Comet 'siblings' made closest flyby of Earth ever this week

Tuesday, March 22, 2016, 10:22 AM - A pair of comets swung past us on their closest approach to the Earth on record, and astronomers are thinking that there's more to this astronomical event than mere coincidence.

On Monday, March 21, and Tuesday, March 22, we were treated to a fairly rare event. Two comets, one that we've known about for nearly 16 years and another just recently found, made a relatively close pass by Earth and the Moon within about a day of each other.

Tune in! After giving us a view of Comet P/2016 BA14 (PanSTARRS) on its Monday approach, Gianluca Masi, from the Virtual Telescope Project, returns at around 5 p.m. EDT on Tuesday, March 22 for another look as the comet moves away from Earth. Watch via the embedded video below!

Comet 252P/LINEAR was first spotted on April 7, 2000 by astronomers working with the Lincoln Near Earth Asteroid Research (LINEAR) survey. Now on its third pass by Earth since that discovery, this comet has been rapidly brightening since the end of February, and it may even become visible to the naked eye for observers in the southern hemisphere over the next few days.

Just two months ago, on Jan. 22, 2016, astronomers using the PanSTARRS telescope, located on the island of Maui, detected another near-Earth object that they initially thought was an asteroid, and named it 2016 BA14. Shortly after that new object was discovered, astronomers noted a few strange things about it. First, it was found to be sporting a faint tail, so the initial assumption that it was an asteroid needed to be revised, and it was renamed as comet P/2016 BA14 (PanSTARRS). Second, there was something rather familiar about its orbit, because it very closely matched the path that comet 252P/LINEAR takes as it travels around the Sun.

A coincidence? Maybe not.

"Comet P/2016 BA14 is possibly a fragment of 252P/LINEAR," Paul Chodas, manager of NASA's Center of NEO Studies (CNEOS) at the Jet Propulsion Laboratory, said in a NASA statement. "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. 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."

These two orbital views of the comets reveal their similarities. Credit: NASA/JPL/S. Sutherland

The two comets passed by Earth relatively close, at least when measured against the size of the solar system, however they each remained far enough away to make their passing completely safe for us.

For the Monday pass, roughly 230 metre-wide 252P/LINEAR came as close as 5.2 million kilometres (13.9 times the distance to the Moon). On Tuesday, P/2016 BA14 (PanSTARRS) - with an estimated diameter of around 120 metres - flew by at a distance of 3.5 million kilometres (9.2 times the distance to the Moon). According to the International Astronomical Union, only two other comets have come closer than P/2016 BA14's Tuesday pass - comet 55P/1366 U1 (Tempel-Tuttle) in October 1366, and Lexell's Comet, aka D/1770 L1 (Lexell), in June of 1770. NASA's NEO office also notes another periodic comet, P/1999 J6 (SOHO), passed by Earth at just 1.8 million km on June 12, 1999.

The relative paths of the two comets, compared to Earth and the orbit of the Moon. Credit: NASA/JPL-Caltech

As comet P/2016 BA14 (PanSTARRS) drew closer to its closest approach, which occurred at around 10:30 a.m. EDT on Tuesday, a view of the tiny ball of ice was captured on Sunday night by Gianluca Masi of the Virtual Telescope Project.

With the observatory's telescope tracking P/2016 BA14 (PanSTARRS), the background stars stream past while the comet remains stationary in the center of the field of view.

Based on NASA's calculations, this was the closest pass for both of these comets for the foreseeable future, and both are now headed back out towards the orbit of Jupiter.

Now that they're gone, it will be some time before we even see this pair again. It only takes them roughly 5.3 years to go around the Sun, but that extra 94 days or so means that they're enough out of sync with Earth's orbit that they need at least three orbits for another close pass.

As it stands now, 252P/LINEAR is expected back for a March 16, 2032 encounter, at a distance of 8.6 million kilometres from Earth, while P/2016 BA14 won't be coming that close until Jan 30, 2048, when it flies past at a distance of 7.8 million kilometres.

(Hat-tip to Phil Plait for pointing to Gianluca Masi's P/2016 BA14 video)

Sources: Slooh | NASA/JPL-Caltech | Seiichi Yoshida | IAU | Virtual Telescope Project

Watch below: NASA's animation of the orbit of these two comets shows just how close they come to the Earth-Moon system as they flew past on Monday and Tuesday.