Showing posts with label asteroid. Show all posts
Showing posts with label asteroid. Show all posts

June 30 - Asteroid Day

Posted on June 30, 2020

Today is Asteroid Day, and tonight is also National Meteor Watch Day (in the U.S.). 


The two are somewhat related. Here's the deal:

The solar system formed from a dense cloud of gas and dust. It started collapsing, much of the gas and dust being pulled by gravity into the center. It started rotating as well. 



About 99.8% of the matter (the gas and dust) in the cloud ended up being pulled into the center and thus created the Sun. A fair amount of the leftover matter formed the eight planets and the various dwarf planets (aka Plutoids). A lot of the smaller bits became moons and rings - and a bunch of smaller-sized rubble that circles the Sun between Mars and Jupiter makes up the asteroid belt.



Asteroids, therefore, are leftovers in the formation of the solar system. They are defined as small rocky bodies that circle the Sun. (Moons and rings primarily circle planets or dwarf planets, and even though they also circle the Sun as their planet orbits our star, since their own orbit is around something other than the Sun, moons and particles that make up planetary rings are not considered asteroids.)

Asteroids range in size from dwarf planets like Ceres, which is about half the size of Pluto, down to grains of dust. Scientists' best guess of the number of asteroids is one to two million.

Meteors are any small rocky or metallic body of matter from outer space that enters the Earth's atmosphere. Most meteors burn up in our atmosphere because of the friction from running into so many air molecules . These are the beautiful streaks of light - often called shooting stars - that we are urged to look for tonight on National Meteor Watch Day.


Any meteor that is large enough to get all the way through the atmosphere and hit ground (or, more likely, ocean) is called a meteorite. 
When we talk about the theory that an asteroid hit the Earth and killed off the dinosaurs, we are talking about a really large meteor that formed a huge crater and probably mostly vaporized - causing an awful climate change event that resulted in lots and lots of species dying off.

And that is why Asteroid Day and National Meteor Watch Day are related. Asteroids can become meteors, and bits of asteroids that get hit by something can chip off and become meteors. The likelihood of a person or even a building being hit by a meteorite is surprisingly small; some sources say that there is only one confirmed case of a human being hit and (mildly) injured by a meteorite in all of history, but there is some evidence that it has happened at least a handful of times. 

But scientists say that a really large impact could have disastrous results, so we should watch for asteroids and other space debris that could become meteors!






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October 29 – Gaspra Gets a Close-Up

Posted October 29, 2016

Gaspra's colors are
exaggerated in this photo.
On this date in 1991, the American Galileo spacecraft became the first probe to visit an asteroid.

Galileo made its closest approach to 951 Gaspra by passing it fewer than 1,600 kilometers away (about 994 miles away); it took 57 photos that imaged about 80% of the asteroid.

Of course, Galileo was on its way to bigger and better things – Jupiter, to be exact. And it did a slightly more distant flyby of 243 Ida, in 1993, so it was also the second probe to visit an asteroid!

Since the early 1990s, there have been other space probe flyby successes, plus a few that orbited, landed on, and even returned samples from asteroids! Check out the asteroid probes listed in Wikipedia. 

Why flyby asteroids?

Asteroids are minor planets or hunks of rock that circle the Sun, as opposed to circling a planet like a moon or satellite.

Although the eight planets of the Solar System are always in different spots in their orbits, the orbits seem to be spaced pretty nicely, with the inner planets spaced closer together than the outer planets. Just where it seems that there SHOULD be a planet, between Mars and Jupiter, instead there is a ring of small worlds and rocks and rubble. The first asteroid was discovered way back in 1801.

There are enough asteroids in that region, between the two planets, that the term asteroid belt began to be used in the 1850s. About a thousand asteroids had been discovered by 1921, and by now we can estimate that the asteroid belt includes between one and two million asteroids larger than 1 km (0.6 mile) in diameter, along with millions of smaller ones!

There are asteroids located elsewhere, including some that are near Earth and some that accompany Jupiter in its orbit, located in clumps before and after the huge planet. The latter are named the Trojan and Greek asteroids.

Asteroids in the asteroid belt appear here in white.
Can you see the scattering of near-Earth asteroids,
 inside of Mars's orbit, shown here as colored dots? 

The diagram of the location of the various asteroids, above, and diagrams like it cannot show both the location and the size of asteroids in the same scale. It looks as if traveling through the asteroid belt would look like this:


But instead it would look like this:


In other words, it would look like you were traveling through empty space rather than through a field of rubble. However, you would be traveling quickly, and asteroids travel quickly, so even a tiny impact could be dangerous. That's why it would be important to track all the known and viewable asteroids and make sure that there would be no impact.

By the way...

