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Permalink Reply by Dr. Krishna Kumari Challa on May 3, 2016 at 9:41am

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http://www.scientificamerican.com/article/which-came-first-on-earth...

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Our solar system is exceptional because of one thing, Saturn. In the vast majority of solar systems the inner rocky planets are pushed into the parent star by the Jupiter equivalents. The “Hot Jupiters” as they are called then eventually merge with the parent star as well leaving the ice giants similar to Neptune and Uranus as what we first started calling “Super Earths” behind. Saturn stopped this process from happening by creating a tug on Jupiter preventing it from its suicidal march into the sun.

We are exceptional because we have long lived rocky planets. That is a very rare thing in the Universe.

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Paucity of phosphorus hints at precarious path for extraterrestrial life

Work by Cardiff University astronomers suggests there may be a cosmic lack of a chemical element essential to life. Dr. Jane Greaves and Dr. Phil Cigan will present their results at the European Week of Astronomy and Space Science in Liverpool.

Greaves has been searching for phosphorus in the universe, because of its link to life on Earth. If this element—with the chemical code P—is lacking in other parts of the cosmos, then it could be difficult for extra-terrestrial life to exist.

She explains: "Phosphorus is one of just six chemical elements on which Earth organisms depend, and it is crucial to the compound adenosine triphosphate (ATP), which cells use to store and transfer energy. Astronomers have just started to pay attention to the cosmic origins of phosphorus and found quite a few surprises. In particular, P is created in supernovae—the explosions of massive stars—but the amounts seen so far don't match our computer models. I wondered what the implications were for life on other planets if unpredictable amounts of P are spat out into space and later used in the construction of new planets."

The team used the UK's William Herschel Telescope, sited on La Palma in the Canary islands, to observe infrared light from phosphorus and iron in the Crab Nebula, a supernova remnant around 6500 light years away in the direction of the constellation of Taurus.

Cigan, an expert on these stellar remnants, says: "This is only the second such study of phosphorus that has been made. The first looked at the Cassiopeia A (Cas A) supernova remnant, and so we are able to compare two different stellar explosions and see if they ejected different proportions of phosphorus and iron. The first element supports life, while the second is a major part of our planet's core".

The astronomers struggled with foggy nights at the telescope, back in November 2017, and are only just starting to get scientific results from a few hours of data.

Cigan cautions "These are our preliminary results, which we extracted only in the last couple of weeks! But at least for the parts of the Crab Nebula we were able to observe so far, there seems to be much less phosphorus than in Cas A. The two explosions seem to differ from each other, perhaps because Cas A results from the explosion of a rare super-massive star. We've just asked for more telescope time to go back and check, in case we've missed some phosphorus-rich regions in the Crab Nebula."

The preliminary results suggest that material blown out into space could vary dramatically in chemical composition. Greaves remarks: "The route to carrying phosphorus into new-born planets looks rather precarious. We already think that only a few phosphorus-bearing minerals that came to the Earth—probably in meteorites—were reactive enough to get involved in making proto-biomolecules.

'If phosphorus is sourced from supernovae, and then travels across space in meteoritic rocks, I'm wondering if a young planet could find itself lacking in reactive phosphorus because of where it was born? That is, it started off near the wrong kind of supernova? In that case, life might really struggle to get started out of phosphorus-poor chemistry, on another world otherwise similar to our own."

The researchers now plan to continue their search, to establish whether other supernova remnants also lack phosphorus, and whether this element, so important for complex life, is rarer than we thought.

Source: Royal Astronomical Society

Permalink Reply by Dr. Krishna Kumari Challa on August 9, 2016 at 2:06pm

Hellish Venus Might Have Been Habitable for Billions of Years

A team of astronomers think the torrid and toxic world was once a cozy home for potential life

http://www.scientificamerican.com/article/hellish-venus-might-have-...

