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Jaw-dropping Images: Uranus' Hidden Rings and Moons
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By NASA
The study of X-ray emission from astronomical objects reveals secrets about the Universe at the largest and smallest spatial scales. Celestial X-rays are produced by black holes consuming nearby stars, emitted by the million-degree gas that traces the structure between galaxies, and can be used to predict whether stars may be able to host planets hospitable to life. X-ray observations have shown that most of the visible matter in the universe exists as hot gas between galaxies and have conclusively demonstrated that the presence of “dark matter” is needed to explain galaxy cluster dynamics, that dark matter dominates the mass of galaxy clusters, and that it governs the expansion of the cosmos.
X-ray observations also enable us to probe mysteries of the Universe on the smallest scales. X-ray observations of compact objects such as white dwarfs, neutron stars, and black holes allow us to use the Universe as a physics laboratory to study conditions that are orders of magnitude more extreme in terms of density, pressure, temperature, and magnetic field strength than anything that can be produced on Earth. In this astrophysical laboratory, researchers expect to reveal new physics at the subatomic scale by conducting investigations such as probing the neutron star equation of state and testing quantum electrodynamics with observations of neutron star atmospheres. At NASA’s Marshall Space Flight Center, a team of scientists and engineers is building, testing, and flying innovative optics that bring the Universe’s X-ray mysteries into sharper focus.
A composite X-ray/Optical/Infrared image of the Crab Pulsar. The X-ray image from the Chandra X-ray Observatory (blue and white), reveals exquisite details in the central ring structures and gas flowing out of the polar jets. Optical light from the Hubble Space Telescope (purple) shows foreground and background stars as pinpoints of light. Infrared light from the Spitzer Space Telescope (pink) traces cooler gas in the nebula. Finally, magnetic field direction derived from X-ray polarization observed by the Imaging X-ray Polarimetry Explorer is shown as orange lines. Magnetic field lines: NASA/Bucciantini et al; X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech Unlike optical telescopes that create images by reflecting or refracting light at near-90-degree angles (normal incidence), focusing X-ray optics must be designed to reflect light at very small angles (grazing incidence). At normal incidence, X-rays are either absorbed by the surface of a mirror or penetrate it entirely. However, at grazing angles of incidence, X-rays reflect very efficiently due to an effect called total external reflection. In grazing incidence, X-rays reflect off the surface of a mirror like rocks skipping on the surface of a pond.
A classic design for astronomical grazing incidence optics is the Wolter-I prescription, which consists of two reflecting surfaces, a parabola and hyperbola (see figure below). This optical prescription is revolved around the optical axis to produce a full-shell mirror (i.e., the mirror spans the full circumference) that resembles a gently tapered cone. To increase the light collecting area, multiple mirror shells with incrementally larger diameters and a common focus are fabricated and nested concentrically to comprise a mirror module assembly (MMA).
Focusing optics are critical to studying the X-ray universe because, in contrast to other optical systems like collimators or coded masks, they produce high signal-to-noise images with low background noise. Two key metrics that characterize the performance of X-ray optics are angular resolution, which is the ability of an optical system to discriminate between closely spaced objects, and effective area, which is the light collecting area of the telescope, typically quoted in units of cm2. Angular resolution is typically measured as the half-power diameter (HPD) of a focused spot in units of arcseconds. The HPD encircles half of the incident photons in a focused spot and measures the sharpness of the final image; a smaller number is better.
Schematic of a full-shell Wolter-I X-ray optic mirror module assembly with five concentrically nested mirror shells. Parallel rays of light enter from the left, reflect twice off the reflective inside surface of the shell (first off the parabolic segment and then off the hyperbolic segment), and converge at the focal plane. NASA MSFC NASA Marshall Space Flight Center (MSFC) has been building and flying lightweight, full-shell, focusing X-ray optics for over three decades, always meeting or exceeding angular resolution and effective area requirements. MSFC utilizes an electroformed nickel replication (ENR) technique to make these thin full-shell X-ray optics from nickel alloy.
