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  • richardmitnick 10:10 am on July 3, 2022 Permalink | Reply
    Tags: "Webb Telescope Will Look for Signs of Life Way Out There", , , , , , , The TRAPPIST-1 star and planet system.   

    From “The New York Times” : “Webb Telescope Will Look for Signs of Life Way Out There” 

    From “The New York Times”

    July 2, 2022
    Carl Zimmer

    1
    The folded-up James Webb Space Telescope as it was prepared for mounting on a rocket and launch last year at the European spaceport in Kourou, French Guiana. Credit: Chris Gunn/NASA.

    The first question astronomers want to answer about exoplanets: Do they have atmospheres friendly to life?

    This month will mark a new chapter in the search for extraterrestrial life, when the most powerful space telescope yet built will start spying on planets that orbit other stars. Astronomers hope that the James Webb Space Telescope will reveal whether some of those planets harbor atmospheres that might support life.

    Identifying an atmosphere in another solar system would be remarkable enough. But there is even a chance — albeit tiny — that one of these atmospheres will offer what is known as a biosignature: a signal of life itself.

    “I think we will be able to find planets that we think are interesting — you know, good possibilities for life,” said Megan Mansfield, an astronomer at the University of Arizona. “But we won’t necessarily be able to just identify life immediately.”

    So far, Earth remains the only planet in the universe where life is known to exist. Scientists have been sending probes to Mars for almost 60 years and have not yet found Martians. But it is conceivable that life is hiding under the surface of the Red Planet or waiting to be discovered on a moon of Jupiter or Saturn. Some scientists have held out hope that even Venus, despite its scorching atmosphere of sulfur dioxide clouds, might be home to Venusians.

    Even if Earth turns out to be the only planet harboring life in our own solar system, many other solar systems in the universe hold so-called exoplanets.

    In 1995, French astronomers spotted the first exoplanet orbiting a sunlike star. Known as 51 Pegasi b, the exoplanet turned out to be an unpromising home for life — a puffy gas giant bigger than Jupiter, and a toasty 1,800 degrees Fahrenheit.

    In the years since, scientists have found more than 5,000 other exoplanets. Some of them are far more similar to Earth — roughly the same size, made of rock rather than gas and orbiting in a “Goldilocks zone” around their star, not so close as to get cooked but not so far as to be frozen.

    2
    An artist’s rendering of the exoplanet 51 Pegasi b, the first exoplanet ever discovered. Credit: The European Southern Observatory [La Observatorio Europeo Austral][Observatoire européen austral][Europäische Südsternwarte](EU)(CL).

    Unfortunately, the relatively small size of these exoplanets has made them extremely difficult to study, until now. The James Webb Space Telescope, launched last Christmas, will change that, acting as a magnifying glass to let astronomers look more closely at these worlds.

    Since its launch from Kourou, French Guiana, the telescope has traveled a million miles from Earth, entering its own orbit around the sun at L2.

    There, a shield protects its 21-foot mirror from any heat or light from the sun or Earth. In this profound darkness, the telescope can detect faint, distant glimmers of light, including those that could reveal new details about faraway planets.

    The space telescope “is the first big space observatory to take the study of exoplanet atmospheres into account in its design,” Dr. Mansfield said.

    NASA engineers began taking pictures of an array of objects with the Webb telescope in mid-June and will release its first images to the public on July 12.

    Exoplanets will be in that first batch of pictures, said Eric Smith, the program’s lead scientist. Because the telescope will spend relatively little time observing the exoplanets, Dr. Smith considered those first images a “quick and dirty” look at the telescope’s power.

    Those quick looks will be followed by a series of much longer observations, starting in July, offering a much clearer picture of the exoplanets.

    A number of teams of astronomers are planning to look at the seven planets that orbit a star called Trappist-1.

    _______________________________________
    The TRAPPIST-1 star and planet system; the ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile.


    _______________________________________

    Earlier observations have suggested that three of the planets occupy the habitable zone.

    “It’s an ideal place to look for traces of life outside of the solar system,” said Olivia Lim, a graduate student at the University of Montreal who will be observing the Trappist-1 planets starting around July 4.

