- 3194 - PLANETS - how to discover life? The Deuterium / Hydrogen ratio is measured by exoplanet hunters to determine some of the atmospheric and hydrological history of new exoplanets. This will improve our understanding of the chemistry taking place on exoplanets and refine atmospheric models. What does it take for a planet to be habitable.
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- Thousands of exoplanets have been discovered in the past several years. Planet hunter satellites like “TESS” and ‘Kepler“, as well as numerous ground-based efforts, have pushed the field and we are starting to get a total number of planets that will allow us to perform effective statistical analysis on some of them.
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- Not only do the detected number of planets show us how common they are; it exposes our lack of understanding about how planets form, what conditions are present, and when planets may be habitable.
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- The “transit detection” of an exoplanet primarily yields the orbital period, or the length of a year on the planet, and the relative size of the planet with respect to the star. The next steps are to characterize the planet. This usually requires follow up studies, using different observational strategies and more powerful telescopes.
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- After studying the occurrence, sizes, orbital periods, and the amount of light they receive, the composition of the atmospheres of exoplanets can provide much insight into our understanding of these new worlds.
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- The composition of the atmospheres can be revealed by observing the palets using space-based telescopes, such as the “Hubble Space Telescope“, or from the ground using observatories like the “Very Large Telescope” or“Keck“.
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- These remote observations rely on interaction of the molecules in the atmosphere with light, and are highly specific to the conditions in the atmosphere, serving as a strong diagnostic for both the planet’s composition and its temperature.
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- However, not all molecules are equally visible and the light from exoplanets are very faint. We are only able to see the brightest molecules, such as water, methane, carbon monoxide, sodium, as well as a number of metal-oxides.
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- For the rest of the atmosphere, the planets in our solar system provide a first start to what may be present, but scientists strongly rely on chemical and physical models to assess what may be hidden from their spectroscopic studies.
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- The detectable molecules can teach us many things about the conditions in the atmosphere. The carbon to oxygen (C/O) ratio, inferred from the abundance of carbon monoxide, carbon dioxide, methane, and water, essentially indicates whether the chemistry in the atmosphere is oxygen or carbon dominated.
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- These are different chemical end members, and lead to very different environments. Titan’s atmosphere for instance is carbon dominated, leading to a hazy world with hydrocarbon lakes.
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- Mars’ atmosphere is an example of a C/O ratio of less than 1. As the C/O ratio can also be determined in protoplanetary disks, this is a valuable ratio that may link the birthplace of planets to their current state.
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- Another stochiometric ratio that has proven to be very insightful in the solar system, is that of hydrogen (H), the most common element in the universe, to its slightly heavier isotope, deuterium (D). Known as the D/H ratio, it can provide a glimpse into the history and planet and its atmosphere.
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- The D/H ratio was originally set as part of the Big Bang at about 1 / 8700 , or, 8700 atoms of hydrogen for every one of deuterium. There are not many natural processes that have changed that ratio over time, with the exception of some active processes in stars.
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- That 1/8700 ratio is then passed on to planets as they begin to form, yet the initial endowment value can differ across the formation region in the nebula, where stars and planets form.
- This is because of the different temperatures at which hydrogen and deuterium containing molecules freeze out. Particularly for the extremely cold regions, the amount of deuterium is substantially higher. Planets can therefore have very different primordial D/H values depending on when and how they form. Our solar system is a good example where that original ratio was in place during the planetary formation process.
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- The higher deuterium content of primordial ices is which is why the ice giant Uranus and Neptune have a higher D/H ratio than Jupiter and Saturn. After the planets were formed, though, the ratio on some planets changed.
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- For the rocky planets, it is believed that they received their water from asteroids and comets, which formed at very different locations in the nebula as those planets, resulting in higher deuterium content in the atmospheres of Earth, Venus, and Mars.
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- Subsequently, that ratio was increased even more by significant water loss. This effect, which can be most starkly seen on Mars and Venus, can be understood as following. As much of the hydrogen and deuterium in planetary atmospheres is tied up in water, which is easily destroyed by sunlight, resulting in elemental oxygen and hydrogen.
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- That hydrogen, floating high in the atmosphere, is then susceptible to being accelerated into space by the solar wind, then flying fast enough to escape the gravity of the terrestrial planets.
