A ball of fire streaked across the sky at daytime in Texas last week. Thousands of Texans witnessed the incident. The ball of fire burned so brightly in the sky that one San Antonio resident described it as "like a little piece of the sun falling."
IB Times reports another witness described the fireball, saying: "The size of the object appeared similar to Venus, which was higher in the sky. The object was orange in color and pulsated in brightness. The object seemed to be moving north-northwest and eventually faded from view."
This is not the first time Texans have witnessed the incident of a "piece of the sun falling." Fox News reports that in February 2009, a fireball streaked across the sky in Texas on a Sunday morning. The incident caused some concern and left local authorities baffled.
But according to Live Science, astronomers have come forward to explain that the phenomenon is a rare event known as spring fireball because it peaks in the spring season.
NASA astronomers have observed the phenomenon for 30 years and have found there is a considerable increase in number of the fireballs during spring compared to other periods of the year. According to Bill Cooke, head of NASA's Meteoroid Environment Office: "There are two peaks: one around February and the other at the end of March and early April. And this remains a mystery."
Cooke told Live Science that scientists do not know why there is a 10 to 30 percent increase in occurrence of the fireballs at springtime. He said: "I can tell you a lot of the bright and slow fireballs appear to be coming from the direction opposite the sun, but they have not much in common other than that. You see a lot more ordinary meteors in the fall, but the spring seems to have the big slow movers — the ones that are really impressive."
According to Live Science, Cooke and his colleagues at NASA are working to uncover the mystery of the spring fireballs. They set up a network of "smart meteor cameras" around the United States to triangulate the trajectories of the meteors. The cameras allow the scientists to determine the positions of the fireballs more accurately as they enter the atmosphere and map their origins in the sky. They are also hoping to increase accuracy of detection so that they will be able to locate and retrieve meteorites after they have fallen. This will give them opportunity to study what the meteorites are composed of and trace them back to their asteroid sources.
About 1,800 meteor events have been recorded by the camera network so far, and indicate that the spring fireballs probably originate from asteroids, while fall meteors come from comets. IB Times reports Cooke said: "The [spring fireballs'] orbits indicate they come from the main asteroid belt. A lot of the smaller meteors in the fall come from comets, which are made of icy bits of dust, and they don't last long in the atmosphere. Those ones are generally not big enough to make fireballs."
But why the Earth encounters more asteroids during the spring season is a question the scientists are hoping they will be able to answer after collecting enough data from their observations. Cooke said: "It appears that a lot of the stuff out there in the asteroid belt is clumping up in the springtime more than other times of the year."