Close Passing Asteroid 2013 ET Gets Its Picture Taken

Article written: 19 Mar , 2013
Updated: 23 Dec , 2015
by

Another space rock sat pretty for NASA’s big dish photographer. The 70-meter (230-feet) Goldstone antenna zinged radio waves at 2013 ET on March 10 when the asteroid flew by Earth at 2.9 lunar distances or about 693,000 miles (1.1 million km).

By studying the returned echoes, astronomers pieced together 18 images of a rugged, irregular-shaped object about 130 feet (40 m) across. Radar measurements of an asteroid’s distance and speed nail down its orbit with great accuracy, enabling scientists to predict whether or not  it might become a danger to the planet at a future date.

The Goldstone dish dish, based in the Mojave Desert near Barstow, Cal. is used for radar mapping of planets, comets, asteroids and the moon. Credit: NASA

The Goldstone dish dish, based in the Mojave Desert near Barstow, Cal. is used for radar mapping of planets, comets, asteroids and the moon. Credit: NASA

It’s also the only way outside of a sending a spacecraft to the object of seeing a small asteroid’s shape and surface features. Most optical telescopes cannot resolve asteroids as anything more than points of light.

By convention, radar images appear “lit” from above. That’s the side closest to the antenna. As you examine a radar image from top to bottom, distance from the antenna increases and the asteroid fades. If the equator of the asteroid faces the antenna, it will appear brightly illuminated at the top of the image. If the antenna faces one of the poles, the pole will be on top and lit up. It takes a bit of getting used to.

Nine radar images of near-Earth asteroid 2007 PA8 obtained between by NASA's 230-foot-wide (70-meter) Deep Space Network antenna. The part of the asteroid closest to the antenna is at top. Credit: NASA/JPL-Caltech

Nine radar images of near-Earth asteroid 2007 PA8 obtained between by NASA’s 230-foot-wide (70-meter) Deep Space Network antenna. The part of the asteroid closest to the antenna is at top. Credit: NASA/JPL-Caltech

The asteroid’s width in the images depends on the asteroid’s rotation rate and the antenna’s perspective. If the antenna stares directly down over the equator and the asteroid rotates rapidly, the images will be stretched from Doppler-shifting of the returned radar echo.

Radio waves are a form of light just like the familiar colors of the rainbow. If radio light is moving toward you, its waves bunch together more tightly and appear slightly bluer than if they were at rest. Astronomers call this a Doppler shift or blueshift.  If they’re moving away, the light waves get stretched and become “redshifted”.

Three views of asteroid 4179 Toutatis made in early Dec. 2012 by Goldstone. In all three, distance from the antenna increases from top to bottom and Doppler frequency increases toward the right, indicating Toutatis rotates from right to left, since that's the side of the asteroid approaching the observer. Credit: NASA/JPL-Caltech

Three views of asteroid 4179 Toutatis made in early Dec. 2012 by Goldstone. In all three, distance from the antenna increases from top to bottom and Doppler frequency increases toward the right, indicating Toutatis rotates from right to left, since that’s the side of the asteroid approaching the observer. Credit: NASA/JPL-Caltech

A slow-rotating asteroid will appear narrower to radar eyes, and if it doesn’t rotate at all, will show up as a “spike” of light. When the antenna happens to be point directly at a pole, the asteroid will appear to be rotating neither toward nor away from the observer and also look like a spike.

Most asteroids fall somewhere in between, and their radar portraits are close to their true shapes. Radar images show us surface textures, shape, size, rotation rate and surface features like craters. 2013 ET joins the ranks of numerous asteroids probed by radio waves from Earth as we try to grasp the complexity of our planetary neighborhood while hoping for we don’t stare down cosmic disaster anytime soon.

