With the Hollywood hype of asteroids on a collision course with Earth and Obama's goal to land a manned mission on an asteroid before we head for Mars, it might be useful to know a little more about the most notable asteroids in our solar system.
Ceres - With a diameter of almost 600 miles (952 km), this is the largest object scientists have observed in the Asteroid Belt. It was discovered at the start of the 19th century by Giuseppe Piazzi, an Italian Catholic priest and astronomer, and is named after the Roman goddess of agriculture and fertility. Ceres makes up a whopping 32% of the entire Asteroid Belt mass and is in fact so large that its gravity turned it into a spherical shape, rather than an irregular one like most asteroids, and thus it has been dubbed a "dwarf planet," the only one in the belt. For a long time, it was thought to have been the actual core remain of a planet between Mars and Jupiter that broke apart, creating the Asteroid Belt. Based on its electromagnetic spectrum and shape, scientists have concluded that the surface of Ceres is made up of a rocky core and an icy crust, containing a mixture of water ice, carbonates and iron-rich clays. Because of this, Ceres is a hopeful for containing a subsurface water ocean.
Vesta - Only six years later, a physician and astronomy enthusiast of the name Heinrich Wilhelm Olbers discovered this asteroid, named for the Roman goddess of home and hearth. Containing 9% of the mass of the Asteroid Belt, Vesta is referred to as a "protoplanet," a planetary embryo that collides with others of its type to eventually form a dominant planet. Much of the evidence scientists have about Vesta is found in HED meteorites, debris from the asteroid that have fallen to Earth. These meteorites are believed to have come from Vesta because the Hubble Space Telescope has observed a giant crater on Vesta 300 miles in diameter. Some of the meteorites are made up almost entirely of the mineral pyroxene, which is found in lava flows. Further telescopic observations indicate that the surface is made of basaltic rock, which is essentially frozen lava. This is why Vesta is thought to have what scientists call a differentiated, or active, center (an iron-nickel core) beneath the surface. Vesta's unusually bright surface makes it actually visible to the naked eye if the night sky is dark enough. Vesta is fast, with a rotation period of only 5 hours, and cold, with an average daytime temperature of -76 F and dipping below -200 F at night. Along with Ceres, Vesta is a main focus point for NASA's Dawn program.
Eros - Taking its name from the Greek god of love, this is the first near-Earth asteroid discovered. It is called a near-Earth asteroid because it is known to have crossed Mars's orbit, thereby putting it in the neighborhood of Earth. This could potentially pose a threat, which is why Eros is an asteroid of interest. It is the only asteroid to have had a space probe successfully land on it (in 2001). With a diameter of 10 km, Eros is thought to be even larger than the asteroid that supposedly killed the dinosaurs. Although the daytime temperature on Eros can reach up to 212 F, it gets as low as -238 F. It is not spherical but instead peanut-shaped and even has its own gravity, though extremely weak.
Hermes - Another near-Earth asteroid, Hermes is famous for its disappearance act and thus was accordingly named after the Greek messenger of the gods. In 1937, the astronomer Karl Reinmuth noticed a moving bright spot amidst the photos he was taking of the night sky. The bright spot turned out to be the asteroid Hermes, which came as close to Earth as twice the distance of the Moon. It actually approaches Earth's orbit twice every 777 days but Earth isn't always near the spot where it crosses. After Reinmuth observed Hermes, something strange happened - it seemed to disappear. It was not until 2003 that another astronomer of the name Brian Skiff found Hermes again and by studying its orbit, was able to conclude that this asteroid had actually come dangerously near Earth several times while it was unobserved, making it the near-Earth asteroid with the most chaotic orbit.
Ceres, Vesta, Eros and Hermes. Two large asteroids with possibilities of oceans (and subsequently, life) and two smaller asteroids with possibilities of colliding with Earth. As such, keeping up to date with them is a good idea!