A stone thrown into water quickly loses speed. A meteor entering the atmosphere should behave the same way: air slows it down, and friction burns up its material. But cameras of the Global Fireball Observatory network have captured hundreds of bright fireballs over ten years that streak across the sky with almost no deceleration. These 'minimally decelerating objects' (MDOs) — about a third of all observations — have long remained a puzzle.
Previously, for such meteors, neither mass nor mass-loss rate could be calculated: the standard method required noticeable deceleration. The authors of the study proposed a new approach. They took data on how real fallen meteorites and large bodies from meteor streams lose mass and applied these values to MDOs. It turned out that MDOs are mostly small objects occupying a special region on the 'deceleration–mass loss' plot.
The new method has already helped identify ten small iron meteoroids: their emission spectra revealed the composition, and calculations confirmed that they should behave exactly like MDOs. Now other types can be studied — stony, carbonaceous, icy. This is important for estimating how much material falls to Earth each year and what materials come from space.
So a third of celestial 'bullets' will no longer remain a blank spot. Now astronomers have a ruler to measure even those meteors that refuse to slow down.
An iron meteoroid the size of a pea can weigh as much as several paperclips, but upon entering the atmosphere it heats up to thousands of degrees and shines brighter than the full Moon.