rover landed on Gale Crater on August 6, 2012, and has been roaming the Martian terrain ever since. Perseverance rover landed on Mars on February 18, 2012. The mission aims to search for signs of ancient life on Mars.
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- Although Mars is cold and barren today, it may have once had flowing rivers and pooling lakes. Scientists believe that the planet may have once been habitable and possibly hosted ancient microbial life during its early history.
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- To search for that life, scientists look for biosignatures on Mars which are certain chemicals that may have been produced by some form of past or present life. Scientists also search for organic molecules. Organic molecules are considered the building blocks of life on Earth.
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- In March 2017, Curiosity collected dirt samples from the Bagnold Dune on Mars. Because Curiosity’s drill was out of service at the time, the team decided to conduct a first-of-its-kind experiment. The rover has 74 cups inside its belly, and nine of those cups are pre-filled with a chemical mixture.
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- In the regular process they collect the sample with the robot arm of Curiosity, dropping it into one of those cups. But in this case, they dropped the sample into one of the fields filled with chemical reagents.
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- The team did not expect the sample to be rich in well-preserved organic molecules since ionizing radiation had long battered the ancient soil. But after testing the sample with the chemical mixture, the team behind the mission identified organic molecules never before seen on Mars.
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- The two most significant molecules were benzoic acid and ammonia. Although these molecules are not biosignatures, they are good indicators of the presence of biosignatures.
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- But since Curiosity took the sample from Gale Crater, which is hypothesized to have had water in the past, then the molecules could be possible indicators of past habitability.
The team of scientists behind the study are awaiting the launch of the European Space Agency’s ExoMars mission in 2022 to collect more samples from Mars.
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- The “Perseverance rover” is also collecting samples from the Martian surface, which will later be brought to Earth to be analyzed inside a lab. The wet chemistry experiments on the Sample Analysis at Mars instrument on NASA’s Curiosity rover were designed to facilitate gas chromatography mass spectrometry analyses of polar molecules such as amino acids and carboxylic acids.
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- Chemically derivatized experiment on Mars has expanded the inventory of molecules present in Martian samples and demonstrated a powerful tool to further enable the search for polar organic molecules of biotic or prebiotic relevance.
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- It is not just Mars that is seeing the search for life. Astronomers are studying the farthest stars. They are studying the similarities in composition between a star and its rocky planets, finding a strong correlation between the elements that formed both objects and helping scientists in their search for habitable Earth-like rocky exoplanet
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- This study first selected 32 roughly Earth-size exoplanets to examine. They then narrowed it down to 22 exoplanets that they knew for sure to be rocky planets so that they could be somewhat confident of their composition.
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- It's hard to gather data on exoplanets most of the time, when looking at distant exoplanets, scientists wait for the planet to transit in front of their stars from their observing view from a space-based or ground-based telescope.
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- To infer the potential composition, they look at the light from the star. This corresponds to the different elements that might make up the planet, and scientists can estimate the composition of the exoplanets.
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- The researchers found a correlation between the composition of a star and its planets, but it wasn't one-to-one. Instead, the planets tend to be more metallic than their stars. If the star consists of 30 percent iron, the planet might be 60 percent iron. The researchers aren't for sure yet why this is.
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- A planet's habitability depends largely on the elements that make up the planet. Carbon, hydrogen, oxygen, and nitrogen are considered vital elements for life on a planet.
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- Figuring out the composition of a planet is much more complicated than identifying the elements of a star since planets are a lot dimmer than their host stars, and therefore harder to observe.
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- With the European Space Agency's upcoming PLATO (Planetary Transits and Oscillations of stars) mission, which is set to launch in the year 2026, hoping to add more planets to the study sample.
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- Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions.
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- Scientists are estimating the iron-mass fraction of rocky exoplanets from their masses and radii and comparing it with the compositions of their host stars, which we assume reflect the compositions of the proto planetary disks.
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- We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.
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- Scientists have found water in the galaxy, which is located nearly 12.88 billion light years away. This marks the most distant detection of H2O in a star-forming galaxy, and the most comprehensive look at molecular gas that early in the universe’s timeline.
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- Gravitational lensing is a cosmic effect that acts like a giant magnifying lens. When a large object like a star or galaxy passes in front of an object in the background from the observer’s point of view, it distorts and amplifies the light coming from a distant source, making it appear brighter.
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- The molecules in the galaxy are magnified by this other galaxy, making it easier to observe them. Scientists are able to detect H2O as the dust absorbs the ultraviolet radiation from the stars in the galaxy and re-emits it as far-infrared photons, which excites the water molecules. This creates water emissions which scientists can observe.
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- Water is the third most abundant molecule in the universe after molecular hydrogen and carbon monoxide, but scientists were surprised to see water molecules so early on in the universe. The galactic pair are located in an era known as the Epoch of Reionization.
