A small asteroid, known as 2009 DD45, has passed close by the Earth at a distance of 38,000 miles, astronomers have declared.

The object, thought to be 21-47 meters or 68-152 feet in diameter, raced by the earth at 1344 GMT on Monday.

According to astronomers, the gap was just 72,000 km (44,750 miles), a near-miss in terms of cosmic distances.

Asteroid 2009 DD45 was discovered by Robert McNaught of the Australian National University last week.

"It's not something to worry about, but something to be aware of," McNaught said on Tuesday. "No object of that size, or larger, has been observed to come closer to the Earth."

"If discovered in advance and with enough lead time, there is the possibility of pushing it off course, if you have decades of advance warning," he added. "If you have only a few days, you can evacuate the area of impact, but there's not a great deal you can do."

McNaught pointed out that the 2009 DD45 asteroid circles the sun every 18 months, but its path will not threaten this planet until the next century at the earliest.

According to McNaught, the number of "potentially harmful asteroids" discovered each year has grown dramatically over the past decade as systematic programs to scan the skies have been put in place.

In 1908 an object possibly up to 50 meters across flattened 2,000 square kilometers of Siberian forest near the Tunguska River. It had the force of a multi-megaton nuclear blast, and leveled everything for a distance of twenty-five kilometers around the epicenter.

If it had crashed into the ocean "I imagine it would produce a tsunami," McNaught concluded.

HRF/JG