Nearly one year ago, NASA flung the DART spacecraft into the asteroid Dimorphos at 14,000 miles per hour. It was the first test to see whether they could slightly deflect a space rock’s trajectory using a high-speed collision, a technique that could be used to protect Earth from future killer asteroids. It worked. But now they’re trying to figure out the details of the crash. And if people have to defend earthly life from a potential asteroid impact, those details will surely matter.
Scientists are starting by studying the ejecta, boulders, and numerous smaller bits the strike cast off. They predicted there would be debris, but they didn’t know exactly what to expect. After all, compared to stars and galaxies, asteroids are tiny and dim, so it’s hard to ascertain their density and composition from afar. When you strike one, will it simply bounce? Will the probe thud into it and create a crater? Or if the asteroid is brittle, will slamming a craft into it risk creating space shrapnel that is still big enough to threaten Earth?
“This is exactly why we needed to do an in-space test of this technology. People had done laboratory experiments and models. But how would an actual asteroid, of the size we’re concerned about for planetary defense, react to a kinetic impactor?” says Nancy Chabot, the DART coordination lead and a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory, which developed the craft in partnership with NASA.
Many asteroids appear to be “rubble piles,” dirt, rocks, and ice loosely held together, rather than something hard and dense like a billiard ball. The asteroid Ryugu, visited by the Japanese space agency’s Hayabusa2 in June 2018, and the asteroid Bennu, which NASA’s OSIRIS-REx took samples from in 2020, both count as rubble piles. A new study published in July in Astrophysical Journal Letters shows that Dimorphos appears to be built like that too, which means that an impact is likely to create a crater and to fling off debris on or near the asteroid’s surface.
To figure out what happened after the crash, David Jewitt, a University of California, Los Angeles astronomer, and his colleagues used the Hubble Space Telescope to zoom in repeatedly on Dimorphos. The combined deep observations allowed them to discern objects that are otherwise too faint to see. A few months after the DART probe’s impact, they found a swarm of about three dozen boulders not seen before—the largest of which is 7 meters in diameter—slowly drifting away from the asteroid. “It’s a slow-speed cloud of shrapnel from the impact that’s carrying away a significant amount of mass: about 5,000 tons in boulders. That’s quite a lot, considering the impactor itself was only half a ton. So it blew out a tremendous mass in boulders,” Jewitt says.
Other researchers, including the DART team, have also been investigating the cloud of rocks thrown off by the spacecraft’s swift punch. Chabot and her colleagues published a study in Nature earlier this year, also using Hubble photos, imaging the ejecta. They showed that at first the pieces flew off in a cone-shaped cloud, but over time, that cone turned into a tail, not so different from a comet’s tail. That finding also means that models of the behavior of comets could be applied to impactors like DART, Chabot says.
Dimorphos was never a threat to Earth, but details like these would matter in a real asteroid deflection scenario. Boulders and smaller ejecta would have to be knocked out of the way, along with the rest of the asteroid, in order to spare the planet. Or let’s say the asteroid wasn’t spotted until it was very close to Earth, and its trajectory couldn’t be altered enough to avoid a crash. Could it at least be pulverized into boulders small enough to burn up in Earth’s atmosphere? “Is it better to be shot by a high-velocity rifle bullet or a bunch of pellets from a shotgun?” asks Jewitt. “The answer is: The shotgun is better, because the smaller boulders are more likely to be cushioned or dissipated by the impact with the atmosphere.”
And nations should avoid cluttering those spots with mechanical detritus, which could complicate future missions. Like campers heading into the backcountry, it’s important to think carefully about what you pack with you and what you take out, Birk says.
India’s success doesn’t mean the end of the race toward the moon’s south pole, but it does boost India’s standing. “This will certainly contribute to its status as a rising power with technological prowess. What’s happening in space is a reflection of what’s happening geopolitically on Earth,” says Cassandra Steer, an expert on space law and space security at the Australian National University in Canberra. And while Roscosmos suffered a setback, this isn’t the end of their moon program either, or their role in the new lunar competition. The Soviets beat the US at every stage of the 20th-century space race, Steer says, except for the landing of astronauts on the moon. Next, Russia intends to collaborate with China on a lunar research station.
