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Smashing into an asteroid shows researchers how to better protect Earth

asteroids, jpl, NASA, Space, syndication / Ryan Harris / May 15, 2024

Connecting with a fastball —

Slowing down an asteroid by just one-tenth of a second makes all the difference.

Theo Nicitopoulos, Undark Magazine – May 15, 2024 2: 54 pm UTC

Enlarge / Riding atop a SpaceX Falcon 9 rocket, NASA’s Double Asteroid Redirection Test, or DART, spacecraft sets off to collide with an asteroid in the world’s first full-scale planetary defense test mission in November 2021.

On a fall evening in 2022, scientists at the Johns Hopkins University Applied Physics Laboratory were busy with the final stages of a planetary defense mission. As Andy Rivkin, one of the team leaders, was getting ready to appear in NASA’s live broadcast of the experiment, a colleague posted a photo of a pair of asteroids: the half-mile-wide Didymos and, orbiting around it, a smaller one called Dimorphos, taken about 7 million miles from Earth.

“We were able to see Didymos and this little dot in the right spot where we expected Dimorphos to be,” Rivkin recalled.

After the interview, Rivkin joined a crowd of scientists and guests to watch the mission’s finale on several big screens: As part of an asteroid deflection mission called DART, a spacecraft was closing in on Dimorphos and photographing its rocky surface in increasing detail.

Then, at 7: 14 pm, a roughly 1,300-pound spacecraft slammed head-on into the asteroid.

Within a few minutes, members of the mission team in Kenya and South Africa posted images from their telescopes, showing a bright plume of debris.

In the days that followed, researchers continued to observe the dust cloud and discovered it had morphed into a variety of shapes, including clumps, spirals, and two comet-like tails. They also calculated that the impact slowed Dimorphos’ orbit by about a tenth of an inch per second, proof-of-concept that a spacecraft—also called a kinetic impactor—could target and deflect an asteroid far from Earth.

The final five-and-a-half minutes of images from the DART spacecraft as it approached and then intentionally collided with asteroid Dimorphos. The video is 10 times faster than reality, except for the last six images.

NASA/Johns Hopkins APL/YouTube

Ron Ballouz, a planetary scientist at the lab, commented that what is often seen in the movies is a “sort of last-ditch-effort, what we like to call a final-stage of planetary defense.” But if hazardous objects can be detected years in advance, other techniques like a kinetic impactor can be used, he added.

If a deflection were necessary, scientists would need to change the speed of a hazardous object, such as an asteroid or comet, enough that it doesn’t end up at the same place and time as Earth as they orbit the Sun. Rivkin said this translates into at least a seven-minute change in the arrival time: If a Dimorphos-sized object were predicted to collide with Earth 67 years from now, for instance, the slow-down that DART imparted would be just enough to add up to the seven minutes, he added.

With less lead time, researchers could use a combination of multiple deflections, larger spacecrafts, or boosts in speed, depending on the hazardous object. “DART was designed to validate a technique, and specific situations would inevitably require adapting things,” said Rivkin.

Researchers use data from DART and smaller-scale experiments to predict the amount of deflection using computer simulations.

Scientists are also focusing on the type of asteroid that Dimorphos appears to be: a “rubble pile,” as they call it, because objects of this kind are thought to be made of clumps of many rocks.

In fact, scientists think that most asteroids the size of Dimorphos and larger are rubble piles. As scientists continue to learn more about rubble piles, they will be able to make better predictions about deflecting asteroids or comets. And in 2026, a new mission will arrive at Didymos and Dimorphos to collect more data to fine-tune the computer models.

In the meantime, researchers are trying to learn as much as possible in the unwelcome case an asteroid or comet is discovered to be a threat to Earth and a more rapid response is necessary.

Scientists first suspected that many asteroids are rubble piles about 50 years ago. Their models showed that when larger asteroids smashed into one another, the collisions could throw off fragments that would then reassemble to form new objects.

It wasn’t until 2005, though, that scientists saw their first rubble pile: asteroid Itokawa, when a spacecraft visited it and photographed it. Then, in 2018, they saw another called Ryugu, and later that year, one more, asteroid Bennu. DART’s camera also showed Didymos and Dimorphos are likely of the same variety.

