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  • richardmitnick 12:04 pm on August 6, 2017 Permalink | Reply
    Tags: , , , , Habitable zones, ,   

    From NASA: “An Earth-like Atmosphere May Not Survive Proxima b’s Orbit” 

    NASA image
    NASA

    July 31, 2017
    Last Updated: Aug. 4, 2017
    Editor: Rob Garner

    1
    This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system. The double star Alpha Centauri AB also appears in the image. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.
    Credits: ESO/M. Kornmesser

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    A newly discovered, roughly Earth-sized planet orbiting our nearest neighboring star might be habitable, according to a team of astronomers using the European Southern Observatory’s 3.6-meter telescope at La Silla, Chile, along with other telescopes around the world.

    ESO 3.6m telescope & HARPS at LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    The exoplanet is at a distance from its star that allows temperatures mild enough for liquid water to pool on its surface.

    Proxima b, an Earth-size planet right outside our solar system in the habitable zone of its star, may not be able to keep a grip on its atmosphere, leaving the surface exposed to harmful stellar radiation and reducing its potential for habitability.

    At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn’t been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.

    One such computer model considered what would happen if Earth orbited Proxima Centauri, our nearest stellar neighbor and Proxima b’s host star, at the same orbit as Proxima b. The NASA study, published on July 24, 2017, in The Astrophysical Journal Letters, suggests Earth’s atmosphere wouldn’t survive in close proximity to the violent red dwarf.

    “We decided to take the only habitable planet we know of so far — Earth — and put it where Proxima b is,” said Katherine Garcia-Sage, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study. The research was supported by NASA’s NExSS coalition — leading the search for life on planets beyond our solar system — and the NASA Astrobiology Institute.

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    At its orbit, the exoplanet Proxima b likely couldn’t sustain an Earth-like atmosphere. Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith.

    Just because Proxima b’s orbit is in the habitable zone, which is the distance from its host star where water could pool on a planet’s surface, doesn’t mean it’s habitable. It doesn’t take into account, for example, whether water actually exists on the planet, or whether an atmosphere could survive at that orbit. Atmospheres are also essential for life as we know it: Having the right atmosphere allows for climate regulation, the maintenance of a water-friendly surface pressure, shielding from hazardous space weather, and the housing of life’s chemical building blocks.

    Garcia-Sage and her colleagues’ computer model used Earth’s atmosphere, magnetic field and gravity as proxies for Proxima b’s. They also calculated how much radiation Proxima Centauri produces on average, based on observations from NASA’s Chandra X-ray Observatory.

    NASA/Chandra Telescope

    With these data, their model simulates how the host star’s intense radiation and frequent flaring affect the exoplanet’s atmosphere.

    “The question is, how much of the atmosphere is lost, and how quickly does that process occur?” said Ofer Cohen, a space scientist at the University of Massachusetts, Lowell and co-author of the study. “If we estimate that time, we can calculate how long it takes the atmosphere to completely escape — and compare that to the planet’s lifetime.”

    An active red dwarf star like Proxima Centauri strips away atmosphere when high-energy extreme ultraviolet radiation ionizes atmospheric gases, knocking off electrons and producing a swath of electrically charged particles. In this process, the newly formed electrons gain enough energy that they can readily escape the planet’s gravity and race out of the atmosphere.

    Opposite charges attract, so as more negatively charged electrons leave the atmosphere, they create a powerful charge separation that pulls positively charged ions along with them, out into space.

    In Proxima Centauri’s habitable zone, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.

    The model shows Proxima Centauri’s powerful radiation drains the Earth-like atmosphere as much as 10,000 times faster than what happens at Earth.

    “This was a simple calculation based on average activity from the host star,” Garcia-Sage said. “It doesn’t consider variations like extreme heating in the star’s atmosphere or violent stellar disturbances to the exoplanet’s magnetic field — things we’d expect provide even more ionizing radiation and atmospheric escape.”

    To understand how the process can vary, the scientists looked at two other factors that exacerbate atmospheric loss. First, they considered the temperature of the neutral atmosphere, called the thermosphere. They found as the thermosphere heats with more stellar radiation, atmospheric escape increases.

    The scientists also considered the size of the region over which atmospheric escape happens, called the polar cap. Planets are most sensitive to magnetic effects at their magnetic poles. When magnetic field lines at the poles are closed, the polar cap is limited and charged particles remain trapped near the planet. On the other hand, greater escape occurs when magnetic field lines are open, providing a one-way route to space.