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- With that loss of hydrogen, the water molecule cannot reform, and the planet is left with a lower total quantity of water. Over the course of billions of years, this process, if it continues, can cause a significant drop in the water content of a planet’s atmosphere.
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- However, there is one confounding factor in this story of lost water – deuterium, which is approximately twice as heavy as elemental hydrogen, is much less likely to be blown into space. Therefore, any “heavy” water molecule that is split in the atmosphere is much less likely to lose its deuterium atom than a normal water molecule is to lose its regular hydrogen atom. Over billions of years, this increases the D/H ratio in those atmospheres.
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- To be able to investigate the D/H ratio on exoplanets researchers had to pull information from huge spectroscopic databases. The databases have been incorporated into a tool they built called the Planetary Spectrum Generator (PSG).
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- PSG is an online tool that allows the simulation spectra of exoplanets, taking into consideration all elements of the calculations (the Solar/stellar spectrum, the planets’ surface and atmosphere, as well as absorption by the Earth’s atmosphere and the specifics of the telescope used).
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- Using the Planetary Spectrum Generator to simulate the interaction of the exoplanet Trappist 1b with the light of its star while passing in front of it, the researchers have investigated the possibility of detecting the D/H ratio using the soon-to-be-launched James Webb Space Telescope. They demonstrated that for atmospheres rich in water, the D/H ratio could be constrained by observing a few transits of the planet in front of its host star.
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- With a better understanding of the D / H ratio, exoplanet hunters should be able to determine some of the atmospheric and hydrological history of these new planets. This will improve our understanding of the chemistry taking place on exoplanets and refine atmospheric models.
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- Ultimately, we may enable a better grip on what it takes for a planet to be habitable.
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------------------------------See more reviews about planets:
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- 3173 - PLANETS - travel time to each? So, we find a new planet, so what? We better be worrying about the planet we have. In 500,000 years our oceans will have evaporated due to the Sun turning into a Red Giant then a Planetary Nebulae. That is how much time we’ve got, if no other disaster hits us sooner. Whatever we figure out let’s hope they do the math
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-- 3154 - PLANETS - which one to move to? Venus is too toxic, hot, and inhospitable. Mars is deadly too. Just as Venus is extremely hot, Mars is frigid cold. Venus has a thick, poisonous atmosphere, but Mars has a paper-thin one. Mars has all that radiation exposure to deal with. How do we choose?
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- 3148 - PLANETS - in our Solar System? The order of the planets in the solar system, starting nearest the sun and working outward is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and then the possible Planet Nine.
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- 3043 - PLANETS - how many are out there? We are content in thinking we have discovered the planets in our solar system. We have eight planets circling he Sun. Nine if you count Pluto. Then more planetoids are being discovered orbiting farther from the Sun than Pluto.
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- 2666 - PLANET NINE . I always thought that Pluto was Planet Nine. Then Pluto got demoted to a “ Dwarf Planet”. Now astronomers are telling us there are many more dwarf planet out there, and also one “real planet nine“. We still have more to discover in our own Solar System.
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- 2647 - PLANET NINE - may be a blackhole? One theory is that it is a “blackhole“. Maybe there is an ancient, grapefruit-size blackhole hiding out in our solar system. This tiny, heavy object might in fact take the place of a theoretical planet that might be tugging on other objects in our solar system. This so-called “Planet 9” could explain the math calculations and why we cannot find it.
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- 2448 - PLANET NINE - could it be a blackhole? Maybe there is an ancient, grapefruit-size blackhole hiding out in our solar system. This tiny, heavy object might in fact take the place of a theoretical planet that might be tugging on other objects in our solar system.
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- 965 - The chemistry of planet formation. . Astronomers are using 2 different methods to find these planets. The “Transit Method” and the “Radial Velocity Method”. With both of these methods we have to be lucky and happen to be viewing the planet orbits edge-on. If we are viewing the orbits face-on we can never discover planets with these methods.
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- 935 - Planet temperatures.
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- 928 - Planet formation. . Astronomers have found more than 4,000 planets in other solar systems. How they formed and how they contain such wide diversity is a new mystery. We thought we had a design for planet formation that matched our Solar System. In contrast, other solar systems are so diverse and supposedly formed out of chaos.
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- June 20, 2021 PLANETS - how to discover life? 3185
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--------------------- --- Monday, June 21, 2021 ---------------------------
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