An asteroid with the destructive power of thousands of nuclear warheads could collide with Earth – so NASA is hunting it down.

Image: NASA/Goddard/University of Arizona

Deep in outer space, a diamond-shaped asteroid is hurtling towards Earth. If the two bodies collide, the space rock – known as Bennu – is big enough to extinguish life on our planet. But the asteroid is not alone. No, a NASA probe has been chasing the massive space rock for years. And having caught up with the colossal asteroid, the craft is preparing to land on its rocky surface. It’s a high-risk maneuver that demands absolute precision, but it’s one that could help secure the safety of humankind.

Approximately 66 million years ago, a large asteroid slammed into the Earth near Mexico’s Yucatán Peninsula. That in turn triggered a cataclysm – an extinction event that led to the loss of three quarters of the planet’s biodiversity, including the dinosaurs. But the impact transformed the environment into one that allowed Homo sapiens to evolve and flourish. A similar asteroid collision today, however, would mean the end of human civilization as we know it.

For decades, scientists have known that Earth faces the risk of a major asteroid collision. It’s more than a risk, in fact, as the chances of such a strike happening are 100 percent certain; it’s merely a question of when. And several Hollywood movies have, of course, already imagined the asteroid apocalypse – the 1998 box-office smash Armageddon, for instance. But while Armageddon is a light sci-fi adventure starring Bruce Willis and Ben Affleck, the threat of Bennu is real.

Image: T. A. Rector & B. A. Wolpa, NOAO, AURA via ScienceBlogs

So where has this potentially devastating space rock come from? Well, it’s thought that asteroids were forged in the same high energy crucible that gave birth to our solar system. These rocky bodies range in size from small pebbles to enormous hunks of stone measuring hundreds of miles across. Their creation – along with that of the Sun, planets and moons – came about approximately 4.6 billion years ago when an enormous molecular cloud containing dust and gas collapsed in on itself.

Now, small pieces of asteroids and other space rocks sometimes fall to Earth. And although most such bodies burn up in the atmosphere as “shooting stars,” occasionally – around ten times a year – a small piece of rock makes it to the surface. Known as meteorites, these rocky fragments often leave a small impact crater. But unless you have the cosmic misfortune of being hit by one of these falling space rocks, they pose no serious threat to human life.

An asteroid the size of Bennu is another matter, though. You see, the impact of such a large space rock would unleash kinetic energy equivalent to tens of thousands of atomic bombs. And the subsequent shockwaves would cause earthquakes and tsunamis. Meanwhile, the resulting dust cloud would probably cool the planet for hundreds of years – thereby devastating Earth’s ecology.

Image: NASA/Goddard/University of Arizona via OSIRIS-REx

There are thousands of space rocks currently traveling in close proximity to the Earth too – although “close” in this case refers to around 120 million miles out. Most such rocks are, in fact, concentrated in the area between Jupiter and Mars. But Bennu is one of 200 known asteroids with a solar orbit much like that of Earth, and one Bennu year is equivalent to 436 Earth days. What’s more, the body passes perilously close to our planet on a regular basis – once every half a dozen years.

The asteroid is certainly of note, then, and scientists originally gave it the rather catchy name 1999 RQ36. Bennu’s new moniker, however, was conjured up in 2013 by nine-year-old Mike Puzio, who won a competition to rename the rock. And the youngster was inspired by NASA’s OSIRIS-REx probe. Indeed, Puzio thought that the craft looked like the neck and wings of the Egyptian deity Bennu – who is often represented in the form of a heron.

At 1,650 feet wide, Bennu is a comparatively big asteroid. And the larger the asteroid, the easier it is to land a probe on it. Indeed, smaller space rocks – 650 feet across or less – tend to spin rapidly, making them unsuitable for landing on. With technological improvements, though, we may be able to explore a wider range of asteroids in the future.

For now, though, Bennu is of particular interest to NASA, and the agency has sent OSIRIS-REx to learn more about the asteroid. An acronym for “Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer,” OSIRIS-REx is an $800 million space probe tasked with tracking Bennu. And with the help of the craft’s sensitive detection instruments and cutting-edge robotics, NASA scientists hope to extract two ounces of sample material from the surface of the rocky body. The sample will then be brought back to Earth for further study.

And there are good reasons why NASA wants to examine the sample on terra firma – the main advantage simply being that a far wider range of tests can be carried out back on Earth than in space. You see, while OSIRIS-REx boasts sophisticated technology, the most advanced scientific analyses require large, bulky equipment that cannot fit on a probe. But flying the sample home makes the mission riskier and more complicated, of course.

