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By NASA
9 Min Read Towards Autonomous Surface Missions on Ocean Worlds
Artist’s concept image of a spacecraft lander with a robot arm on the surface of Europa. Credits:
NASA/JPL – Caltech Through advanced autonomy testbed programs, NASA is setting the groundwork for one of its top priorities—the search for signs of life and potentially habitable bodies in our solar system and beyond. The prime destinations for such exploration are bodies containing liquid water, such as Jupiter’s moon Europa and Saturn’s moon Enceladus. Initial missions to the surfaces of these “ocean worlds” will be robotic and require a high degree of onboard autonomy due to long Earth-communication lags and blackouts, harsh surface environments, and limited battery life.
Technologies that can enable spacecraft autonomy generally fall under the umbrella of Artificial Intelligence (AI) and have been evolving rapidly in recent years. Many such technologies, including machine learning, causal reasoning, and generative AI, are being advanced at non-NASA institutions.
NASA started a program in 2018 to take advantage of these advancements to enable future icy world missions. It sponsored the development of the physical Ocean Worlds Lander Autonomy Testbed (OWLAT) at NASA’s Jet Propulsion Laboratory in Southern California and the virtual Ocean Worlds Autonomy Testbed for Exploration, Research, and Simulation (OceanWATERS) at NASA’s Ames Research Center in Silicon Valley, California.
NASA solicited applications for its Autonomous Robotics Research for Ocean Worlds (ARROW) program in 2020, and for the Concepts for Ocean worlds Life Detection Technology (COLDTech) program in 2021. Six research teams, based at universities and companies throughout the United States, were chosen to develop and demonstrate autonomy solutions on OWLAT and OceanWATERS. These two- to three-year projects are now complete and have addressed a wide variety of autonomy challenges faced by potential ocean world surface missions.
OWLAT
OWLAT is designed to simulate a spacecraft lander with a robotic arm for science operations on an ocean world body. The overall OWLAT architecture including hardware and software components is shown in Figure 1. Each of the OWLAT components is detailed below.
Figure 1. The software and hardware components of the Ocean Worlds Lander Autonomy Testbed and the relationships between them. NASA/JPL – Caltech The hardware version of OWLAT (shown in Figure 2) is designed to physically simulate motions of a lander as operations are performed in a low-gravity environment using a six degrees-of-freedom (DOF) Stewart platform. A seven DOF robot arm is mounted on the lander to perform sampling and other science operations that interact with the environment. A camera mounted on a pan-and-tilt unit is used for perception. The testbed also has a suite of onboard force/torque sensors to measure motion and reaction forces as the lander interacts with the environment. Control algorithms implemented on the testbed enable it to exhibit dynamics behavior as if it were a lightweight arm on a lander operating in different gravitational environments.
Figure 2. The Ocean Worlds Lander Autonomy Testbed. A scoop is mounted to the end of the testbed robot arm. NASA/JPL – Caltech The team also developed a set of tools and instruments (shown in Figure 3) to enable the performance of science operations using the testbed. These various tools can be mounted to the end of the robot arm via a quick-connect-disconnect mechanism. The testbed workspace where sampling and other science operations are conducted incorporates an environment designed to represent the scene and surface simulant material potentially found on ocean worlds.
Figure 3. Tools and instruments designed to be used with the testbed. NASA/JPL – Caltech The software-only version of OWLAT models, visualizes, and provides telemetry from a high-fidelity dynamics simulator based on the Dynamics And Real-Time Simulation (DARTS) physics engine developed at JPL. It replicates the behavior of the physical testbed in response to commands and provides telemetry to the autonomy software. A visualization from the simulator is shown on Figure 4.
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Figure 7. Screenshot of OceanWATERS lander on a terrain modeled from the Atacama Desert. A scoop operation has just been completed. NASA/JPL – Caltech The autonomy software module shown at the top in Figure 1 interacts with the testbed through a Robot Operating System (ROS)-based interface to issue commands and receive telemetry. This interface is defined to be identical to the OceanWATERS interface. Commands received from the autonomy module are processed through the dispatcher/scheduler/controller module (blue box in Figure 1) and used to command either the physical hardware version of the testbed or the dynamics simulation (software version) of the testbed. Sensor information from the operation of either the software-only or physical testbed is reported back to the autonomy module using a defined telemetry interface. A safety and performance monitoring and evaluation software module (red box in Figure 1) ensures that the testbed is kept within its operating bounds. Any commands causing out of bounds behavior and anomalies are reported as faults to the autonomy software module.