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Hydrogen volcanoes may increase habitability of exoplanets

Does TRAPPIST-1 have three potentially habitable planets or four? New research by scientists at Cornell University led by Ramses Ramirez, indicates that number four is a possibility if there are hydrogen volcanoes on it. According to the astronomers, worlds where hydrogen spews out from volcanic vents could enjoy a greenhouse effect that would warm their atmosphere enough to sustain life.

When the discovery of seven Earthlike planets with three occupying the habitable zone of the Jupiter-sized red dwarf star TRAPPIST-1 was announced last week, it caused a minor sensation in the scientific world. The habitable, or Goldilocks, zone is that band of orbits where it is not too hot and not too cold, but just right for a planet to potentially have liquid water on its surface.

In our solar system, the habitable zone extends from about the orbit of Venus to slightly beyond that of Mars, so three planets in the system could potentially support life and one definitely does. While exoplanets orbiting other stars have been found in their local habitable zone, finding seven Earth-like planets revolving around a small, cold dwarf star with three in the right place is the astronomical equivalent of drawing to an inside straight.

Not surprisingly, this makes scientists think that there may be more habitable planets than previously believed and the new Cornell study indicates that the habitable zone of TRAPPIST-1 and other stars may extend farther out than previously thought.

One thing that keeps the Earth at a habitable temperature is the greenhouse effect of water vapor, carbon dioxide, and other gases in the atmosphere. Remove their effect and the surface temperatures would be more like Mars. According to Cornell, if an otherwise icy exoplanet had an atmosphere of hydrogen, carbon dioxide, and water vapor, it, too, would enjoy a greenhouse effect, which could warm it enough for liquid water to exist and effectively extend the habitable zone by 30 to 60 percent. In addition, the planet would contain biosignatures, such as methane or ozone, in its atmosphere that our next generation of space telescopes could detect.

The only snag is that hydrogen is a gas that does not like to stick around. In our solar system, only gas giants like Jupiter have enough gravity to keep most of their hydrogen in the atmosphere. On small rocky worlds like Earth, any hydrogen simply floats up and off into space. Cornell's research indicates that if an Earth-like planet had volcanoes that belched out hydrogen at a steady rate, it could maintain a high enough level of the gas in the atmosphere to sustain a greenhouse effect.

If such a planet existed in our solar system, it could orbit as far as 2.4 times the distance from the Sun as the Earth, which would place it roughly in the asteroid belt between Mars and Jupiter. For TRAPPIST-1, if the outermost seventh planet has hydrogen volcanoes, it means that the system has four potentially habitable worlds instead of three.

"Finding multiple planets in the habitable zone of their host star is a great discovery because it means that there can be even more potentially habitable planets per star than we thought," says Lisa Kaltenegger, Cornell professor of astronomy and director of the Carl Sagan Institute. "Finding more rocky planets in the habitable zone – per star – increases our odds of finding life."

The results were published in The Astrophysical Journal Letters,

Source:

Cornell University

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Permalink Reply by Dr. Krishna Kumari Challa on May 6, 2020 at 7:13am

Exoplanets: How we'll search for signs of life

https://phys.org/news/2020-05-exoplanets-life.html?utm_source=nwlet...

A framework, called a "detectability index" which may help prioritize exoplanets that require additional study. 

 Donald M Glaser et al, Detectability of Life Using Oxygen on Pelagic Planets and Water Worlds, The Astrophysical Journal (2020). DOI: 10.3847/1538-4357/ab822d

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Possible atmospheric destruction of a potentially habitable exoplanet

Astrophysicists studying a popular exoplanet in its star's habitable zone have found that electric currents in the planet's upper atmosphere could create sufficient heating to expand the atmosphere enough that it leaves the planet, likely leaving the planet uninhabitable.

Until now, planetary scientists have thought that a habitable planet needs a strong magnetic field surrounding it to act as a shield, directing ionized particles, X-rays and ultraviolet radiation in the stellar wind around and away from its atmosphere.