    “This study looks at an under-appreciated aspect of habitability, which is atmospheric loss in the context of stellar physics,” said Shawn Domagal-Goldman, a Goddard space scientist not involved in the study. “Planets have lots of different interacting systems, and it’s important to make sure we include these interactions in our models.”

    The scientists show that with the highest thermosphere temperatures and a completely open magnetic field, Proxima b could lose an amount equal to the entirety of Earth’s atmosphere in 100 million years — that’s just a fraction of Proxima b’s 4 billion years thus far. When the scientists assumed the lowest temperatures and a closed magnetic field, that much mass escapes over 2 billion years.

    “Things can get interesting if an exoplanet holds on to its atmosphere, but Proxima b’s atmospheric loss rates here are so high that habitability is implausible,” said Jeremy Drake, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and co-author of the study. “This questions the habitability of planets around such red dwarfs in general.”

    Red dwarfs like Proxima Centauri or the TRAPPIST-1 star are often the target of exoplanet hunts, because they are the coolest, smallest and most common stars in the galaxy. Because they are cooler and dimmer, planets have to maintain tight orbits for liquid water to be present.

    The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

    But unless the atmospheric loss is counteracted by some other process — such as a massive amount of volcanic activity or comet bombardment — this close proximity, scientists are finding more often, is not promising for an atmosphere’s survival or sustainability.

    For more information, go to:

    https://exoplanets.nasa.gov

    See the full article here .

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    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 4:55 pm on March 31, 2017 Permalink | Reply
    Tags: , , Habitable zones,   

    From Astronomy: “Rethinking the habitable zone” 

    Astronomy magazine

    Astronomy Magazine

    March 28, 2017
    K.N. Smith

    1
    NASA

    With proof of liquid water in the farthest reaches of the solar system, it’s clear that the habitable zone isn’t the only place life might exist, but it may be years before that knowledge changes how — and where — astrobiologists look for habitable exoplanets.

    If you want to look for life in space, most astronomy textbooks will tell you to stick to the Goldilocks Zone: the region around a star that’s the right temperature range for liquid water to exist on the surface of a planet, also called the habitable zone. The trouble is that water seems to be everywhere on icy moons in the outer solar system, well beyond the textbook habitable zone, and some planetary scientists have even suggested that there could be liquid seas out in the Kuiper Belt. Thanks to those discoveries, some experts are suggesting that it could be time to rethink how we define the habitable zone. But does that mean changing how we search for potentially habitable worlds in other solar systems?

    2
    Wilfried Bauer

    Beyond the Goldilocks Zone

    Until the last few decades, scientists assumed that the conditions for life, starting with liquid water, could only exist in a planetary neighborhood exactly like ours.

    “It’s been a big shift, but it’s been kind of gradual; it just kind of kept creeping up on people,” JPL’s Diana Blaney, principal investigator on the Mapping Imaging Spectrometer for Europa, said.

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    Prototype MISE spectrometer

    That shift happened in two parts, fueled by discoveries in broadly different fields. First came the idea that life could live in colder, darker, stranger places than biologists could have dreamed. Second came the idea that the most basic conditions for survival – chiefly the presence of liquid water – could turn up in unexpected places.

    Most of the liquid water we’ve found in the solar system is concealed beneath the icy crusts of moons orbiting Jupiter and Saturn, but before scientists sent Voyager, Galileo, and Cassini out into the outer solar system to find those sub-surface oceans, they found analogues here on Earth. In 1970, airborne radio-echo sounding surveys found the first evidence of lakes hidden beneath several kilometers of glacial ice in Antarctica. Researchers have found 379 such lakes so far, and a series of discoveries in the last few years have confirmed the presence of microbial life beneath several of them.

    Just before the first mission to the outer solar system, in 1976 – while Viking 1 was searching for life on Mars – botanists discovered bacteria eking out a living in porous sandstone in the cold, dry, thoroughly inhospitable mountains of Antarctica’s Ross Desert. The following year, in 1977, a marine geology expedition discovered hydrothermal vents in the Galapagos Rift, deep beneath the eastern Pacific Ocean. In the lightless depths of the ocean, they found a thriving ecosystem based on chemosynthesis.

    Looking back, it’s easy to see how discoveries of extremophiles and sub-glacial lakes here on Earth pointed toward the idea that wildly unexpected environments out there might be habitable.

