The James Webb Space Telescope’s Mid-Infrared Instrument (MIRI) has four observing modes. On Aug. 24, a mechanism that supports one of these modes, known as medium-resolution spectroscopy (MRS), exhibited what appears to be increased friction during setup for a science observation. This mechanism is a grating wheel that allows scientists to select between short, medium, and longer wavelengths when making observations using the MRS mode. Following preliminary health checks and investigations into the issue, an anomaly review board was convened Sept. 6 to assess the best path forward.
The Webb team has paused in scheduling observations using this particular observing mode while they continue to analyze its behavior and are currently developing strategies to resume MRS observations as soon as possible. The observatory is in good health, and MIRI’s other three observing modes – imaging, low-resolution spectroscopy, and coronagraphy – are operating normally and remain available for science observations.
Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
NASA’s James Webb Space Telescope captured its first images and spectra of Mars Sept. 5. The telescope, an international collaboration with ESA (European Space Agency) and CSA (Canadian Space Agency), provides a unique perspective with its infrared sensitivity on our neighboring planet, complementing data being collected by orbiters, rovers, and other telescopes.
Webb’s unique observation post nearly a million miles away at the Sun-Earth Lagrange point 2 (L2) provides a view of Mars’ observable disk (the portion of the sunlit side that is facing the telescope). As a result, Webb can capture images and spectra with the spectral resolution needed to study short-term phenomena like dust storms, weather patterns, seasonal changes, and, in a single observation, processes that occur at different times (daytime, sunset, and nighttime) of a Martian day.
Because it is so close, the Red Planet is one of the brightest objects in the night sky in terms of both visible light (which human eyes can see) and the infrared light that Webb is designed to detect. This poses special challenges to the observatory, which was built to detect the extremely faint light of the most distant galaxies in the universe. Webb’s instruments are so sensitive that without special observing techniques, the bright infrared light from Mars is blinding, causing a phenomenon known as “detector saturation.” Astronomers adjusted for Mars’ extreme brightness by using very short exposures, measuring only some of the light that hit the detectors, and applying special data analysis techniques.
Webb’s first images of Mars, captured by the Near-Infrared Camera (NIRCam), show a region of the planet’s eastern hemisphere at two different wavelengths, or colors of infrared light. This image shows a surface reference map from NASA and the Mars Orbiter Laser Altimeter (MOLA) on the left, with the two Webb NIRCam instrument field of views overlaid. The near-infrared images from Webb are on shown on the right.
The NIRCam shorter-wavelength (2.1 microns) image [top right] is dominated by reflected sunlight, and thus reveals surface details similar to those apparent in visible-light images [left]. The rings of the Huygens Crater, the dark volcanic rock of Syrtis Major, and brightening in the Hellas Basin are all apparent in this image.
The NIRCam longer-wavelength (4.3 microns) image [lower right] shows thermal emission – light given off by the planet as it loses heat. The brightness of 4.3-micron light is related to the temperature of the surface and the atmosphere. The brightest region on the planet is where the Sun is nearly overhead, because it is generally warmest. The brightness decreases toward the polar regions, which receive less sunlight, and less light is emitted from the cooler northern hemisphere, which is experiencing winter at this time of year.
However, temperature is not the only factor affecting the amount of 4.3-micron light reaching Webb with this filter. As light emitted by the planet passes through Mars’ atmosphere, some gets absorbed by carbon dioxide (CO2) molecules. The Hellas Basin – which is the largest well-preserved impact structure on Mars, spanning more than 1,200 miles (2,000 kilometers) – appears darker than the surroundings because of this effect.
“This is actually not a thermal effect at Hellas,” explained the principal investigator, Geronimo Villanueva of NASA’s Goddard Space Flight Center, who designed these Webb observations. “The Hellas Basin is a lower altitude, and thus experiences higher air pressure. That higher pressure leads to a suppression of the thermal emission at this particular wavelength range [4.1-4.4 microns] due to an effect called pressure broadening. It will be very interesting to tease apart these competing effects in these data.”
Villanueva and his team also released Webb’s first near-infrared spectrum of Mars, demonstrating Webb’s power to study the Red Planet with spectroscopy.
Whereas the images show differences in brightness integrated over a large number of wavelengths from place to place across the planet at a particular day and time, the spectrum shows the subtle variations in brightness between hundreds of different wavelengths representative of the planet as a whole. Astronomers will analyze the features of the spectrum to gather additional information about the surface and atmosphere of the planet.
This infrared spectrum was obtained by combining measurements from all six of the high-resolution spectroscopy modes of Webb’s Near-Infrared Spectrograph (NIRSpec). Preliminary analysis of the spectrum shows a rich set of spectral features that contain information about dust, icy clouds, what kind of rocks are on the planet’s surface, and the composition of the atmosphere. The spectral signatures – including deep valleys known as absorption features – of water, carbon dioxide, and carbon monoxide are easily detected with Webb. The researchers have been analyzing the spectral data from these observations and are preparing a paper they will submit to a scientific journal for peer review and publication.