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- The Epoch of Reionization marks the end of the universe’s dark ages and refers to the period in the universe’s timeline when neutral hydrogen was reionized. Before this, neutral hydrogen caused interstellar space to be opaque, blocking light from extending far. This marked the arrival of the first large galaxies.
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- This period took place when the universe was approximately 780 million years old. If the first galaxies were just starting to emerge, the latest discovery has scientists wondering how these molecules were able to form so quickly. How has so much dust and gas accumulated so early on in the universe? The dust is mostly from stars, which are pulsating and giving out their outer layer of dust into the galaxy.
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- These ancient galaxies formed stars at a rate thousands of times that of the Milky Way. Therefore, studying distant galaxies informs scientists just how many stars were being produced and the rate at which gas in early galaxies was converted into stars.
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- Polluted white dwarf stars are dense, compact stars that have recently digested one of the rocky planets that formerly orbited them, and the mineral composition of those planets can be seen, for a time, in the spectral information from the star’s light.
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- By examining polluted white dwarfs in our Solar System’s neighborhood astronomers can learn what those exoplanets had been made of, and how similar they were to Earth or other rocky planets around our Sun.
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- White dwarfs are small, dense zombie stars around the size of Earth, but were once stars not unlike our Sun. When they age, they swell into a red giant, incinerating closely orbiting planets and disrupting the orbits of the survivors.
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- When a red giant sheds its outer layers and leaves behind a white dwarf, the disrupted planets can swing too close to the dense star’s gravity and get pulled to pieces, raining rocky material onto the star.
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- Examining 23 polluted white dwarfs within 650 light years of our Sun and measuring the composition of the stars and the material falling into them. Then they compared those compositions to Earth and the other rocky planets of our Solar System, as well as local asteroids and meteorites.
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- The values of magnesium, calcium, silicon, and iron in those systems differed widely from each other, and from the rocky planets of our Solar System. Astronomers have studied polluted white dwarfs for around 100 years and noted some such stars showed signs of lots of calcium in their spectra.
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- Astronomers knew enough geology to know continental crust, like Earth’s, is high in calcium and theorized that, perhaps, the calcium was coming from the crusts of planets swallowed by the white dwarfs.
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- “Silica is a much better identifier of continental crust than calcium. While the stars they studied had high calcium levels, they had low levels of silicon, and high levels of magnesium, which is more typical of the Earth’s mantle.
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- If a planet is thrown into a star and the whole thing dissolves. The crust is just a tiny fraction, about half a percent by weight of the material.
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- The Earth, our Solar System’s other rocky planets, and chondritic asteroids all show mineral profiles similar to heavier elements in the Sun’s spectra. The idea was that as planets and their stars form out of the same solar nebula, they would share similar mineral compositions.
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- The polluted white dwarfs and their planets do not. It seems to work pretty well in our Solar System. But it might not work so well in other solar systems. The findings are important both for understanding exoplanets and Earth’s place in the larger scheme of planetary bodies in the universe.
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- A wider range of mineral compositions on exoplanets could mean a wider range of behavior, different evolutionary paths to the development of planetary crusts, oceans, and atmospheres, all of which resulted on Earth from the partial melting of the mantle early in our planet’s history.
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- Life as we know it on Earth depends a great deal on continental crust and plate tectonics. Plate tectonics is part of our planet’s water cycle, affects the development of the oceans, and gave life someplace to live other than the oceans. We don’t exist without continental crust. Biological evolution would have taken some other path if there was no dry land.
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- Geologists and planetary science have done a whole lot of experiments with rocks and heat and pressure chambers to try and understand how planets evolve geologically. But all of those experiments used mineral compositions based on Earth and our Solar System’s planets.
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- Researchers can synthesize rocks based on the compositional values detected in these distant exoplanets and heat, stress, compress and otherwise test them to get a sense of how crusts and oceans, and atmosphere might develop on these strange new worlds.
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- Prior studies have hypothesized that some polluted white dwarfs record continent-like granitic crust, which is abundant on Earth and perhaps uniquely indicative of plate tectonics.
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- Studies find no evidence for continental crust, or other crust types, even after correcting for core formation. However, the silicate mantles of such exoplanets are discernable: one case is Earth like, but most are exotic in composition and mineralogy.
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- Because these exoplanets exceed the compositional spread of >4,000 nearby main sequence stars, their unique silicate compositions are unlikely to reflect variations in parent star compositions.
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- Instead, polluted white dwarfs reveal greater planetary variety in our solar neighborhood than currently appreciated, with consequently unique planetary accretion and differentiation paths that have no direct counterparts in our Solar System.
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- Are we unique?
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- November 5, 2021 LIFE - on Mars and other planets? 3329
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--------------------- --- Sunday, November 7, 2021 ---------------------------
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