Did you ever imagine that our Earth had a minimoon? Astronomers have revealed, apart from the moon, there is another natural satellite. If you stare at the sky during night time at a dark site, you can surely come across a handful of meteors every hour. Our planet's gravity continually captures small space rocks and pulls them into orbit. Meteors are dust and debris from space that burn up immediately coming into the Earth's atmosphere. These bright fireballs are also known as shooting stars, creating bright streaks across the sky.
Meteors or Fireballs
Whenever we notice any meteor, they rapidly cross the sky, burning up 90-100 km above the ground. Their speed depends on their orbit around the Sun. When they orbit in the opposite direction of the Earth, their motion becomes very fast after burning up. If their orbit is similar to Earth, they burn up relatively slow. Now, here Earth’s escape velocity matters, which is the minimum speed for a free, non-propelled object to escape from the gravitational influence of the Earth.
When any meteor comes from outside the Earth-Moon system, orbiting the Sun, their speed must be 11 kilometers per second, Earth’s escape velocity. On the other side, anything is slower than that must be in actual orbit around the Earth first, and not coming from deep space.
Desert Fireball Network
A group of astronomers observed data depending on the information from the Desert Fireball Network. The Desert Fireball Network (DFN) is a network of cameras spread across western and southern Australia. It aims to provide enough information to be able to backtrack to determine a rough orbit of the object before it entered our atmosphere. Presently, it operates 50 autonomous cameras covering an area of 2.5 million kilometers. Researchers using this information to calculate the object’s trajectories and observe where a meteorite may have hit the ground. The DFN observatories capture ≈30 second exposures of the sky every night until dawn, and the DFN team is automatically alerted if any meteor or fireball is detected.
Minimoons or Natural Earth Satellites
Sometimes, objects coming from space come close to the Earth, but our planet's gravity does not immediately draw them. So they orbit for a short period before being pulled into the atmosphere. Otherwise, they hurled back into space. These objects are called temporarily captured orbiters (TCOs). They are commonly referred to as natural Earth satellites or minimoons.
Detection of Minimoons
Finally, on 22 August 2016, a very slow-moving meteor was caught on six of the cameras near Lake Frome in South Australia. It came in capture when it was just 74 km up which is unusual for an artificial object. But it burned about 5 seconds later at an altitude of 24 km. Initially, it was moving at just under 11km/sec and slowed to just under 4 before it burned up. It was approximately 12 kilograms before it hit us. According to experts, there is more than a 95% chance of being a TCO. Another TCO was detected in 2006, RH120 as a fast rotator with a diameter of approximately 2-3 meters that orbited the Earth for 11 months from 2006-2007. It’s only the second fireball that scientists suspect came from a minimoon. Their findings were published in The Astronomical Journal. Patrick Shober, a planetary scientist at Curtin University in Australia and an author of the new paper, said, “It is an extremely rare event that only the largest fireball networks in the world would have a chance of observing.” Isn’t that amazing? It is likely to say that in future we will able to reveal more unknown facts in the sky because of these high-resolution cameras.