    The Voyager spacecraft launched later that year, on their way to the outer solar system; it was a mission that some in the scientific community at the time didn’t expect much from – after all, the moons of the outer solar system were far outside the bounds of the Goldilocks Zone.


    NASA/Voyager 1

    “It was really Voyager that broke all of this open, because a lot of scientists thought that most of the outer solar system was just dead balls of ice and rock,” said planetary scientist Jonathan Lunine of Cornell University. From 1979 to 1981, Voyager sent home images of active, complex worlds: Io with its violent, volcanic surface; Titan with its thick, hazy atmosphere; and Europa with a cracked crust that hinted at tidal movements of an ocean beneath.

    Once scientists realized that the moons of the outer solar system were dynamic, unexpectedly complex worlds, some began to speculate that they could host life, warmed not just by the light of the Sun, but by the tidal pull of a gas giant. Meanwhile, discoveries here on Earth continued apace, feeding into astrobiologists’ ideas about where life might flourish.

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    NASA Goddard/Katrina Jackson

    All these worlds are yours …

    The Galileo spacecraft left Earth in 1989, bound for Jupiter amid intensifying speculation about what it might find waiting beneath the ice at Europa.


    ESA Galileo Spacecraft

    Galileo’s close flybys of the Jovian moons confirmed what Voyager’s images had hinted at: liquid water exists well outside the familiar confines of the Goldilocks Zone, beneath the ice of Europa and Ganymede. Then, in 2005, the Cassini spacecraft captured surprising images of watery plumes jetting out from the southern surface of Enceladus.


    NASA/ESA/ASI Cassini Spacecraft

    As the data came back from Galileo and Cassini, it collided with research on extremophiles here on Earth, fueling discussions about which unexpected corners of our solar system might turn out to be habitable.

    “I think they actually reinforced each other, you know?” said Blaney. “A lot of the stuff, I think, was happening in parallel. You were sitting in [science conferences] listening to people talk about the building evidence for an ocean on Europa, and then you would go next door and listen to someone talk about life in the Antarctic dry valleys, and that kind of cross-communication between the different communities, I think, got people thinking more about Europa potentially having life now.”

    Now astrobiologists may have to rethink the limits of habitability again. In late 2016, William McKinnon, a planetary scientist at Washington University in St. Louis, and his colleagues concluded that orientation of Sputnik Planitia, the icy heart-shaped basin in Pluto’s northern hemisphere, could only be explained by an uneven distribution of mass in the planet’s crust.

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    Original discription: This image contains the initial, informal names being used by the New Horizons team for the features on Pluto’s Sputnik Planum (plain). Names were selected based on the input the team received from the Our Pluto naming campaign. Names have not yet been approved by the International Astronomical Union (IAU).
    Date 29 July 2015
    Source http://pluto.jhuapl.edu/Multimedia/Images/index.php
    Author JPL/NASA

    That, in turn, the researchers claimed, could only be explained by a liquid ocean of (mostly) water beneath the ice. There’s no proof yet that Pluto hosts a subglacial lake similar to those beneath Antarctica’s ice, but the research proves it’s theoretically possible for Kuiper Belt Objects to hold liquid water.

    “We know oceans exist beneath icy crusts, generally maintained by tidal heating (Europa and Enceladus). What Pluto does is to push the potential limits of habitable zones to icy dwarf planets in deep solar space,” said McKinnon.

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    NASA / JHUAPL / SwRI

    Miniature Habitable Zones

    The current view among many astrobiologists is that, because there are so many environments where liquid water – and therefore the basic ingredients for life – might exist, there are many habitable zones in a solar system. There’s the traditional Goldilocks Zone, where solar heating keeps the planet at just the right temperature; there are orbits around gas giants, where tidal heating could keep water liquid and potentially habitable beneath the ice.

    “The data point I seize on is more the number of potential habitable environments we have in our single solar system. I don’t think that’s a fluke,” said Curt Niebur, program scientist for NASA’s Europa Multiple Flyby Mission. “I think as we peer outward, we are going to find that in most solar systems we explore, either in person or via telescopes, that there is likely to be multiple habitable zones in every solar system.”

    In fact, we’ve found more liquid water on icy moons in the outer solar system than in the temperate belt of the Habitable Zone. Some planetary scientists are even beginning to talk about the idea that gas giants, like Jupiter and Saturn, create their own habitable zones through their tidal heating of icy moons like Europa and Enceladus. And if McKinnon and his colleagues turn out to be right about what lies beneath Pluto’s Sputnik Planum, then there may even be little habitable zones far out in the frozen reaches of the Kuiper Belt.

