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By European Space Agency
Image: This image shows Webb’s recent observation of the asteroid 2024 YR4 using both its Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). Data from NIRCam shows reflected light, while the MIRI observations show thermal light.
On 8 March 2025, the NASA/ESA/CSA James Webb Space Telescope turned its watchful eye toward asteroid 2024 YR4, which we now know poses no significant threat to Earth in 2032 and beyond.
This is the smallest object targeted by Webb to date, and one of the smallest objects to have its size directly measured.
Observations were taken to study the thermal properties of 2024 YR4, including how quickly it heats up and cools down and how hot it is at its current distance from the Sun. These measurements indicate that this asteroid does not share properties observed in larger asteroids. This is likely a combination of its fast spin and lack of fine-grained sand on its surface. Further research is needed, however this is considered consistent with a surface dominated by rocks that are roughly fist-sized or larger.
Asteroid 2024 YR4 was recently under close watch by the team at ESA's Near Earth Objects Coordination Centre, located in Italy. Planetary defence experts from the Agency's Space Safety programme worked with NASA and the international asteroid community to closely watch this object and refine its orbit, which was eventually determined to not pose a risk of Earth impact. Read details on this unusual campaign via ESA's Rocket Science blog and in news articles here and here.
Webb’s observations indicate that the asteroid measures roughly 60 meters (comparable to the height of a 15-story building).
The new observations from Webb not only provide unique information about 2024 YR4’s size, but can also complement ground-based observations of the object's position to help improve our understanding of the object’s orbit and future trajectory.
Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
[Image description: A collage of three images showing the black expanse of space. Two-thirds of the collage is taken up by the black background sprinkled with small, blurry galaxies in orange, blue, and white. There are two images in a column at the right side of the collage. On the right side of the main image, not far from the top, a very faint dot is outlined with a white square. At the right, there are two zoomed in views of this area. The top box is labeled NIRCam and shows a fuzzy dot at the center of the inset. The bottom box is labeled MIRI and shows a fuzzy pinkish dot.]
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
NASA’s SPHEREx, which will map millions of galaxies across the entire sky, captured one of its first exposures March 27. The observatory’s six detectors each captured one of these uncalibrated images, to which visible-light colors have been added to represent infrared wavelengths. SPHEREx’s complete field of view spans the top three images; the same area of the sky is also captured in the bottom three images. NASA/JPL-Caltech Processed with rainbow hues to represent a range of infrared wavelengths, the new pictures indicate the astrophysics space observatory is working as expected.
NASA’s SPHEREx (short for Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) has turned on its detectors for the first time in space. Initial images from the observatory, which launched March 11, confirm that all systems are working as expected.
Although the new images are uncalibrated and not yet ready to use for science, they give a tantalizing look at SPHEREx’s wide view of the sky. Each bright spot is a source of light, like a star or galaxy, and each image is expected to contain more than 100,000 detected sources.
There are six images in every SPHEREx exposure — one for each detector. The top three images show the same area of sky as the bottom three images. This is the observatory’s full field of view, a rectangular area about 20 times wider than the full Moon. When SPHEREx begins routine science operations in late April, it will take approximately 600 exposures every day.
Each image in this uncalibrated SPHEREx exposure contains about 100,000 light sources, including stars and galaxies. The two insets at right zoom in on sections of one image, showcasing the telescope’s ability to capture faint, distant galaxies. These sections are processed in grayscale rather than visible-light color for ease of viewing.NASA/JPL-Caltech “Our spacecraft has opened its eyes on the universe,” said Olivier Doré, SPHEREx project scientist at Caltech and NASA’s Jet Propulsion Laboratory, both in Southern California. “It’s performing just as it was designed to.”
The SPHEREx observatory detects infrared light, which is invisible to the human eye. To make these first images, science team members assigned a visible color to every infrared wavelength captured by the observatory. Each of the six SPHEREx detectors has 17 unique wavelength bands, for a total of 102 hues in every six-image exposure.
Breaking down color this way can reveal the composition of an object or the distance to a galaxy. With that data, scientists can study topics ranging from the physics that governed the universe less than a second after its birth to the origins of water in our galaxy.
“This is the high point of spacecraft checkout; it’s the thing we wait for,” said Beth Fabinsky, SPHEREx deputy project manager at JPL. “There’s still work to do, but this is the big payoff. And wow! Just wow!”
During the past two weeks, scientists and engineers at JPL, which manages the mission for NASA, have executed a series of spacecraft checks that show all is well so far. In addition, SPHEREx’s detectors and other hardware have been cooling down to their final temperature of around minus 350 degrees Fahrenheit (about minus 210 degrees Celsius). This is necessary because heat can overwhelm the telescope’s ability to detect infrared light, which is sometimes called heat radiation. The new images also show that the telescope is focused correctly. Focusing is done entirely before launch and cannot be adjusted in space.
“Based on the images we are seeing, we can now say that the instrument team nailed it,” said Jamie Bock, SPHEREx’s principal investigator at Caltech and JPL.
How It Works
Where telescopes like NASA’s Hubble and James Webb space telescopes were designed to target small areas of space in detail, SPHEREx is a survey telescope and takes a broad view. Combining its results with those of targeted telescopes will give scientists a more robust understanding of our universe.
The observatory will map the entire celestial sky four times during its two-year prime mission. Using a technique called spectroscopy, SPHEREx will collect the light from hundreds of millions of stars and galaxies in more wavelengths any other all-sky survey telescope.
Track the real-time location of NASA’s SPHEREx space observatory using the agency’s 3D visualization tool, Eyes on the Solar System. When light enters SPHEREx’s telescope, it’s directed down two paths that each lead to a row of three detectors. The observatory’s detectors are like eyes, and set on top of them are color filters, which are like color-tinted glasses. While a standard color filter blocks all wavelengths but one, like yellow- or rose-tinted glasses, the SPHEREx filters are more like rainbow-tinted glasses: The wavelengths they block change gradually from the top of the filter to the bottom.
“I’m rendered speechless,” said Jim Fanson, SPHEREx project manager at JPL. “There was an incredible human effort to make this possible, and our engineering team did an amazing job getting us to this point.”
More About SPHEREx
The SPHEREx mission is managed by JPL for the agency’s Astrophysics Division within the Science Mission Directorate at NASA Headquarters. BAE Systems (formerly Ball Aerospace) built the telescope and the spacecraft bus. The science analysis of the SPHEREx data will be conducted by a team of scientists located at 10 institutions in the U.S., two in South Korea, and one in Taiwan. Caltech managed and integrated the instrument. Data will be processed and archived at IPAC at Caltech. The mission’s principal investigator is based at Caltech with a joint JPL appointment. The SPHEREx dataset will be publicly available at the NASA-IPAC Infrared Science Archive. Caltech manages JPL for NASA.
For more about SPHEREx, visit:
https://science.nasa.gov/mission/spherex/
News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov
2025-045
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Last Updated Apr 01, 2025 Related Terms
SPHEREx (Spectro-Photometer for the History of the Universe and Ices Explorer) Astrophysics Galaxies Origin & Evolution of the Universe The Search for Life The Universe Explore More
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