Could we really deflect an asteroid heading for Earth? An expert explains NASA's latest DART mission
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Could we really deflect an asteroid heading
for Earth? An expert explains NASA's latest
DART mission
26 November 2021, by Gail Iles
asteroids?
We've all seen disaster movies in which an asteroid
hits Earth, creating an extinction event similar to the
one that killed off the dinosaurs millions of years
ago. Could that happen now?
Well, Earth is actually bombarded frequently by
small asteroids, ranging from 1-20 metres in
diameter. Almost all asteroids of this size
disintegrate in the atmosphere and are usually
harmless.
There is an inverse relationship between the size of
these object and the frequency of impact events.
This means we get hit much more frequently by
Small asteroid impacts showing day-time impacts (in small objects than larger ones—simply because
yellow) and night-time impacts (in blue). The size of
there are many more smaller objects in space.
each dot is proportional to the optical radiated energy of
the impact. Credit: NASA JPL
Asteroids with a 1km diameter strike Earth every
500,000 years, on average. The most "recent"
impact of this size is thought to have formed the
A NASA spacecraft the size of a golf cart has been Tenoumer impact crater in Mauritania, 20,000
directed to smash into an asteroid, with the years ago. Asteroids with an approximate 5km
intention of knocking it slightly off course. The test diameter impact Earth about once every 20 million
aims to demonstrate our technological readiness in years.
case an actual asteroid threat is detected in the
future. The 2013 Chelyabinsk meteoroid, which damaged
buildings in six Russian cities and injured around
The Double Asteroid Redirection Test (DART) 1,500 people, was estimated to be about 20m in
lifted off aboard a SpaceX rocket from California on diameter.
November 23, and will arrive at the target asteroid
system in September, next year. Assessing the risk
The mission will travel to the asteroid Didymos, a NASA's DART mission has been sparked by the
member of the Amor group of asteroids. Every 12 threat and fear of a major asteroid hitting Earth in
hours Didymos is orbited by a mini-moon, or the future.
"moonlet", Dimorphos. This smaller half of the pair
will be DART's target. The Torino scale is a method for categorising the
impact hazard associated with a near-Earth object
Are we facing an extinction threat from (NEO). It uses a scale from 0 to 10, wherein 0
1/4
means there is negligibly small chance of collision, towards Didymos and, when it's close by, will
and 10 means imminent collision, with the change direction slightly to crash into Dimorphos at
impacting object being large enough to precipitate a a speed of about 6.6km per second.
global disaster.
The larger Didymos is 780m in diameter and thus
The Chicxulub impact (which is attributed to the makes a better target for DART to aim for. Once
extinction of non-avian dinosaurs) was a Torino DART has detected the much smaller Dimorphos,
scale 10. The impacts that created the Barringer just 160m in diameter, it can make a last-minute
Crater, and the 1908 Tunguska event, both course correction to collide with the moonlet.
correspond to Torino Scale 8.
The mass of Dimorphos is 4.8 million tonnes and
With the increase of online news and individuals' the mass of DART at impact will be about 550kg.
ability to film events, asteroid "near-misses" tend to Travelling at 6.6km/s, DART will be able to transfer
generate fear in the public. Currently, NASA is a huge amount of momentum to Dimorphos, to the
keeping a close eye on asteroid Bennu, which is point where it's expected to actually change the
the object with the largest "cumulative hazard moonlet's orbit around Didymos.
rating" right now. (You can keep up to date too).
This change, to the tune of about 1%, will be
With a 500m diameter, Bennu is capable of detected by ground telescopes within weeks or
creating a 5km crater on Earth. However, NASA months. While this may not seem like a lot, 1% is
has also said there is a 99.943% chance the actually a promising shift. If DART were to slam into
asteroid will miss us. a lone asteroid, its orbital period around the Sun
would change by only about 0.000006%, which
Brace for impact would take many years to measure.
At one point in their orbit around the Sun, Didymos So we'll be able to detect the 1% change from
and Dimorphos come within about 5.9 million km of Earth, and meanwhile the pair will continue along
Earth. This is still further away than our Moon, but its orbit around the Sun. DART will also deploy a
it's very close in astronomical terms, so this is when small satellite ten days before impact to capture
DART will hit Dimorphos. everything.
This is NASA's first mission dedicated to
demonstrating a planetary defence technique. At a
cost of US$330 million, it's relatively cheap in space
mission terms. The James Webb Telescope set to
launch next month, costs close to US$10 billion.
There will be little to no debris from DART's impact.
We can think of it in terms of a comparable event
on Earth; imagine a train parked on the tracks but
with no brakes on. Another train comes along and
collides with it.
The trains won't break apart, or destroy one
another, but will move off together. The stationary
The DART mission dates and timeline events. Credit:
Johns Hopkins University one will gain some speed, and the one impacting it
will lose some speed. The trains combine to
become a new system with different speeds than
before.
DART will spend about ten months travelling
2/4
So we won't experience any impact, ripples or speeds. This device could also be used to fire
debris from the DART mission. masses at close-passing asteroids.
This article is republished from The Conversation
under a Creative Commons license. Read the
original article.
Typical asteroid orbits remain between Mars and Jupiter, Provided by The Conversation
but some with elliptical orbits can pass close to Earth.
Credit: Pearson
Is the effort really worth it?
Results from the mission will tell us just how much
mass and speed is needed to hit an asteroid that
may pose a threat in the future. We already track
the vast majority of asteroids that come close to
Earth, so we would have early warning of any such
object.
That said, we have missed objects in the past. In
October 2021, Asteroid UA_1 passed about
3,047km from Earth's surface, over Antarctica. We
missed it because it approached from the direction
of the Sun. At just 1m in size it wouldn't have
caused much damage, but we should have seen it
coming.
Building a deflection system for a potential major
asteroid threat would be difficult. We would have to
act quickly and hit the target with very good aim.
One candidate for such a system could be the new
technology developed by the US spaceflight
company SpinLaunch, which has designed
technology to launch satellites into orbit at rapid
3/4APA citation: Could we really deflect an asteroid heading for Earth? An expert explains NASA's latest
DART mission (2021, November 26) retrieved 5 December 2021 from
https://phys.org/news/2021-11-deflect-asteroid-earth-expert-nasa.html
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