Killer asteroids fly close to Earth; Maybe we can see one

This week, two asteroids will pass by our planet — one large enough to destroy a city and the other so large that it could wipe out civilization.

Don’t panic.

Both have a zero percent chance of hitting the ground. Depending on where you are in the world, you may also be able to see one.

The larger of the two, (415029) 2011 UL21, will travel more than 17 times the Moon’s distance on Thursday at 4:14 p.m. ET. It is 2,000 meters long, but would be too far away to be easily seen without a powerful telescope.

However, two days later, the smaller space rock, called 2024 MK, will come very close to humanity. On Saturday, at 9:46 a.m. ET, it will pass close to Earth at 75 percent of its distance from the Moon. If you have a good telescope or even binoculars, and your sky is clear, you can see the 400- to 850-foot rock as a point of light streaming through the starry night.

“The object will be moving quickly, so you have to have certain skills to detect it,” said Juan Luis Cano, a member of ESA’s Planetary Defense Office.

Stargazers in the United States, especially those in the southwest, will be able to see the asteroid hovering next to the planet. Those on top of Mauna Kea volcano in Hawaii will be in a good position to see the asteroid pass by before dawn. However, according to Andrew Rifkin, a planetary astronomer at the Johns Hopkins University Applied Physics Laboratory, South Americans will have it easier.

Small asteroids and comet fragments occasionally pass through Earth’s atmosphere, creating a harmless light show. Many rock and ice fragments do not reach the planet, and often slip between the Earth and the Moon.

An asteroid about the size of 2024 MK connects this celestial needle less frequently. “It’s rare for asteroids to pass this close to Earth, but they do happen on a ten-year cycle: this would be the third[that we know of]this century,” Rivkin said in an email.

Anyone who hasn’t seen MK 2024 shouldn’t feel left out for long. On April 13, 2029, Apophis, a 1,100-foot asteroid, will fly 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.

These methods are useful to researchers in the field of planetary defense. The asteroids will be monitored this week by radars on Earth, which will allow their dimensions and paths to be determined accurately.

“These measurements will greatly reduce uncertainties about their motion and allow us to calculate their trajectories in the future,” said Lance Penner, principal investigator of the Asteroid Radar Research Program at NASA’s Jet Propulsion Laboratory.

The double flyby is also a coincidental preview of Asteroid Day, which will be observed on June 30, a United Nations-backed event to raise awareness about the impacts of asteroids.

On that day in 1908, a space rock about 200 feet in diameter exploded over a remote strip of Siberia, instantly leveling 800 square miles of forest, roughly the size of the Washington, D.C., metropolitan area. It is known as the Tunguska Event because of the river that flowed through the area it devastated.

Although more are discovered every year, most of the near-Earth asteroids capable of destroying a city have not yet been found. Fortunately, a pair of telescopes under construction — the Vera C. Rubin Multipurpose Observatory in Chile and NASA’s Near-Earth Object Survey spacecraft — will likely find out more.

Asteroid MK 2024 is at least twice as long as the Tunguska object. Without a doubt, it is estimated that the asteroid was found before it collided with Earth, and that it will pass. But astronomers discovered the space rock on June 16.

“The case of MK 2024 is another reminder that there are still many big things to find,” Dr. Kano said. Space agencies have the plans and technology to defend the planet from killer asteroids, but only if they find them before they find us.