Nasa has only just spotted an asteroid about to skim between Earth and Moon in 21,000mph near-miss

An asteroid which was first tracked by Nasa just three days ago will skim past Earth and the Moon in an astronomical near-miss today (28 December).

The near-earth object, named 2017 YZ4, could be up to 49 feet in diameter and is expected to pass close to our planet at 3.56pm GMT today while travelling at around 21,000mph.

The rock will pass between the Earth and the Moon at a distance of ~139,433mis from us, which is close enough for astronomers to classify it as a near-miss. The Earth and Moon are ~238,855mi apart.

A statement from Nasa released this week said: "This is the first known asteroid to flyby Earth within one lunar distance since two such asteroids flew past us 35 minutes apart on November 21, and the 52nd this year.

"As of December 24, there are 17,495 known Near-Earth Objects (NEOs) around our planet; 17,389 are asteroids. This year, we discovered 1,985 new near Earth asteroids. There were 1888 such objects discovered in 2016 and 1,571 in 2015."

The asteroid was first spotted by astronomers in Arizona's Mount Mount Lemmon Survey Observatory on Christmas Day.

According to The Watchers, which has analysed data from Minor Planet Center and Center for Near Earth Object Studies, YZ4 belongs to the Apollo group of asteroids and has an estimated diameter of 22.6 to 49 feet. It is thought that although this is relatively small, it could cause destruction and injuries if it were to hit Earth.

Nasa describes near-earth objects as "comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood".

Today's asteroids are pieces left over from the initial accretion of the inner planets, including Mercury, Venus, Earth and Mars.

The flyby comes a month after the 3mi-wide Phaethon, classed as a Potentially Hazardous Asteroid, came within 10 million kilometres of Earth, its closest approach since 1974. It will not make another approach as close until after 2093.