Catch A Falling Asteroid…


The center dot is an asteroid being followed by the sequence; the object that flashes by during the clip is an artificial satellite. Timelapse of Asteroid 2004 FH's flyby (NASA/JPL Public Domain)
The center dot is an asteroid being followed by the sequence; the object that flashes by during the clip is an artificial satellite. NASA/JPL via Wikipedia

NASA plans to catch an asteroid and tow it into orbit around the Moon.

Whatever for? What are asteroids anyway? Won’t it crash into Earth?

What is an asteroid?

Some asteroids are very old, so let’s take a brief look back in time…about 4.6 billion years ago.

Experts believe that the Solar System formed out of a vast dusty nebula where our Sun first lit up.


The Hubble telescope has spotted similar proto-solar systems in the Orion Nebula.  The dark spot is probably Thor on his way to a fight somewhere.  Image source.
The Hubble telescope has spotted similar proto-solar systems in the Orion Nebula. The dark spot is probably Thor. Image source.

Only rocky material could withstand the energetic solar winds near this new star. Most of that accreted into four planets – Earth, Mercury, Venus, and Mars. The remainder of it – millions of tiny objects – mostly ended up orbiting the Sun as asteroids or dwarf planets in a belt between the orbits of Mars and Jupiter.

Incidentally, the Solar System is big enough to allow plenty of room around each of these asteroids – the belt is nowhere near as packed as it appears in the movies!

A few asteroids share orbits with but never approach planets (Earth has at least one of these). Some 10,000 near-Earth asteroids, as we’ll see below, have orbits that cross our own planet’s orbital path.

Their name comes from the Greek asteroeides “star-like,” which is how these small, rocky objects appeared in 19th-century telescopes. Today, thanks to observations from Earth as well as more than 10 spacecraft missions to the belt, we know that asteroids are way too cold to be stars.

They’re solid and irregularly shaped. While all are too small to have an atmosphere, some asteroids do have at least one moon. One asteroid even has rings.

NASA says:

Asteroids are lumps of metals, rock and dust, sometimes laced with ices and tar, which are the cosmic “leftovers” from the solar system’s formation about 4.5 billion years ago. There are hundreds of thousands of them, ranging in size from a few yards to hundreds of miles across.

In size, asteroids range from 590 miles (950 km) to less than a mile (1 km) in diameter. Here are a few that have been imaged in high resolution (top image), and how the two largest of those compare with the size of the Moon (bottom image, at 20 km per pixel):

NASA via Wikipedia
NASA via Wikipedia

Generally speaking, asteroids come in three “flavors”:

  • Chondrite (C), or clay and silicate rock that’s dark in appearance
  • Stony (S), made out of silicates and nickel-iron
  • Metallic (M), just nickel-iron.

The different compositions are related to the temperature and pressure under which they formed.

While some asteroids experienced high temperatures after formation that partially melted them, so that iron sank into the center, the C-class asteroids are believed to contain mostly original material dating back some 4.6 billion years.

This is of huge scientific interest, of course, but planetary explorers are also interested in those chondrites.

Clay is loaded with water. That’s why some believe that chondrites in the asteroid belt might be good water sources when human venture out into the very dry Solar System. Good old H2O can also be broken down into hydrogen and oxygen – rocket fuel. Chondrites may also carry organic material that could be used as fertilizer to grow food for extraterrestrial colonies.

These visionaries don’t exactly see it as a mini-mart/fuel station, but the asteroid belt will probably play a key role in humanity’s eventual exploration of the Solar System.

But asteroids are dangerous to us, as well.

An animation showing the impact, and subsequent crater formation. University of Arizona, Space Imagery Center via Wikipedia
An animation showing the Chicxulub impact, and subsequent crater formation. University of Arizona, Space Imagery Center via Wikipedia

Near-Earth objects

According to NASA:

As of June 19, 2013, 10,003 near-Earth asteroids are known and the number over 1 kilometer in diameter is thought to be 861, with 1,409 classified as potentially hazardous asteroids – those that could pose a threat to Earth.