    “Sometimes it’s around giant planets like Jupiter, sometimes it’s on Earth-like planets, sometimes it’s in the deep solar system like at Pluto,” said Niebur. “I think every one of those three cases is a Goldilocks zone, and I think that there are more Goldilocks zones out there remaining to be discovered.”

    That means that we may not be giving gas giants enough credit as hosts for potentially habitable worlds. For one thing, they seem to be much more common – or at least easier to detect from Earth – than rocky planets, especially rocky planets that happen to orbit just the right distance from their stars, which means the odds are in favor of a gas giant winning the lottery of biochemistry.

    “I think it’s probably likely that gas giants are more common than terrestrial worlds, so just by sheer numbers, I think that they could either directly or indirectly provide far more habitable zones, far more Goldilocks zones, than terrestrial planets,” said Niebur.

    That’s an eye-opening concept for astrobiology, but in practice it could be nearly impossible to draw a neat map of that type of habitable zone. Mapping a star’s Goldilocks Zone is pretty straightforward; the temperature of a planet depends on its distance from the star, as well as how much heat the star produces. Figuring out the region of potential habitability around a gas giant, on the other hand, requires a lot more information about the gas giant, its moons, and how they all interact.

    The oceans of Europa, Enceladus, and Ganymede rely on tidal heating to keep them liquid, and those tidal forces come not only from the gravitational pull of the gas giants, but from gravitational interactions with other moons. For instance, every time Ganymede orbits Jupiter, Europa makes exactly two orbits, and Io makes exactly four. That means that the planets line up regularly, giving each other a gravitational tug that stretches their orbits out, making them more elliptical.

    Thanks to orbital resonance, the tidal effects of the planet’s gravity are much more pronounced. In simple terms, that’s because the difference between “high tide” and “low tide” is exaggerated. That, in turn, keeps the moons’ interiors in motion – and warm.

    That’s why Io is such a hotbed of volcanic activity, and it’s why Europa and Ganymede have enough geothermal heat to maintain liquid water so far from the Goldilocks Zone. Around Saturn, Enceladus is in a similar orbital resonance with its sister moon Dione, and that’s what keeps the plumes erupting from cracks in the moon’s icy crust.

    Astronomers have a very good understanding of the dynamics that make the moons of Jupiter and Saturn so active, but beyond our solar system, there’s no way to spot tidally heated habitable zones – yet. To predict whether a moon might experience enough tidal heating to keep water liquid in its interior, astronomers would need to know how many other moons were orbiting the same planet and whether those orbits are in resonance with each other.
    “The broader definition of habitable zones will also include some that we just can’t observe with the missions that we’re anticipating in the next decades,” said Lunine. “That includes icy moons around gas giants, which may be harboring life, or at least habitable oceans, that we can’t see yet.”

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    Danielle Futselaar / Franck Marchis / SETI Institute.

    Observable Habitable Zones

    It’s fascinating to think that an interesting new gas giant in a solar system like 51 Eridani may play host to another Enceladus or Europa, but with our current technology, those potentially habitable icy exo-moons are still invisible to astronomers here on Earth.

    “The problem, of course, is that if you really have something the size of Enceladus or even Europa orbiting around a giant planet, around another star, you have a really tough time observing it, and if it’s habitable five or ten kilometers below the surface, you’re sort of out of luck,” said Lunine. “It would be a very, very difficult challenge to make the kinds of observations of a Europa or an Enceladus that are required to determine its habitability.”

    Of course, that kind of observation is feasible for icy moons in our own solar system, because we can send probes to fly through the plumes of Enceladus or perhaps one day land on the surface of Europa, but to study objects in other solar systems, astronomers have to stick with looking for spectra through a telescope. So even if there might be miniature habitable zones in the other reaches of most solar systems, Earthbound astrobiologists can only speculate.

    Instead, Lunine says that in the search for potentially habitable exoplanets, what really matters is something he calls the observable habitable zone: the area where water might exist, and in a place where we could see evidence of it with a telescope. That means a planet that telescopes can actually observe, and it means liquid water existing stably on the surface, not hidden beneath a layer of ice. Essentially, it means the traditional Goldilocks Zone.

    “The technology limitations mean that you’re going to have to restrict yourself to the traditional definition of the Goldilocks, but I think that as our technology increases, we can pursue the more modern and accurate Goldilocks zone concept as well,” said Niebur.

