This Monday and Tuesday, two smaller sized comets will come very close to earth. The two rocks probably have a common descendant - a larger comet that broke up some time ago.
On Monday, March 21, comet 252P/LINEAR will pass the Earth at a distance of 3.3 million miles (5.2 million kilometers). It is about 14 times the distance of the moon. Then, shortly afterwards, another comet, called P/2016 BA14, will follow. That rock will get even closer to earth - only about 2.2 million miles (3.5 million kilometers). That's equal to nine times the lunar distance.
The first of the two, which is also the larger one, has been known since April 7, 2000. Astronomers from the Massachusetts Institute of Technology (MIT) then discovered the rock with a diameter of about 750 feet (230 meters). The other one was discovered much more recently. Researchers from the University of Hawaii discovered it with their PanSTARRS telescope this year - on January 22. Its diameter is estimated at about 300 feet (100 meters).
Break up during fly-by close to the Sun or to Jupiter
NASA astrophysicists think that P/2016 BA14 could be a large fragment of 252P/LINEAR. "The two could be related because their orbits are so remarkably similar," said Paul Chodas, manager of NASA's Center of Near Earth Object Studies (CNEOS) at the Jet Propulsion Laboratory in Pasadena, California. In a statement, NASA suggests that the comet may have broken up either during a previous passing through of the inner solar system or during a fly-by of Jupiter.
NASA will observe the two comets during the fly-by of Earth with its Space Telescope Hubble and ist Infrared Telescope Facility. The scientists hope to further clarify the twin comet thesis.
Not visible for laymen
Hobby astronomers will not be able to spot the two comets. Only with special telescopes will the event become visible. The fly-by poses no danger for us on Earth, but it is possible that during the two days there may be an increased activity of shooting stars.
Nonetheless, astronomers consider the fly-by an extraordinary event, which happens only every few hundred years. According to NASA, it is the third closest approach of a comet to Earth since the beginning of systematic human celestial observations. Only the comets D/1770 L1 (Lexell) in 1770 and C/1983 H1 (IRAS-Araki-Alcock) in 1983 came closer than that.
Much more common than even small comets are comparably large asteroids. On March 8, 2013 TX68 got as close to earth as 13 lunar orbits. And for Halloween last year, the "Great Pumpkin" was much closer still at only 1.3 times as far as the moon.