NASA recalculates the odds of asteroid Bennu striking Earth, and now China would like to
tear it apart!
September 24, 2023, Utah desert, United States: a bright trail crosses the sky.
No, it is not a meteor, but a small capsule that a few minutes earlier has been released
from an interplanetary probe that has crossed the Earth ten thousand kilometers away.
A group of Nasa researchers and Air Force soldiers immediately rushed to collect the
capsule containing it.
It might sound like the plot of a science fiction film, but it is what will happen in
the near future, when the NASA probe Osiris-Rex will deliver to our doorstep some dust collected
a year earlier on the surface of the asteroid Bennu.
But if we anticipate the timing, already talking about how the mission will end, it is because
this small asteroid has recently been the focus of attention that has little to do with
mineralogy and a lot to do with its danger.
On August 11, NASA has even called a press conference to announce important news, and
even China has surprised a bit 'all with some of his "belligerent" statements...
Follow me, let's go and find out why all this is happening, maybe taking two steps back
first.
The mission of Osiris-Rex, one of the most ambitious of recent times for NASA, had begun
in 2016 with the launch from Earth which was followed by a long journey of hundreds of
millions of kilometers to reach Bennu in 2018, an asteroid, which has a mass estimated at
around 70 million tons and a maximum diameter of 565 meters.
In late October 2020, the probe had maneuvered to approach Bennu and touch it for about five
seconds with its mechanical arm.
In doing so, it had emitted a puff of nitrogen to cause the debris on the asteroid's surface
to be lifted up and collected in the lower part of the same mechanical arm.
The operation had been a success, although the probe had a little exaggerated collecting
more material than expected, complicating the subsequent operations to insert the debris
inside the container that will be then parachuted to Earth.
The probe had remained in the company of Bennu for a few more months, for further observations
and to study the same small crater caused by the impact of its mechanical arm.
Finally, on May 10, Osiris-Rex turned on its engines to move away from the asteroid and
begin its journey to Earth.
To arrive in our vicinity, the probe will make two different orbits around the Sun,
covering a total distance of about 2.3 billion kilometers.
In the vicinity of our planet, Osiris-Rex will release the container with the fragments,
so that it can undertake the turbulent re-entry into our atmosphere.
The capsule has a maximum diameter of 81 centimeters and reaches a height of about 50 centimeters,
with a shape reminiscent of a spinning top.
After recovery, it will be transferred with its rare contents to the Johnson Space Center
in Houston, Texas, where NASA keeps much of the lunar rocks collected with the Apollo
missions.
NASA plans to make about a quarter of the material collected on Bennu available to researchers,
while the remainder will be stored for future research.
The idea is that in the coming decades, new tools will be developed to conduct analysis,
with technologies that we don't know yet and that could offer new insights and scientific
evidence.
But why was Bennu chosen, among many asteroids?
Bennu was chosen as the target mainly because it is a real "time capsule".
But not only ... Let us try to list together with the possible reasons.
To begin with, Bennu is the typical asteroid from "mining exploitation".
Not very big, about 490 meters in diameter, quite close to Earth (even too much, as we
shall see), since it is part of the group of Apollo objects, or those asteroids that
have an orbital semi-major axis greater than that of the Earth, but perihelion distances
less than the Earth's aphelion distance.
All space agencies in the world are interested in understanding what could be the best way
to exploit its resources: to work the asteroid where it is or even bring it home in Earth's
orbit?
Bennu is also a dark, very dark asteroid...
It is classified as a B-type asteroid, which means it contains a lot of carbon in and along
with its various minerals.
Bennu's carbon content creates a surface on the asteroid that reflects about four percent
of the light that hits it - and that's not a lot.
In contrast, the solar system's brightest planet, Venus, reflects around 65 percent
of incoming sunlight, and Earth reflects about 30 percent.
Bennu is a carbonaceous asteroid that hasn't undergone drastic, composition-altering change,
meaning that on and below its deeper-than-pitch-black surface are chemicals and rocks from the birth
of the solar system.
Bennu is very dark, but also very ancient... has been mostly undisturbed for billions of
years.
Not only is it conveniently close and carbonaceous, but it is also so primitive that scientists
calculated it formed in the first 10 million years of our solar system's history - over
4.5 billion years ago.
Thanks to the Yarkovsky effect -- the slight push created when the asteroid absorbs sunlight
and re-emits that energy as heat -- and gravitational tugs from other celestial bodies, it has drifted
closer and closer to Earth from its likely birthplace: the Main Asteroid Belt between
Mars and Jupiter.
Another interesting thing about Bennu is that it is believed to be a "Rubble-Pile asteroid”.
I know, it could almost sound like an insult, but it's actually a real astronomy classification.
Rubble-pile asteroids are celestial bodies made from lots of pieces of rocky debris that
gravity compressed together.
This kind of detritus is produced when an impact shatters a much larger body.
It likely took just a few weeks for these shards of space wreckage to coalesce into
the rubble-pile that is Bennu.
Bennu is full of holes inside, with 20 to 40 percent of its volume being empty space.
The asteroid is actually in danger of flying apart if it starts to rotate much faster or
interacts too closely with a planetary body.
And apparently, it's not just made of carbon...
Bennu, in fact, is likely to be rich in platinum and gold compared to the average crust on
Earth.
