Space rocks have hit Earth with devastating impact. Just ask the dinosaurs.
The good news: At present, astronomers do not know of any asteroids that have any chance of hitting Earth in the next century or so.
The bad news: Astronomers estimate they have not yet found another 15,000 or so near-Earth asteroids that are big enough to wipe out a city.
If an asteroid that is on a collision path with Earth is discovered, there could be a chance to divert it before it hits.
That’s where NASA’s Double Asteroid Redirection Test spacecraft — DART, for short — comes in.
On Monday at 7:14 p.m. Eastern time, DART is set to crash into a small asteroid at 14,000 miles per hour.
This isn’t like the movie “Armageddon” — no one is going to blow up an asteroid. Rather it is a proof of principle that colliding with a space rock and pushing it into a different orbit could be a feasible strategy for planetary defense.
NASA TV will broadcast coverage of the end of this mission beginning at 6 p.m..
If all you want to watch is a stream of photos from the spacecraft as it closes in on the asteroid, NASA’s media channel started broadcasting those at 5:30 p.m. Or you can watch it in the video player above.
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When DART collides with its asteroid target, we’ll see nothing.
Rather, the stream of pictures of the small asteroid Dimorphos getting bigger and bigger as the DART spacecraft gets closer and closer will freeze.
Then, if triumphant, the engineers will cheer. There is nothing like a severing of communications to confirm a successful crash.
That final image, which will be taken about two and a half seconds before impact, with the surface of the asteroid filling the camera’s field of view, is the last we will see of Dimorphos on Monday evening.
It will not be the last image, however.
Trailing behind DART is a tiny spacecraft named the Light Italian CubeSat for Imaging of Asteroids, or the LICIACube. Built by the Italian Space Agency, the LICIACube tagged along with DART for the first nine months of the mission, then separated and went on its own way on a slightly shifted trajectory that will miss Dimorphos.
The LICIACube will capture images of DART’s demise as well as the resulting crater. But because it is so small — its antenna is small, too — it will only be able to send data slowly via a weak radio signal to the radio dishes of NASA’s Deep Space Network. It will probably be a day or two before the first of the LICIACube’s images are available.
About 40 telescopes on Earth and several in space will also be pointed at Dimorphos and its parent asteroid, Didymos, before and after the impact. None of them can see Dimorphos, much less the divot that DART will carve out.
But the expectation is that the Didymos-Dimorphos system will become brighter in the hours after the impact.
“What we’re looking for there is an overall brightening of the whole system, indicating how much dust and other debris got kicked up because that ejecta goes into space, and it is also lit up by the sun,” said Thomas Statler, the DART program scientist, during a news conference last week.
How much and how quickly the brightening occurs “is a measure of something about the consistency of the material that was lofted up and how much there was,” Dr. Statler said.
The telescopes include NASA’s Hubble and James Webb space telescopes and the camera on the Lucy spacecraft that is headed toward a rendezvous with asteroids trapped in the orbit of Jupiter. The Lucy mission launched about a month before DART did.
Hubble will not have a view of Didymos at the time of impact because Earth will be in the way. Instead, the telescope will start observing about 15 minutes later. “That’s OK because we don’t really expect anything to be really observable from the exact moment of impact,” Dr. Statler said.
Whether the Webb telescope, which spends much of its time peering at galaxies billions of miles away, can track a small speeding asteroid fewer than seven million miles from Earth, is not clear.
“Let me stress here, this is not what J.W.S.T. is designed to do,” Nancy Chabot, a planetary scientist at Johns Hopkins University in Baltimore who serves as the coordination lead for the DART mission, said during a news conference on Sept. 12. “This is a challenging measurement for them.”
Still, it’s worth a try, she said.
“This is a unique opportunity in a unique moment to take all the resources that we possibly can to maximize what we learn,” Dr. Chabot said, “so they will be looking. We’ll see what they get.”
The key measurement will be the change in the time it takes Dimorphos to complete an orbit around Didymos. The head-on crash of DART will sap some of Dimorphos’s angular momentum, causing it to fall a bit closer to Didymos. That is predicted to speed up Dimorphos and shorten its orbital period, currently 11 hours, 55 minutes by about 1 percent.
“We will notice that the binary asteroid system is running fast,” Dr. Statler said.
That measurement, by radar and by the periodic dimming as Dimorphos passes in front of or behind Didymos, will take some time.
“I would be surprised if we had a firm measurement of the period change in less than a few days,” Dr. Statler said. “And I would be really surprised if it took more than three weeks.”
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Most asteroids in the solar system orbit in the main belt, between Mars and Jupiter and never come close to Earth.
But others, through billions of years of gravitational do-si-do, have been slung into other orbits. Some of those now cross paths with Earth’s orbit, and thus potentially could crash into Earth someday. If astronomers discover an asteroid that is on a collision course with Earth, they would want to prevent it.
Hence, the DART mission.
