This week, two asteroids – one big enough to destroy a city, and the other so big it could end civilization – will fly near our planet.
Do not panic.
Both have a zero percent chance of impacting Earth. And depending on where you are in the world, you might even see one.
The larger of the pair, (415029) 2011 UL21, will travel at a distance more than 17 times farther than the moon on Thursday at 4:14 PM Eastern Time. It is a whopping 2,000 meters long, but without a strong telescope it will be too far to see it easily.
However, two days later, the smaller space rock, called 2024 MK, will come significantly closer to humanity. On Saturday at 9:46 a.m. Eastern Time, it will fly past Earth at 75 percent of the distance to the moon. If you have a decent telescope in the backyard or maybe even a good pair of binoculars, and your sky is cloud-free, you might see the 400- to 800-foot rock as a point of light flashing through the starry sky before the sun rises.
“The object will be moving quickly, so you need some skills to recognize it,” said Juan Luis Cano, member of the European Space Agency’s Planetary Defense Office.
Stargazers in the United States, especially those further southwest, can see the asteroid flash past the planet. Those atop Hawaii’s Mauna Kea volcano will be well positioned to see it as the asteroid zooms by before sunrise. People in South America, however, may have the easiest viewing experience, says Andrew Rivkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory.
Small asteroids and comet fragments occasionally pierce Earth’s atmosphere, producing a harmless light show. Many more rocky and icy shards narrowly miss the planet, often squeezing between Earth and the moon.
An asteroid the size of 2024 MK threading this celestial needle is less common. “Things this close are rare, but happen on decadal timescales – this will be the third (as far as we know) this century,” said Dr. Rivkin in an email.
Anyone who doesn’t see 2024 MK shouldn’t feel left out for too long. On April 13, 2029, Apophis, a 350-meter-long asteroid, will fly less than 32,000 kilometers above Earth’s surface, closer than the orbits of geosynchronous satellites – meaning it will be visible to the naked eye.
Such close approaches are useful for planetary defense researchers. This week’s asteroids will be pinged by radar systems on Earth, making it possible to accurately determine their sizes and onward journeys.
“These measurements will significantly reduce the uncertainties in their motion and allow us to calculate their trajectories further into the future,” said Lance Benner, the principal investigator of the asteroid radar research program at NASA’s Jet Propulsion Laboratory.
The double flight also serves as a fortuitous preview of Asteroid Day on June 30 – a United Nations-sanctioned occasion designed to raise awareness about asteroid impacts.
On that day in 1908, a space rock about 50 meters in diameter exploded over a remote part of Siberia, instantly leveling 1,300 square kilometers of forest – roughly the size of the Washington DC metro area. It is known as the Tunguska Event, after a river flowed through the region destroying it.
Although more are discovered every year, most of the near-Earth asteroids capable of destroying a city have not yet been found. Fortunately, many more can be spotted through a pair of telescopes under construction: Chile’s multi-purpose Vera C. Rubin Observatory and NASA’s Near-Earth Object Surveyor spacecraft.
The 2024 MK asteroid is at least twice as long as the Tunguska impactor. It is certainly welcome that the asteroid was found before its encounter with Earth, and that it will be missed by us. But astronomers only discovered the space rock on June 16.
“The case of 2024 MK is yet another reminder that there are still many large objects to be found,” said Dr. Cano. Space agencies have the plans and the technology to defend the planet from deadly asteroids – but only if they find them before the asteroids find us.