NASA’s first ever ‘planetary defence’ mission is ready for launch THIS WEEK to test if an asteroid can be deflected by crashing a spacecraft into it at 15,000mph
美国宇航局‘s first ever ‘planetary defence’ mission to deflect an asteroid 6.8 million miles from Earth is set to launch this week.
Double Asteroid Redirection Test (DART), a box-shaped space probe, will launch aboard a 太空X Falcon 9 rocket at 22:20 PT on Tuesday, 十一月 23 (星期三 06:20am GMT) from Vandenberg Space Force Base in 加利福尼亚州.
Following its 6.8 million-mile journey, DART will smash into the small asteroid Dimorphos, which orbits a larger asteroid called Didymos, 在 13,500 英里每小时 (21,700 km per hour) 在十月 2022.
When it hits Dimorphos, 的 1,210 pound space probe will change the speed of the 525-foot-wide space rock by a fraction of a per cent.
Although Dimorphos doesn’t pose a danger to Earth, NASA wants to measure the asteroid’s altered orbit caused by the collision.
This demonstration of ‘planetary defence’ will inform future missions that could one day save Earth from a deadly asteroid impact.
This artist’s illustration obtained from NASA shows the DART spacecraft prior to impact with the asteroid Dimorphos
DART will smash into Dimorphos, which orbits a larger asteroid called Didymos, 在 13,500 英里每小时 (21,700 km per hour). Dimorphos is depicted here to scale with Rome’s Colosseum
WHAT IS THE NASA DART MISSION?
DART will be the world’s first planetary defence test mission.
It is heading for the small moonlet asteroid Dimorphos, which orbits a larger companion asteroid called Didymos.
When it gets there it will be intentionally crashing into the asteroid to slightly change its orbit.
While neither asteroid poses a threat to Earth, DART’s kinetic impact will prove that a spacecraft can autonomously navigate to a target asteroid and kinetically impact it.
然后, using Earth-based telescopes to measure the effects of the impact on the asteroid system, the mission will enhance modeling and predictive capabilities to help us better prepare for an actual asteroid threat should one ever be discovered.
After impact in October 2022, post-impact observations from Earth-based optical telescopes and planetary radars will measure the change in Dimorphos’ orbit around Didymos, according to NASA.
The space agency provided details of the DART mission, which carries a price tag of $330 百万 (£244 million), in a briefing for reporters earlier this month.
It’s livestreaming the launch on its official YouTube channel, 开始于 05:30 GMT on Wednesday.
‘Although there isn’t a currently known asteroid that’s on an impact course with the Earth, we do know that there is a large population of near-Earth asteroids out there,’ said Lindley Johnson, NASA’s Planetary Defense Officer.
‘The key to planetary defence is finding them well before they are an impact threat. We don’t want to be in a situation where an asteroid is headed towards Earth and then have to test this capability.’
The target asteroid, Dimorphos, which means ‘two forms’ in Greek, 关于 525 feet in diameter and orbits around Didymos (‘twin’ in Greek).
Neither asteroid poses a immediate threat to Earth, although NASA lists Didymos as ‘potentially hazardous’.
But both are ideal candidates for the test because of the ability to observe them with ground-based telescopes.
Dimorphos completes an orbit around Didymos every 11 小时和 55 minutes ‘just like clockwork’, said Nancy Chabot of the Johns Hopkins Applied Physics Laboratory, which built DART.
NASA is targeting to be as nearly head-on as possible ‘to cause the biggest deflection’, but DART will not ‘destroy’ the asteroid.
Dimorphos and Didymos are depicted here to scale with some of Earth’s most famous landmarks
The DART spacecraft will head towards the Didymos binary (depicted here) 在十一月 24 aboard a SpaceX Falcon 9 rocket. 大致 525 脚 (160 米) 在直径上, Didymoon orbits the larger Didymos, 这是 2,559 脚 (780 米) 跨越
DIMORPHOS AND DIDYMOS
Dimorphos completes an orbit around Didymos every 11 小时和 55 分钟. It was discovered in 1996 by the Spacewatch survey at Kitt Peak in the US.
The sub-kilometer asteroid is classified as both a potentially hazardous asteroid and a near-Earth object.
Orbiting Didymos is a ‘moonlet’ called Dimorphos, which was discovered in 2003.
‘It’s just going to give it a small nudge,’ Chabot said. ‘It’s going to deflect its path around the larger asteroid.
‘It’s only going to be a change of about 1 per cent in that orbital period, so what was 11 小时和 55 minutes before might be like 11 小时和 45 分钟。’
The amount of deflection will depend to a certain extent on the composition of Dimorphos. 目前, scientists are not entirely certain how porous the asteroid is.
Dimorphos is the most common type of asteroid in space and is some 4.5 billion years old, Chabot said.
‘It’s like ordinary chondrite meteorites,’ 她说. ‘It’s a fine grain mixture of rock and metal together.’
Images of the impact will also be collected by a miniature camera-equipped satellite – called LICIACube – contributed by the Italian Space Agency that will be ejected by the DART spacecraft 10 days before impact.
LICIACube is a mini satellite that weighs just 31 pounds and measures roughly the length of an adult’s hand and forearm.
