An asteroid discovered days ago will narrowly miss Earth | RNZ News

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By Jacopo Prisco, CNN

Radio telescopes inform astronomers about asteroids through the planetary radar data they collect.<br>Photo: Zhou Guoqiang/VCG/Getty Images/FILE via CNN Newsource

An asteroid roughly the size of one to two school buses will soon fly by Earth, coming as close as 91,593 kilometres (56,913 miles), according to the European Space Agency - equivalent to about one quarter of the distance between Earth and the Moon.

Astronomers at the Mount Lemmon Survey in Tucson, Arizona, discovered the asteroid on 10 May and named it 2026JH2. The object belongs to a class of asteroids called Apollo, which orbit the sun on trajectories that intersect with Earth's own orbit around the sun.

At its closest pass, 2026JH2 will be about 24 percent of the average distance between Earth and the Moon, and about two and a half times the distance at which hundreds of geosynchronous satellites orbit, providing services such as telecommunications and weather forecasts. The close pass is expected to occur on Tuesday just before 10am (NZT), according to NASA's JPL Small-Body Database.

Near-Earth Asteroid 2026JH2 in an image taken by the Virtual Telescope Project on 16 May, when the object was 1.5 million kilometres (930,000 miles) from Earth.<br>Photo: Gianluca Masi/Virtual Telescope Project via CNN Newsource

Despite the proximity, the space rock poses no danger, according to Richard Binzel, a professor of planetary sciences at the Massachusetts Institute of Technology and the inventor of the Torino Scale, a tool for categorizing potential collisions of space objects with Earth.

"2026JH2 will pass safely by the Earth," he said in an email. "This is actually a rather normal occurrence, car-sized objects pass between the Earth and the Moon every week. At the size of a school bus, these pass through our neighborhood several times per year. We are only recently developing surveys that are sensitive enough to see them," he added, noting that before these surveys, objects of this kind would simply zoom by completely unnoticed.

Exact size unknown

The asteroid originates from the asteroid belt, an area between Mars and Jupiter, Binzel explained. "Occasional collisions in the asteroid belt, plus gravitational tugs by Jupiter, can send small asteroids into Earth's vicinity. This fact has been known for many decades and many thousands of asteroids that can pass near the Earth are already known."

Even though astronomers have directly observed the object hurtling toward Earth, its exact size is unknown. The uncertainty is due to the fact that when an optical telescope sees a new object, the only information it gathers is the object's luminosity in visible light. There is no way to know how much light the object absorbs or reflects, according to Patrick Michel, an astrophysicist and director of research at the National Centre for Scientific Research in France.

"Thus, at the same luminosity, an object can be bigger and darker, or smaller and more reflective," he said in an email. "To know the size, we would need observations in the infrared, because the luminosity in the infrared is directly proportional to the size. But such observations are more difficult to do from the Earth and are not used to discover new objects."

We may not notice them, but it's not usual for a bus-size asteroid to pass through our earthly neighborhood several times every year.<br>Photo: JPL-Caltech/NASA via CNN Newsource

Based on assumptions about how much light is reflected, 2026JH2 is currently estimated to be between 15 and 30 metres (50 and 100 feet) in diameter. At the smaller end of that range, Michel said, it would be similar in size to a bolide, or fireball, that exploded in the atmosphere over the city of Chelyabinsk, Russia, in 2013, shattering windows and injuring 1000 people.

At the highest end of the range, it would be closer in size to an object that exploded near the Podkamennaya Tunguska River in Siberia in 1908, which pulverized large swaths of forest. Unlike both of these objects, however, 2026JH2 will not even enter the atmosphere, so there is no risk it will explode.

Although the distance at which the asteroid will pass seems very close, it is still "far enough that there is absolutely nothing to worry about," Michel said. But he noted that predicting 2026JH2's future trajectory is difficult, and we can't rule out that it might eventually be on a collision course with Earth. "The good news is that so far, no asteroid that we know of poses a risk for the timescale of our predictions, which is about a century on average," he added.

Waiting for Apophis

An object at least 10 times bigger than 2026JH2, called Apophis, will pass much closer to Earth, at a projected 32,000km (20,000 miles), on 13 April, 2029, "Yet, we are not worried at all, and on the contrary very excited," Michel said....