Over the past decade, only China’s space program has achieved considerable success landing spacecraft on the moon, including its Chang’e 3, 4, and 5 missions in 2013, 2019, and 2020. India’s Chandrayaan-2 and Israel’s Beresheet lander failed in 2019, and Japan’s Ispace lander failed this April.
In fact, until China made its first landing, the moon had arguably been neglected for decades. NASA ended its Apollo mission in 1972, and the USSR’s Luna-24 mission in 1976 was the last successful lunar landing. That could mean limited institutional memory, especially for Russia, making it tough to develop and deploy new moon missions, Metzger says.
Over the past few decades, Russia has been trying to resuscitate its program, but with little success. Roscosmos has Luna-26 and Luna-27 planned for 2027 and 2029, as the agency aims to bring an orbiter and a larger lander to the moon. But their limited funding, thanks to sanctions following the Ukraine invasion, means these followup missions will likely be delayed, Zak says. And if the space agency decides to overhaul their propulsion system design after investigating the failure of Luna-25, that could be another reason for delays, he adds.
NASA has fared better with its Artemis program, which last year sent the uncrewed Artemis 1 to orbit the moon and is aiming for a crewed landing in 2026. But the program has faced its own challenges: NASA plans on using a SpaceX Starship lander, though, as its abortive test flight in April shows, Starship clearly has a long way to go. More than half of the 10 cubesat satellites deployed by Artemis 1 experienced technical glitches or lost contact with Earth, including the Japanese Omotenashi probe, which was unable to land on the moon as planned.
NASA has increasingly relied on commercial partners in a bid to boost the speed and lower the price of moon exploration—moving some of the costs onto businesses, rather than taxpayers. But these companies, too, are new players in the space race. In late 2024, NASA plans to send its Viper rover on an Astrobotic lander, though that company’s first moon lander, meant to demonstrate the technology, hasn’t even launched yet. NASA has also charged Firefly Aerospace, Intuitive Machines, and Draper with delivering a variety of payloads to the lunar surface over the next couple years.
In the meantime, nations like India, Japan, and Israel have begun moon programs from scratch. India next plans to collaborate with Japan on the Lunar Polar Exploration rover, which would launch no sooner than 2026.
“We have set the bar now so high. Nothing less spectacular than this is going to be inspiring for any of us in the future,” said Shri M. Sankaran, director of ISRO’s U R Rao Satellite Centre, speaking on today’s telecast. “We will now be looking at putting a man in space, putting a spacecraft on Venus, and landing on Mars. Those efforts have been ongoing for years. This success today will inspire us and spur us to take those efforts even more strongly to make our country proud again and again and again.”
Updated 8/23/2023 12:00 pm ET: This story was updated to correct the ISRO chief’s name.
After Euclid blasts off, it will travel to a spot called Lagrange point 2, about 1.5 million kilometers from Earth, where the telescope will have a clear view of deep space while being able to communicate with astronomers and enjoy continuous sunlight on its solar panels. The telescope is equipped with two instruments that will be used simultaneously: a visible-wavelength camera with 36 sensitive detectors called charge coupled devices, for measuring the shapes of billions of galaxies, and a near-infrared spectrometer and photometer, with 16 detectors that will provide a larger infrared field of view than any other space telescope. Euclid will begin its science mission later this year, after a few months of testing and calibrating those instruments.
It will share an L2 orbital parking spot near NASA’s James Webb Space Telescope, but “it’s kind of an anti-JWST. Instead of focusing on a very small piece of sky, the whole aim of Euclid is to widen out and look over a huge part of the sky,” says Mark McCaughrean, ESA’s senior adviser for science and exploration. Unlike the JWST and Hubble telescopes, Euclid won’t be zooming in on unique objects, but getting a panoramic view. “It’s a statistics mission. The aim is to drown yourself in so much data and so many galaxies, and then you can start teasing out the subtle signals,” McCaughrean says.