X-ray optics development at MSFC began in the early 1990s with the fabrication of optics to support NASA’s Advanced X-ray Astrophysics Facility (AXAF-S) and then continued via the Constellation-X technology development programs. In 2001, MSFC launched a balloon payload that included two modules each with three mirrors, which produced the first focused hard X-ray (>10 keV) images of an astrophysical source by imaging Cygnus X-1, GRS 1915, and the Crab Nebula. This initial effort resulted in several follow-up missions over the next 12 years, and became known as the High Energy Replicated Optics (HERO) balloon program.
In 2012, the first of four sounding rocket flights of the Focusing Optics X-ray Solar Imager (FOXSI) flew with MSFC optics onboard, producing the first focused images of the Sun at energies greater than 5 keV. In 2019 the Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) instrument on the Spectr-Roentgen-Gamma Mission launched with seven MSFC-fabricated X-ray MMAs, each containing 28 mirror shells. ART-XC is currently mapping the sky in the 4-30 keV hard X-ray energy range, studying exotic objects like neutron stars in our own galaxy as well as active galactic nuclei, which are spread across the visible universe. In 2021, the Imaging X-ray Polarimetry Explorer (IXPE), flew and is now performing extraordinary science with an MSFC-led team using three, 24-shell MMAs that were fabricated and calibrated in-house.
Most recently, in 2024, the fourth FOXSI sounding rocket campaign launched with a high-resolution MSFC MMA. The optics achieved 9.5 arcsecond HPD angular resolution during pre-flight test with an expected 7 arcsecond HPD in gravity-free flight, making this the highest angular resolution flight observation made with a nickel-replicated X-ray optic. Currently MSFC is fabricating an MMA for the Rocket Experiment Demonstration of a Soft X-ray (REDSoX) polarimeter, a sounding rocket mission that will fly a novel soft X-ray polarimeter instrument to observe active galactic nuclei. The REDSoX MMA optic will be 444 mm in diameter, which will make it the largest MMA ever produced by MSFC and the second largest replicated nickel X-ray optic in the world.
Scientists Wayne Baumgartner (left, crouched) and Nick Thomas (left, standing) calibrate an IXPE MMA in the MSFC 100 m Beamline. Scientist Stephen Bongiorno (right) applies epoxy to an IXPE shell during MMA assembly. NASA MSFC The ultimate performance of an X-ray optic is determined by errors in the shape, position, and roughness of the optical surface. To push the performance of X-ray optics toward even higher angular resolution and achieve more ambitious science goals, MSFC is currently engaged in a fundamental research and development effort to improve all aspects of full-shell optics fabrication.
Given that these optics are made with the Electroformed Nickel Replication technique, the fabrication process begins with creation of a replication master, called the mandrel, which is a negative of the desired optical surface. First, the mandrel is figured and polished to specification, then a thin layer of nickel alloy is electroformed onto the mandrel surface. Next, the nickel alloy layer is removed to produce a replicated optical shell, and finally the thin shell is attached to a stiff holding structure for use.
Each step in this process imparts some degree of error into the final replicated shell. Research and development efforts at MSFC are currently concentrating on reducing distortion induced during the electroforming metal deposition and release steps. Electroforming-induced distortion is caused by material stress built into the electroformed material as it deposits onto the mandrel. Decreasing release-induced distortion is a matter of reducing adhesion strength between the shell and mandrel, increasing strength of the shell material to prevent yielding, and reducing point defects in the release layer.
Additionally, verifying the performance of these advanced optics requires world-class test facilities. The basic premise of testing an optic designed for X-ray astrophysics is to place a small, bright X-ray source far away from the optic. If the angular size of the source, as viewed from the optic, is smaller than the angular resolution of the optic, the source is effectively simulating X-ray starlight. Due to the absorption of X-rays by air, the entire test facility light path must be placed inside a vacuum chamber.