In the future, the Mars team will be using this imaging and spectroscopic data to explore regional differences across the planet, and to search for trace gases in the atmosphere, including methane and hydrogen chloride.
Right now, NASA’s James Webb Space Telescope is in space capturing spectacular images and spectrum of the universe; all of these data reside in the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute (STScI), the science operations center for Webb. However, it takes time for these exciting new observations to make their way from raw data to published, peer-reviewed science.
Scientific peer review is a long-established, quality-control system, where new scientific discoveries are scrutinized by experts before they are published in a journal. The peer review process begins when a scientist or group of scientists completes a study of a particular object in the sky and then submits their written findings to an accredited journal for publication. The journal’s editors will then circulate the article to other scientists within the same field to gather their reviews and feedback. Only articles that meet good scientific standards, acknowledging and building upon other known works, make it through this process and are published in the journal. NASA relies on this peer-review process to ensure quality and accuracy of scientific results before sharing them with the public.
Since Webb’s discoveries are so new, they require time to be vetted by the peer-review process, and a pipeline of articles under peer review is growing as the telescope continues to make observations from its first year of planned science. This pipeline of articles will feed future Webb news as scientists with peer-reviewed articles submit their findings to the STScI news office for consideration for promotion.
Many Webb investigators, however, are also taking advantage of the way that the scientific publication landscape has changed in the last decade. They create draft papers that are sometimes publicly posted as “preprints” before the full peer-review process is complete. This previewing stage allows for discussion within the science community, and researchers sometimes use this feedback to improve their written papers before they formally submit to a journal. At this stage, papers, imagery, figures, and initial analyses are public – but not yet considered part of the fully peer-reviewed scientific literature.
NASA and STScI, in collaboration with the science community, may share some imagery or spectra from papers prior to peer review, much like the recently published exoplanet images, as well as images from Webb data publicly available in the MAST archive. Those shared, but still awaiting peer review, will be labeled appropriately to describe where in the process the image or data and results are. Important scientific conclusions and discoveries from these images will be shared later, after peer review.
What to Expect
Starting the week of Sep. 19, NASA will share a new Webb image or spectrum at least every other week. Check the Webb blog every other Monday to find out when to expect that week’s image.
NASA will also hold media availability calls with subject matter experts as needed to answer questions about the latest images, spectra, and science from Webb.
-Thaddeus Cesari, NASA’s Goddard Space Flight Center
Editor’s Note: This post highlights images from Webb science in progress, which has not yet been through the peer-review process.
For the first time, astronomers have used NASA’s James Webb Space Telescope to take a direct image of a planet outside our solar system. The exoplanet is a gas giant, meaning it has no rocky surface and could not be habitable.
The image, as seen through four different light filters, shows how Webb’s powerful infrared gaze can easily capture worlds beyond our solar system, pointing the way to future observations that will reveal more information than ever before about exoplanets.
“This is a transformative moment, not only for Webb but also for astronomy generally,” said Sasha Hinkley, associate professor of physics and astronomy at the University of Exeter in the United Kingdom, who led these observations with a large international collaboration. Webb is an international mission led by NASA in collaboration with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
The exoplanet in Webb’s image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could help narrow that down even further. It is young as planets go — about 15 to 20 million years old, compared to our 4.5-billion-year-old Earth.
Astronomers discovered the planet in 2017 using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile and took images of it using short infrared wavelengths of light. Webb’s view, at longer infrared wavelengths, reveals new details that ground-based telescopes would not be able to detect because of the intrinsic infrared glow of Earth’s atmosphere.
Researchers have been analyzing the data from these observations and are preparing a paper they will submit to journals for peer review. But Webb’s first capture of an exoplanet already hints at future possibilities for studying distant worlds.
Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is sufficiently distant from the star that Webb can easily separate the planet from the star in the image.
Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) are both equipped with coronagraphs, which are sets of tiny masks that block out starlight, enabling Webb to take direct images of certain exoplanets like this one. NASA’s Nancy Grace Roman Space Telescope, slated to launch later this decade, will demonstrate an even more advanced coronagraph.
“It was really impressive how well the Webb coronagraphs worked to suppress the light of the host star,” Hinkley said.
Taking direct images of exoplanets is challenging because stars are so much brighter than planets. The HIP 65426 b planet is more than 10,000 times fainter than its host star in the near-infrared, and a few thousand times fainter in the mid-infrared.
In each filter image, the planet appears as a slightly differently shaped blob of light. That is because of the particulars of Webb’s optical system and how it translates light through the different optics.
“Obtaining this image felt like digging for space treasure,” said Aarynn Carter, a postdoctoral researcher at the University of California, Santa Cruz, who led the analysis of the images. “At first all I could see was light from the star, but with careful image processing I was able to remove that light and uncover the planet.”
While this is not the first direct image of an exoplanet taken from space – the Hubble Space Telescope has captured direct exoplanet images previously – HIP 65426 b points the way forward for Webb’s exoplanet exploration.
“I think what’s most exciting is that we’ve only just begun,” Carter said. “There are many more images of exoplanets to come that will shape our overall understanding of their physics, chemistry, and formation. We may even discover previously unknown planets, too.”