That's what happens on Earth, preventing dangerous radiation from reaching life on the surface, and what does not occur on Mars, which now lacks a global magnetic field, meaning any initial inhabitants of the red planet will probably need to live in underground caves and cavities for solar wind protection.

The new research, by Ofer Cohen of the Lowell Center for Space Science and Technology at the University of Massachusetts Lowell and colleagues, published in The Astrophysical Journal, examined whether electric currents generate in the ionosphere of the exoplanet Trappist-1e would lead to enough heating and expansion of the atmosphere that it might dissipate away from the planet's gravity and be lost to space.

TRAPPIST-1e is a cool M-dwarf star in the constellation Aquarius about 41 light-years from Earth. Its planetary system, which has seven observed exoplanets, is the most closely studied system outside our own solar system.

Three of these planets are in the star's habitable zone, with surface temperatures where liquid water could exist. Because M-dwarfs, which comprise about 70% of stars in the universe, are cooler than our sun, these zones are much closer to these stars.

Trappist-1e, an exoplanet discovered in 2017, orbits just 0.028 AU from its star (where 1 AU is the average distance from the sun to Earth; Mercury orbits at about 0.4 AU). Rocky and Earth-like, its average density is only 2% larger than Earth's, and its surface gravity 82%. What's more, it has a equilibrium temperature of 246 Kelvin, just 9 K below Earth's.

These properties make Trappist-1e one of the most interesting of all exoplanets discovered to date. But does it have an atmosphere? Because it is located much closer to its star, atmospheric stripping by stellar winds should be much stronger than, say, Mercury's, which has no atmosphere.

Earlier work showed that stellar winds from Trappist-1 could potentially strip a hydrogen-rich atmosphere from its exoplanets by photoevaporation, but modeling complexity means these planets could have a host of atmospheric environments.

But another potential stripping mechanism is when external charged stellar winds impact the ionized upper atmosphere. In earlier work Cohen and others found that when the conductance and impedance of each are similar in magnitude, the three Trappist exoplanets e, f and g, could experience direct current (DC) resistive heating of up to 1 watt per square-meter, 1% of the incoming solar irradiance and 5 to 15 times the stellar energy from extreme-ultraviolet radiation. Such "Joule heating" could potentially strip the atmosphere from any of these planets. (On Earth, Joule heating is about 0.01 W/m².)

Now Cohen and colleagues have modeled a second phenomenon that could also impact Trappist-1 planetary atmospheres: heating due to the planet's motion itself. Alternating electric currents (AC) will be generated in the planet's upper atmosphere as it encounters a changing stellar magnetic field as the planet orbits its star (Faraday's law of induction).

Close-in planets orbit very quickly—Trappist-1e's orbital period is just 6.1 Earth-days—and the rapid change in the background magnetic field leads to the generation of strong ionospheric currents that dissipate and create potentially very high heating, which they call voltage-driven Joule heating.

Because astronomers do not have measurements of Trappist-1's stellar wind and magnetic field, the group used validated physics-based models to calculate its energy output, its solar wind and the changing magnetic field at the Trappist-1e distance. Using reasonable estimates for the width of Trappist 1e's ionosphere, its conductance and the magnitude of the changing magnetic field, their results show that the Joule heating energy flux in the upper atmosphere of the planet would vary from 0.01 to 100 W/m², a significant amount of heating that may be greater than that due to extreme-ultraviolet and 1 to 10% of the stellar energy flux at the planet.

They conclude that such intense values could cause a strong atmospheric escape and "could lead to a rapid loss of the atmosphere." It means astrobiologists and others should take Joule heating into account when considering an exoplanet's habitability.

"It is likely that both mechanisms operate together in close-in exoplanets," said Cohen. "Therefore, our work (and our solar system knowledge) may suggest that exoplanets located very close to the star are likely bare planets with no atmosphere."

Cohen notes that their work has a political element, as many teams are investigating the atmospheres of Trappist-1 planets. The James Webb Space Telescope (JWST) has already started to observe this system's planetary atmospheres (finding none), and there are plans to do more. "This may be a bit of a waste of resources if there is no atmosphere to study," said Cohen.