At MSFC, a group of scientists and engineers operate the Marshall 100-meter X-ray beamline, a world-class end-to-end test facility for flight and laboratory X-ray optics, instruments, and telescopes. As per the name, it consists of a 100-meter-long vacuum tube with an 8-meter-long, 3-meter-diameter instrument chamber and a variety of X-ray sources ranging from 0.25 – 114 keV. Across the street sits the X-Ray and Cryogenic Facility (XRCF), a 527-meter-long beamline with an 18-meter-long, 6-meter-diameter instrument chamber. These facilities are available for the scientific community to use and highlight the comprehensive optics development and test capability that Marshall is known for.
Within the X-ray astrophysics community there exist a variety of angular resolution and effective area needs for focusing optics. Given its storied history in X-ray optics, MSFC is uniquely poised to fulfill requirements for large or small, medium- or high-angular-resolution X-ray optics. To help guide technology development, the astrophysics community convenes once per decade to produce a decadal survey. The need for high-angular-resolution and high-throughput X-ray optics is strongly endorsed by the National Academies of Sciences, Engineering, and Medicine report, Pathways to Discovery in Astronomy and Astrophysics for the 2020s.In pursuit of this goal, MSFC is continuing to advance the state of the art in full-shell optics. This work will enable the extraordinary mysteries of the X-ray universe to be revealed.
Project Leads
Dr. Jessica Gaskin and Dr. Stephen Bongiorno, NASA Marshall Space Flight Center (MSFC)
Sponsoring Organizations
The NASA Astrophysics Division supports this work primarily through the Internal Scientist Funding Model Direct Work Package and competed solicitations. This work is also supported by the Heliophysics Division through competed solicitations, as well as by directed work from other government entities.
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Last Updated Oct 15, 2024 Related Terms
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Sols 4331-4333: Today’s Rover ABC – Aurora, Backwards Driving, and Chemistry, with a Side of Images
This image shows just how variable and interesting the terrain is in the area that NASA’s Mars rover Curiosity is currently investigating. Curiosity captured this long-distance Remote Micro Imager (RMI) image using the Chemistry & Camera (ChemCam) aboard the rover on sol 4329 — Martian day 4,329 of the Mars Science Laboratory mission — on Oct. 10, 2024 at 02:30:12 UTC. NASA/JPL-Caltech/LANL Earth planning date: Friday, Oct. 11, 2024
This blogger is in the United Kingdom, just north of London, where we yesterday had beautiful night skies with a red aurora that was even visible with the unaided eye, and looked stunning on photographs. That reminded me of the solar storm that made it all the way to Mars earlier this year. Here is my colleague Deborah’s blog about it: “Aurora Watch on Mars.” And, of course, that was a great opportunity to do atmospheric science and prepare for future crewed missions, to assess radiation that future astronauts might encounter. You can read about it in the article, “NASA Watches Mars Light Up During Epic Solar Storm.” But now, back from shiny red night skies north of London, and auroras on Mars six months ago, to today’s planning!
Power — always a negotiation! Today, I was the Science Operations Working Group chair, the one who has to watch for the more technical side of things, such as the question if all the activities will fit into the plan. Today there were many imaging ideas to capture the stunning landscape in detail with Mastcam and very close close-ups with the long-distance imaging capability of ChemCam (RMI). Overall, we have two long-distance RMIs in the plan to capture the details of the ridge we are investigating. You can see in the accompanying image an example from last sol of just how many stunning details we can see. I so want to go and pick up that smooth white-ish looking rock to find out if it is just the light that makes it so bright, or if the surface is different from the underside… but that’s just me, a mineralogist by training, used to wandering around a field site! Do you notice the different patterns — textures as we call them in geology — on the rocks to the left of that white-ish rock and the right of it? So much stunning detail, and we are getting two more RMI observations of 10 frames each in today’s plan! In addition there are more than 80 Mastcam frames planned. Lots of images to learn from!