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8 Responses

  1. ASTEROIDS,
    COMETS, AND METEORS ORIGINATED FROM EARTH: In the Earth’s past there
    were powerful volcanic explosions propelling millions of tons of earth
    soil and rock (now asteroids and meteors which may contain organic
    molecules or organisms) into space. Read my popular Internet article,
    ANY LIFE ON MARS CAME FROM EARTH. The article explains how millions of
    tons of Earth soil may exist on Mars, and how debris we call asteroids
    and meteors could have originated from Earth. According to a Newsweek
    article of September 21, 1998, p. 12 that quotes a NASA scientist,
    SEVEN MILLION tons of Earth soil may exist on Mars! How could this be
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    • Member
      Aqua4U says

      Ditto Dan… Ummm, it is entirely possible that SOME pieces of Earth may have been blasted into space by volcanoes (doubtful), asteroids or comets, later to return as co-incidental orbits aligned, BUT stating that ALL asteroids and comets came from Earth is stretching your credibility to the breaking point Babu… The orbital paths of comets show they generally come from either the Kuiper Belt or the Oort Cloud – spectroscopic analysis demonstrates fundamental differences between Earth rocks, gases, ices and outer system objects. There is no denying this fact.. check your sources and do the math.

      • Yeah, we have some Mars rocks here. Earth has a deeper gravity well so it would be more difficult to blast rocks off our planet. Agree that volcanoes probably can’t blast rock to escape velocity, but I’m not a physicist/geologist so maybe someone can chime in. Certainly, comets do not come from here. Comets are thought to be the origination of water to some extent on our planet (probably Mars too) and their orbits can be traced to Oort cloud unless perturbed by planets/moons into different orbits.
        So if life was discovered on Mars, and assuming it was carbon based, would it use DNA similar to ours? DNA helix only evolved once on Earth. You could really tell if there was panspermia between planets if the DNA molecules were different. Which brings me to another thought. Many of us watch Star Trek/Star Wars, etc. on these forums. You always see aliens getting along fine with native lifeforms (at least in the non-horror sci-fi flicks) If a Mars/other exoplanet lifeform existed and was based on DNA (but different from Earth DNA), would that make this life form edible (assuming it is made of carbon, nitrogen, etc., but DNA is not the same almost assuredly), poisonous, cause allergic reactions, other issues? I write some science fiction (not published yet) and would be curious to know if any experts on this forum would have some insight into how alien life perhaps one day found on Mars would affect future explorers there. Could be any other exoplanets for that matter. Even on Earth, invasive species with the same DNA can cause health concerns/risks for native species.

      • Member
        Aqua4U says

        You’ve probably read where all earth life MAY have actually begun on Mars and later blasted off the surface via asteroid or cometary impact? And you are right. It is MUCH more likely an object reach escape velocity by volcanic means on Mars rather than on the Earth. So, if there IS life on Mars, we _may_ share a DNA progeny?

        But think about this… Evolution is continuous and partially reliant on genome mutation via radiation(s). Martian lifeforms will have evolved for millions or billions of years under very different circumstances than those found on Earth. Surface conditions on Mars exhibit a higher CO2 content per volume, much higher temperature variation, dessication and exposure to UV, cosmic ray and other radiations. Underground life around hot springs seems to be the only place where life as we know it might exist? But then again…What mutations would allow martian surface life? A hard shell seems prudent. “Hey! Wasn’t that rock over there just a minute ago?” (inspired by the lowly Hermit Crab who may want your helmet)

      • space_sailor says

        Asteroids are better explanation as source of Earth`s water than comets. But water presence from the begining of planet formation is best option – there is a lot of water inside Earth and inside other planets in form of hydrates.

  2. Member
    Aqua4U says

    Thanks Bob! Good stuff in here.. The expanded info. on radar sounding techniques and results is something I hadn’t read much about prior to your article.

  3. Me says

    Great pics! The radar images look pretty decent. You can see it revolving. Just short of 700,000 miles from our Eden Earth, that is still a bit too close for me. One of them will be a direct hit over Eden Earth like a Tunguska. God, I hope not. They are “city killers”. Before we had t-scopes, radar & sats, it was for the most part, in the back burner of our minds eye. Now that we all can have a front row seat to them bullet rocks. That back burner thinking is now on the front burner. Yeah, the odds are 20K to 1. But 1908 and this month is Russia were that “1 in 20K”. Complacency is no excuse. We are behind funding for sats etc…for locating all those we have not yet seen. PEACE!

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