Astrophysicists on the Euclid team plan to make two kinds of critical measurements, both heavily involving statistics. The first will be a measurement of weak gravitational lensing, which happens when the gravity of massive objects—mostly dark matter—slightly bends the light coming from more distant galaxies, distorting their images. It can only be studied with catalogs containing lots and lots of galaxies.
That also goes for studying baryon acoustic oscillations. In the primordial universe, sound waves undulated through normal matter—a mix of particles and radiation. This created a measurable pattern in the density distribution of galaxies as they formed. Studying the patterns left behind by these oscillations at multiple snapshots in cosmic time will help Euclid scientists understand the expansion of the universe and the nature of dark energy.
To make headway on such statistics, Euclid’s instruments will collect troves of data, with image quality that’s similar to Hubble’s but spans 15,000 square degrees of the sky. That would take centuries to do using Hubble, says Luca Valenziano, a cosmologist at Italy’s National Institute for Astrophysics and member of the Euclid collaboration. “This is an incredible potential, and only Euclid can do that because it can explore the infrared sky, which is not accessible from the ground,” he says.
The use of infrared is a key way that Euclid will differ from surveying telescopes on the ground, like the Dark Energy Survey, the Dark Energy Spectroscopic Instrument, and the upcoming Vera Rubin Observatory. Earthbound telescopes can’t observe most infrared wavelengths, because the atmosphere blocks them. But space telescopes like Euclid and JWST can, provided they’re kept cool enough. (Infrared light is basically heat radiation.) Infrared instruments allow Euclid to penetrate dust clouds when examining galaxies, and enable a deeper probe into the universe’s past.
In recent years, astrophysicists like Mat Madhavacheril have used the Atacama Cosmology Telescope to study the biggest question related to the universe’s expansion: Why the measured expansion rate appears slightly different when using probes of the distant universe compared to when using nearby objects, like supernova explosions. Euclid could help finally resolve the puzzle, he says, because it will be their most powerful tool yet, able to systematically map a wide swath of the universe. “Euclid has a lot to offer. We’re excited about it, and when the Euclid data are public, we’ll jump on it,” he says.
Nearly 400,000 years after the Big Bang, the primordial plasma of the infant universe cooled enough for the first atoms to coalesce, making space for the embedded radiation to soar free. That light—the cosmic microwave background (CMB)—continues to stream through the sky in all directions, broadcasting a snapshot of the early universe that’s picked up by dedicated telescopes and even revealed in the static on old cathode-ray televisions.
After scientists discovered the CMB radiation in 1965, they meticulously mapped its tiny temperature variations, which displayed the exact state of the cosmos when it was a mere frothing plasma. Now they’re repurposing CMB data to catalog the large-scale structures that developed over billions of years as the universe matured.
“That light experienced a bulk of the history of the universe, and by seeing how it’s changed, we can learn about different epochs,” said Kimmy Wu, a cosmologist at SLAC National Accelerator Laboratory.
Over the course of its nearly 14-billion-year journey, the light from the CMB has been stretched, squeezed, and warped by all the matter in its way. Cosmologists are beginning to look beyond the primary fluctuations in the CMB light to the secondary imprints left by interactions with galaxies and other cosmic structures. From these signals, they’re gaining a crisper view of the distribution of both ordinary matter—everything that’s composed of atomic parts—and the mysterious dark matter. In turn, those insights are helping to settle some long-standing cosmological mysteries and pose some new ones.
“We’re realizing that the CMB does not only tell us about the initial conditions of the universe. It also tells us about the galaxies themselves,” said Emmanuel Schaan, also a cosmologist at SLAC. “And that turns out to be really powerful.”