However, even if OSIRIS-REx is successful, it won’t be the first time that a space craft has delivered an asteroid sample to Earth. Japan earned that accolade in 2010 with their Hayabusa spacecraft. And the probe’s successor, Hayabusa 2, is currently en route to the Ryugu asteroid.

OSIRIS-REx, though, is part of NASA’s New Frontiers program – which uses smaller spacecraft to explore our local solar system. Other missions have included New Horizons and Juno, which have helped glean new information about Pluto and Jupiter. Meanwhile, the proposal for OSIRIS-REx was selected from a range of finalists in 2011.

Image: University of Arizona/Symeon Platts

And having been given the green light, the mission is now well underway. The probe itself has five specific instruments for surveying and analyzing the surface of Bennu. The craft’s Visible and Infrared Spectrometer (OVIRS), for starters, will be used for detecting organic chemicals and minerals by measuring both near-infrared and visible light. You see, OVIRS identifies material properties by detecting the light frequencies absorbed by their molecular structure.

Secondly, the probe’s Thermal Emission Spectrometer will measure the rock’s temperature. Like the OVIRS, this device will also locate concentrations of chemicals and minerals. And together, these two instruments will enable NASA scientists to map the surface of Bennu and choose the most interesting site to extract samples from.

The third array of instruments is a high-resolution camera suite composed of three units: PolyCam, MapCam and SamCam. PolyCam will gather initial images of the asteroid as well as potential sample sites, and MapCam will then scour the rock for satellites and stitch together topographic maps. Finally, SamCam will film the extraction of the sample.

Meanwhile, the OSIRIS-REx Laser Altimeter (OLA) will conduct a detailed scan of Bennu’s surface. And the data that the instrument collects and relays back to Earth will be used to create extremely detailed models of the asteroid in 3D. Interestingly, similar technology was recently used to reveal the location of Mayan pyramids in the jungle.

Finally, the probe is also fitted with a Regolith X-ray Imaging Spectrometer (RExIS), which will detect the X-rays coming from the asteroid. And the results collected by this device will contribute data to a map of the rock’s elemental properties. Specifically, the information gathered by the RExIS will reveal the atomic structure of the asteroid.

OSIRIS-REx should help experts discover new information about our solar system, then. Indeed, just as the fossil record contained within the strata of the Earth underpins our knowledge of geological time, so the asteroids in our solar system are vital to our understanding of cosmic time. And to this end, scientists hope that by studying material created at the dawn of the Sun, we will gain new insights into planetary formation.

NASA is also interested in the theory that biological life did not begin in Earth’s primordial ocean; rather, life migrated to our planet on an asteroid. And interestingly, Bennu appears to have a particularly high level of carbon-based components. Further analyses of the space rock’s composition may yet provide new insights on the origins of life, then.

There’s the asteroid’s monetary worth too. That’s right: the rock could be a valuable new source of resources. “The mission will develop important technologies for space exploration that will benefit anyone interested in exploring or mining asteroids,” Dante Lauretta, OSIRIS-REx’s Principal Investigator, explained in a space agency press statement in 2013.

Whether that interested party is a private enterprise or a space agency such as NASA is hard to say, though. But given the recent growth of private investment in the space sector, it is not hard to imagine a future where asteroids are regularly mined for fuel or metallurgical resources. It may, in fact, one day be cheaper to mine asteroids in space than to mine the Earth.

Above all, though, the data gleaned from the mission will enable scientists to better predict the trajectories of asteroids – and, presumably, influence their respective courses. But one possible application of such knowledge could be terraforming – the intentional alteration of a planetary body in an attempt to make it habitable. In 2017, for example, scientists from the Lake Matthew Team proposed a scheme called the Mars Terraformer Transfer. And believe it or not, the plan involved crashing an asteroid into the planet.

You see, the scientists say that such a collision would cause the Martian bedrock to heat up and release its frozen groundwater. This, in turn, would create a lake lasting for millennia. And it’s theorized that the water from the new lake could then be used to supply a city-sized colony – effectively side-stepping the big technical challenges of terraforming an entire planet.

Of course, understanding the orbit of asteroids such as Bennu is also necessary for averting collisions with Earth. In Armageddon, a plucky band of oil rig workers save the day by planting a nuclear device inside the rogue space rock and blowing it to pieces. And in the future, probes such as OSIRIS-REx may well be able to carry out such an operation but with more precision.

OSIRIS-REx could be crucial to the future of our planet, then. And having launched in September of 2016, the probe’s first maneuver involved setting up for a gravity assist before performing a flyby of Earth. This slingshot strategy – intended to add speed for the onward voyage – saw the craft use our planet’s gravitational pull to catapult itself into space. So, just over a year after leaving, the probe caught a brief glimpse of Earth before heading onwards to Bennu.