Infographic showing the effect of DART’s impact on Dimorphos and its orbit of Didymos. Also shown is deployment of italian LICIACube
DART (图为) is the first part of NASA’s asteroid defense strategy, designed in collaboration with the European Space Agency to protect Earth from a possible impact from a ‘hazardous asteroid’
Both Didymos and the smaller Dimorphos were discovered relatively recently; Didymos in 1996 and the smaller Dimorphos in 2003.
The year it was discovered, Dimorphos came within 3.7 million miles of Earth – 15 times farther away than the Moon.
美国宇航局 considers any near-Earth object ‘potentially hazardous’ if it comes within 0.05 天文单位 (4.6 百万英里) and measures more than 460 feet in diameter.
多于 27,000 near-Earth asteroids have been catalogued but none currently pose a danger to our planet.
这些 14 radar images show the near-Earth asteroid Didymos (65803) and its moonlet as seen by the Arecibo Observatory radio telescope in Puerto Rico in November 2003
An asteroid discovered in 1999 called Bennu will pass within half the distance of the Earth to the Moon in the year 2135 but the probability of an impact is considered very slight.
Bennu, which is about a third of a mile wide, has a slightly greater chance of hitting Earth than previously thought, NASA revealed in August.
The space agency upgraded the risk of Bennu impacting Earth at some point over the next 300 years to one in 1,750. Bennu also has a one-in-2,700 chance of hitting Earth on the afternoon of September 24, 2182.
根据 recent experiments, deflecting an asteroid such as Bennu could require multiple small impacts from some sort of massive human-made deflection device.
DEFLECTING AN ASTEROID WOULD REQUIRE ‘MULTIPLE BUMPS’, STUDY SAYS
Deflecting an asteroid such as Bennu, which has a small chance of hitting Earth in about a century and a half, could require multiple small impacts from some sort of massive human-made deflection device, 根据专家.
Scientists in California have been firing projectiles at meteorites to simulate the best methods of altering the course of an asteroid so that it wouldn’t hit Earth.
According to the results so far, an asteroid like Bennu that is rich in carbon could need several small bumps to charge its course.
Bennu, which is about a third of a mile wide, has a slightly greater chance of hitting Earth than previously thought, 美国宇航局 revealed earlier this month.
The space agency upgraded the risk of Bennu impacting Earth at some point over the next 300 years to one in 1,750.
Bennu also has a one-in-2,700 chance of hitting Earth on the afternoon of September 24, 2182, according to the NASA study.
Scientists have been seriously considering how to stop an asteroid from ever hitting Earth since the 1960s, but previous approaches have generally involved theories on how to blow the cosmic object into thousands of pieces.
The problem with this is these pieces could potentially zoom towards Earth and present almost as dangerous and humanity-threatening an issue as the original asteroid.
A more recent approach, called kinetic impact deflection (KID), involves firing something into space that more gently bumps the asteroid off course, away from Earth, while keeping it intact.
Recent KID efforts were outlined at the 84th annual meeting of the Meteoritical Society held in Chicago this month and led by Dr George Flynn, a physicist at State University of New York, Plattsburgh.
‘You might have to use multiple impacts,’ Dr Flynn said in conversation with 纽约时报. '它 [Bennu] may barely miss, but barely missing is enough.’
Researchers have been working at NASA’s Ames Vertical Gun Range, built in the 1960s during the Apollo era and based at Moffett Federal Airfield in California’s Silicon Valley, for the recent KID experiments.
They fired small, spherical aluminum projectiles at meteorites suspended by pieces of nylon string.
The team used 32 meteorites – which are fragments of asteroids that have fallen to Earth from space – that were mostly purchased from private dealers.
The tests have allowed them to work out at what point momentum from a human-made object fired towards an asteroid turns it into thousands of fragments, rather than knocking it off course as desired.
‘If you break it into pieces, some of those pieces may still be on a collision course with Earth,’ Dr Flynn said.
Carbonaceous chondrite (C-type) asteroids, such as Bennu, are the most common in the solar system.
They are darker than other asteroids due to the presence of carbon and are some of the most ancient objects in the solar system – dating back to its birth.
According to the findings from experiments at AVGR, the type of asteroid being targeted (and how much carbon it has in it) may dictate how much momentum would be directed at it from any human-made KID device.
From the experiments, the researchers found C-type meteorites could withstand only about one-sixth of the momentum that the other chondrites could withstand before shattering.
‘[C-type] asteroids are much more difficult to deflect without disruption than ordinary chondrite asteroids,’ the experts concluded.
‘These results indicate multiple successive impacts may be required to deflect rather than disrupt asteroids, particularly carbonaceous asteroids.’
因此, 周围 160 years in the future – when Bennu is most likely to collide with Earth, according to NASA – a KID device would have to give it a series of gentle nudges to prevent it from breaking up and sending dangerous splinter fragments flying towards Earth.
NASA’s recent study about Bennu, published in the journal Icarus, did point out there is more than a 99.9 per cent probability Bennu will not smash into Earth over the next three centuries.
‘Although the chances of it hitting Earth are very low, Bennu remains one of the two most hazardous known asteroids in our solar system, along with another asteroid called 1950 DA,’ 美国宇航局在一份声明中说.