EB, EC and now ET – The Asteroids Keep on Coming


Short movie of the asteroid 2013 ET tracking across the sky made over a half-hour on March 4, 2013

Like cars on a freeway, they come out of nowhere, blow by and disappear in the distance. Asteroid 2013 EB passed within a moon’s distance of Earth on Feb. 28, while 2013 EC did the same four days later. Both spanned between 40-50 feet across or slightly smaller than the object that lit up Russian skies three weeks ago.

Radar image of the 230-foot-wide asteroid 2005 YU55 obtained during a flyby of Earth on November 7, 2011. 2013 ET is a tad larger. Both are rocky bodies orbiting the sun in Earth’s vicinity. Credit: NASA / JPL-Caltech

Next up is the heftier 2013 ET which cruises by Earth Saturday morning (6:09 a.m. CST) at a distance of 600,000 miles. That’s about 2 1/2 times the distance of the moon. Astronomers estimate ET’s diameter at 328 feet (100 meters).

None of the earlier flybys posed a threat to Earth and neither will 2013 ET as it diligently follows its path around the sun. You can keep your eyes on the asteroid courtesy of astrophysicist Gianluca Masi and his robotic telescope setup in Italy starting at 1 p.m. (CST) tomorrow March 8. Masi will broadcast the live photos of 2013 ET on WebTV and provide commentary.

Diagram showing the difference in the orbits of typical near-Earth asteroids (in blue) and the smaller subset of potentially hazardous asteroids (PHAs). PHA’s come within 5 million miles of Earth and have the potential, if they survive their flight through the atmosphere, to cause regional or larger-scale damage. Credit: NASA

All three building-sized rocks were discovered very recently. 2013 ET was spotted on March 3 by the Catalina Sky Survey based in the Catalina Mountains north of Tucson, Arizona. Discoveries like these are almost a daily occurrence and highlight the fact that of the estimated one million small near-Earth asteroids out there, we’ve discovered and tracked only 9,754 as of March 4, 2013. That’s less than 1%.

Of these, 861 have diameters of 1 kilometer (0.6 mile) or larger and 1,379 are classified as potentially hazardous, meaning their orbits take them threatening close to our planet. This doesn’t necessarily mean we’ll be hit, just that the potential exists.

Artist’s rendering of the gravity anomaly map of the Chicxulub Crater area. Red and yellow are gravity highs; green and blue are gravity lows. White areas indicate multiple sinkholes. The shaded area is the Yucatán Peninsula. Variations in the density of the rock were used to discover the crater which is buried under several thousand feet of limestone. Credit: Milan Studio

But there’s a silver lining. We’ve already discovered over 90% of the big, kilometer-plus-sized asteroids, greatly reducing the uncertainty of “what’s out there” when it comes to the worst potential impacts. The last really big smack-down of which we’re aware was the impact of a 6-mile-wide asteroid that triggered the mass extinction that wiped out the dinosaurs 65 million years ago. The 110-mile-diameter Chicxulub Crater in the Yucutan Peninsula remains as a testament to this Earth-altering event.

14 thoughts on “EB, EC and now ET – The Asteroids Keep on Coming

  1. But is it the case that even if we map all (large) asteroids, there is always the chance of a short or long period comet crossing our path? Like C/2013 A1 that is currently heading to Mars? And besides comets and asteroids, are there any other rocks mother nature can throw at us?

    • Steven,
      Yes, there is a comet possibility too but it is less. There are approximately 85 near-Earth comets known, only a few of which I’ve heard are potentially hazardous (but there may be others we haven’t discovered). As far as I know, any rocks coming our way in future would be from these classes of objects.

  2. HI Bob
    A lot of people are saying there seems to be an increase in the amount of neo’s recently, do you think this or is it just because we have so many astronomer’s on the lookout that we are finding more, it just seems recently that there is a lot going on, or is this just hearsay. Thanks :-)

  3. As of the potentially hazardous comets, are they just classified the same as the asteroid’s or is it worked out different, and also Bob are these comets listed on the JPL site. It is strange how you always hear about the worry of neo’s coming close to earth but not so much as comets, so I presume there is maybe less danger from comets than asteroid’s, Thanks

    • Lynn,
      There are far, far more asteroids in the inner solar system (between the sun and the outer edge of the main asteroid belt) than there are comets. Most comets formed and still reside in the outer solar system. I haven’t found a listing of those that pass near Earth but I’ve not looked closely yet.

  4. I am glad that Panstaars is not that close, but I wish that it came a little closer, but despite being over 100 million miles away, Terry Lovejoy now says that it is about magnitude 1.5. It may brighten farther.

  5. Hi Bob,
    Sorry another question, as you said above that there is 85 near earth comets known, so is there a website that you know of where they are listed, I just think it is a little scarey about these comets, or should I not worry with these as i’m sure there is many eyes on the 85, I really am wondering where the information comes from where you know about these, i’m just a bit curious and a tad worried. Thanks Bob.

    • Lynn,
      That was an older statistic. There are currently 93 near-Earth comets or NECs. Here’s a link to a table (go to last table on page) showing totals for all NECs and the various asteroid classes. Here’s the link: http://neo.jpl.nasa.gov/stats/
      Unfortunately it doesn’t name the comets. The comets are really no different than near-Earth asteroids except they’re icy. Since they grow tails when near Earth and the sun, I should think we’d also see them much sooner than a bare rock.

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