    In the future, that might change. In the meantime, it’s worth keeping in mind that the search for habitable worlds probably still has surprises in store.

    “People have to kind of keep an open mind about what’s possible and – and let the data take you where it takes you, because sometimes it takes you to places that are unexpected – like Europa,” said Blaney.

    See the full article here .

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  • richardmitnick 2:22 pm on January 17, 2017 Permalink | Reply
    Tags: , , , Habitable zones, SF State,   

    From SF State: “SF State astronomer searches for signs of life on Wolf 1061 exoplanet” 

    SFSU bloc

    San Fransisco State University

    January 13, 2017
    Jamie Oppenheim

    1
    An artist’s rendering of an exoplanet is shown. An exoplanet is a planet that exists outside Earth’s solar system. Illustration credit: NASA/Ames/JPL-Caltech

    SF State astronomer Stephen Kane searches for signs of life in one of the extrasolar systems closest to Earth.

    Is there anybody out there? The question of whether Earthlings are alone in the universe has puzzled everyone from biologists and physicists to philosophers and filmmakers. It’s also the driving force behind San Francisco State University astronomer Stephen Kane’s research into exoplanets — planets that exist outside Earth’s solar system.

    As one of the world’s leading “planet hunters,” Kane focuses on finding “habitable zones,” areas where water could exist in a liquid state on a planet’s surface if there’s sufficient atmospheric pressure. Kane and his team, including former undergraduate student Miranda Waters, examined the habitable zone on a planetary system 14 light years away. Their findings will appear in the next issue of Astrophysical Journal in a paper titled Characterization of the Wolf 1061 Planetary System.

    “The Wolf 1061 system is important because it is so close and that gives other opportunities to do follow-up studies to see if it does indeed have life,” Kane said.

    But it’s not just Wolf 1061’s proximity to Earth that made it an attractive subject for Kane and his team. One of the three known planets in the system, a rocky planet called Wolf 1061c, is entirely within the habitable zone. With assistance from collaborators at Tennessee State University and in Geneva, Switzerland, they were able to measure the star around which the planet orbits to gain a clearer picture of whether life could exist there.

    When scientists search for planets that could sustain life, they are basically looking for a planet with nearly identical properties to Earth, Kane said. Like Earth, the planet would have to exist in a sweet spot often referred to as the “Goldilocks zone” where conditions are just right for life. Simply put, the planet can’t be too close or too far from its parent star. A planet that’s too close would be too hot. If it’s too far, it may be too cold and any water would freeze, which is what happens on Mars, Kane added.

    Conversely, when planets warm, a “runaway greenhouse effect” can occur where heat gets trapped in the atmosphere. Scientists believe this is what happened on Earth’s twin, Venus. Scientists believe Venus once had oceans, but because of its proximity to the sun the planet became so hot that all the water evaporated, according to NASA. Since water vapor is extremely effective in trapping in heat, it made the surface of the planet even hotter. The surface temperature on Venus now reaches a scalding 880 degrees Fahrenheit.

    Since Wolf 1061c is close to the inner edge of the habitable zone, meaning closer to the star, it could be that the planet has an atmosphere that’s more similar to Venus. “It’s close enough to the star where it’s looking suspiciously like a runaway greenhouse,” Kane said.

    Kane and his team also observed that unlike Earth, which experiences climatic changes such as an ice age because of slow variations in its orbit around the sun, Wolf 1061c’s orbit changes at a much faster rate, which could mean the climate there could be quite chaotic. “It could cause the frequency of the planet freezing over or heating up to be quite severe,” Kane said.

    These findings all beg the question: Is life possible on Wolf 1061c? One possibility is that the short time scales over which Wolf 1061c’s orbit changes could be enough that it could actually cool the planet off, Kane said. But fully understanding what’s happening on the planet’s surface will take more research.

    In the coming years, there will be a launch of new telescopes like the James Webb Space Telescope, the successor to the Hubble Space Telescope, Kane said, and it will be able to detect atmospheric components of the exoplanets and show what’s happening on the surface.

    See the full article here .

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    San Francisco State University (commonly referred to as San Francisco State, SF State and SFSU) is a public comprehensive university located in San Francisco, California, United States. As part of the 23-campus California State University system, the university offers 118 different Bachelor’s degrees, 94 Master’s degrees, 5 Doctoral degrees including two Doctor of Education, a Doctor of Physical Therapy, a Ph.D in Education and Doctor of Physical Therapy Science, along with 26 teaching credentials among six academic colleges.

     
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