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What Is the Habitable Zone?


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    • By NASA
      This artist’s concept features one of multiple initial possible design options for NASA’s Habitable Worlds Observatory. Credits: NASA’s Goddard Space Flight Center Conceptual Image Lab NASA announced Friday it selected three industry proposals to help develop technologies for future large space telescopes and plan for the agency’s Habitable Worlds Observatory mission concept, which could be the first space telescope designed to search for life outside our solar system.
      The mission would directly image Earth-like planets around stars like our Sun and study their atmospheres for the chemical signatures of life, as well as enable other investigations about our solar system and universe. NASA is currently in the early planning stages for this mission concept, with community-wide working groups exploring its fundamental science goals and how best to pursue them. The agency is also in the process of establishing a Habitable Worlds Observatory Technology Maturation project office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
      “The Habitable Worlds Observatory will be a historically ambitious mission, so we are taking a deliberate, strategic approach to its development and laying the groundwork now. We will need to bring together diverse expertise from government, academia, and industry, while building on technologies and lessons learned from our previous large space telescopes,” said Mark Clampin, director of the Astrophysics Division at NASA Headquarters in Washington. “With these awards, we’re excited to engage industry to help close technology gaps to make this groundbreaking mission a reality.”
      In January 2024, NASA solicited industry proposals to help advance key technologies that will eventually be necessary for the Habitable Worlds Observatory. For example, the mission will require a coronagraph – an instrument that blocks the light of a star so we can better see nearby objects – thousands of times more capable than any prior space coronagraph, and a stable optical system moving no more than the width of an atom during its observations.
      To help further the readiness of these technologies, NASA has now selected the following proposals for two-year, fixed-price contracts with a combined value of $17.5 million, targeted to begin by late summer 2024:
      “Ultra-stable Telescope Research and Analysis – Critical Technologies (ULTRA-CT)”This project will focus on high-fidelity modeling and subsystem demonstrations to support future development of “ultra-stable” optical systems beyond current state-of-the-art technologies. Principal investigator: Laura Coyle, Ball Aerospace (now BAE Systems) “Technology Maturation for Astrophysics Space Telescopes (TechMAST)”This project seeks to advance the integrated modeling infrastructure required to navigate design interdependencies and compare potential mission design options. Principal investigator: Alain Carrier, Lockheed Martin “STABLE: Systems Technologies for Architecture Baseline”This project will focus on maturing technologies that support telescope features, such as a deployable baffle and a structure to support the optical train, while mitigating the impact of system or environmental disturbances. Principal investigator: Tiffany Glassman, Northrop Grumman This work will continue industry involvement started in 2017 under NASA’s “System-Level Segmented Telescope Design” solicitations, which concluded in December 2023. The new selected proposals will help inform NASA’s approach to planning for the Habitable Worlds Observatory, as the agency builds on technologies from its James Webb Space Telescope and future Nancy Grace Roman Space Telescope and identifies where future investments are needed.
      To learn more about NASA’s Habitable Worlds Observatory visit:
      https://go.nasa.gov/HWO
      -end-
      Alise Fisher
      Headquarters, Washington
      202-358-2546
      alise.m.fisher@nasa.gov
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      Last Updated May 31, 2024 LocationNASA Headquarters Related Terms
      Science & Research Astrophysics Exoplanet Science Science Mission Directorate The Search for Life View the full article
    • By NASA
      4 min read
      Discovery Alert: A ‘Super-Earth’ in the Habitable Zone
      This illustration shows one way that planet TOI-715 b, a super-Earth in the habitable zone around its star, might appear to a nearby observer. NASA/JPL-Caltech The discovery: A “super-Earth” ripe for further investigation orbits a small, reddish star that is, by astronomical standards, fairly close to us – only 137 light-years away. The same system also might harbor a second, Earth-sized planet.
