A Rock Comet Approaches Earth on- Dec-16-2017

https://www.youtube.com/watch?v=CkNXvZhM-pk

On Dec. 16, 2017, an unusual space rock named "3200 Phaethon" will fly past Earth only 10.3 million km away. It's the closest approach in 40 years for this large object.

Measuring 5 km across, 3200 Phaethon is half the size of the asteroid that wiped out the dinosaurs 65 million years ago.

It is close enough to see through backyard telescopes. On Dec. 8th, The Astronomy Club of the Sing Yin Secondary School in Hong Kong recorded 3200 Phaethon using a 4-inch refractor.

"They observed 3200 Phaethon, the parent body of the Geminid meteor shower, from the basketball court of their school campus," the club reports.

"school is located close to the city center where the visual limiting magnitude is about 2 to 3. Despite the glare, They were able to record the motion of this object against the background stars for about 1 hour.

What is 3200 Phaethon?

Astronomers have struggled with this question for years. When 3200 Phaethon was discovered in 1983 by NASA's IRAS satellite, astronomers quickly realized that they had found the source of the annual Geminid meteor shower.

The orbit of 3200 Phaethon was such a close match to that of the Geminid debris stream, no other conclusion was possible.

Yet here was a puzzler: Meteor showers are usually caused by comets. Everything about 3200 Phaethon suggests it is an asteroid.

In fact, 3200 Phaethon resembles main belt asteroid Pallas so much, it could well be a 5-kilometer chip off that 544 km block.

If 3200 Phaethon broke apart from asteroid Pallas long ago, as some researchers believe, then Geminid meteoroids might be debris from the breakup.

There is, however, another possibility: Perhaps 3200 Phaethon is a "rock comet.

" A "rock comet" is, essentially, an asteroid that comes very close to the sun--so close that solar heating scorches plumes of dust right off its rocky surface.

Rock comets could thus grow comet-like tails made of gravely debris that produce meteor showers on Earth. 3200 Phaethon may well be this kind of object.

It comes extremely close to the sun, only 0.14 AU away, less than half the distance of Mercury, so hot that lead would flow like water across its sun-blasted surface.

This year's close approach of 3200 Phaethon to Earth happens only days away from the peak of the Geminid meteor shower on Dec. 13th and 14th.

Forecasters don't expect to see any extra Geminids, however. Meteoroids leaving 3200 Phaethon need time to drift over to the orbit of our planet.

"It would take at least another revolution around the sun before material from this flyby could encounter Earth - probably longer," explains Bill Cooke of NASA's Meteoroid Environment Center.

Fortunately, the Geminids don't need any help. As usual, more than 100 meteors per hour are expected on the nights of Dec. 13th and 14th when Earth crosses the debris stream.