This week, two asteroids – one big enough to destroy a city and the other big enough to end civilization – are set to fly by our planet.
Don’t be scared.
Both have a zero percent chance of hitting Earth. And, depending on where you are in the world, you may even be able to see one of them.
The larger of the pair, (415029) 2011 UL21, will travel a distance more than 17 times farther than Monday at 4:14 pm ET on Thursday. It’s a whopping 7,600 feet long, but it will be too far to see easily without a strong telescope.
However, two days later, the smallest space rock, called 2024 MK will come very close to humanity. At 9:46 a.m. ET on Saturday, it will pass Earth at 75 percent of its distance from the Moon. If you have a good telescope in your backyard or maybe even some good binoculars, and your sky is clear, you can see the 400- to 850-foot rock as a speck of light creeping across the starry night.
“The object will be moving fast, so you have to have some skill to spot it,” said Juan Luis Cano, a member of the Planetary Protection Office at the European Space Agency.
Stargazers in the United States, especially those farther southwest, may catch the asteroid flying past the planet. Those atop Hawaii’s Mauna Kea volcano will be well positioned to see it as the asteroid zooms by before sunrise. However, people in South America may have the easiest viewing experience, said Andrew Rivkin, a planetary astronomer at Johns Hopkins University’s Applied Physics Laboratory.
Small asteroids and comet fragments occasionally pierce Earth’s atmosphere, creating a harmless light show. Many other rocky and icy chunks simply miss the planet and are often squeezed between the Earth and the Moon.
An asteroid the size of 2024 MK that threads this celestial needle is less common. “Passes this close to objects this large are rare, but occur on decadal timescales – this will be the third (that we know of) this century,” said Dr. Rivkin in an email.
Anyone who can’t spot 2024 MK shouldn’t feel left out for long. On April 13, 2029, Apophis, a 1,100-foot-long asteroid, will fly by less than 20,000 miles 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 checked by radar arrays on Earth, making it possible to accurately determine their dimensions and onward journeys.
“These measurements will reduce the uncertainties in their motion significantly and enable us to calculate their trajectories further into the future,” said Lance Benner, principal investigator of the Asteroid Radar Research Program at the Jet Propulsion Laboratory of NASA.
The double flyby also serves as a great preview of Asteroid Day on June 30 – a United Nations-sanctioned occasion designed to raise awareness of asteroid impacts.
On that day in 1908, a space rock approximately 160 meters in size exploded over a remote area of Siberia, instantly flattening 800 square miles of forest – about the area of the Washington DC metro area. It is known as the Tunguska event after a river flowing through the region that destroyed it.
Although more are discovered every year, most near-Earth asteroids capable of destroying a city have yet to be found. Fortunately, many more can be observed by a pair of telescopes under construction—the Vera C. Rubin Multipurpose Observatory in Chile and NASA’s Near-Earth Object Surveyor spacecraft.
Asteroid 2024 MK is at least twice the length of the Tunguska impact. It is certainly welcome that the asteroid was found before its encounter with Earth and that we will miss it. But astronomers just discovered the space rock on June 16.
“The case of 2024 MK is another reminder that there are still many large objects to be found,” said Dr. Cano. Space agencies have the plans and technology to protect the planet from killer asteroids — but only if they find them before the asteroids find us.