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Has ESA's GAIA spacecraft discovered the missing link in Black Holes?
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By NASA
Explore This Section Overview Science Science Findings Juno’s Orbits Spacecraft People Stories Multimedia JunoCam Images Jupiter hosts the brightest and most spectacular auroras in the Solar System. Near its poles, these shimmering lights offer a glimpse into how the planet interacts with the solar wind and moons swept by Jupiter’s magnetic field. Unlike Earth’s northern lights, the largest moons of Jupiter create their own auroral signatures in the planet’s atmosphere — a phenomenon that Earth’s Moon does not produce. These moon-induced auroras, known as “satellite footprints,” reveal how each moon interacts with its local space environment.
Juno capturing the marks on Jupiter of all four Galilean moons. The auroras related to each are labeled Io, Eur (for Europa), Gan (for Ganymede), and Cal (for Callisto). NASA/JPL-Caltech/SwRI/UVS team/MSSS/Gill/Jónsson/Perry/Hue/Rabia Before NASA’s Juno mission, three of Jupiter’s four largest moons, known as Galilean moons — Io, Europa, and Ganymede — were shown to produce these distinct auroral signatures. But Callisto, the most distant of the Galilean moons, remained a mystery. Despite multiple attempts using NASA’s Hubble Space Telescope, Callisto’s footprint had proven elusive, both because it is faint and because it most often lies atop the brighter main auroral oval, the region where auroras are displayed.
NASA’s Juno mission, orbiting Jupiter since 2016, offers unprecedented close-up views of these polar light shows. But to image Callisto’s footprint, the main auroral oval needs to move aside while the polar region is being imaged. And to bring to bear Juno’s arsenal of instruments studying fields and particles, the spacecraft’s trajectory must carry it across the magnetic field line linking Callisto and Jupiter.
These two events serendipitously occurred during Juno’s 22nd orbit of the giant planet, in September 2019, revealing Callisto’s auroral footprint and providing a sample of the particle population, electromagnetic waves, and magnetic fields associated with the interaction.
Jupiter’s magnetic field extends far beyond its major moons, carving out a vast region (magnetosphere) enveloped by, and buffeted by, the solar wind streaming from our Sun. Just as solar storms on Earth push the northern lights to more southern latitudes, Jupiter’s auroras are also affected by our Sun’s activity. In September 2019, a massive, high-density solar stream buffeted Jupiter’s magnetosphere, briefly revealing — as the auroral oval moved toward Jupiter’s equator — a faint but distinct signature associated with Callisto. This discovery finally confirms that all four Galilean moons leave their mark on Jupiter’s atmosphere, and that Callisto’s footprints are sustained much like those of its siblings, completing the family portrait of the Galilean moon auroral signatures.
An international team of scientists led by Jonas Rabia of the Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS, CNES, in Toulouse, France, published their paper on the discovery, “In situ and remote observations of the ultraviolet footprint of the moon Callisto by the Juno spacecraft,” in the journal Nature Communications on Sept. 1, 2025.
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Last Updated Sep 02, 2025 Related Terms
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By European Space Agency
In the past decade, the European Space Agency’s Gaia mission has revealed the nature, history, and behaviour of billions of stars. Our pioneering stargazer has reshaped our view of the skies around us like no other, revealing that star clusters are more connected than expected over vast distances.
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Written by Michael Allen
An international team of astronomers using NASA’s IXPE (Imaging X-ray Polarimetry Explorer), has challenged our understanding of what happens to matter in the direct vicinity of a black hole.
With IXPE, astronomers can study incoming X-rays and measure the polarization, a property of light that describes the direction of its electric field.
The polarization degree is a measurement of how aligned those vibrations are to each other. Scientists can use a black hole’s polarization degree to determine the location of the corona – a region of extremely hot, magnetized plasma that surrounds a black hole – and how it generates X-rays.
This illustration of material swirling around a black hole highlights a particular feature, called the “corona,” that shines brightly in X-ray light. In this depiction, the corona can be seen as a purple haze floating above the underlying accretion disk, and extending slightly inside of its inner edge. The material within the inner accretion disk is incredibly hot and would glow with a blinding blue-white light, but here has been reduced in brightness to make the corona stand out with better contrast. Its purple color is purely illustrative, standing in for the X-ray glow that would not be obvious in visible light. The warp in the disk is a realistic representation of how the black hole’s immense gravity acts like an optical lens, distorting our view of the flat disk that encircles it. NASA/Caltech-IPAC/Robert Hurt In April, astronomers used IXPE to measure a 9.1% polarization degree for black hole IGR J17091-3624, much higher than they expected based on theoretical models.
“The black hole IGR J17091-3624 is an extraordinary source which dims and brightens with the likeness of a heartbeat, and NASA’s IXPE allowed us to measure this unique source in a brand-new way.” said Melissa Ewing, the lead of the study based at Newcastle University in Newcastle upon Tyne, England.
In X-ray binary systems, an extremely dense object, like a black hole, pulls matter from a nearby source, most often a neighboring star. This matter can begin to swirl around, flattening into a rotating structure known as an accretion disc.