There are other smaller-than-planet bodies that circle the Sun at a much greater distance. We don't call them asteroids if they orbit the Sun among the outermost of the planets or beyond; instead, we commonly call them Kuiper Belt Objects, plutoids or dwarf planets. KBOs tend to be icier and some become comets with long, eliptical orbits, burning off the icy elements as they approach the Sun.


Back to 951 Gaspra

Like most asteroids, Gaspra isn't large enough to have a spherical shape. (If a body is large, gravity pulls hard enough that even rock is pulled into a sphere.)

Like other asteroids, Gaspra has many small craters that speak to the fact that it was born out of collision (it was likely was once part of a larger body, called a parent asteroid) and continues to suffer from collisions.

Because of its irregular shape, Gaspra looks like it changes shape as it rotates. It has very weak gravity, of course, since it is teeny (the Moon has only one-sixth of the Earth's gravity, and Gaspra is maybe a millionth the size of the Moon!), but the gravitational field is also lopsided...because the asteroid is lopsided!



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March 23 – Near Miss Day

Posted on March 23, 2014

^ THIS is so much better than THAT. v
In 1989, an asteroid larger than an aircraft carrier whistled by the Earth, missing all of us by about 400,000 miles (640,000 km)!

It was traveling 46,000 miles per hour!
The asteroid passed through the exact spot where the Earth was just six hours before!

But...it may surprise you to know that the asteroid, called 4581 Asclepius, wasn't even discovered by scientists until AFTER it had passed!

If we had gotten hit, it would have been a huge shock—in more ways than one—we hadn't even seen it coming!

That near miss, which we didn't even know about until we were out of danger, acted as a wake-up call. The U.S. Congress directed NASA to study near-Earth objects such as asteroids and comets, to determine as exactly as possible their orbits. It also directed NASA to come up with some strategies of how to deal with a space rock that turns out to be on a trajectory to hit us.

The public got interested in the topic of a possible city-ending—or even civilization-ending, or world-ending—impact. There have been at least six (count 'em, six!) movies about space rocks hitting—or threatening to hit—the Earth since 1989: Deep Impact, Armageddon, Meteorites, Asteroid, Doomsday Rock, and Seeking a Friend for the End of the World.

Of course, space rocks have come closer to Earth than 4581 Asclepius—indeed, as you know, some meteorites have actually struck our planet!—but nothing the size of 4581 Asclepius has hit in recorded history. To give you a comparison, the Chelyabinsk meteor that made such big news in February 2013 was estimated to be about 20 meters (65 feet) across, and the powerful Tunguska explosion of 1908 was caused by an asteroid from 45 to 70 meters (150 to 230 feet) across—but 4581 Asclepius is about 300 meters (1,000 feet) in diameter!

We have a lot of footage of the Chelyabinsk
meteor, thanks to dashboard cameras.

These days, at least 8 surveys are part of the Spaceguard effort to discover and study near-Earth objects. (The name “Spaceguard” was first created by science fiction author Arthur C. Clarke in his book Rendezvous with Rama.) The effort to observe and catalog near-Earth objects and keep track of their orbits and whereabouts is the first step to protecting us from an impact like the one believed to have wiped out the mighty dinosaurs.

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Anniversary of the coining of the word “okay” (America's “Greatest Word”)







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December 22 – Anniversary of the Discovery of an Asteroid

Posted on December 22, 2013


On this date in 1891, an asteroid was discovered.

Granted, a lot of asteroids had already been discovered. Astronomers—professionals and amateurs—had been staring into telescopes and spotting asteroids for almost a century by 1891. However, this discovery was like no other, because Max Wolf spotted this particular asteroid using photography!
Astrophotography, to be exact.


Wolf was an expert at spotting astronomical bodies, often using photographs taken of telescopic images. He discovered several comets, supernovae, dark nebulae, and dim-yet-nearby stars. He also discovered 248 asteroids!

But today commemorates his first asteroid find. Wolf had noticed that a time-exposure photo would reveal asteroids as short streaks, because they had planetary motion with respect to the stars. Stars are in motion, too, but they are so far away, they seem fixed in the sky. (Although of course the earth is in motion, rotating on its axis, so that the stars seem to circle around the North and South Pole! It's all very complicated, isn't it?)

So...if Wolf discovered an asteroid using photography, you would expect the asteroid to be named Wolf, right?

Actually, discoverers often get to name the lands and astronomical bodies they discover, but they don't always name them after themselves. In this case, Wolf named this particular asteroid 323 Brucia. This was to honor a woman named Catherine Wolfe Bruce; she had donated $10,000 for the construction of the telescope he used.

Did you notice...His name was Wolf, hers was C. Wolfe Bruce. That's pretty coincidental, don't you think?


Enjoy Astrophotography
  • Here are the Astronomy Photographer of the Year 2013 Awards.
  • Here is a gallery of Hubble Space Telescope images.
  • Here is an article entitled “The 27 Most Mind-Blowing Space Photos of 2013 Will Put your Life on Earth in Perspective.”


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