Figure 5. Erica Tevere (at the operator’s station) and Ashish Goel (at the robot arm) setting up the OWLAT testbed for use. NASA/JPL – Caltech OceanWATERS
At the time of the OceanWATERS project’s inception, Jupiter’s moon Europa was planetary science’s first choice in searching for life. Based on ROS, OceanWATERS is a software tool that provides a visual and physical simulation of a robotic lander on the surface of Europa (see Figure 6). OceanWATERS realistically simulates Europa’s celestial sphere and sunlight, both direct and indirect. Because we don’t yet have detailed information about the surface of Europa, users can select from terrain models with a variety of surface and material properties. One of these models is a digital replication of a portion of the Atacama Desert in Chile, an area considered a potential Earth-analog for some extraterrestrial surfaces.
Figure 6. Screenshot of OceanWATERS. NASA/JPL – Caltech JPL’s Europa Lander Study of 2016, a guiding document for the development of OceanWATERS, describes a planetary lander whose purpose is collecting subsurface regolith/ice samples, analyzing them with onboard science instruments, and transmitting results of the analysis to Earth.
The simulated lander in OceanWATERS has an antenna mast that pans and tilts; attached to it are stereo cameras and spotlights. It has a 6 degree-of-freedom arm with two interchangeable end effectors—a grinder designed for digging trenches, and a scoop for collecting ground material. The lander is powered by a simulated non-rechargeable battery pack. Power consumption, the battery’s state, and its remaining life are regularly predicted with the Generic Software Architecture for Prognostics (GSAP) tool. To simulate degraded or broken subsystems, a variety of faults (e.g., a frozen arm joint or overheating battery) can be “injected” into the simulation by the user; some faults can also occur “naturally” as the simulation progresses, e.g., if components become over-stressed. All the operations and telemetry (data measurements) of the lander are accessible via an interface that external autonomy software modules can use to command the lander and understand its state. (OceanWATERS and OWLAT share a unified autonomy interface based on ROS.) The OceanWATERS package includes one basic autonomy module, a facility for executing plans (autonomy specifications) written in the PLan EXecution Interchange Language, or PLEXIL. PLEXIL and GSAP are both open-source software packages developed at Ames and available on GitHub, as is OceanWATERS.
Mission operations that can be simulated by OceanWATERS include visually surveying the landing site, poking at the ground to determine its hardness, digging a trench, and scooping ground material that can be discarded or deposited in a sample collection bin. Communication with Earth, sample analysis, and other operations of a real lander mission, are not presently modeled in OceanWATERS except for their estimated power consumption. Figure 7 is a video of OceanWATERS running a sample mission scenario using the Atacama-based terrain model.
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Figure 7. Screenshot of OceanWATERS lander on a terrain modeled from the Atacama Desert. A scoop operation has just been completed. NASA/JPL – Caltech Because of Earth’s distance from the ocean worlds and the resulting communication lag, a planetary lander should be programmed with at least enough information to begin its mission. But there will be situation-specific challenges that will require onboard intelligence, such as deciding exactly where and how to collect samples, dealing with unexpected issues and hardware faults, and prioritizing operations based on remaining power.
Results
All six of the research teams funded by the ARROW and COLDTech programs used OceanWATERS to develop ocean world lander autonomy technology and three of those teams also used OWLAT. The products of these efforts were published in technical papers, and resulted in development of software that may be used or adapted for actual ocean world lander missions in the future. The following table summarizes the ARROW and COLDTech efforts.
