Japan Joins the New Moon Race, and Launches an X-Ray Telescope, Too


On Thursday morning in Japan, a bus-size telescope with X-Ray vision soared into space.

It wasn’t alone. Along for the ride was a robotic moon lander about the size of a small food truck. The two missions — XRISM and SLIM — would soon part ways, one headed off to spy on some of the hottest spots in our universe, the other to help Japan’s space agency, JAXA, test technologies that are to be used in larger-scale lunar landings in the future.

The liftoff from the shores of Tanegashima, an island in the southern part of the Japanese archipelago, was picturesque, with the Japanese H-IIA rocket soaring over the remote launch site and disappearing into the blue skies that were punctuated by a few clouds. About 47 minutes after the flight began, launch officials were shown in a live video stream to be celebrating in the mission control room as the XRISM and SLIM spacecrafts headed toward their diverging cosmic destinations.

The X-Ray Imaging and Spectroscopy Mission — XRISM for short (and pronounced like “chrism”) — is the launch’s primary passenger. From an orbit 350 miles above Earth, XRISM will study exotic environments that emit X-Ray radiation, including the accretion of material swirling around black holes, the blistering plasma permeating galaxy clusters, and the remnants of exploding massive stars.

Data from the telescope will shed light on the motion and chemistry of these cosmic locales with a technique called spectroscopy, which relies on changes in the brightness of sources at different wavelengths to extract information about their composition. The technique gives scientists a view into some of the universe’s highest energy phenomena and will add to astronomers’ comprehensive, multiwavelength picture of the universe.

XRISM’s spectroscopy will “reveal energy flows among the celestial objects in different scales” with unprecedented resolution, Makoto Tashiro, the telescope’s principal investigator and an astrophysicist at JAXA, wrote in an email.

The Japanese space agency is leading the mission in collaboration with NASA. The European Space Agency contributed to the telescope’s construction, which means that astronomers from Europe will be allotted a portion of the telescope’s observing time.

XRISM is a rebuild of the Hitomi mission, a JAXA spacecraft that launched in 2016. The Hitomi telescope spun out of control weeks into its mission, and Japan lost contact with the spacecraft.

“It was a devastating loss,” said Brian J. Williams, an astrophysicist at NASA Goddard Space Flight Center who was on the Hitomi team and is now a XRISM project scientist. The little data collected from Hitomi was a tantalizing taste of what a mission like it could offer.

“We realized that we really had to go and build this mission again, because this is the future of X-ray astronomy,” Dr. Williams said.

Unlike other wavelengths of light, cosmic X-rays can only be detected from above Earth’s atmosphere, which shields us from the harmful radiation. XRISM will join a slew of other X-ray telescopes already in orbit, including NASA’s Chandra X-ray Observatory, which launched in 1999, and NASA’s Imaging X-ray Polarimetry Explorer, which joined the party in 2021.

What distinguishes XRISM from those missions is a tool called Resolve, which must be cooled to just a fraction above absolute zero so that the instrument can measure tiny changes in temperature when X-rays hit its surface. The mission team expects Resolve’s spectroscopic data to be 30 times as sharp as the resolution of Chandra’s instruments.

Lia Corrales, an astronomer at the University of Michigan who was selected as a participating scientist on the mission, sees XRISM as “a pioneer vehicle” that represents “the next step in X-ray observations.” With its state-of-the-art spectroscopy, Dr. Corrales will analyze the composition of interstellar dust to glean insight into the chemical evolution of our universe.

Jan-Uwe Ness, an astronomer at the European Space Agency who will be managing the proposal selection process for Europe’s allotted observing time, said that the superior quality of data collected by XRISM’s spectroscopy may feel almost like visiting these extreme environments themselves.

“I’m looking forward to the spectral revolution,” he said, adding that it will set the stage for even more ambitious X-ray telescopes in the future.

XRISM also carries a second instrument named Xtend that will operate simultaneously with Resolve. While Resolve zooms in, Xtend will zoom out, providing scientists with complementary views of the same X-ray sources over a larger area. According to Dr. Williams, Xtend is less powerful than the imager on the older Chandra telescope, which has generated some of the most striking views of the X-ray universe to date. But, Xtend will photograph the cosmos with a resolution comparable to the way our eyes might perceive it if we were to have X-ray vision.

Once XRISM arrives at low-Earth orbit, researchers will spend the next few months turning the instruments on and running tests of their performance. Science operations will begin in January, but initial studies from the data might not appear for a year or more, Dr. Tashiro said. Ahead of any discoveries, he’s just excited to see the instruments up and running, adding that “we will surely see the new world of X-ray astronomy once they work.”

More than anything, Dr. Williams is looking forward to the “unknown unknowns” that XRISM might unearth. “Every time we launch a new capability, we discover something new about the universe,” he said. “What will it be for this one? I don’t know, but I’m excited to find out.”

The Smart Lander for Investigating Moon, or SLIM, is the next robotic spacecraft headed for the moon but may not be the next one to land.

SLIM will be taking a long, roundabout journey of at least four months that requires less propellant. The lander will take several months to reach lunar orbit, then spend a month circling the moon before attempting to set down on the surface near Shioli crater on the lunar near side.

That means two American spacecraft, by Astrobotic Technology of Pittsburgh and Intuitive Machines of Houston, which might launch later this year and will take more direct trajectories to the moon, could beat SLIM to the surface.

Although SLIM is carrying a camera that can identify the composition of rocks around the landing site, the primary objectives of the mission are not scientific. Rather, it is to demonstrate a pinpoint navigation system, aiming to set down within about the length of a football field of the targeted site.

Currently, lunar landers can try to set down within several miles of a selected landing site. For example, the landing zone for India’s Chandrayaan-3 spacecraft, which last month became the first to successfully set down in the moon’s south polar region, was seven miles wide and 34 miles long.

The vision-based systems on many landing craft are limited because space-hardened computer chips possess only about one one-hundredth of the processing power of top-of-the-line chips used on Earth, JAXA said in its press kit.

For SLIM, JAXA developed image-processing algorithms that can run quickly on the slower space chips. As SLIM nears its landing, a camera will help guide the spacecraft’s descent to the lunar surface; radar and a laser will measure the spacecraft’s altitude and downward velocity.

Because of the risks of a crash that come with current systems, lunar landers are typically directed to flatter, less interesting terrain. A more precise navigation system would enable future spacecraft to land closer to rugged terrain that is of scientific interest, like the craters that contain frozen water near the moon’s south pole.

At launch, SLIM weighs more than 1,500 pounds; more than two-thirds of the weight is propellant. By contrast, the Indian lunar lander and its small rover weighed about 3,800 pounds, and the accompanying propulsion module that pushed the two out of Earth’s orbit toward the moon added 4,700 pounds.

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