    Because Trappist-1 is a small, cool star, its habitable zone is closer to it than in our own solar system. As a result, its potentially habitable planets orbit at close range, taking just a few days to circle the star. Every time the planets pass in front of Trappist-1, scientists will be able tackle a basic but crucial question: Do any of them have an atmosphere?

    “If it doesn’t have air, it’s not habitable, even if it’s in the habitable zone,” said Nikole Lewis, an astronomer at Cornell University.

    Dr. Lewis and other astronomers would not be surprised to find no atmospheres surrounding Trappist-1’s planets. Even if the planets had developed atmospheres when they formed, the star might have blasted them away long ago with ultraviolet and X-ray radiation.

    “It’s possible that they could just strip away all of the atmosphere on a planet before it even had a chance to like start forming life,” Dr. Mansfield said. “That’s the first-order question that we’re trying to answer here: whether these planets could have an atmosphere long enough that they’d be able to develop life.”

    A planet passing in front of Trappist-1 will create a tiny shadow, but the shadow will be too small for the space telescope to capture. Instead, the telescope will detect a slight dimming in the light traveling from the star.

    “It’s like looking at a solar eclipse with your eyes shut,” said Jacob Lustig-Yaeger, an astronomer doing a postdoctoral fellowship at the Johns Hopkins Applied Physics Laboratory. “You might have some sense that the light has dimmed.”

    A planet with an atmosphere would dim the star behind it differently than a bare planet would. Some of the star’s light will pass straight through the atmosphere, but the gases will absorb light at certain wavelengths. If astronomers look only at starlight at those wavelengths, the planet will dim Trappist-1 even more.

    The telescope will send these observations of Trappist-1 back to Earth. “And then you get an email that’s like, ‘Hello, your data are available,’” Dr. Mansfield said.

    But the light coming from Trappist-1 will be so faint that it will take time to make sense of it. “Your eye is used to dealing with millions of photons per second,” Dr. Smith said. “But these telescopes, they’re just collecting a few photons a second.”

    Before Dr. Mansfield or her fellow astronomers will be able to analyze exoplanets passing in front of Trappist-1, they will have to first distinguish it from tiny fluctuations produced by the telescope’s own machinery.

    “A lot of the work that I actually do is making sure that we’re carefully correcting for anything weird that the telescope is doing, so that we can see those teeny-tiny signals,” Dr. Mansfield said.

    3
    An artist’s concept of the view from one of the planets in the Trappist-1 system. Credit: M. Kornmesser/European Southern Observatory, via European Pressphoto Agency.

    It is possible that at the end of those efforts, Dr. Mansfield and her colleagues will discover an atmosphere around a Trappist-1 planet. But that result alone will not reveal the nature of the atmosphere. It might be rich in nitrogen and oxygen, like on Earth, or more akin to the toxic stew of carbon dioxide and sulfuric acid on Venus. Or it could be a mix that scientists have never seen before.

    “We have no idea what these atmospheres are made of,” said Alexander Rathcke, an astronomer at the Technical University of Denmark. “We have ideas, simulations, and all this stuff, but we really have no idea. We have to go and look.”

    The James Webb Space Telescope, sometimes called the J.W.S.T., may prove powerful enough to determine the specific ingredients of exoplanet atmospheres because each kind of molecule absorbs a different range of wavelengths of light.

    But those discoveries will depend on the weather on the exoplanets. A bright, reflective blanket of clouds could prevent any starlight from entering an exoplanet’s atmosphere, ruining any attempt to find alien air.

    “It is really hard to distinguish between an atmosphere with clouds or no atmosphere,” Dr. Rathcke said.

    If the weather cooperates, astronomers are especially eager to see if the exoplanets have water in their atmospheres. At least on Earth, water is an essential requirement for biology. “We think that would probably be a good starting point to look for life,” Dr. Mansfield said.

    But a watery atmosphere will not necessarily mean that an exoplanet harbors life. To be sure a planet is alive, scientists will have to detect a biosignature, a molecule or a combination of several molecules that is distinctively made by living things.

    Scientists are still debating what a reliable biosignature would be. Earth’s atmosphere is unique in our solar system in that it contains a lot of oxygen, largely the product of plants and algae. But oxygen can also be produced without life’s help, when water molecules in the air are split. Methane, likewise, can be released by living microbes but also by volcanoes.