Principal Investigator (PI) PI Institution Project Testbed Used Purpose of Project ARROW Projects Jonathan Bohren Honeybee Robotics Stochastic PLEXIL (SPLEXIL) OceanWATERS Extended PLEXIL with stochastic decision-making capabilities by employing reinforcement learning techniques. Pooyan Jamshidi University of South Carolina Resource Adaptive Software Purpose-Built for Extraordinary Robotic Research Yields (RASPBERRY SI) OceanWATERS & OWLAT Developed software algorithms and tools for fault root cause identification, causal debugging, causal optimization, and causal-induced verification. COLDTech Projects Eric Dixon Lockheed Martin Causal And Reinforcement Learning (CARL) for COLDTech OceanWATERS Integrated a model of JPL’s mission-ready Cold Operable Lunar Deployable Arm (COLDarm) into OceanWATERS and applied image analysis, causal reasoning, and machine learning models to identify and mitigate the root causes of faults, such as ice buildup on the arm’s end effector. Jay McMahon University of Colorado Robust Exploration with Autonomous Science On-board, Ranked Evaluation of Contingent Opportunities for Uninterrupted Remote Science Exploration (REASON-RECOURSE) OceanWATERS Applied automated planning with formal methods to maximize science return of the lander while minimizing communication with ground team on Earth. Melkior Ornik U Illinois, Urbana-Champaign aDaptive, ResIlient Learning-enabLed oceAn World AutonomY (DRILLAWAY) OceanWATERS & OWLAT Developed autonomous adaptation to novel terrains and selecting scooping actions based on the available image data and limited experience by transferring the scooping procedure learned from a low-fidelity testbed to the high-fidelity OWLAT testbed. Joel Burdick Caltech Robust, Explainable Autonomy for Scientific Icy Moon Operations (REASIMO) OceanWATERS & OWLAT Developed autonomous 1) detection and identification of off-nominal conditions and procedures for recovery from those conditions, and 2) sample site selection Acknowledgements: The portion of the research carried out at the Jet Propulsion Laboratory, California Institute of Technology was performed under a contract with the National Aeronautics and Space Administration (80NM0018D0004). The portion of the research carried out by employees of KBR Wyle Services LLC at NASA Ames Research Center was performed under a contract with the National Aeronautics and Space Administration (80ARC020D0010). Both were funded by the Planetary Science Division ARROW and COLDTech programs.
Project Leads: Hari Nayar (NASA Jet Propulsion Laboratory, California Institute of Technology), K. Michael Dalal (KBR, Inc. at NASA Ames Research Center)
Sponsoring Organizations: NASA SMD PESTO
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By NASA
8 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Virtual meetings feeling a little stale? NASA has just unveiled a suite of new Artemis backgrounds to elevate your digital workspace.
From the majesty of the Artemis I launch lighting up the night sky to the iconic image of the Orion spacecraft with the Moon and Earth in view, these virtual backgrounds allow viewers to relive the awe-inspiring moments of Artemis I and glimpse the bright future that lies ahead as the Artemis campaign enables humans to live and work at the Moon’s South Pole region.
Scroll through to download your next virtual background for work, school, or just for fun, and learn about all things Artemis as the agency and its partners cross off milestones leading up to Artemis II and missions beyond.
Artemis I Launch
Credit: NASA/Bill Ingalls NASA’s SLS (Space Launch System) rocket carrying the Orion spacecraft launches on the Artemis I flight test on Nov. 16, 2022, from Launch Complex 39B at NASA’s Kennedy Space Center in Florida. NASA’s Artemis I mission was the first integrated flight test of the agency’s deep space exploration systems: the Orion spacecraft, SLS rocket, and ground systems. SLS and Orion launched at 1:47 a.m. EST from Launch Pad 39B at Kennedy.
Artemis II Crew
Credit: NASA Meet the astronauts who will fly around the Moon during the Artemis II mission. From left are Commander Reid Wiseman, Pilot Victor Glover, and Mission Specialist Christina Koch from NASA, and Mission Specialist Jeremy Hansen from the Canadian Space Agency.
Astronaut Regolith
Credit: NASA An artist’s concept of two suited Artemis crew members working on the lunar surface. The samples collected during future Artemis missions will continue to advance our knowledge of the solar system and help us understand the history and formation of Earth and the Moon, uncovering some of the mysteries that have long eluded scientists.
Exploration Ground Systems
Credit: NASA NASA’s mobile launcher, atop Crawler Transporter-2, is at the entrance to High Bay 3 at the Vehicle Assembly Building (VAB) on Sept. 8, 2018, at NASA’s Kennedy Space Center in Florida. This is the first time that the modified mobile launcher made the trip to the pad and the VAB. The mobile launcher is the structure that is used to assemble, process, and launch the SLS rocket.