Astronomers estimate that there are about 25,000 of these near-Earth asteroids that are 460 feet or wider in diameter. Those are big enough that a collision with Earth would release more energy than the largest of thermonuclear weapons — more than enough to destroy a city, but not enough to inflict a planet-wide mass extinction. (The asteroid blamed for the extinction of the dinosaurs was much bigger, about six miles wide. Astronomers have located all of those, and none of them pose any imminent danger to Earth.)
One of them is Bennu, an asteroid as wide as the Empire State Building is tall that NASA’s OSIRIS-REX spacecraft visited recently. There is no chance of Bennu hitting Earth in the next century. But then in 2135, it will come close, within 125,000 miles or so, or about half the distance from the Earth to the moon.
The uncertainties in just how close it will be make the numerical simulations after 2135 more uncertain, and some of the possible trajectories collide with Earth. Last year, NASA calculated a 1-in-1,750 chance of an impact between now and 2300, with concern rising in the 2100s.
NASA continues to search for thousands of asteroids that are believed to be 460 feet or wider and in orbits not far from Earth. A new U.S.-financed ground-based telescope in Chile, the Vera Rubin Observatory, will perform sweeps of the night sky and will find most of the missing asteroids. NASA is also working on a space telescope called NEO Surveyor that will also discover many near-Earth objects, including asteroids. At present, NASA is aiming for a launch in 2028.
Even when all of the 460-foot-diameter asteroids are found, the task is not done. Impacts of smaller asteroids, which are even more numerous, could also inflict major damage. The meteor that exploded over Chelyabinsk, Russia, in 2013 was about 60 feet in diameter. It did not cause any deaths, but it caused numerous injuries, mostly from glass shattered by the shock wave.
Sept. 26, 2022, 5:36 p.m. ET
Michael Roston
Editing spaceflight coverage
NASA has just started a feed of pictures from the camera on the DART spacecraft. It’s embedded in the video player above. For now, all you will see is a dot, but watch for that dot to grow as the spacecraft approaches Didymos and Dimorphos.
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The asteroid now known as Didymos was discovered on April 11, 1996, by Joseph Montani of the Spacewatch project at the University of Arizona.
About half a mile wide, Didymos travels in an orbit that crosses Earth, making it what astronomers call a potentially hazardous object. In November 2003, it passed pretty close to Earth, missing by less than 4.5 million miles. Next year, it will miss by even less, coming within 3.6 million miles of our planet. Nonetheless, Didymos is not on a path to hit Earth — for context, the moon is typically some 238,000 miles from Earth.
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A few years later, echoes bounced back when radar signals were directed at Didymos. That suggested the asteroid was not alone, but possessed a moon. That was supported by visual observations that showed a clocklike dip in brightness whenever the moon passed in front of or behind Didymos. Radar images taken in 2003 by the giant Arecibo radio telescope in Puerto Rico directly confirmed the moon.
Mr. Montani then suggested the name of Didymos, which means “twin” in Greek. The smaller asteroid was nicknamed “Didymoon” before gaining the name of Dimorphos, which means “having two forms” in Greek.
Asteroids with moons have turned out to be surprisingly common, with more than 300 found to have orbiting companions.
Dimorphos orbits Didymos once every 11 hours and 55 minutes. Dimorphos is estimated to be about 560 feet wide with a mass of about 5 billion kilograms, or more than 10 billion pounds.
DART will be crashing head-on with Dimorphos, which will impart more momentum to the asteroid and a larger, more easily observed, change in the orbital period of Dimorphos around Didymos.
Sept. 26, 2022, 4:01 p.m. ET
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NASA is not spending $324 million to crash a spacecraft just for fun. The agency is doing its job.
In 2005, Congress mandated NASA to find 90 percent of near-Earth asteroids big enough to destroy a city — those that are 460 feet or wider in diameter. That task was to be accomplished by 2020, but Congress never gave NASA much money to perform the task, so it has remained more than half unfinished, with about 15,000 more asteroids of this size to discover.
As the agency searches the heavens for deadly space rocks, it is also developing techniques for what to do if it finds one that is on a collision course with Earth.
That’s where the DART mission comes in: It is to demonstrate that hitting an oncoming asteroid with a projectile can nudge it into a different orbit.
For a dangerous oncoming asteroid, that nudge could be enough to alter the trajectory from a direct hit to a near miss.
The 1,200-pound DART spacecraft launched last November. Think of it as a refrigerator-size bullet aimed at a target 500 feet wide. The recoil of the impact will impart a force on the target — the asteroid Dimorphos — and that gives it a push that will alter its orbit around a larger asteroid, Didymos.
DART is testing both the technology needed to hit a small target at high speeds — some of the algorithms are based on those in the guidance of missiles, which also try to strike small targets at high speeds — as well as the scientific understanding of what happens to an asteroid when it is hit. The ejection of debris from the surface of Didymos would amplify the recoil effect.
from
https://collincountynewsonline.com/watch-nasas-dart-mission-to-crash-into-an-asteroid-and-defend-the-earth-live-updates-the-new-york-times/
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