Like the other rocky/icy objects regions, the Oort Cloud is thought to be a remnant of the early Solar System. Based on this evidence, the Oort cloud appears to be populated mainly by comets, but there are some asteroids as well. The cloud is technically just a theory because astronomers can’t observe it directly yet, but there is a lot of indirect information that supports its existence. You can think of it as a sort of shell for the solar system, like how a traditional Chinese paper lantern surrounds a candle. Meanwhile, the Oort Cloud is much bigger and even more distant. As a consolation prize, Pluto is the largest object in this region. In fact, being beyond Neptune’s orbit and in resonance with it is one of the reasons why it Pluto has lost its classification of a planet. Pluto and many comets can be found in the Edgeworth-Kuiper Belt. Scientists believe the region is what was left of material to make a planet, but Neptune was more efficient and got the larger stuff to form itself, so the smaller rocks remained there without being massive enough to coalesce. The doughnut-shaped Edgeworth-Kuiper Belt is located beyond Neptune’s orbit. Those are both very distant regions in the Solar System that are far enough from the Sun to allow solid ice to exist. Comets are found both in the Edgeworth-Kuiper Belt and the Oort cloud. 2010 TK7 is thought to be 300 meters wide, but thankfully it is in a stable position not threatening us. It’s called 2010 TK7 and it was detected by the Wide-field Infrared Survey Explorer (WISE). One was studied by astronomers, although it doesn’t have a charming name. Credits: Astronomical Institute of CAS/Petr Scheirichīelieve it or not, Earth has its own trojans as well. The L4 Trojans lead Jupiter in its orbit and the L5 Trojans follow. The time-lapsed animation above shows the movements of the inner planets, Jupiter and both swarms of Trojans (green) during the time period of the Lucy mission. The system is in a constant astronomical dance: Jupiter’s gravity pulls the trojans towards it, the Sun (which is much larger but also much farther away) also pulls the trojans, and the result is the swarm rotating in the Lagrange point and never leaving the area. Jupiter has two large groups of trojans, the Trojan Camp and the Greek Camp - yes, astronomers really like wordplay. These regions of equilibrium make it so that a collision with neighboring planets is nearly impossible. They are so-called co-orbital objects found near the Lagrange points (points of gravitational equilibrium) of planets or larger moons - the Lagrange points, L4 and L5, to be precise. Trojans are a special group of asteroids that share a planet’s orbit. This can be traced back to where they formed (asteroids generally formed closer to the Sun, where it was impossible to keep their ice). So the main difference between asteroids and comets is in their composition: asteroids are made of metals and rock, whereas comets also contain ice and dust. Image Credit & Copyright: Rolando Ligustri (CARA Project, CAST) and Lukas Demetz. This is what happens to Halley which can be seen every 75 years from Earth. The orbits of comets are abnormal, typically very elongated ellipses that make them come really close to the Sun and then go away for a long time. The melting helps form the comet’s tail, along with ionized particles from gas molecules that are excited by the solar radiation. However, it’s hard to study them because they are basically small rocks with nothing to light them up.Ĭomets, on the other hand, have ice in their interior, and when they get close enough to the Sun, some of that ice starts melting away. There are over a million asteroids larger than 1 kilometer (0.6 miles) in diameter, and millions of smaller ones in the asteroid belt. Most asteroids can be found in or nearby the Main Asteroid Belt - an area between Mars and Jupiter whose gravitational field keeps the dangerous rocks trapped and keeps them from flying about in the solar system (thanks for that, by the way). Most are small, but some can be pretty big - like Vesta, which measures 525 kilometers across, or Ceres the largest asteroid in our solar system, with a whopping 946-kilometer diameter. Overall, though, asteroids are usually quite small, and their combined mass is approximately equal to (or perhaps even smaller than) that of the Earth’s moon. Asteroids vs Comets Image credits: Giulia Forsythe.Īsteroids are essentially rocks that orbit the Sun.
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