Credit: NASA/Joel Kowsky NASA’s SLS rocket with the Orion spacecraft aboard is seen atop a mobile launcher at Launch Pad 39B on Nov. 4, 2022, as Crawler Transporter-2 departs the pad following rollout at NASA’s Kennedy Space Center in Florida.
Credit: NASA After Orion splashed down in the Pacific Ocean, west of Baja California, the spacecraft was recovered by personnel on the USS Portland from the U.S. Department of Defense, including Navy amphibious specialists, Space Force weather specialists, and Air Force specialists, as well as engineers and technicians from NASA’s Kennedy Space Center in Florida, the agency’s Johnson Space Center in Houston, and Lockheed Martin Space Operations. Personnel from NASA’s Exploration Ground Systems led the recovery efforts.
Credit: NASA/Keegan Barber NASA’s SLS (Space Launch System) rocket with the Orion spacecraft aboard is seen atop a mobile launcher as it rolls out to Launch Complex 39B for the first time on March 17, 2022, at NASA’s Kennedy Space Center in Florida. At left is the Vehicle Assembly Building.
First Woman
Credit: NASA “First Woman” graphic novel virtual background featuring an illustration of the inside of a lunar space station outfitted with research racks and computer displays. To learn more about the graphic novel and interactive experiences, visit: nasa.gov/calliefirst/
Credit: NASA “First Woman” graphic novel virtual background featuring the illustration of the inside of a lunar space station outfitted with research racks and computer displays, along with zero-g indicator suited rubber duckies floating throughout. To learn more about the graphic novel and interactive experiences, visit: nasa.gov/calliefirst/
Credit: NASA This “First Woman” graphic novel virtual background features an illustrated scene from a lunar mission. At a lunar camp, one suited astronaut flashes the peace sign while RT, the robot sidekick, waves in the foreground. To learn more about the graphic novel and interactive experiences, visit: nasa.gov/calliefirst/
Gateway
Credit: NASA The Gateway space station hosts the Orion spacecraft and SpaceX’s deep space logistics spacecraft in a polar orbit around the Moon, supporting scientific discovery on the lunar surface during the Artemis IV mission.
Credit: Northrop Grumman and Thales Alenia Space The Gateway space station’s HALO (Habitation and Logistics Outpost) module, one of two of Gateway’s habitation elements where astronauts will live, conduct science, and prepare for lunar surface missions, successfully completed welding in Turin, Italy. Following a series of tests to ensure its safety, the future home for astronauts will travel to Gilbert, Arizona, for final outfitting ahead of launch to lunar orbit. Gateway will be humanity’s first space station in lunar orbit and is an essential component of the Artemis campaign to return humans to the Moon for scientific discovery and chart a path for human missions to Mars.
Lunar Surface
Credit: SpaceX Artist’s concept of SpaceX Starship Human Landing System, or HLS, which is slated to transport astronauts to and from the lunar surface during Artemis III and IV.
Credit: Blue Origin Artist’s concept of Blue Origin’s Blue Moon MK-2 human lunar lander, which is slated to land astronauts on the Moon during Artemis V.
Credit: NASA The “Moon buggy” for NASA’s Artemis missions, the Lunar Terrain Vehicle (LTV), is seen here enabling a pair of astronauts to explore more of the Moon’s surface and conduct science research farther away from the landing site. NASA has selected Intuitive Machines, Lunar Outpost, and Venturi Astrolab to advance capabilities for an LTV.
Credit: JAXA/Toyota An artist’s concept of the pressurized rover — which is being designed, developed, and operated by JAXA (Japan Aerospace Exploration Agency) — is seen driving across the lunar terrain. The pressurized rover will serve as a mobile habitat and laboratory for the astronauts to live and work for extended periods of time on the Moon.
Logo
Credit: NASA The NASA “meatball” logo. The round red, white, and blue insignia was designed by employee James Modarelli in 1959, NASA’s second year. The design incorporates references to different aspects of NASA’s missions.