 Ofer Cohen et al, Heating of the Atmospheres of Short-orbit Exoplanets by Their Rapid Orbital Motion through an Extreme Space Environment, The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad206a

https://phys.org/news/2024-02-atmospheric-destruction-potentially-h...

Permalink Reply by Dr. Krishna Kumari Challa on June 20, 2023 at 9:04am

***Plate tectonics not required for the emergence of life
Scientists have taken a journey back in time to unlock the mysteries of Earth’s early history, using tiny mineral crystals called zircons to study plate tectonics billions of years ago. The research sheds light on the conditions that existed in early Earth, revealing a complex interplay between Earth’s crust, core, and the emergence of life.

Plate tectonics allows heat from Earth’s interior to escape to the surface, forming continents and other geological features necessary for life to emerge. Accordingly, there has been the assumption that plate tectonics is necessary for life.
However, a paper published in Nature examining plate tectonics from a time 3.9 billion years ago, when scientists think the first traces of life appeared on Earth shows a different view. The researchers found that mobile plate tectonics was not occurring during this time. Instead, they discovered, Earth was releasing heat through what is known as a stagnant lid regime. The results indicate that although plate tectonics is a key factor for sustaining life on Earth, it is not a requirement for life to originate on a terrestrial-like planet.
Researchers found that there wasn’t plate tectonics when life is first thought to originate, and that there wasn’t plate tectonics for hundreds of millions of years after. The data suggests that when scientists are looking for exoplanets that harbor life, the planets do not necessarily need to have plate tectonics.
Stagnant lid tectonics: an alternative to plate tectonics

Earth is a heat engine, and plate tectonics is ultimately the release of heat from Earth. But stagnant lid tectonics—which results in cracks in Earth’s surface—are another means allowing heat to escape from the interior of the planet to form continents and other geological features.

Plate tectonics involves the horizontal movement and interaction of large plates on Earth’s surface. Tarduno and his colleagues report that, on average, plates from the last 600 million years have moved at least 8,500 kilometers (5280 miles) in latitude. In contrast, stagnant lid tectonics describes how the outermost layer of Earth behaves like a stagnant lid, without active horizontal plate motion. Instead, the outer layer remains in place while the interior of the planet cools. Large plumes of molten material originating in Earth’s deep interior can cause the outer layer to crack. Stagnant lid tectonics is not as effective as plate tectonics at releasing heat from Earth’s mantle, but it can still lead to the formation of continents.

Early Earth was not a planet where everything was dead on the surface. Things were still happening on Earth’s surface; This new research indicates they just weren’t happening through plate tectonics. Researchers had at least enough geochemical cycling provided by the stagnant lid processes to produce conditions suitable for the origin of life.

While Earth is the only known planet to experience plate tectonics, other planets, such as Venus, experience stagnant lid tectonics.
People have tended to think that stagnant lid tectonics would not build a habitable planet because of what is happening on Venus. Venus is not a very nice place to live: it has a crushing carbon dioxide atmosphere and sulfuric acid clouds. This is because heat is not being removed effectively from the planet’s surface.

Without plate tectonics, Earth may have met a similar fate. While the researchers hint that plate tectonics may have started on Earth soon after 3.4 billion years, the geology community is divided on a specific date.

Scientists think plate tectonics, in the long run, is important for removing heat, generating the magnetic field, and keeping things habitable on our planet. But, in the beginning, and a billion years after, the data indicates that we didn’t need plate tectonics.

John A. Tarduno, Rory D. Cottrell, Richard K. Bono, Nicole Rayner, William J. Davis, Tinghong Zhou, Francis Nimmo, Axel Hofmann, Jaganmoy Jodder, Mauricio Ibañez-Mejia, Michael K. Watkeys, Hirokuni Oda, Gautam Mitra. Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism. Nature, 2023; 618 (7965): 531 DOI: 10.1038/s41586-023-06024-5