The corona, which lies in the inner region of this accretion disc, can reach extreme temperatures up to 1.8 billion degrees Fahrenheit and radiate very luminous X-rays. These ultra-hot coronas are responsible for some of the brightest X-ray sources in the sky.
Despite how bright the corona is in IGRJ17091-364, at some 28,000 light-years from Earth, it remains far too small and distant for astronomers to capture an image of it.
“Typically, a high polarization degree corresponds with a very edge-on view of the corona. The corona would have to be perfectly shaped and viewed at just the right angle to achieve such a measurement,” said Giorgio Matt, professor at the University of Roma Tre in Italy and a co-author on this paper. “The dimming pattern has yet to be explained by scientists and could hold the keys to understanding this category of black holes.”
The stellar companion of this black hole isn’t bright enough for astronomers to directly estimate the system’s viewing angle, but the unusual changes in brightness observed by IXPE suggest that the edge of the accretion disk was directly facing Earth.
The researchers explored different avenues to explain the high polarization degree.
In one model, astronomers included a “wind” of matter lifted from the accretion disc and launched away from the system, a rarely seen phenomenon. If X-rays from the corona were to meet this matter on their way to IXPE, Compton scattering would occur, leading to these measurements.
Fast Facts
Polarization measurements from IXPE carry information about the orientation and alignment of emitted X-ray light waves. The high the degree of polarization, the more the X-ray waves are traveling in sync. Most polarization in the corona come from a process known as Compton scattering, where light from the accretion disc bounces off the hot plasma of the corona, gaining energy and aligning to vibrate in the same direction. “These winds are one of the most critical missing pieces to understand the growth of all types of black holes,” said Maxime Parra, who led the observation and works on this topic at Ehime University in Matsuyama, Japan. “Astronomers could expect future observations to yield even more surprising polarization degree measurements.”
Another model assumed the plasma in the corona could exhibit a very fast outflow. If the plasma were to be streaming outwards at speeds as high as 20% the speed of light, or roughly 124 million miles per hour, relativistic effects could boost the observed polarization.
In both cases, the simulations could recreate the observed polarization without a very specific edge-on view. Researchers will continue to model and test their predictions to better understand the high polarization degree for future research efforts.
More about IXPE
IXPE, which continues to provide unprecedented data enabling groundbreaking discoveries about celestial objects across the universe, is a joint NASA and Italian Space Agency mission with partners and science collaborators in 12 countries. IXPE is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. BAE Systems, Inc., headquartered in Falls Church, Virginia, manages spacecraft operations together with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder.
Learn more about IXPE’s ongoing mission here:
https://www.nasa.gov/ixpe
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Last Updated Aug 12, 2025 EditorBeth RidgewayContactCorinne Edmistoncorinne.m.edmiston@nasa.govLocationMarshall Space Flight Center Related Terms
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By NASA
Science: NASA, ESA, CXC, Yi-Chi Chang (National Tsing Hua University); Image Processing: Joseph DePasquale (STScI) NASA’s Hubble Space Telescope and NASA’s Chandra X-ray Observatory teamed up to identify a new possible example of a rare class of black holes, identified by X-ray emission (in purple) in this image released on July 24, 2025. Called NGC 6099 HLX-1, this bright X-ray source seems to reside in a compact star cluster in a giant elliptical galaxy. These rare black holes are called intermediate-mass black holes (IMBHs) and weigh between a few hundred to a few 100,000 times the mass of our Sun.
Learn more about IMBHs and what studying them can tell us about the universe.
Image credit: Science: NASA, ESA, CXC, Yi-Chi Chang (National Tsing Hua University); Image Processing: Joseph DePasquale (STScI)
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By NASA
Software designed to give spacecraft more autonomy could support a future where swarms of satellites navigate and complete scientific objectives with limited human intervention.
Caleb Adams, Distributed Spacecraft Autonomy project manager, monitors testing alongside the test racks containing 100 spacecraft computers at NASA’s Ames Research Center in California’s Silicon Valley. The DSA project develops and demonstrates software to enhance multi-spacecraft mission adaptability, efficiently allocate tasks between spacecraft using ad-hoc networking, and enable human-swarm commanding of distributed space missions. Credit: NASA/Brandon Torres Navarrete Astronauts living and working on the Moon and Mars will rely on satellites to provide services like navigation, weather, and communications relays. While managing complex missions, automating satellite communications will allow explorers to focus on critical tasks instead of manually operating satellites.
Long duration space missions will require teaming between systems on Earth and other planets. Satellites orbiting the Moon, Mars, or other distant areas face communications delays with ground operators which could limit the efficiency of their missions.
The solution lies within the Distributed Spacecraft Autonomy (DSA) project, led by NASA’s Ames Research Center in California’s Silicon Valley, which tests how shared autonomy across distributed spacecraft missions makes spacecraft swarms more capable of self-sufficient research and maintenance by making decisions and adapting to changes with less human intervention.
Adding autonomy to satellites makes them capable of providing services without waiting for commands from ground operators. Distributing the autonomy across multiple satellites, operating like a swarm, gives the spacecraft a “shared brain” to accomplish goals they couldn’t achieve alone.