Credit: NASA The NASA meatball logo (left) and Artemis logo side by side.
Moon Phases
Credit: NASA The different phases of the Moon, shown in variations of shadowing, extend across this virtual background.
Orion
Credit: NASA On flight day 5 during Artemis I, the Orion spacecraft took a selfie while approaching the Moon ahead of the outbound powered flyby — a burn of Orion’s main engine that placed the spacecraft into lunar orbit. During this maneuver, Orion came within 81 miles of the lunar surface.
Credit: NASA On flight day 13 during Artemis I, Orion reached its maximum distance from Earth at 268,563 miles away from our home planet, traveling farther than any other spacecraft built for humans.
Credit: NASA This first high-resolution image, taken on the first day of the Artemis I mission, was captured by a camera on the tip of one of Orion’s solar arrays. The spacecraft was 57,000 miles from home and distancing itself from planet Earth as it approached the Moon and distant retrograde orbit.
Silhouettes
Credit: NASA In this virtual background, various scenes from Earth, Moon, and Mars are depicted within the silhouette outlines of three suited astronauts, artistically representing the interconnected nature of human space exploration from low Earth orbit to the Moon and, one day, human missions to Mars.
SLS (Space Launch System)
Credit: Joel Kowsky In this sunrise photo at NASA’s Kennedy Space Center in Florida, NASA’s SLS rocket with the Orion spacecraft aboard is seen atop the mobile launcher at Launch Pad 39B as preparations continued for the Artemis I launch.
Credit: NASA/Joel Kowsky In this close-up image, NASA’s SLS rocket with the Orion spacecraft aboard is seen atop the mobile launcher at Launch Pad 39B on Nov. 12, 2022, at NASA’s Kennedy Space Center in Florida.
Credit: NASA/Joel Kowsky NASA’s SLS rocket with the Orion spacecraft aboard is seen at sunrise atop the mobile launcher at Launch Pad 39B on Nov. 7, 2022, at NASA’s Kennedy Space Center in Florida.
Earth, Moon, and Mars
Credit: NASA From left, an artist’s concept of the Moon, Earth, and Mars sharing space. NASA’s long-term goal is to send humans to Mars, and we will use what we learn at the Moon to help us get there. This is the agency’s Moon to Mars exploration approach.
Credit: NASA In this artist’s concept, the upper portion of a blended sphere represents the Earth, Moon, and Mars.
Credit: NASA An artist’s concept showing, from left, the Earth, Moon, and Mars in sequence. Mars remains our horizon goal for human exploration because it is a rich destination for scientific discovery and a driver of technologies that will enable humans to travel and explore far from Earth.
About the Author
Catherine E. Williams
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Last Updated Dec 02, 2024 Related Terms
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By NASA
NASA and the U.S. Agency for International Development (USAID) invite media to the official launch celebration of the new SERVIR Central America regional hub, located in Costa Rica, on Tuesday, Dec. 3, at 11 a.m. EST. The event will be hosted by NASA SERVIR Program Manager Daniel Irwin, U.S. Ambassador to El Salvador William H. Duncan, and a representative from El Salvador’s Ministry of Environment and Natural Resources (MARN).
Betzy Hernandez from SERVIR’s Science Coordination Office leads a land cover mapping workshop in Belize. NASA and the U.S. Agency for International Development (USAID) are opening a new SERVIR Central America regional hub, located in Costa Rica, on Tuesday, Dec. 3. NASA Central America is the latest addition to SERVIR’s global network, a NASA and USAID initiative that has been operating in Asia, Africa, and Latin America since 2005.
Implemented by the Tropical Agricultural Research and Higher Education Center (CATIE), SERVIR Central America will strengthen climate resilience, sustainable resource management, and biodiversity conservation through satellite data and geospatial technology. The SERVIR Central America hub will support evidence-based decision-making at local, national, and regional levels, strengthening the resilience of more than 40 million people in one of the world’s most climate-vulnerable regions.
The event will be in Spanish with English translation available.
For press access and location details, please RSVP to Belarminda Quijano at belarminda@bqcomunicaciones.com by Monday, Dec. 2. NASA’s media accreditation policy is online. The event will be livestreamed.