Unlike the other rocky planets, Earth’s surface is relatively uncratered, thanks to weathering and plate tectonics. Nonetheless, impacts from outer space have been recent enough to give us an idea what to expect if one of these near-Earth asteroids hits our planet:

  • Per NASA, an approximately 100-foot-wide (not 80 feet as in the video below) M-class object, traveling at almost 45,000 mph (20 km/s) did this 50,000 years ago in what is now Arizona, USA:


  • On February 15, 2013, a 66-foot-wide C-class near-Earth asteroid blew up during its atmospheric flight over Russia’s Chelyabinsk Oblast area, sending over 1,200 people to the hospital:


    Luckily that didn’t happen back during a high-tension point of the Cold War, when it might have triggered a nuclear strike!

  • And, of course, there’s the big one – the 6-mile-wide, possibly C-class “dinosaur killer.”


Then, why, oh why is NASA thinking about hauling an asteroid into Earth’s neighborhood?

The Asteroid Initiative

Well, if you can move an asteroid to Earth, you can also deflect away one that’s heading in for a collision.

We’re not able to do that yet, but we’re working on it.

There are eyes on the skies now, per NASA:

Because their orbits take them close to Earth’s orbit, some NEAs [near-earth asteroids] are potential Earth impact threats. NASA has a program to detect NEAs, estimate their orbits, and assess whether they pose an impact risk. The automated Sentry system identifies potentially hazardous Near-Earth Objects (NEOs – “objects” includes comets as well as asteroids) using observations from telescopes at observatories around the world and in space. Sentry was designed and implemented, and is managed, by NASA’s NEO Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California.

All telescopic observations of NEOs (professional and amateur) to determine their position and orbit are transmitted to the Minor Planet Center (MPC), which is the International Astronomical Union (IAU) sanctioned global clearinghouse for all such observational data. Once an initial orbit is determined, the MPC delivers the observational data for NEOs to JPL, which then computes a higher precision orbit for the NEOs based on the observational data. The orbit data for each NEO can be accessed through JPL’s Small-Body Database, and the JPL Horizons system provides an interface through which ephemeris data (position and velocity versus time) can be accessed for each of the NEOs.

[Brent] Barbee [who is head of NHATS – NASA’s automated system that computes possible spacecraft trajectories for a round-trip mission opportunities to visit a NEA] developed the NHATS system to find easily accessible asteroid mission opportunities based on the JPL/Horizons data. “In a sense, the NHATS system complements hazard tracking,” said Barbee. “The NHATS system monitors the opportunities offered by NEAs, while the JPL Sentry system monitors the hazards NEAs may pose to Earth.”


Yes. They want to see if it can be done.

After all, they’re not planning on bringing back 10-mile-wide Old Grampa Asteroid.

A manned NASA craft bags an asteroid in the 2020s.  NASA
A manned NASA craft bags an asteroid in the 2020s. You should have seen the one that got away! NASA

If Wikipedia has it correctly, in the 2020s Asteroid Redirect Mission (ARM), they’re just going to literally bag something very small, or perhaps dig a boulder-sized chunk out of one of the larger asteroids, and then redirect the catch into a Moon orbit.

It’s a start. If any attempt at asteroid redirection can be made successfully, then it’s realistic to hope for a system that one day can deflect large incoming near-Earth asteroids. Let’s not pin all our hopes on Bruce Willis and a wacky, lovable crew of oil drillers.

Too, ARM will be a manned mission, using technologies and gaining experiences that will come in when it’s time (in the 2030s, according to present schemes) to send human beings to Mars.

So, NASA is still at the proposal stage, but they want to do this. While it seems like a crazy idea, it actually might be the best way to protect Earth from asteroid strikes. It will also be a good training step for more ambitious plans. Asteroids may also provide the raw materials needed to help us venture out beyond Earth.

Neighbor, threat, or boon companion on our way to Mars?  Source
Neighbor, threat, or boon companion on our way to Mars? Source


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