A Universe of Shadows
Standard optical surveys, which track the light emitted by stars, overlook most of the galaxies’ underlying mass. That’s because the vast majority of the universe’s total matter content is invisible to telescopes—tucked out of sight either as clumps of dark matter or as the diffuse ionized gas that bridges galaxies. But both the dark matter and the strewn gas leave detectable imprints on the magnification and color of the incoming CMB light.
“The universe is really a shadow theater in which the galaxies are the protagonists and the CMB is the backlight,” Schaan said.
Many of the shadow players are now coming into relief.
When light particles, or photons, from the CMB scatter off electrons in the gas between galaxies, they get bumped to higher energies. In addition, if those galaxies are in motion with respect to the expanding universe, the CMB photons get a second energy shift, either up or down, depending on the relative motion of the cluster.
This pair of effects, known respectively as the thermal and kinematic Sunyaev-Zel’dovich (SZ) effects, were first theorized in the late 1960s and have been detected with increasing precision in the past decade. Together, the SZ effects leave a characteristic signature that can be teased out of CMB images, allowing scientists to map the location and temperature of all the ordinary matter in the universe.
Finally, a third effect known as weak gravitational lensing warps the path of CMB light as it travels near massive objects, distorting the CMB as though it were viewed through the base of a wineglass. Unlike the SZ effects, lensing is sensitive to all matter—dark or otherwise.
Taken together, these effects allow cosmologists to separate the ordinary matter from the dark matter. Then scientists can overlay these maps with images from galaxy surveys to gauge cosmic distances and even trace star formation.
SWOT could turn out to be a major improvement over measurements by previous satellites. “Instead of a ‘pencil beam’ moving along the Earth’s surface from a satellite, it’s a wide swath. It’ll provide a lot more information, a lot more spatial resolution, and hopefully better coverage up close to the coasts,” says Steve Nerem, a University of Colorado scientist who uses satellite data to study sea-level rise and is not involved with SWOT. And KaRIn’s swath-mapping technology is a brand-new technique, he says. “It’s never been tested from orbit before, so it’s kind of an experiment. We’re looking forward to the data.”
SWOT has other instruments in its toolkit too, including a radar altimeter to fill in the gaps between the swaths of data KaRIn collects, a microwave radiometer to measure the amount of water vapor between SWOT and the Earth’s surface, and an array of mirrors for laser-tracking measurements from the ground.
New satellite data is important because the future of sea-level rise, floods, and droughts may be worse than some experts previously forecast. “Within our satellite record, we’ve seen sea-level rise along US coastlines going up fast over the past three decades,” says Ben Hamlington, a sea-level rise scientist at JPL on the SWOT science team. The rate of sea-level rise is in fact accelerating, especially on the Gulf Coast and East Coast of the United States. “The trajectory we’re on is pointing us to the higher end of model projections,” he says, a point he made in a study last month in the journal Communications Earth & Environment.
Hamlington sees SWOT as a boon for mapping rising sea waters and for researchers studying ocean currents and eddies, which affect how much atmospheric heat and carbon oceans absorb. The satellite will also aid scientists who model storm surges—that is, when ocean water flows onto land.
The new spacecraft’s data will have some synergy with many other Earth-observing satellites already in orbit. Those include NASA’s Grace-FO, which probes underground water via gravity fluctuations, NASA’s IceSat-2, which surveys ice sheets, glaciers, and sea ice, and commercial flood-mapping satellites that use synthetic aperture radar to see through clouds. It also follows other altimeter-equipped satellites, like the US-European Jason-3, the European Space Agency’s Sentinel-6 Michael Freilich satellite, China’s Haiyang satellites, and the Indian-French Saral spacecraft.
Data from these satellites has already shown that some degree of sea-level rise, extreme floods, storms, and droughts are already baked into our future. But we’re not doomed to climate catastrophes, Hamlington argues, because we can use this data to fend off the most extreme projected outcomes, like those that cause rapid glacier or ice sheet melt. “Reducing emissions takes some of the higher projections of sea-level rise off the table,” he says. “Since catastrophic ice sheet loss will only occur under very warm futures, if we can limit warming going forward, we can avoid worst-case scenarios.”