For more information on SERVIR, visit:
https://www.nasa.gov/servir
Elizabeth Vlock
Headquarters, Washington
202-358-1600
elizabeth.a.vlock@nasa.gov
Lane Figueroa
Huntsville, Alabama
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lane.e.figueroa@nasa.gov
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By NASA
Hubble Space Telescope Home Hubble Captures an Edge-On… Hubble Space Telescope Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Hubble News Archive Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts E-books Lithographs Fact Sheets Glossary Posters Hubble on the NASA App More Online Activities 2 min read
Hubble Captures an Edge-On Spiral with Curve Appeal
This NASA/ESA Hubble Space Telescope image features spiral galaxy UGC 10043. ESA/Hubble & NASA, R. Windhorst, W. Keel
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This NASA/ESA Hubble Space Telescope image features a spiral galaxy, named UGC 10043. We don’t see the galaxy’s spiral arms because we are seeing it from the side. Located roughly 150 million light-years from Earth in the constellation Serpens, UGC 10043 is one of the somewhat rare spiral galaxies that we see edge-on.
This edge-on viewpoint makes the galaxy’s disk appear as a sharp line through space, with its prominent dust lanes forming thick bands of clouds that obscure our view of the galaxy’s glow. If we could fly above the galaxy, viewing it from the top down, we would see this dust scattered across UGC 10043, possibly outlining its spiral arms. Despite the dust’s obscuring nature, some active star-forming regions shine out from behind the dark clouds. We can also see that the galaxy’s center sports a glowing, almost egg-shaped ‘bulge’, rising far above and below the disk. All spiral galaxies have a bulge similar to this one as part of their structure. These bulges hold stars that orbit the galactic center on paths above and below the whirling disk; it’s a feature that isn’t normally obvious in pictures of galaxies. The unusually large size of this bulge compared to the galaxy’s disk is possibly due to UGC 10043 siphoning material from a nearby dwarf galaxy. This may also be why its disk appears warped, bending up at one end and down at the other.
Like most full-color Hubble images, this image is a composite, made up of several individual snapshots taken by Hubble at different times, each capturing different wavelengths of light. One notable aspect of this image is that the two sets of data that comprise this image were collected 23 years apart, in 2000 and 2023! Hubble’s longevity doesn’t just afford us the ability to produce new and better images of old targets; it also provides a long-term archive of data which only becomes more and more useful to astronomers.
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Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, MD
claire.andreoli@nasa.gov
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Last Updated Nov 21, 2024 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
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Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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By NASA
Hubble Space Telescope Home NASA’s Hubble Finds… Hubble Space Telescope Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Hubble News Archive Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts E-books Lithographs Fact Sheets Glossary Posters Hubble on the NASA App More Online Activities 5 Min Read NASA’s Hubble Finds Sizzling Details About Young Star FU Orionis
An artist’s concept of the early stages of the young star FU Orionis (FU Ori) outburst, surrounded by a disk of material. Credits:
NASA-JPL, Caltech In 1936, astronomers saw a puzzling event in the constellation Orion: the young star FU Orionis (FU Ori) became a hundred times brighter in a matter of months. At its peak, FU Ori was intrinsically 100 times brighter than our Sun. Unlike an exploding star though, it has declined in luminosity only languidly since then.
Now, a team of astronomers has wielded NASA’s Hubble Space Telescope‘s ultraviolet capabilities to learn more about the interaction between FU Ori’s stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. They find that the inner disk touching the star is extraordinarily hot — which challenges conventional wisdom.
The observations were made with the telescope’s COS (Cosmic Origins Spectrograph) and STIS (Space Telescope Imaging Spectrograph) instruments. The data includes the first far-ultraviolet and new near-ultraviolet spectra of FU Ori.
“We were hoping to validate the hottest part of the accretion disk model, to determine its maximum temperature, by measuring closer to the inner edge of the accretion disk than ever before,” said Lynne Hillenbrand of Caltech in Pasadena, California, and a co-author of the paper. “I think there was some hope that we would see something extra, like the interface between the star and its disk, but we were certainly not expecting it. The fact we saw so much extra — it was much brighter in the ultraviolet than we predicted — that was the big surprise.”
