Telescopes at the ready: stargazers are treated to a double delight this week as two comets brush past Earth in one of the closest flybys in recorded history.
Comet 252P/LINEAR will zoom past just 5.3 million kilometres from Earth, or around 14 times the distance to the Moon, around 12.15pm UTC on Monday 21 March (8.15am EDT; 11.15pm AEDT).
But right behind will be P/2016 BA14, which will whiz by a mere 3.5 million kilometres away, or within nine Moon distances, around 2.30pm UTC the following day (10.30am EDT; 1.30am Wednesday AEDT).
BA14 will be the third closest flyby of a comet in recorded history next to D/1770 L1 in 1770 and C/1983 H1 in 1983. And as a bonus, 252P appears to be brightening on approach, and should be visible through binoculars.
Discovered on 7 April 2000, 252P – which is only around 230 metres wide – orbits the Sun. But unlike Earth’s fairly circular orbit, 252P’s path is highly elliptical. Astronomers calculated it's tugged, and its path altered, whenever it zooms past Jupiter.
Comet BA14 is a new one. Discovered on 22 January this year, astronomers originally thought it was an asteroid. But on closer inspection, they saw the tiny chunk, about half the size of 252P, sported a faint dusty tail – a telltale sign of a comet.
And as remarkably close travelling companions, the two comets may well have once been one larger comet, with BA14 literally a chip off the old block.
“We know comets are relatively fragile things, as in 1993 when comet Shoemaker-Levy 9 was discovered and its pieces linked to a flyby of Jupiter,” says Paul Chodas, manager of NASA's Centre of NEO Studies at the Jet Propulsion Laboratory in Pasadena, California.
“Perhaps during a previous pass through the inner-solar system, or during a distant flyby of Jupiter, a chunk that we now know of as BA14 might have broken off of 252P.”
Any chance BA14 might get a little too close to Earth, get hooked by our gravity and collide?
No chance, Chodas says: "Comet P/2016 BA14 is not a threat. Instead, it is an excellent opportunity for scientific advancement on the study of comets."
Edit: Comet 252P will be visible to southern hemisphere stargazers; those in the northern hemisphere will see BA14.