      Key facts: The bigger planet, dubbed TOI-715 b, is about one and a half times as wide as Earth, and orbits within the “conservative” habitable zone around its parent star. That’s the distance from the star that could give the planet the right temperature for liquid water to form on its surface. Several other factors would have to line up, of course, for surface water to be present, especially having a suitable atmosphere. But the conservative habitable zone – a narrower and potentially more robust definition than the broader “optimistic” habitable zone – puts it in prime position, at least by the rough measurements made so far. The smaller planet could be only slightly larger than Earth, and also might dwell just inside the conservative habitable zone.

      The Planet That Shouldn’t Be There

      Details: Astronomers are beginning to write a whole new chapter in our understanding of exoplanets – planets beyond our solar system. The newest spaceborne instruments, including those onboard NASA’s James Webb Space Telescope, are designed not just to detect these distant worlds, but to reveal some of their characteristics. That includes the composition of their atmospheres, which could offer clues to the possible presence of life.
      The recently discovered super-Earth, TOI-715 b, might be making its appearance at just the right time. Its parent star is a red dwarf, smaller and cooler than our Sun; a number of such stars are known to host small, rocky worlds. At the moment, they’re the best bet for finding habitable planets. These planets make far closer orbits than those around stars like our Sun, but because red dwarfs are smaller and cooler, the planets can crowd closer and still be safely within the star’s habitable zone. The tighter orbits also mean those that cross the faces of their stars – that is, when viewed by our space telescopes – cross far more often. In the case of planet b, that’s once every 19 days, a “year” on this strange world. So these star-crossing (“transiting”) planets can be more easily detected and more frequently observed. That’s the case for TESS (the Transiting Exoplanet Survey Satellite), which found the new planet and has been adding to astronomers’ stockpile of habitable-zone exoplanets since its launch in 2018. Observing such transits for, say, an Earth-sized planet around a Sun-like star (and waiting for an Earth year, 365 days, to catch another transit) is beyond the capability of existing space telescopes.
      Planet TOI-175 b joins the list of habitable-zone planets that could be more closely scrutinized by the Webb telescope, perhaps even for signs of an atmosphere. Much will depend on the planet’s other properties, including how massive it is and whether it can be classed as a “water world” – making its atmosphere, if present, more prominent and far less difficult to detect than that of a more massive, denser and drier world, likely to hold its lower-profile atmosphere closer to the surface.
      Fun facts: If the possible second, Earth-sized planet in the system also is confirmed, it would become the smallest habitable-zone planet discovered by TESS so far. The discovery also exceeded early expectations for TESS by finding an Earth-sized world in the habitable zone.
      The discoverers: An international team of scientists led by Georgina Dransfield of the University of Birmingham, United Kingdom, published a paper in January 2024 on their discovery, “A 1.55 R⊕ habitable-zone planet hosted by TOI-715, an M4 star near the ecliptic South Pole,” in the journal, “Monthly Notices of the Royal Astronomical Society.” An international array of facilities used to confirm the planet included Gemini-South, Las Cumbres Observatory telescopes, the ExTrA telescopes, the SPECULOOS network, and the TRAPPIST-south telescope.
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      Last Updated Jan 31, 2024 Related Terms
      Exoplanets Goddard Space Flight Center James Webb Space Telescope (JWST) Super-Earth Exoplanets TESS (Transiting Exoplanet Survey Satellite) Explore More
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      Preparations for Next Moonwalk Simulations Underway (and Underwater)
      A NASA study expands the search for life beyond our solar system by indicating that 17 exoplanets (worlds outside our solar system) could have oceans of liquid water, an essential ingredient for life, beneath icy shells. Water from these oceans could occasionally erupt through the ice crust as geysers. The science team calculated the amount of geyser activity on these exoplanets, the first time these estimates have been made. They identified two exoplanets sufficiently close where signs of these eruptions could be observed with telescopes.
      The search for life elsewhere in the Universe typically focuses on exoplanets that are in a star’s “habitable zone,” a distance where temperatures allow liquid water to persist on their surfaces. However, it’s possible for an exoplanet that’s too distant and cold to still have an ocean underneath an ice crust if it has enough internal heating. Such is the case in our solar system where Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, have subsurface oceans because they are heated by tides from the gravitational pull of the host planet and neighboring moons.