A Better Understanding of Stellar Accretion
Originally deemed to be a unique case among stars, FU Ori exemplifies a class of young, eruptive stars that undergo dramatic changes in brightness. These objects are a subset of classical T Tauri stars, which are newly forming stars that are building up by accreting material from their disk and the surrounding nebula. In classical T Tauri stars, the disk does not touch the star directly because it is restricted by the outward pressure of the star’s magnetic field.
The accretion disks around FU Ori objects, however, are susceptible to instabilities due to their enormous mass relative to the central star, interactions with a binary companion, or infalling material. Such instability means the mass accretion rate can change dramatically. The increased pace disrupts the delicate balance between the stellar magnetic field and the inner edge of the disk, leading to material moving closer in and eventually touching the star’s surface.
This is an artist’s concept of the early stages of the young star FU Orionis (FU Ori) outburst, surrounded by a disk of material. A team of astronomers has used the Hubble Space Telescope’s ultraviolet capabilities to learn more about the interaction between FU Ori’s stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. They found that the inner disk, touching the star, is much hotter than expected—16,000 kelvins—nearly three times our Sun’s surface temperature. That sizzling temperature is nearly twice as hot as previously believed. NASA-JPL, Caltech
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The enhanced infall rate and proximity of the accretion disk to the star make FU Ori objects much brighter than a typical T Tauri star. In fact, during an outburst, the star itself is outshined by the disk. Furthermore, the disk material is orbiting rapidly as it approaches the star, much faster than the rotation rate of the stellar surface. This means that there should be a region where the disk impacts the star and the material slows down and heats up significantly.
“The Hubble data indicates a much hotter impact region than models have previously predicted,” said Adolfo Carvalho of Caltech and lead author of the study. “In FU Ori, the temperature is 16,000 kelvins [nearly three times our Sun’s surface temperature]. That sizzling temperature is almost twice the amount prior models have calculated. It challenges and encourages us to think of how such a jump in temperature can be explained.”
To address the significant difference in temperature between past models and the recent Hubble observations, the team offers a revised interpretation of the geometry within FU Ori’s inner region: The accretion disk’s material approaches the star and once it reaches the stellar surface, a hot shock is produced, which emits a lot of ultraviolet light.
Planet Survival Around FU Ori
Understanding the mechanisms of FU Ori’s rapid accretion process relates more broadly to ideas of planet formation and survival.
“Our revised model based on the Hubble data is not strictly bad news for planet evolution, it’s sort of a mixed bag,” explained Carvalho. “If the planet is far out in the disk as it’s forming, outbursts from an FU Ori object should influence what kind of chemicals the planet will ultimately inherit. But if a forming planet is very close to the star, then it’s a slightly different story. Within a couple outbursts, any planets that are forming very close to the star can rapidly move inward and eventually merge with it. You could lose, or at least completely fry, rocky planets forming close to such a star.”
Additional work with the Hubble UV observations is in progress. The team is carefully analyzing the various spectral emission lines from multiple elements present in the COS spectrum. This should provide further clues on FU Ori’s environment, such as the kinematics of inflowing and outflowing gas within the inner region.
“A lot of these young stars are spectroscopically very rich at far ultraviolet wavelengths,” reflected Hillenbrand. “A combination of Hubble, its size and wavelength coverage, as well as FU Ori’s fortunate circumstances, let us see further down into the engine of this fascinating star-type than ever before.”
These findings have been published in The Astrophysical Journal Letters.
The observations were taken as part of General Observer program 17176.
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, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
Facebook logo @NASAHubble @NASAHubble Instagram logo @NASAHubble Media Contacts:
Claire Andreoli (claire.andreoli@nasa.gov)
NASA’s Goddard Space Flight Center, Greenbelt, MD
Abigail Major, Ray Villard
Space Telescope Science Institute, Baltimore, MD
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Last Updated Nov 21, 2024 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center Related Terms
Astrophysics Astrophysics Division Goddard Space Flight Center Hubble Space Telescope Stars Keep Exploring Discover More Topics From Hubble
Hubble Space Telescope
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
Exploring the Birth of Stars
Hubble’s Night Sky Challenge
Hubble Focus: The Lives of Stars
This e-book highlights the mission’s recent discoveries and observations related to the birth, evolution, and death of stars.
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