Image: NASA’s Goddard Space Flight Center/University of Arizona

And it seems that the probe’s flyby of Earth went perfectly. It brought the spacecraft within 11,000 miles of Antarctica, in fact, and caused it to accelerate by an additional 8,500 miles per hour. What’s more, before departing for the distant asteroid of Bennu, OSIRIS-REx took some haunting images of the Earth and the Moon.

Image: NASA/Goddard/University of Arizona

Then, on December 3, 2018, OSIRIS-REx came within sight of its target. It marked the end of a 27-month chase that had taken the probe over a billion miles through space. Now, though, NASA scientists would have to perform the tricky task of putting the probe into orbit around Bennu.

To complete the move, the expert team first had to take detailed measurements of the rock’s shape and mass. “Maneuvering around a small body that basically has no gravity is very challenging,” Heather Enos, Deputy Principal Investigator for OSIRIS-REx, explained to Space.com. “So, we do have to get a little more information to proceed every step of the way.”

Image: NASA/Goddard/University of Arizona

But NASA safely placed OSIRIS-REx into orbit around the asteriod on the last day of 2018. And in doing so, the space agency established a couple of records. Firstly, Bennu became the smallest space rock ever to be orbited by a spacecraft. Secondly, the probe broke the record for the nearest orbit of a body that small in space; and at one point, the craft traveled just a single mile from the asteroid’s surface.

Image: NASA’s Goddard Space Flight Center

Locked in orbit around Bennu, then, OSIRIS-REx has since been conducting surveys of the asteroid’s surface. The probe will generally complete flybys at distance of around four miles and has been charting the asteroid’s north and south poles as well as its equator. And scientists are now analyzing the data to make future decisions about the craft.

Of course, the biggest decision concerns where exactly to land the probe. The sample site will, in fact, only be selected after a year and a half of data gathering and analysis. Mission managers will then present two potential landing sites in July 2020, and the winning location will be selected shortly thereafter. And after this decision has been made, OSIRIS-REx will carry out its next important task.

Image: NASA Goddard Space Flight Center via OSIRIS-REx

Yes, the probe will then move in to collect a sample. However, the landing will be extremely brief. So fleeting, in fact, that OSIRIS-REx scientists have compared it to a kiss, lasting just a couple of seconds. That short period, though, should be enough for the craft to acquire its sample; at least, that’s the idea behind its Touch-And-Go Sample Acquisition Mechanism (TAGSAM).

Indeed, TAGSAM does the work of digging and collecting rock. Using blasts of nitrogen gas, the device fractures the surface of the asteroid to release broken rock and dust, which is then collected inside a sample chamber. And to allow for several attempts at obtaining a sample, the probe carries three gas-filled containers.

Image: NASA’s Goddard Space Flight Center

For the mission to be a success, then, NASA must acquire a minimum of two ounces of asteroid material. However, to compensate for any measuring errors, they will attempt to gather around five ounces. And should the mission demand it, TAGSAM actually has the capacity to carry an additional 70 ounces.

Once the sample has been collected, OSIRIS-REx will commence its long journey home. The return trip is scheduled to start in March 2021 and will take some two and a half years to complete. Then, in September 2023, the probe will dispatch its cargo of asteroid rock. And if all goes to plan, the sample should parachute to Earth and land somewhere in the deserts of Utah.

But while Bennu is certainly capable of inflicting disaster on Earth, the asteroid is unlikely to ever actually hit our planet. In fact, according to NASA, there is a one-in-2,700 chance that the rock will hit Earth in the 22nd century’s final quarter. For that to happen, though, the asteroid’s present track would have to change during its 2,135th orbit.

There is, however, still an important reason for NASA scientists to conduct a thorough risk assessment of the rock: the Yarkovsky effect. This theory – discovered by Polish engineer Ivan Yarkovsky – refers to the way an asteroid’s path can be altered over time by the Sun heating the rock’s surface. An unpredictable Yarkovsky effect, then, could potentially cause Bennu to be redirected towards Earth.

But even if Bennu were to collide with Earth, a hypothetical doomsday impact is actually a matter of dispute. Yes, while British tabloid The Sun has compared a potential impact to “80,000 Hiroshima atomic bombs,” experts believe the destruction would likely be limited to a more localized area. An extinction event is, therefore, unlikely.

Nonetheless, the possibility of an asteroid colliding with the Earth at some point in the future is almost completely certain. Whether or not humans will be around to experience it, much less have the technology to avert it, is less certain. But, in any case, there will always be a sensible, powerful and scientific argument for studying space rocks.