Chemistry is also featuring in the plan. The rover is stable on its wheels, which means we can get the arm out and do an APXS measurement on the target “Midnight Lake,” which MAHLI also images. The LIBS investigations are seconding the APXS investigation on Midnight Lake, and add another target to the plan, “Pyramidal Pinnacle.” On the third sol there is an AEGIS, the LIBS measurement where the rover picks its own target before we here on Earth even see where it is! Power was especially tight today, because the CheMin team does some housekeeping, in particular looking at empty cells in preparation for the next drill. The atmosphere team adds many investigations to look out for dust devils and the dustiness of the atmosphere, and APXS measures the argon content of the atmosphere. This is a measure for the seasonal changes of the atmosphere, as argon is an inert gas that does not react with other components of the atmosphere. It is only controlled by the temperature in various places of the planet — mainly the poles. DAN continues to monitor water in the subsurface, and RAD — prominently featured during the solar storm I was talking about earlier — continues to collect data on the radiation environment.
Let’s close with a fun fact from planning today: During one of the meetings, the rover drivers were asked, “Are you driving backwards again?” … and the answer was yes! The reason: We need to make sure that in this rugged terrain, with its many interesting walls (interesting for the geologists!), the antenna can still see Earth when we want to send the plan. So the drive on sol 4332 is all backwards. I am glad we have hazard cameras on the front and the back of the vehicle!
Written by Susanne Schwenzer, Planetary Geologist at The Open University
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Last Updated Oct 13, 2024 Related Terms
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NASA’s Hubble, New Horizons Team Up for a Simultaneous Look at Uranus
NASA’s Hubble Space Telescope (left) and NASA’s New Horizon’s spacecraft (right) images the planet Uranus. NASA, ESA, STScI, Samantha Hasler (MIT), Amy Simon (NASA-GSFC), New Horizons Planetary Science Theme Team; Image Processing: Joseph DePasquale (STScI), Joseph Olmsted (STScI)
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NASA’s Hubble Space Telescope and New Horizons spacecraft simultaneously set their sights on Uranus recently, allowing scientists to make a direct comparison of the planet from two very different viewpoints. The results inform future plans to study like types of planets around other stars.
Astronomers used Uranus as a proxy for similar planets beyond our solar system, known as exoplanets, comparing high-resolution images from Hubble to the more-distant view from New Horizons. This combined perspective will help scientists learn more about what to expect while imaging planets around other stars with future telescopes.
“While we expected Uranus to appear differently in each filter of the observations, we found that Uranus was actually dimmer than predicted in the New Horizons data taken from a different viewpoint,” said lead author Samantha Hasler of the Massachusetts Institute of Technology in Cambridge and New Horizons science team collaborator.
In this image, two three-dimensional shapes (top) of Uranus are compared to the actual views of the planet from NASA’s Hubble Space Telescope (bottom left) and NASA’s New Horizon’s spacecraft (bottom right). Comparing high-resolution images from Hubble to the smaller view from New Horizons offers a combined perspective that will help researchers learn more about what to expect while imaging planets around other stars with future observatories. NASA, ESA, STScI, Samantha Hasler (MIT), Amy Simon (NASA-GSFC), New Horizons Planetary Science Theme Team; Image Processing: Joseph DePasquale (STScI), Joseph Olmsted (STScI)
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Direct imaging of exoplanets is a key technique for learning about their potential habitability, and offers new clues to the origin and formation of our own solar system. Astronomers use both direct imaging and spectroscopy to collect light from the observed planet and compare its brightness at different wavelengths. However, imaging exoplanets is a notoriously difficult process because they’re so far away. Their images are mere pinpoints and so are not as detailed as the close-up views that we have of worlds orbiting our Sun. Researchers can also only directly image exoplanets at “partial phases,” when only a portion of the planet is illuminated by their star as seen from Earth.
Uranus was an ideal target as a test for understanding future distant observations of exoplanets by other telescopes for a few reasons. First, many known exoplanets are also gas giants similar in nature. Also, at the time of the observations, New Horizons was on the far side of Uranus, 6.5 billion miles away, allowing its twilight crescent to be studied—something that cannot be done from Earth. At that distance, the New Horizons view of the planet was just several pixels in its color camera, called the Multispectral Visible Imaging Camera.
