Near Earth Objects (especially asteroids)

This page surveys efforts to protect Earth from asteroid impacts or mine them for their resources.  [Updated: 2013 Nov 3 to include 2013 TV135 Chelyabinsk, and the NASA Asteroid Redirect Mission; 2013 Nov 10 to reference report in Nature on asteroid frequency.]

The legacy of asteroids can be found in at least two major events:

  • Extinction of the dinosaurs – It is now widely accepted that the dinosaurs became extinct due to an asteroid impact 65 million years ago on the Yucatan Peninsula of Mexico.
  • Tunguska event – On June 30, 1908, a meteroid or comet hit the Earth’s atmosphere and burst about 5-10 kilometers above Siberia.  The Tunguska blast knocked down trees over an area of 2,150 sq meters (830 sq miles).

Such an asteroid impact could ruin your day. Former astronaut Ed Lu discussed protection against this in a TedTalk. 

Impact Risks

JPL Sentry Risk Table.  Table of potential future Earth impact events that the JPL Sentry System has detected based on currently available observations.  Table includes links to pages that list details about each of these asteroids, and provides interactive plots of where the asteroids and planets are over time.

Among the asteroids that made big news in 2011-2013:

  • 2011 AG5 is 140 meters in diameter. At one point, it had 1 chance in 500 of hitting Earth.  As the orbit was refined, the potential impact on Feb. 5, 2040, was completely removed. [JPL article Feb. 28, 2012] [article by Phil Platt in Discover]
  • 99942 Apophis (2004 MN4) is 325 meters in diameter.  At one point , the possibility of impact was 2.7% in 2029.  Or it could also barely miss in 2029, and come back and hit in 2036.  We now know that on Friday the 13th of April 2029, it will pass within the orbit of geosynchronous satellites, but no closer than 19,400 miles (31,300 km).  And the possibility of impact in 2036 has been almost completely removed.
  • 2013 TV135 is 450 meters in diameter.  This is a fairly large asteroid, but has a very small chance of impact on August 26, 2032.  During the early characterization of its orbit, Earth impact risk was 1 chance in 5,800.  As of Nov. 2, 2013, the chances dropped to 1 in 345,000.


While asteroid discovery techniques are improving, near Earth asteroids are still often discovered just as they are passing by the Earth, with little to no advance notice.  In effect, if an object is coming almost straight at you, you won’t notice that the object is moving until there is some change against the background.  In fact, the closer it is to hitting you, the less likely that you will see it.

Such was the case on February 15, 2013.  In fact, the astronomical community was prepared for the arrival and near miss of asteroid 2012 DA14.  However, a few hours before it was to happen, a meteor hit the atmosphere over  Chelyabinsk, Russia, shattering windows and injuring about 1,500 people.  (See the blog entry titled “A couple of shots in the cosmic shooting gallery“.)

In November 2013, an article in Nature reported that the population of small impactors like Chelyabinsk is probably an order of magnitude higher, but blast damage lower than previously thought.  Potentially, there could be 20 million asteroids of that size (roughly 20 meters in diameter) in the solar system.  An airburst from that size asteroid was expected roughly once in 150 years.  Revised estimates put it at once in 30 years.  [AP]

Asteroid Discovery Projects

WISE.  The NASA Wide-field Infrared Survey Explorer (WISE) mission has vastly increased the catalog of known asteroids.

Sentinel.  A space-based infrared survey mission of the B612 Foundation to discovery and catalog 90 percent of asteroids larger than 140 meters in Earth’s region of the solar system.

Astronomer / physicist / “astronogamer” Scott Manley has put the roughly 30 year history of asteroid discovery to music.  The video below covers the period from 1980 to 2011.  Note as more powerful instruments come on-line how to rate of discovery increases.  

Manley produced a new video for 1980 to 2012.  But instead of music, he personally narrates the video, explains the color scheme, and notes what is beyond some of the sets of discoveries.

Asteroid Mining Projects and Companies

Planetary Resources.  A commercial enterprise developing robotic spacecraft to explore asteroids, and deliver resources from asteroid mining to locations where they will be needed in the solar system.

Deep Space Industries.  The company made its public announcement on January 22, 2013.  [YouTube of announcement]

Asteroid Redirect Mission

NASA is embarking on an asteroid redirect mission.  The original mission was in response to President Obama’s announcement of a manned asteroid rendezvous.  He said on April 15, 2010, “Early in the next decade, a set of crewed flights will test and prove the systems required for exploration beyond low Earth orbit. And by 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the Moon into deep space. So we’ll start — we’ll start by sending astronauts to an asteroid for the first time in history. By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow. And I expect to be around to see it.”

This was interpreted by some as a human visit to the asteroid belt.  Others understood this to be a visit to a near Earth asteroid as it is flying by.  In either interpretation, this would mean leaving the influence of the Earth’s gravitational field, requiring a delta V for a manned vehicle that had never been achieved before, roughly comparable to going to Mars.

For whatever reasons, this is not the mission.  Instead, an asteroid will be brought into the Earth-Moon system, and astronauts will rendezvous with it there.  The notion of bringing a small asteroid into the Earth-Moon system was principally pioneered through a study by the Keck Institute for Space Studies in 2011 and 2012. NASA found this proposed asteroid retrieval mission to be an easier target for a human mission than leaving the Earth-Moon system.

An example of a possible retrieval is this animation showing a mission to 2009 BD, an asteroid about 7 meters long.   In the scenario, the mission begins in late 2018, and culminates in early 2024 with the asteroid roughly in orbit around the Moon.  Thus, humans would not visit the asteroid until that time. (Note that the red line is thrusting, and blue is coasting.)

This scenario employs a long-duration, low-thrust engine.  There may be other possible schemes using higher thrust engines and an asteroid when it is in Earth’s vicinity; the retrieval mission would thus be shorter duration.

NASA has released an notional animation of crew operations for the human portion of the mission. 

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