    It is possible that there is a particular balance of gases that can provide a clear biosignature, one that cannot be maintained without the help of life.

    “We need extremely favorable scenarios to find these biosignatures,” said Dr. Rathcke. “I’m not saying that it’s not possible. I just think it’s far-fetched. We need to be extremely lucky.”

    Joshua Krissansen-Totton, a planetary scientist at the University of California-Santa Cruz, said that finding such a balance may require the Webb telescope to observe a planet repeatedly passing in front of Trappist-1.

    “If anyone comes forward in the next five years and says, ‘Yes, we’ve found life with J.W.S.T.,’ I’ll be very skeptical of that claim,” Dr. Krissansen-Totton said

    It is possible that the James Webb Space Telescope simply will not be capable of finding biosignatures. That task may have to wait for the next generation of space telescopes, more than a decade away. These will study exoplanets the same way that people look at Mars or Venus in the night sky: by observing starlight reflecting off them against the black background of space, rather than observing them as they pass in front of a star.

    “Mostly, we’ll be doing the very important groundwork for future telescopes,” Dr. Rathcke predicted. “I would be very surprised if J.W.S.T. delivers biosignature detections, but I hope to stand corrected. I mean, this is basically what I’m doing this work for.”

    See the full article here.

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  • richardmitnick 8:09 am on June 25, 2022 Permalink | Reply
    Tags: , , , , , Guest post "Planets on a Magnetic Roller Coaster Ride", If the planet is hosted by a magnetically active star atmospheric outflow could be accelerated leading to faster atmospheric depletion., Mimicing transit observations of the Lyman-alpha line., The authors choose 4 characteristic points and model the outflow of the planet’s atmosphere using a 3D magnetohydrodynamics code., the ESO Belgian robotic Trappist National Telescope at Cerro La Silla Chile altitude 2400 meters.., The hypothetical planet has the properties of TRAPPIST-1e so its size is close to the Earth., The main conclusion is that the shape and velocity of the gas leaving the planet’s atmosphere varies with the conditions of the stellar wind and thus with the orbital position of the planet., The observation of the Lyman-alpha absorption line during a transit of such a planet would show highly temporal variations., The TRAPPIST-1 star and planet system., These planets are probably not a good place to find life.   

    From astrobites : Guest post “Planets on a Magnetic Roller Coaster Ride” 

    Astrobites bloc

    From astrobites

    Jun 24, 2022

    This guest post was written by Fabienne Nail, a first year PhD student at the University of Amsterdam.

    Title: Stellar Winds Drive Strong Variations in Exoplanet Evaporative Outflows and Transit Absorption Signatures

    Authors: Laura M. Harbach, Sofia P. Moschou, Cecilia Garraffo, et al.

    First Author’s institution: University of Southampton, Southampton, UK

    Status: Published in The Astrophysical Journal [open access]

    Aliens, Magnetic Fields, and Atmospheric Loss

    How cool would it be to find aliens? Maybe they exist, and maybe there are already countless interstellar graffiti with the meaning “I was here,” but we, the human species, are unable to see them. Indeed, it seems that we are well on our way to finding signs of extraterrestrial life: we are getting better at understanding the atmospheres of exoplanets, a key in the search for extraterrestrial life. There is just one thing that astronomers tend to steer clear of… magnetic fields.

    Magnetic fields make things just super complicated. However, their impact on the evolution and habitability of a planet is enormous. For example, consider atmospheric loss. Did you know that the Earth’s atmosphere is losing about 3kg of hydrogen per second? It is important to understand how quickly the atmosphere is depleted in an exoplanet to get a time scale on which the emergence of life would be possible. Or could you imagine living on a planet without an atmosphere?

    So far, the focus in exoplanet research has been on hydrodynamic escape. Planets absorb the radiation of the central star high in their atmospheres.. The atmospheric gas heats up, expands, and escapes the planet’s gravity. But reality is much more complicated! For example, what about highly energetic particles from the host star’s stellar wind that hit the upper atmosphere of the planet? The work presented here takes a step in the right direction towards unraveling the effects of stellar winds on atmospheric loss.

