On February 15, 2020, another small satellite that was orbiting the Earth was discovered. The object named as “2020 CD3” is only 1.9-3.5 meters in size. However, it has such a chaotic orbit that it does not roam around the Earth on a regular basis. In fact, it was expected to get rid of Earth’s gravity and continue its irregular journey in April 2020.
We all know that there are eight planets in the Solar System. While Mercury, Venus, Mars, Jupiter and Saturn have been known since prehistoric times, Uranus was discovered by William Herschel in 1781 with the invention of telescopes, Neptune was first mathematically estimated and then observed in 1846 and Pluto was discovered in 1930. But when we ask, how many satellites of each planet in the Solar System have? most probably your answer will be, ” I can look at Wikipedia and tell you.” Actually, you would be disappointed with it, because it is not correct to say that we know exactly how many satellites the planets in the Solar System have.
I am sure you are surprised when you read this answer. I feel like you are confused by considering that the telescopes detecting black hole collisions, the galaxies across the universe, how they cannot detect the satellites of the planets on the doorstep. Even if this logic is right, the main problem is related with where we view and how we use our telescopes. All of the satellites are dark and small objects that do not have energy sources, they reflect the light they receive from the Sun and generally have a very low albedo (reflectance coefficient). When we look at the other sides of the universe, we do not discover such small pieces of rock. We observe the most violent explosions of the universe, or energetic objects. We can see them with our telescopes because they produce large energies instantly. Same reality with that we can see lighthouses from miles away, but we cannot see the rock under it.
So how many satellites does the Earth have? Well, we know the Moon. Sometimes I even ask the students about who discovered the Moon, mixed with humor, some of them seriously thought and believe that it is discovered by someone. In fact, the Moon has been standing where it is for billions of years. I think they all saw the Moon, from the first creatures to our homo sapiens ancestors.
WE HAVE A NEW SATELLITE; A small satellite around the Earth was discovered at the Lemmon Mountain Observatory in Arizona as part of the Catalina Sky Scan program. The object, which was discovered by Theodore Pruyne and Kacper Wierzchoś and announced by the Small Planet Center of the International Astronomical Union on February 25, was named the “2020 CD3”. According to the initial calculations, the small object, which is only 1.9-3.5 meters in size, has only one jeep size and carbon structure. Still, we could not be excited because the object has an extremely chaotic trajectory according to the JPL Small-Body database. So it doesn’t rotate around the Earth regularly like the Moon. According to the preliminary results when it was simulated into the past, it was caught by the Earth’s gravity around 2016, but it was not able to enter into a regular orbit due to the gravitational force created by the Moon. Its orbit is so irregular that when it is closest to the Earth, it is about 77 thousand km, and when it is farthest, it goes away to 1.73 million km. Because it is an irregular orbit, its turn around the Earth can vary from 47 days to 90 days. In fact, it was expecting to get rid of the Earth’s gravity around April 2020 but it is likely left our orbit on March 7th. Thus, our excitement for new satellite unfortunately did not last for a long time.
Of course, 2020 CD3 is not the first object which temporarily entered the Earth orbit. Probably we are constantly experiencing similar ones, but such objects might be defined as a result of wide and deep sky scanning observations together with too much luck. Previously discovered The 2006 RH120 asteroid, temporarily entered to orbit of Earth-Moon system between 2006-07 (and it is estimated to enter and exit the system by every 20 years). We can’t state certain cycles, orbits or dates about them because they are very small objects, so they can completely deviate from the expected orbit, even with the slightest orbital deviation. In other words, in order to know where these objects will be in the future, continuous and regular observations should be made.
Well, do we know the exact number of satellites of other planets? I’m sure your answer will be that if we even know Earth’s satellites hardly, we would never know other planets’. Nevertheless, we can answer without losing your confidence in astronomy: Of course, we have discovered the larger satellites so far, but the very small satellites are still waiting to be discovered. Even if they are in irregular orbit like the 2020 CD3, or in temporary orbit we always have a chance.
THE PLANET WITH THE MOST SATELLITES; For many years, the planet with the most satellites was known as Jupiter. After Galileo’s telescope turned to Jupiter in 1610, we first discovered the satellites near the planet (Io, Europa, Ganymede, Callisto) and then others. You can also see them with a small telescope. Over time, smaller satellites were discovered with the use of photo plates in astronomy. In 1979, Voyagers had to go to Jupiter to discover Metis, Adrastea and Thebe. New satellite of Jupiter was not discovered for a long time. We know it has a total of 79 satellites today.
Saturn, whose visible rings are incredibly beautiful, would be expected to have more satellites than Jupiter, but for a long time it was known as a planet with 62 satellites. Finally, about 20 satellites were discovered in October 2019. Thus, Saturn became the planet with the most satellites of the Solar System with 82 satellites. Satellites are not only objects that we interest with their numbers, also many of them are very different from their planets and show very interesting features. In some satellites, there are two or three times more amount of water than Earth. So these satellites are the first targets when investigating whether there is life elsewhere in the Solar System or not. Of course, this is the subject of another article. With the development of technology, we will continue to improve our satellite knowledge over time.