An asteroid barely missed Earth last week, and no one knew it was coming

A small asteroid the size of a refrigerator sailed past Earth last week. Astronomers were unaware that the object existed until several hours later.
It was close (from a cosmic perspective). The space rock's orbit on Oct. 24, carried it over Antarctica within 1,800 (3,000 km) of Earth, making it the third closest asteroid to the planet.

Because the object was approaching Earth's daytime side in the direction of sun, scientists were unaware of it. According to CNET, the visitor, which was comparatively small and dim, went unnoticed until 4 hours after passing close to Earth, CNET reports.

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UA1's diameter was only 6.6 feet (2 metres), so it wasn't dangerous. CNET reported that even if it had hit Earth, the majority of its rocky bodies would have burned away in space before reaching the ground.

Near-Earth objects (NEOs) are comets and asteroids which orbit in our cosmic neighborhood and approach Earth within 1.3 astronomical unit (120.9 million miles or 194.5 millions kilometers). NASA's Center for Near-Earth Object Studies is (CNEOS). NASA uses telescopes in space and on the ground to monitor NEOs, track their orbits, identify their size, shape, and composition, and to locate potentially dangerous objects. This is done through NASA's Planetary Defense Coordination Office.

NASA states that objects must be at least 460 feet in diameter (140 meters) to be considered hazardous. Although UA1 was not large enough to pose a threat to the planet, it could have been a sign of larger asteroids. NASA is also researching defensive technologies to protect Earth from collisions with larger space rocks.

NASA representatives stated in a statement that the Double Asteroid Redirection Test will launch on Nov. 24 and test a method of diverting asteroids using high-speed remote controlled spaceships. The DART spacecraft will be launched into Didymos, a near-Earth binary star. It is shaped like an upside down spinning top. It has two bodies. The larger one measures approximately 2,600 feet (780m) and the smaller moonlet around 520 feet (161m).

Schematic of DART mission showing the impact on Didymos' moonlet. After the impact, observations using Earth-based optical telescopes or planetary radars will be made to measure changes in the orbit of the moonlet around the parent body. Image credit: NASA/Johns Hopkins Applied Physics Lab.

Didymos was closest to Earth in 2003. It skimmed it at a distance approximately 4.5 million miles (7.18 millions km). However, it usually circles the sun just outside Earth’s orbital path according to NASA. Although Didymos isn't a threat to Earth, it's large enough to determine if a collision can cause a dangerous NEO to be diverted from its collision course with Earth.

NASA must still detect an asteroid before it hits Earth in order to divert it. NASA is collaborating on this project with the University of Arizona's Lunar and Planetary Laboratory.

NASA has found approximately 27,000 NEOs to date. According to the CNEOS, about 9800 are at least 459 feet (140m) in diameter while 890 measure 0.6 miles (1 km) in circumference.

NASA Jet Propulsion Laboratory's Asteroid Monitor reveals that UA1 was a relatively small asteroids, but other asteroids passing by Earth on Nov. 2, are much larger. These five space rocks have a diameter of 56 feet (17m), which is about the same length as a house. They also measure 170 feet (52m) in size.

NASA claims that none of these space rocks will be within 515,000 miles (829,900 km) of Earth.

Original publication on Live Science