A tiny asteroid measuring just 6ft (2m) across is the smallest to ever be studied by scientists. The asteroid, named 2015 TC25, comes from a much bigger one – around the size of Los Angeles – that orbits between Mars and Jupiter.
Understanding this little space rock will help researchers understand massive asteroids that produce the meteorites which hit Earth.
2015 TC25 was discovered last October by the University of Arizona's Catalina Sky Survey and it was studied extensively as it passed by Earth. At its closest, it came within 128,000km of Earth – about a third of the distance between Earth and the Moon.
Now, researchers have published their findings in the Astronomical Journal, showing the physical characteristics of this near-Earth asteroid. The team, led by Vishnu Reddy, found 2015 TC25 is made of bare rock and is spinning extremely quickly – rotating once every two minutes. Rather than being a 'rubble pile' (where a number of rocks are held together by gravity to form an asteroid), it is solid.
As well as being very small, the asteroid is also extremely bright, reflecting around 60% of the sunlight that falls on it. Observations show the surface is similar to aubrite – a type of highly reflective meteorite that consists of bright minerals that form in an oxygen-free environment at very high temperatures.
"This is the first time we have optical, infrared and radar data on such a small asteroid, which is essentially a meteoroid," Reddy said. "You can think of it as a meteorite floating in space that hasn't hit the atmosphere and made it to the ground – yet."
By studying 2015 TC25, astronomers can gain a better understanding of the parent asteroids from which meteorites originate. As most of the meteorites that hit Earth often burn up in the atmosphere, they are difficult to characterise.
"If we can discover and characterise asteroids and meteoroids this small, then we can understand the population of objects from which they originate: large asteroids, which have a much smaller likelihood of impacting Earth," he said. "In the case of 2015 TC25, the likelihood of impacting Earth is fairly small.
"Being able to observe small asteroids like this one is like looking at samples in space before they hit the atmosphere and make it to the ground. It also gives us a first look at their surfaces in pristine condition before they fall through the atmosphere."