Although most aren’t made almost entirely of solid metal, many asteroids do contain
elements that could be used industrially in lieu of Earth’s finite resources.
Closely studying this asteroid will give answers to questions about whether asteroid mining
during deep-space exploration and travel is feasible.
Although rare metals attract the most attention, water is likely to be the most important resource
in Bennu.
Water (two hydrogen atoms bound to an oxygen atom) can be used for drinking or separated
into its components to get breathable air and rocket fuel.
Given the high cost of transporting material into space, if astronauts can extract water
from an asteroid for life support and fuel, the cosmic beyond is closer than ever to being
human-accessible.
Moreover, already before the departure of Osiris-Rex, it was known that Bennu is an
active asteroid, which means that it ejects, from time to time, material from its surface.
It is mostly particles and rock fragments up to 10 centimeters in diameter, perhaps
emitted by processes of cooling and heating due to the cycles of night and day, the surface
rocks could shatter, ejecting material.
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The mission to Bennu was also an excellent opportunity to study closely the slow but
dangerous orbital changes that these bodies can put in place.
Gravity isn't the only factor involved with Bennu's destiny.
The side of Bennu facing the Sun gets warmed by sunlight, but a day on Bennu lasts just
4 hours and 17.8 minutes, so the part of the surface that faces the Sun shifts constantly.
As Bennu continues to rotate, it expels this heat, which gives the asteroid a tiny push
towards the Sun, changing its orbit.
It is the so-called Yarkovsky effect, of which surely you have already heard.
A force no stronger than that exerted by the weight of three grapes, and yet able to send
Bennu drifting about 300 meters per year ... Until two years ago, scientists had calculated
that during its periodic approaches Bennu would have a one in 2700 chance of impacting
the Earth within the next century.
The Osiris-Rex mission, as we are about to see, with the data collected has even worsened
this estimate.
Supporting the thesis that Bennu is one of the most dangerous asteroids in circulation
among those that periodically cross the orbit of our planet.
These days, Osiris-Rex is on the way back, engaged in a phase of the mission that should
not have brought big news.
So that has created a certain sensation, on August 9, the sudden invitation from NASA
to follow a briefing that would be held two days later, and in which would be given news
of some importance on the ongoing mission.
What was going on?
Was the spacecraft off course?
Had we lost contact?
Had the data collected revealed that something exceptional was happening on Bennu?
No, none of that.
As usual, NASA had exaggerated the tone of the announcement and everything was resolved
with the disclosure of important news, but certainly not epochal.
Apparently, using the data collected by Osiris-Rex a team of scientists has managed to make an
absolutely precise calculation of the orbit of Bennu, being able to determine the position
of the asteroid at any time with the accuracy of two meters!
Which is equivalent to measuring the distance between the Empire State Building and the
Eiffel Tower with the error of a few thousandths of a centimeter!
The researchers then analyzed the risk of impact with Earth between now and the year
2300.
finding a 1 in 1,750 chance of a future collision over the next three centuries, a slightly
higher probability than previously estimated.
Nearly all of the riskiest encounters with Bennu will occur between late 2100 and early
2200, with the single most likely impact occurring on the afternoon of September 24, 2182.
On that Tuesday, Bennu will have a 1 in 2,700 chance of hitting Earth.
Despite the slightly higher chance of impact, Bennu's risks shouldn't keep anyone up at
night.
There's more than a 99.9 percent chance that Bennu won't hit Earth in the next three centuries,
and a Bennu impact wouldn't cause a mass extinction like the Chicxulub impact that killed off
the dinosaurs 66 million years ago.
And if indeed our great-grandchildren find themselves cornered by a greater danger, they
will have plenty of time and technology at their disposal to neutralize the threat.
In what way is not yet known.
The debate is open... even if just in these days, scientists at China's National Space
Science Center have calculated that if 23 Long March 5 rockets, each weighing about
990 tons, hit the asteroid at the same time, it would be enough to deflect the asteroid
from its path by almost 9000 kilometers (1.4 times the radius of the Earth).
"Asteroid impacts pose a serious threat to all life on Earth," said Mingtao Li, a space
science engineer at the National Space Science Center in Beijing and lead author of the new
study.
"Deflecting an asteroid on an impact trajectory is critical to mitigating this threat.
A kinetic impactor remains the most feasible asteroid deflection method.
The study also seeks to demonstrate that orbital deflection of large asteroids similar to Bennu
can be accomplished without resorting to a nuclear device, as long as it is planned 10
years in advance of impact."
However, NASA will be the first space agency to take the field and will do so on November
24 this year with the launch of the mission DART (Double Asteroid Redirection), which
will send a vehicle to the asteroid Didymos, 11 million kilometers away.
Once there, the spacecraft will strike Didymos' moon, Dimorphos, a rock orbiting the asteroid.
Then the effects will be measured, trying to derive confirmations to the theoretical
calculations.
But in all this, what will become of Osiris-Rex after it has dropped the capsule with the
samples on the Utah desert?
Leaving its cargo behind, Osiris-Rex will continue to travel through interplanetary
space.
The plans for the probe are still not very clear, but NASA is confident that it can be
reused for another mission to a new asteroid.
Perhaps Apophis itself, another dangerous Near-Earth Asteroid that will approach Earth
in April 2029.
For now, dear Osiris-Rex, have a safe trip, and thank you for everything!