Sunday's UFO is a space junk re-entry

A mystery light was seen around 7.40pm from various parts of Singapore on Sunday, causing some to think that it was a UFO. Watch the news report and a video of the mystery light here. From Channel NewsAsia:

Intermittent bursts of green streaks across Singapore skies on Sunday evening have set communities abuzz with talk of unidentified flying object (UFO) sightings and experts debating the phenomenon.

The light was seen around 7.40pm in areas including Woodlands, Bedok, Bukit Panjang, Clementi and Marina.

While some readers said it was a green light, others observed a blue and white glow. The light resembled a fireball with a "tail", lasting for a few seconds in the sky before disappearing, they said.

"There was a light flying very fast going towards Sentosa and it was shaped like a rocket," said self-employed businessman Mr Abdullah Yusof, 48, who was at Harbourfront Centre with his family. The phenomenon lasted for less than a minute, he added.

Another reader, 25-year-old software engineer Xu Tao saw three green lights "moving from left to right" from his Clementi flat. His first thought? Aliens.

He said: "I thought it might be a UFO because it definitely looks different from aeroplane lights."

Experts have debated the exact nature of the UFO, one calling it a green flash, a phenomenon caused by the scattering of sunlight by small particles in the atmosphere. Another said it is most certainly a bolide, a huge meteor crashing through our atmosphere.

Now, some of you have been sending me emails for the past few days about the UFO and asked me what I thought it was. Well, based on my many years of experience in meteor astronomy (I had setup a meteor section in an astronomical society and served as its meteor recorder and have observed hundreds of meteors and fireballs), here's my own expert opinion.

Amateur astronomers contacted by the press say that the UFO spotted on Sunday could be a bolide or a fireball. There are a lot of meteors shooting into our atmosphere everyday, most are associated with known meteor showers. There is an active meteor shower called the Quadrantids which begins on December 28 and ends on January 7. Could the UFO be a Quadrantid? Most unlikely because Quadrantids generally do not produce bright meteors. And I have never ever come across a Quadrantid fireball before.

Fireballs are actually meteors that are brighter than usual. Some of these fireballs do not come from known meteor showers. A meteor that doesn't belong to any meteor shower is called a sporadic meteor. There are quite a few of them every night but a sporadic fireball is not so common. But I don't think the UFO is a fireball. Judging from some of the witness reports, such as, "three green lights "moving from left to right" and "it's like an aeroplane, very big, the front is like a cannon ball, full of colours - orange, yellow, blue and green", I would have to say a strong possibility for the mystery light is not a fireball but a space junk re-entry!

There are over a million bits of debris left by space missions that are currently orbiting the Earth. About 70,000 objects about the size of a postage stamp have been detected between 850 - 1,000 km above the Earth. Some of them will re-enter the earth's atmosphere from time to time. I have come across reports of re-entries that move in a flat trajectory parallel to the Earth, similar to the UFO seen on Sunday. These space junk re-entries can be visible for up to three minutes as they slowly cross the sky and burn. And only a space junk re-entry can produce the colours described by some of the witnesses. Therefore, I'm certain that the UFO seen on Sunday is a space junk re-entry, not a meteor/bollide, or a craft from outer space.