    Magnetic Roller Coaster

    The authors’ model the outflow of a hypothetical planet that is orbiting a star which is less massive than the sun (only 8% of the solar mass). The atmosphere of this planet is considered to be hydrogen-rich, as they aim to mimic the planet’s teenage years. As a prototype, the researchers decided to take the properties of TRAPPIST- 1.

    _______________________________________
    The TRAPPIST-1 star and planet system; the ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile.

    _______________________________________

    This system is promising to find extraterrestrial life, as it contains 3 planets that are orbiting in the star’s habitable zone. The hypothetical planet has the properties of TRAPPIST-1e, so its size is close to the Earth. The stellar wind is nothing else than ionized particles (plasma) moving along a magnetic field. To simulate the interaction of this particle storm and the planet’s atmosphere, the authors include the magnetic and plasma environment along the orbit of the planet based on prior predictions of the TRAPPIST-1 system.

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    Figure 1: Stellar wind conditions to which the planet is exposed during its orbit, derived from simulations of the host star TRAPPIST-1. The boundary of the global magnetosphere (GM) is representative of the planet’s environment. The strong variations in magnetic field strengths (top) and their influence on the velocity of the plasma (middle) and its density (bottom) are clearly visible.

    The variations of this environment along one orbit can be extreme – like a ride on a roller coaster (see Figure 1)! A reduction in the magnetic field strength slows down and compresses the local plasma. In addition, the geometry of the magnetic field changes along the orbit, which means that the plasma is pulled in different directions. Based on the properties of the plasma environment, the authors choose 4 characteristic points and model the outflow of the planet’s atmosphere using a 3D magnetohydrodynamics code. This kind of code can simulate the behavior of plasma under magnetic forces.

    Stellar winds blow away gas from the planet’s atmosphere, and a tail is formed around the planet, like that of a comet. The shape of this tail is determined by the strength and geometry of the magnetic field in the planet’s environment. You might be wondering if it is possible to observe the tail? And can we see the impact of the stellar wind?

    The authors try to find an answer to these questions and mimic transit observations of the Lyman-alpha line. This line is often used to trace atmospheric escape, as it has its origin from a neutral hydrogen transition and hydrogen is quite abundant in the planetary wind. When the planet is transiting the star, a part of the stellar light is absorbed by hydrogen atoms in the planet’s atmosphere. This absorption takes place at the characteristic Lyman-alpha wavelength of 1215.67 Angstrom. If you are observing the transiting system, you can compare the depth of this absorption line in your spectra before, during, and after the transit. The comparison allows conclusions about the amount and velocity of hydrogen in the planet’s atmosphere at different orbital positions. You see, this tool is pretty useful to characterize the planet’s tail.

    3
    Figure 2: Illustration of the evaporating planet passing the stellar disk from left to right. The stellar disk is represented by a Solar Dynamics observation in the 1600 Angstrom band. The different cases show the shape of the planetary tail for different orbital positions, i.e., different stellar wind conditions.

    Stellar Wind Conditions – The Engines of the Roller Coaster

    As can be seen in Figure 2, the simulations show that for random orbital phases, the tail of the planet can have completely different shapes. Sometimes the outflow is narrower around the planet (case 2), and sometimes it looks more like long hair blown away by the wind while riding a super-fast roller coaster (case 1). The authors found that the variations occur in periods of a few hours. Moreover, the stellar wind changes over a few orbital periods from our perspective. This makes it super difficult to make good predictions for observers. It is generally difficult to interpret the spectra correctly if you have no idea what to expect.

    The main conclusion is that the shape and velocity of the gas leaving the planet’s atmosphere varies with the conditions of the stellar wind and thus with the orbital position of the planet. The interaction with the stellar wind makes the planetary outflow highly asymmetric.

    How does this affect a transit observation?

    The observation of the Lyman-alpha absorption line during a transit of such a planet would show highly temporal variations. We should be careful in its interpretation, especially when we stack several observations of different time stamps. However, the shape and position of the Lyman-alpha absorption line profile allows us to draw conclusions about the outflow’s characteristics.

    How does this affect the evolution of the planet?

    If the planet is hosted by a magnetically active star, atmospheric outflow could be accelerated, leading to faster atmospheric depletion. These planets are probably not a good place to find life.

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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