Three asteroids come close to Earth

Three asteroids come close to Earth

By Eric Mack

September 20, 2017

Astronomers discovered three never-before-seen asteroids as they whizzed by Earth significantly closer than the vast majority of passing space rocks.

The trio pose no threat to our planet, but it is a little unsettling that the largest of the three (Asteroid 2017 SQ2) was spotted in our cosmic rearview on Monday, nearly four days after the warehouse-sized hunk passed a little over 120,000 miles (193,000 kilometers) above our heads.

Asteroid 2017 SM2 is about half that size and passed us early Wednesday morning over 188,000 miles (303,000 kilometers) away.

The closest and smallest piece of space debris just found in our neighborhood is Asteroid 2017 SR2, which is probably about the size of a bus and set to be closest to Earth at around 1:30 p.m. PT Wednesday when it whips by about 55,000 miles (88,500 kilometers) from us.

But the closest buzz of the year could come next month when house-sized Asteroid 2012 TC4 could pass within 5,000 miles of us on Oct. 12.

Asteroid 2012 TC4 to safely pass Earth on October 12, 2017

Jet Propulsion Laboratory

A small asteroid designated 2012 TC4 will pass very close to Earth on Oct. 12, and even though scientists cannot yet predict exactly how close it will approach, they are certain that the asteroid will fly by at a safe distance from our planet. This asteroid has not been seen since the week it was discovered in October 2012, when it sped past Earth at about one-fourth the distance from Earth to the moon. Estimated to be only 30 to 100 feet (10 to 30 meters) in size, the asteroid has been too distant and too faint to be detected over the last five years. As it starts to approach Earth this summer, large telescopes will be used to re-establish its precise trajectory. The new observations are expected to help refine knowledge about its orbit, narrowing the uncertainty about how far it will be from Earth at its closest approach in October.

We know the orbit of 2012 TC4 well enough to be certain that it won’t hit Earth,” said Paul Chodas, manager of the Center for Near-Earth Object Studies (CNEOS), at NASA’s Jet Propulsion Laboratory, Pasadena, California. During the close approach on Oct. 12, the space rock will pass no closer than 4,200 miles (6,800 kilometers) from our planet, and more likely much farther away, as far as 170,000 miles (270,000 kilometers) or two-thirds of the distance from Earth to the moon. These calculations are based on seven days of tracking 2012 TC4 after it was discovered on Oct. 5, 2012, by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) from Haleakala on the island of Maui, Hawaii.

Large Asteroid Florence took a fly by Earth on September 1, 2017

Jet Propulsion Laboratory
Center for Near Earth Object Studies

An asteroid named Florence, one of the largest of the near-Earth asteroids, mad a approach close to Earth at the end of August, and flew safely past our planet on September 1, 2017. At its closest point, Florence was 4.4 million miles (7.0 million kilometers) from Earth, or about 18 times the average Earth-Moon distance. Although many known asteroids have passed by closer than this, all of them were smaller asteroids. Florence is the largest asteroid to pass this close to our planet since the first near-Earth asteroid was discovered over a century ago.

Asteroid Florence was discovered in 1981 and named in honor of Florence Nightingale (1820-1910), the founder of modern nursing. Tracking observations of asteroid Florence span nearly 40 years, and its orbit is already well known. The orbital calculations indicate that asteroid Florence poses no risk of colliding with Earth for many centuries to come.

Radar Reveals Two Moons Orbiting Asteroid Florence

Jet Propulsion Laboratory
Center for Near Earth Object Studies

Radar images of asteroid 3122 Florence obtained at the 70-meter antenna at NASA’s Goldstone Deep Space Communications Complex between August 29 and September 1 have revealed that the asteroid has two small moons, and also confirmed that main asteroid Florence is about 4.5 km (2.8 miles) in size. Florence is only the third triple asteroid known in the near-Earth population out of more than 16,400 that have been discovered to date. All three near-Earth asteroid triples have been discovered with radar observations and Florence is the first seen since two moons were discovered around asteroid 1994 CC in June 2009.

The sizes of the two moons are not yet well known, but they are probably between 100 – 300 meters (300-1000 feet) across. The times required for each moon to revolve around Florence are also not yet known precisely but appear to be roughly 8 hours for the inner moon and 22 to 27 hours for the outer moon. The inner moon of the Florence system has the shortest orbital period of any of the moons of the 60 near-Earth asteroids known to have moons. In the Goldstone radar images, which have a resolution of 75 meters, the moons are only a few pixels in extent and do not reveal any detail.

Video: NASA discovers 2 moons orbiting asteroid Florence


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