Asteroid 2014-YB35, about 1,000 meters across, is set to pass close to Earth on Friday, travelling at more than 23,000 mph, according to NASA.
The rock is expected to pass safely at a distance of 2.8 million miles, about 11.7 times farther away than the moon.
Despite the fact that it will pass farther away than asteroid 2004 BL86 which, on January 6, clipped by the Earth at a distance of 745,000 miles, about 3 times the distance between our planet and the moon, the distance of 2.8 million miles on the astronomical scale is perilously close, according to NASA's Near Earth Object Program.
Asteroid 2014-YB35, first spotted by Catalina Sky Survey late last year, is estimated to be between 500 meters and 1 km wide, but NASA scientists say it is most likely to be about 990 meters.
The close approach of 2014-YB35 highlights the heightening concern about the risk posed by space rocks flying in a path that brings them dangerously close to Earth periodically.
Although, it is not unusual for smaller space rocks to pass close to Earth, a close approach by a rock the size of 2014-YB35 is relatively rare. But having observed a few close shaves by relatively large asteroids in recent years, scientists are growing more concerned, saying it is only a matter of time for the Earth to sustain a bruising collision with a fair-sized asteroid, triggering a disaster unprecedented in recent history.
According Bill Napier, professor of Astronomy at the University of Buckinghamshire, comets and asteroids pose a "very real risk" to the Earth. While a smaller space rock like the Tunguska asteroid could cause local devastation, such as blowing up an entire city, "with something like YB35, we are looking at a scale of global destruction, something that would pose a risk to the continuation of the planet," Napier said.
"These events are however very rare, it is the smaller yet still very damaging impacts which are a very real threat," he added.
The famous asteroid impact event that occurred in Tunguska, Siberia, in 1908 involved a space rock about 50 meters across. Estimates of the energy of the blast are put conservatively between 10 and 15 megatons of TNT, about 1,000 times the energy of the Hiroshima bomb. The explosion destroyed about 80 million trees in an area of about 2,150 square kilometers (830 square miles), generating a shock of about five on the Richter scale.
If the blast had occurred in a densely populated area, it could have wiped out an entire city.
"Smaller scale events like Tunguska are absolutely a real risk, largely they are undiscovered and so we are unprepared... [There is also a great risk] from comets which even if the Earth passes through the tail, can generate a massive plume of smoke with hugely significant consequences. There is absolutely a real risk and if you look at history, certainly biblical records, there are reports of fires in the heavens. Red hot debris resulting from the impact of something a kilometer wide would be capable of incinerating the planet."Collision with Earth by an asteroid the size of 2014-YB35 could unleash an explosive force equivalent to more than 15,000 megatons of TNT, causing massive earthquakes, tsunamis, and throwing up thick clouds of debris that could cause catastrophic changes to the Earth's climate, making the Earth uninhabitable.
An even larger asteroid could wipe out all species of higher life forms on Earth.
However, NASA astronomers are on alert at the Goldstone observatory in California's Mojave Desert. They will be watching 2014-YB35 very closely to learn more about its composition, improve on the accuracy of their estimation of its size, and the precision of their knowledge of its trajectory to enhance their ability to predict its path in future close approaches to Earth.
Scientists could also make surprising and unexpected discoveries. For instance, as asteroid 2004 BL86, measuring 1,100 feet across (325 meters), passed, NASA astronomers taking images of the space rock using NASA's Deep Space Network antenna in Goldstone, Arizona, were surprised to discover for the first time that the asteroid has a companion, a "moon" of its own, about 230 feet (70m) across.
Meanwhile, as part of efforts to focus attention on the dangers of space rocks listed as Potentially Hazardous Asteroids (PHAS), astronomers have declared June 30 as Asteroid Day. The co-founder of the initiative, Grigorij Richters, warned that although scientists have identified more than 1,500 PHAs, there are thousands which have not been identified and many could be large enough to destroy life on Earth.
Asteroids are grouped as PHAs based on their potential to make threatening close approaches to Earth.
"It just takes one asteroid to completely destroy life, not just humanity, but all species. Asteroid Day is all about raising awareness, understanding there's a threat and dealing with it."Two asteroids, 2002 FG7 and 2014 YB35, have been designated as Potentially Hazardous Asteroids, according to the Minor Planet Center.