Introduction and Monthly Reminders
February has brought a mix of clear skies with warm temperatures and days filled with clouds, rain, and snow. Due to the unpredictable weather, I was unfortunately unable to view some of the highlights of the first half of the month. However, I was able to see Venus and the Moon in the morning sky before their close approach on the 7th.
The second half of the month will allow observers to view the Moon passing close by Jupiter and Uranus, weather permitting. Well-equipped stargazers may still view a few comets and the zodiacal light if they bundle up and get away from all sources of light pollution. A conjunction between Mars and Venus may be seen on the 22nd. A clear view of the eastern horizon will be required to view this rare event.
Asteroids
Instead of moving on to Jupiter after discussing Mars last month, I will cover the asteroids in the solar system. A majority of the known asteroids can be found between Mars and Jupiter. These asteroids are known as Main-Belt asteroids. The Asteroid Belt is estimated to contain between one and two million asteroids that are larger than half a mile and millions of smaller asteroids. It is thought that the asteroid belt was created due to the massive amount of gravity produced by Jupiter that is felt in this region of the solar system. If all the material in the asteroid belt were to coalesce to form a planet, it would be about the size of the Earth's Moon. Many movies depict asteroid belts as being tightly packed with chunks of rock, making it nearly impossible to fly a spacecraft through. The asteroid belt of our solar system is not like this! The asteroids are spread far apart making it easy to fly a spacecraft through if needed.
The four largest asteroids in the asteroid belt are Ceres, Vesta, Pallas, and Hygiea. Ceres is the largest having a nearly 300-mile diameter and is considered a dwarf planet, like Pluto. The mass of these four asteroids make up about half of the mass of the entire asteroid belt. Most asteroids have an irregular shape and are often referred to as "space potatoes" by astronomers.
The compositional makeup of asteroids is divided into three different categories: chondrite, stony, and metallic. The chondrite (C-type) asteroids are composed of clay and other silicate rocks. These asteroids have a low albedo and appear dark in color. C-type asteroids are the most common and oldest in our solar system.
The stony (S-type) asteroids are made up of silicate material and nickel-iron. These asteroids make up about 17% of the total known asteroids and have a higher albedo than C-type asteroids. This means that more light is reflected off the surface, making them easier to detect with an optical telescope.
The metallic (M-type) asteroids are made of a nickel-iron compound. These asteroids are the most rare but also have the highest albedo. M-type asteroids are the densest and often the smallest. Metallic asteroids are also thought to be the source of iron meteorites found on Earth.
Asteroids can also be found sharing the orbit of a planet. These asteroids are known as Trojan Asteroids and are found at the L4 Lagrange Point which is in front of the planet, and the L5 Lagrange Point which is trailing the planet. At these two points, the gravity of the Sun and planet balance each other out, allowing the objects in this location be to stable. Most of the known Trojan Asteroids can be found around Jupiter, while others have been detected around Mars, Neptune, and even the Earth. Jupiter's Trojan Asteroids are estimated to be near the same amount as that of the Main-Belt Asteroids.
The final classification of asteroids is known as Near Earth Objects or NEOs. These objects have orbits that pass close to the Earth and have the potential of crashing to the surface of our planet. Thousands of NEOs have been discovered and their orbits have been mapped, allowing scientists to find the objects that will impact the Earth. NASA's Jet Propulsion Laboratory has a website that shows data on these objects including the chance they have of impacting the Earth. There are two specific programs for monitoring NEOs. Sentry monitors long-term NEOs while Scout monitors the newly discovered NEOs. A legend can be found at the bottom of the list of data that describes each column. The ones that most people will gravitate towards will be the Torino Scale of the Sentry list and the Impact Rating of the Scout list. The larger the number, the higher the chance the asteroid has of colliding with the Earth and causing lots of damage. Notice that most of the objects have a zero rating on both lists. Next time there is a big news story about an asteroid that will impact the Earth, be sure to check out the Sentry and Scout data first!
Check back soon for my next Monthly Night Sky Report!
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| Now get outside and look up! |
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