A 100-meter-wide asteroid passed just 70,000km from Earth on Thursday, Australian time. It was discovered by a Brazilian SONEAR study just a few days ago, and its presence was announced just hours before it moved past our planet. The lack of warning shows how quickly asteroids can become dangerous to us.
The asteroid, boldly announced 2019 is not right, is not a threat to Earth right now. However, 2019 OK and other asteroids near Earth are a real threat. The Tunguska explosions in 1908 and the Chelyabinsk meteor in 2013 equated to major nuclear explosions, and under the wrong conditions the impact of a meteor could damage a city.
Finding danger
Astronauts are well aware of the dangers posed by asteroids hitting the Earth. Meteor craters are found all over the world, and some relatively new examples include Wolfe Creek in northern Australia and the Meteor Crater in Arizona. The dinosaur collapse was the massive impact of an asteroid 65 million years ago near Chicxulub in modern-day Mexico.
As a result, astronauts around the globe have made a concerted effort to determine the level of threat posed by asteroids near Earth, and to identify individual asteroids that may be a major threat. Asteroid studies include Pan-STARRS, ATLAS, SONEAR (which saw 2019 OK), and Sky Catalina Survey.
The Chelyabinsk meteor, just 20m across, showed the potential of destructive asteroids.
Asteroids are usually so far from Earth that they look like stars, rather than the rocky rocks they are. However, as asteroids travel around the Solar System, they move in relation to the distant stars. So astronauts can detect asteroids by taking sequences of images and looking for objects that move from image to image.
Using this approach to study large areas of space, astronomers have discovered thousands of asteroids near Earth, including more than 2,000 during 2017 alone.
And yet, some asteroids are still catching on to us. Why?
Astronomers are good at spotting asteroids that are visible at night, but not so good at seeing asteroids during the day. Asteroids are also weaker as far as they can get from Earth.
The 2013 Chelyabinsk meteor is sculpting us from the direction of the sun. 2019 OK was visible at night, and at the closest approach it would be seen with a pair of binoculars as a point of light moving slowly across the skies. But three days earlier he was 1,000 times weaker, and therefore harder to see.
The Wolfe Creek fault was created by a meteor impact thousands of years ago. Credit: Dainis Dravins – Lund Theater, Sweden.
2019 OK was finally detected by the SONEAR survey on Wednesday, and shortly afterwards it was independently detected by the ASAS-SN telescope network. Both of these studies use relatively small telescopes with sensory cameras to explore large areas of sky, rather than using large telescopes to study small patches of sky.
Close calls
Prior to its discovery as an asteroid near Earth, 2019 OK was designed with other telescopes, but its importance was not recognized. But the previous images helped astronauts slow down the orbit of the asteroid.
2019 has a very elliptical orbit OK, taking it from the asteroid belt outside Mars to inside the orbits of both Earth and Venus. Since each orbit takes 2.7 years, it doesn’t always pass as close to Earth as it did this time. It will take close approaches in the future, but hopefully this will not be so close.
Other asteroids near Earth are also on their way to get close to our planet. The 400m wide Apophis will pass about 30,000km from Earth on Friday April 13, 2029, which will only come as bad news if you are particularly superstitious.
Astronauts see more asteroids near Earth all the time. Credit: NASA
Both 2019 OK and Apophis are much larger than the Chelyabinsk meteor, which was just 20m across. The danger of them hitting the Earth may be small, but they would be devastating if they did.
Avoiding Armageddon
If we find an asteroid on the course of a real catastrophe with Earth, is there anything we can do? With just a day or week notice we would be in real trouble, but with more knowledge there are options.
We are already sending spacecraft to asteroids near Earth, with NASA’s OSIRIS-REx currently visiting Bennu and Hayabusa2 from Japan currently visiting Ryugu.
However, these are search missions rather than destruction. In fact, destroying an asteroid near Earth can be fruitful, which can create many destructive asteroids.
So how can we prevent a catastrophe? Perhaps the solution is to give dangerous asteroids a gentle movement rather than a wild kick. If the speed of a speed can be changed by just 1km per hour, over years that add up to a difference of thousands of kilometers in position. With the Earth’s pale blue dot just 12,750 kilometers across, a small spike to a rock may be large enough to avoid disturbance.
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