“It’s one thing to talk about rubble piles, but another to see what looks like a bunch of rocks dumped off a truck up close,” said William Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado.

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Humanity’s most distant space probe jeopardized by computer glitch

An annotated image showing the various parts and instruments of NASA's Voyager spacecraft design. — Enlarge / An annotated image showing the various parts and instruments of NASA’s Voyager spacecraft design.

Voyager 1 is still alive out there, barreling into the cosmos more than 15 billion miles away. However, a computer problem has kept the mission’s loyal support team in Southern California from knowing much more about the status of one of NASA’s longest-lived spacecraft.

The computer glitch cropped up on November 14, and it affected Voyager 1’s ability to send back telemetry data, such as measurements from the spacecraft’s science instruments or basic engineering information about how the probe was doing. So, there’s no insight into key parameters regarding the craft’s propulsion, power, or control systems.

“It would be the biggest miracle if we get it back. We certainly haven’t given up,” said Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory, in an interview with Ars. “There are other things we can try. But this is, by far, the most serious since I’ve been project manager.”

Dodd became the project manager for NASA’s Voyager mission in 2010, overseeing a small cadre of engineers responsible for humanity’s exploration into interstellar space. Voyager 1 is the most distant spacecraft ever, speeding away from the Sun at 38,000 mph (17 kilometers per second).

Voyager 2, which launched 16 days before Voyager 1 in 1977, isn’t quite as far away. It took a more leisurely route through the Solar System, flying past Jupiter, Saturn, Uranus, and Neptune, while Voyager 1 picked up speed during an encounter with Saturn to overtake its sister spacecraft.

For the last couple of decades, NASA has devoted Voyager’s instruments to studying cosmic rays, the magnetic field, and the plasma environment in interstellar space. They’re not taking pictures anymore. Both probes have traveled beyond the heliopause, where the flow of particles emanating from the Sun runs into the interstellar medium.

There are no other operational spacecraft currently exploring interstellar space. NASA’s New Horizons probe, which flew past Pluto in 2015, is on track to reach interstellar space in the 2040s.

State-of-the-art 50 years ago

The latest problem with Voyager 1 lies in the probe’s Flight Data Subsystem (FDS), one of three computers on the spacecraft working alongside a command and control central computer and another device overseeing attitude control and pointing.

The FDS is responsible for collecting science and engineering data from the spacecraft’s network of sensors and then combining the information into a single data package in binary code—a series of ones and zeros. A separate component called the Telemetry Modulation Unit actually sends the data package back to Earth through Voyager’s 12-foot (3.7-meter) dish antenna.

In November, the data packages transmitted by Voyager 1 manifested a repeating pattern of ones and zeros as if it were stuck, according to NASA. Dodd said engineers at JPL have spent the better part of three months trying to diagnose the cause of the problem. She said the engineering team is “99.9 percent sure” the problem originated in the FDS, which appears to be having trouble “frame syncing” data.

A scanned 1970s-era photo of the Flight Data Subsystem computer aboard NASA's Voyager spacecraft. — Enlarge / A scanned 1970s-era photo of the Flight Data Subsystem computer aboard NASA’s Voyager spacecraft.

So far, the ground team believes the most likely explanation for the problem is a bit of corrupted memory in the FDS. However, because of the computer hangup, engineers lack detailed data from Voyager 1 that might lead them to the root of the issue. “It’s likely somewhere in the FDS memory,” Dodd said. “A bit got flipped or corrupted. But without the telemetry, we can’t see where that FDS memory corruption is.”

When it was developed five decades ago, Voyager’s Flight Data Subsystem was an innovation in computing. It was the first computer on a spacecraft to make use of volatile memory. Each Voyager spacecraft launched with two FDS computers, but Voyager 1’s backup FDS failed in 1981, according to Dodd.

The only signal Voyager 1’s Earthbound engineers have received since November is a carrier tone, which basically tells the team the spacecraft is still alive. There’s no indication of any other major problems. Changes in the carrier signal’s modulation indicate Voyager 1 is receiving commands uplinked from Earth.

“Unfortunately, we haven’t cracked the nut yet, or solved the problem, or gotten any telemetry back,” Dodd said.