      NASA’s Cassini spacecraft captured this image of Enceladus on Nov. 30, 2010. The shadow of the body of Enceladus on the lower portions of the jets is clearly visible.NASA/JPL-Caltech/Space Science Institute These subsurface oceans could harbor life if they have other necessities, such as an energy supply as well as elements and compounds used in biological molecules. On Earth, entire ecosystems thrive in complete darkness at the bottom of oceans near hydrothermal vents, which provide energy and nutrients.
      “Our analyses predict that these 17 worlds may have ice-covered surfaces but receive enough internal heating from the decay of radioactive elements and tidal forces from their host stars to maintain internal oceans,” said Dr. Lynnae Quick of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Thanks to the amount of internal heating they experience, all planets in our study could also exhibit cryovolcanic eruptions in the form of geyser-like plumes.” Quick is lead author of a paper on the research published on October 4 in the Astrophysical Journal.
      The team considered conditions on 17 confirmed exoplanets that are roughly Earth-sized but less dense, suggesting that they could have substantial amounts of ice and water instead of denser rock. Although the planets’ exact compositions remain unknown, initial estimates of their surface temperatures from previous studies all indicate that they are much colder than Earth, suggesting that their surfaces could be covered in ice.
      The study improved estimates of each exoplanet’s surface temperature by recalculating using the known surface brightness and other properties of Europa and Enceladus as models. The team also estimated the total internal heating in these exoplanets by using the shape of each exoplanet’s orbit to get the heat generated from tides and adding it to the heat expected from radioactive activity. Surface temperature and total heating estimates gave the ice layer thickness for each exoplanet since the oceans cool and freeze at the surface while being heated from the interior. Finally, they compared these figures to Europa’s and used estimated levels of geyser activity on Europa as a conservative baseline to estimate geyser activity on the exoplanets.
      They predict that surface temperatures are colder than previous estimates by up to 60 degrees Fahrenheit (16 degrees Celsius). Estimated ice shell thickness ranged from about 190 feet (58 meters) for Proxima Centauri b and one mile (1.6 kilometers) for LHS 1140 b to 24 miles (38.6 kilometers) for MOA 2007 BLG 192Lb, compared to Europa’s estimated average of 18 miles (almost 29 kilometers). Estimated geyser activity went from just 17.6 pounds per second (about 8 kilograms/second) for Kepler 441b to 639,640 pounds/second (290,000 kilograms/second) for LHS 1140 b and 13.2 million pounds/second (six million kilograms/second) for Proxima Centauri b, compared to Europa at 4,400 pounds/second (2,000 kilograms/second).
      “Since our models predict that oceans could be found relatively close to the surfaces of Proxima Centauri b and LHS 1140 b, and their rate of geyser activity could exceed Europa’s by hundreds to thousands of times, telescopes are most likely to detect geological activity on these planets,” said Quick, who is presenting this research December 12 at the American Geophysical Union meeting in San Francisco, California.
      This activity could be seen when the exoplanet passes in front of its star. Certain colors of starlight could be dimmed or blocked by water vapor from the geysers. “Sporadic detections of water vapor in which the amount of water vapor detected varies with time, would suggest the presence of cryovolcanic eruptions,” said Quick. The water might contain other elements and compounds that could reveal if it can support life. Since elements and compounds absorb light at specific “signature” colors, analysis of the starlight would let scientists determine the geyser’s composition and evaluate the exoplanet’s habitability potential.
      For planets like Proxima Centauri b that don’t cross their stars from our vantage point, geyser activity could be detected by powerful telescopes that are able to measure light that the exoplanet reflects while orbiting its star. Geysers would expel icy particles at the exoplanet’s surface which would cause the exoplanet to appear very bright and reflective.
      The research was funded by NASA’s Habitable Worlds Program, the University of Washington’s Astrobiology Program, and the Virtual Planetary Laboratory, a member of the NASA Nexus for Exoplanet System Science coordination group.
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      Last Updated Dec 13, 2023 EditorWilliam SteigerwaldContactWilliam Steigerwaldwilliam.a.steigerwald@nasa.govLocationGoddard Space Flight Center Related Terms
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