On the other hand, Hubble, with its high resolution, and in its low-Earth orbit 1.7 billion miles away from Uranus, was able to see atmospheric features such as clouds and storms on the day side of the gaseous world.
“Uranus appears as just a small dot on the New Horizons observations, similar to the dots seen of directly-imaged exoplanets from observatories like Webb or ground-based observatories,” added Hasler. “Hubble provides context for what the atmosphere is doing when it was observed with New Horizons.”
The gas giant planets in our solar system have dynamic and variable atmospheres with changing cloud cover. How common is this among exoplanets? By knowing the details of what the clouds on Uranus looked like from Hubble, researchers are able to verify what is interpreted from the New Horizons data. In the case of Uranus, both Hubble and New Horizons saw that the brightness did not vary as the planet rotated, which indicates that the cloud features were not changing with the planet’s rotation.
However, the importance of the detection by New Horizons has to do with how the planet reflects light at a different phase than what Hubble, or other observatories on or near Earth, can see. New Horizons showed that exoplanets may be dimmer than predicted at partial and high phase angles, and that the atmosphere reflects light differently at partial phase.
NASA has two major upcoming observatories in the works to advance studies of exoplanet atmospheres and potential habitability.
“These landmark New Horizons studies of Uranus from a vantage point unobservable by any other means add to the mission’s treasure trove of new scientific knowledge, and have, like many other datasets obtained in the mission, yielded surprising new insights into the worlds of our solar system,” added New Horizons principal investigator Alan Stern of the Southwest Research Institute.
This illustration shows NASA’s New Horizons spacecraft’s view of our solar system from deep in the Kuiper Belt. New Horizons is currently at an estimated distance of more than 5 billion miles from Earth. The probe was 6.5 billion miles away from Uranus when it recently observed the planet. In this study, researchers used the gas giant as an exoplanet proxy, comparing high-resolution images from NASA’s Hubble Space Telescope to the smaller view from New Horizons to learn more about what to expect while imaging planets around other stars. NASA, ESA, Christian Nieves (STScI), Ralf Crawford (STScI), Greg Bacon (STScI)
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NASA’s upcoming Nancy Grace Roman Space Telescope, set to launch by 2027, will use a coronagraph to block out a star’s light to directly see gas giant exoplanets. NASA’s Habitable Worlds Observatory, in an early planning phase, will be the first telescope designed specifically to search for atmospheric biosignatures on Earth-sized, rocky planets orbiting other stars.
“Studying how known benchmarks like Uranus appear in distant imaging can help us have more robust expectations when preparing for these future missions,” concluded Hasler. “And that will be critical to our success.”
Launched in January 2006, New Horizons made the historic flyby of Pluto and its moons in July 2015, before giving humankind its first close-up look at one of these planetary building block and Kuiper Belt object, Arrokoth, in January 2019. New Horizons is now in its second extended mission, studying distant Kuiper Belt objects, characterizing the outer heliosphere of the Sun, and making important astrophysical observations from its unmatched vantage point in distant regions of the solar system.
The Uranus results are being presented this week at the 56th annual meeting of the American Astronomical Society Division for Planetary Sciences, in Boise, Idaho.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
The Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, built and operates the New Horizons spacecraft and manages the mission for NASA’s Science Mission Directorate. Southwest Research Institute, based in San Antonio and Boulder, Colorado, directs the mission via Principal Investigator Alan Stern and leads the science team, payload operations and encounter science planning. New Horizons is part of NASA’s New Frontiers program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Media Contacts:
Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, MD
claire.andreoli@nasa.gov
Hannah Braun, Ray Villard
Space Telescope Science Institute, Baltimore, MD
Science Contacts:
Samantha Hasler
Massachusetts Institute of Technology, Cambridge, MA
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Last Updated Oct 09, 2024 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Hubble Space Telescope
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