Asteroids—named by British astronomer William Herschel from the Greek expression meaning “star-like"—are rocky, airless worlds that are too small to be called planets. But what they might lack in size they certainly make up for in number: An estimated 1.1 to 1.9 million asteroids larger than 1 kilometer are in the Main Belt between the orbits of Mars and Jupiter. And there are millions more that are smaller in size. Asteroids range in size from Vesta—the largest at about 329 miles (529 kilometers) wide—to bodies that are just a few feet across.
2. What Lies Beneath
Asteroids are generally categorized into three types: carbon-rich, silicate, or metallic, or some combination of the three. Why the different types? It all comes down to how far from the sun they formed. Some experienced high temperatures and partly melted, with iron sinking to the center and volcanic lava forced to the surface. The asteroid Vesta is one example we know of today.
In 1801, Giuseppe Piazzi discovered the first and then-largest asteroid, Ceres, orbiting between Mars and Jupiter. Ceres is so large that it encompasses about one-fourth of the estimated total mass of all the asteroids in the asteroid belt. In 2006, its classification changed from asteroid to as a dwarf planet.
5. Mission to a Metal World
NASA’s Psyche mission will launch in 2022 to explore an all-metal asteroid—what could be the core of an early planet—for the very first time. And in October 2021, the Lucy mission will be the first to visit Jupiter’s swarms of Trojan asteroids.
6. Near-Earth Asteroids
The term ‘near’ in near-Earth asteroid is actually a misnomer; most of these bodies do not come close to Earth at all. By definition, a near-Earth asteroid is an asteroid that comes within 28 million miles (44 million km) of Earth’s orbit. As of June 19, 2017, there are 16,209 known near-Earth asteroids, with 1,803 classified as potentially hazardous asteroids (those that could someday pose a threat to Earth).
7. Comin’ in Hot
About once a year, a car-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface.
8. But We’re Keeping an Eye Out
Ground-based observatories and facilities such as Pan-STARRS, the Catalina Sky Survey, and ATLAS are constantly on the hunt to detect near-Earth asteroids. NASA also has a small infrared observatory in orbit about the Earth: NEOWISE. In addition to detecting asteroids and comets, NEOWISE also characterizes these small bodies.
9. Buddy System
Roughly one-sixth of the asteroid population have a small companion moon (some even have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.
10. Earthly Visitors
Several NASA space missions have flown to and observed asteroids. The NEAR Shoemaker mission landed on asteroid Eros in 2001 and NASA’s Dawn mission was the first mission to orbit an asteroid in 2011. In 2005, the Japanese spacecraft Hayabusa landed on asteroid Itokawa. Currently, NASA’s OSIRIS-REx is en route to a near-Earth asteroid called Bennu; it will bring a small sample back to Earth for study.
May we all be happy and successful in our endeavors!
I tried to make this monthly spread as happy as possible by using green and especially yellow…if you were wondering why: I have my math exam in three days and i need all the luck and cheerfulness i can get BECAUSE I’M STRESSED AND SCARED OF FAILING. (sry this got a little emotional)
But could you imagine how iconic the series ending would be if this was the last scene:
The girls are all together to say goodbye to Aria who is about to go on a three week honeymoon with Ezra.
Aria: “guys I’m leaving for three weeks, why is everybody crying?”
All the girls laugh and let out another sob at those words.
Alison looks at her best friends one by one and says, “I guess it feels like it’s the end of something.”
Everyone grabs onto eachother even tighter and nods while fighting back more tears.
Spencer takes a deep breath and speaks up through everyones sobbing, “Even if it really is the end of something, our story will live on in our hearts.” She looks up and smiles at Aria who almost wishes she didn’t have to go on a honeymoon.
“Yeah, well our story will probably also live on in this godforsaking town too for a long time,” Hanna says with her infamous hint of sarcasm in her voice. The girls all laugh at this and look at eachother again once more.
Emily lets her head rest on Alisons’ shoulder as Alison looks at Hanna and then to Spencer. She can’t help but put on her bold smile she was most known for when she was younger, and as she takes a deep breath she says,
“That’s immortality, my darlings.”