The DSA software, built by NASA researchers, provides the swarm with a task list, and shares each spacecraft’s distinct perspective – what it can observe, what its priorities are – and integrates those perspectives into the best plan of action for the whole swarm. That plan is supported by decision trees and mathematical models that help the swarm decide what action to take after a command is completed, how to respond to a change, or address a problem.
Sharing the Workload
The first in-space demonstration of DSA began onboard the Starling spacecraft swarm, a group of four small satellites, demonstrating various swarm technologies. Operating since July 2023, the Starling mission continues providing a testing and validation platform for autonomous swarm operations. The swarm first used DSA to optimize scientific observations, deciding what to observe without pre-programmed instructions. These autonomous observations led to measurements that could have been missed if an operator had to individually instruct each satellite.
The Starling swarm measured the electron content of plasma between each spacecraft and GPS satellites to capture rapidly changing phenomena in Earth’s ionosphere – where Earth’s atmosphere meets space. The DSA software allowed the swarm to independently decide what to study and how to spread the workload across the four spacecraft.
Because each Starling spacecraft operates as an independent member within the swarm, if one swarm member was unable to accomplish its work, the other three swarm members could react and complete the mission’s goals.
The Starling 1.0 demonstration achieved several firsts, including the first fully distributed autonomous operation of multiple spacecraft, the first use of space-to-space communications to autonomously share status information between multiple spacecraft, the first demonstration of fully distributed reactive operations onboard multiple spacecraft, the first use of a general-purpose automated reasoning system onboard a spacecraft, and the first use of fully distributed automated planning onboard multiple spacecraft. These achievements laid the groundwork for Starling 1.5+, an ongoing continuation of the satellite swarm’s mission using DSA.
Advanced testing of DSA onboard Starling shows that distributed autonomy in spacecraft swarms can improve efficiencies while reducing the workload on human operators.Credit: NASA/Daniel Rutter A Helping Hand in Orbit
After DSA’s successful demonstration on Starling 1.0, the team began exploring additional opportunities to use the software to support satellite swarm health and efficiency. Continued testing of DSA on Starling’s extended mission included PLEXIL (Plan Execution Interchange Language), a NASA-developed programming language designed for reliable and flexible automation of complex spacecraft operations.
Onboard Starling, the PLEXIL application demonstrated autonomous maintenance, allowing the swarm to manage normal spacecraft operations, correct issues, or distribute software updates across individual spacecraft.
Enhanced autonomy makes swarm operation in deep space feasible – instead of requiring spacecraft to communicate back and forth between their distant location and Earth, which can take minutes or hours depending on distance, the PLEXIL-enabled DSA software gives the swarm the ability to make decisions collaboratively to optimize their mission and reduce workloads.
Simulated Lunar Swarming
To understand the scalability of DSA, the team used ground-based flight computers to simulate a lunar swarm of virtual small spacecraft. The computers simulated a swarm that provides position, navigation, and timing services on the Moon, similar to GPS services on Earth, which rely on a network of satellites to pinpoint locations.
The DSA team ran nearly one hundred tests over two years, demonstrating swarms of different sizes at high and low lunar orbits. The lessons learned from those early tests laid the groundwork for additional scalability studies. The second round of testing, set to begin in 2026, will demonstrate even larger swarms, using flight computers that could later go into orbit with DSA software onboard.
The Future of Spacecraft Swarms
Orbital and simulated tests of DSA are a launchpad to increased use of distributed autonomy across spacecraft swarms. Developing and proving these technologies increases efficiency, decreases costs, and enhances NASA’s capabilities opening the door to autonomous spacecraft swarms supporting missions to the Moon, Mars, and beyond.
Milestones:
October 2018: DSA project development begins. April 2020: Lunar position, navigation, and timing (LPNT) simulation demonstration development begins. July 2023: DSA launches onboard the Starling spacecraft swarm. March 2024: DSA experiments onboard Starling reach the necessary criteria for success. July 2024: DSA software development begins for the Starling 1.5+ mission extension. September 2024: LPNT simulation demonstration concludes successfully. October 2024: DSA’s extended mission as part of Starling 1.5+ begins. Partners:
NASA Ames leads the Distributed Spacecraft Autonomy and Starling projects. NASA’s Game Changing Development program within the agency’s Space Technology Mission Directorate provided funding for the DSA experiment. NASA’s Small Spacecraft Technology program within the Space Technology Mission Directorate funds and manages the Starling mission and the DSA project.
Learn More:
Satellite Swarms for Science ‘Grow up’ at NASA Ames (NASA Story, June 2023) NASA’s Starling Mission Sending Swarm of Satellites into Orbit (NASA Story, July 2023) Swarming for Success: Starling Completes Primary Mission (NASA Story, May 2024) NASA Demonstrates Software ‘Brains’ Shared Across Satellite Swarms (NASA Story, February 2025) For researchers:
Distributed Spacecraft Autonomy Mission Page Distributed Spacecraft Autonomy TechPort Project Page Starling Mission Page For media:
Members of the news media interested in covering this topic should reach out to the NASA Ames newsroom.
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