A weekend asteroid is going to make a near miss of planet earth.

In New Zealand, it will be just before 6am on Sunday when the 470m diameter rock passes 1.3 lunar distances – about 487,000km from earth.

Asteroid 2015 TB145, as it is also known, will be close enough for a good view, and because of its relatively slow rotation, NASA radar astronomers plan to make high-resolution maps of the passing space rock.

The asteroid will still be too dim to see with the naked eye when it passes by, but at 10^th magnitude it is considered an easy target for experienced astronomers with mid-sized backyard telescopes.

According to the Minor Planet Centre, 2015 TB145 is the closest known approach by an object this large until 800 metre wide asteroid 1999 AN10 approaches Earth at a distance of 238,000 miles in August 2027.

Astronomers first spotted 2015 TB145 two weeks ago, on October 10th, with the Pan-STARRS 1 survey telescope atop Haleakala on the Hawaiian island of Maui.

Calculations quickly showed that, assuming a modestly reflective surface, 2015 TB145 must be a relatively large near-Earth asteroid. In fact, the IAU's Minor Planet Centre has determined that nothing this large has come this close to Earth since 2004 XP14 in July 2006 — and the next predicted encounter of this size will be 1999 AN10 in August 2027.

Lance Benner, a radar astronomer at JPL, believes 2015 TB145 is not an asteroid.

'The asteroid's orbit is very oblong with a high inclination to below the plane of the solar system," he says in Sky and Telescope.

'Such a unique orbit, along with its high encounter velocity -- about 35 kilometres or 22 miles per second -- raises the question of whether it may be some type of comet. If so, then this would be the first time that the Goldstone radar has imaged a comet from such a close distance.”

The asteroids is believed to have escaped detection because of its unusual 3.04-year-long path around the Sun.

The orbit's extreme eccentricity means that 2015 TB145 ranges in its heliocentric distance from just inside Mercury's orbit to the outer fringes of the asteroid belt. Usually it's well beyond the orbit of Mars. Second, the orbit's 40° inclination made this asteroid rather difficult to detect. It spends most of its time at large southerly ecliptic latitudes, even as it approaches Earth.