The Home Planet Seen from 100 Million Miles Away

By Tom Yulsman | March 31, 2013 6:10 pm

The STEREO-B spacecraft captured this view of Earth and the Comet PanSTARRS on March 13. Also visible is the sun, to the left, which is developing an ejection of material from its outer atmosphere, or corona. (Image: NASA/GSFC/STEREO)

It’s not every day that you get to see what home looks like from 100 million miles away — at the very same time that the sun is throwing material out into space  and a comet is cruising by in the inner solar system.

But that’s exactly what the STEREO-B spacecraft observed on March 13. And it sent this picture postcard back to Earth so that we could enjoy the view. (The vertical line is an artifact of the imaging process.)

This was the image of the day at NASA’s fabulous Earth Observatory. But as I did on Friday with another EO image, I’ve taken some subtle liberties here to enhance what you see. To bring out some definition in the material that the sun, at left, is ejecting from its outer atmosphere, or corona, I’ve added a little local contrast and also a smidgeon of sharpening. In addition, I toned down the luminance of the blues, to accomplish the same goal. Look carefully at the sun and you can see material streaming off into space toward, well, us.

Meanwhile, Comet PanSTARRS is between the spacecraft and Earth. The bright white dots are stars.

STEREO-B also sent home a video of the comet:

A screenshot of a movie produced by the STEREO-B spacecraft between March 9 and 12. Click to watch the movie, which shows the comet and its fluttering tail as it moves through space. (Source: NASA)

Make sure to click on the screenshot to see the movie itself. It’s pretty cool. The sun is off the screen to the left, and in the movie you can see Mercury moving in its orbit.

Speaking of Mercury, I’ve been looking for an excuse to share this image — have you seen it yet?:

Meteorite NWA 7325 is believed to have come to Earth from Mercury. (Image: Stefan Ralew /

This beauty, dubbed Meteorite NWA 7325, was found in Western Sahara in 2012 — and scientists believe that it may well have come from Mercury. If so, it would be a first: No other meteorite from Mercury has ever been found. For the nitty gritty scientific details, check out this paper by Anthony Irving of the University of Washington, which he gave at the recent Lunar and Planetary Science Conference. For a slightly less technical discussion, go here.

CATEGORIZED UNDER: Astronomy, select, Sun, Top Posts
  • smd2008

    Clicking the screenshot reveals a large screenshot, not the movie

    • Tom Yulsman

      Sorry! Will fix that now.

      • smd2008

        Pretty amazing. What gets me is the movement against the star field. It really gives the impression that we’re adrift in space.

        • Tom Yulsman

          I totally agree! I found that movement astonishing.

  • CitizenX

    How much velocity would a rock from mercury need to overcome the suns gravity to reach the orbit of earth?

    • Tom Yulsman

      Really good question!

      Here’s what Emily Lakdawalla had to say about it in a blog post over at the Planetary Society (

      “Dynamically speaking, it’s very, very hard to get a rock from Mercury to Earth. Mercury is located so close to the Sun that you have to impart a tremendous amount of energy to blast a rock off of it and into a high enough orbit to reach Earth. It helps a little bit that Mercury is such a small planet (so its gravity is relatively low). And there’s also a way in which its proximity to the Sun helps: any asteroids that hit Mercury are traveling insanely fast (between 20 and 50 kilometers per second). That would make a big enough bang to spew a lot of rocks into space. Still, it’s never been considered too likely that one of them could get all the way to Earth, and then be found.”

      • CitizenX

        I was just thinking… wouldn’t that leave a mark and if 1 piece made it because the impact was so significant, then there is probably plenty more.

    • Tom Yulsman

      Really good question! Check out the answer from a blog post over at the Planetary Society:

      • CitizenX

        I really didn’t see an answer to the question. As close as the moon is, I would think that we would find lots of meteorites from the moon. After all, its gravity isn’t all that great and any pieces from the moon wouldn’t have to overcome the Suns gravity to reach Earth. Mercury is a different beast all together.

        I don’t know. Something strikes Mercury. A piece flies off into space. It has enough energy in its direction that it could be moving over numerous eons and end up on the Earth?

        Then again, perhaps it slingshotted around the sun on its journey but starting that close to the sun, it would have to be moving awfully fast in it’s initial trajectory.

        • Mike Diamond

          Remember that gravity is dependent on the mass of the object. The small chunk of rock from Mercury would have less mass than Mercury itself, and thus be affected less by the Sun’s gravity. It could therefore travel (relative to the Sun) much slower than Mercury and remain in orbit. A meteorite impacting Mercury would most likely fling material in all directions around the impact site. Were the impact significant enough to fling material into space with enough velocity to escape Mercury’s gravity, it’s very likely that some of that material would be flung “ahead” of Mercury’s orbit, and some “behind” (even outward, inward, upward, and downward, depending on the orientation of the impact). The stuff flung “ahead” would surely be travelling faster than Mercury (relative to the Sun), and easily escape the Sun’s gravity. The stuff flung “behind” may or may not be travelling with enough velocity to escape the Sun’s gravity – but it surely would not need to even “keep up with Mercury” to remain in a stable orbit around the Sun due to its much lower mass. In a nutshell, the biggest obstacle for small objects escaping from Mercury’s orbit would be Mercury’s gravity, not the Sun’s.

          • CitizenX

            Although I wouldn’t understand it (not that I am dumb or anything), I would love to see that math to prove that hypothesis. What the initial velocity would have to be for an object to escape Mercury’s gravity, the suns gravity and have enough energy to accelerate away from the sun all the way to Earth.

          • Mike Diamond

            Well your question has had me doing research off and on throughout the day, and now I am questioning my own conviction and understanding of how mass affects orbital velocity.

            If you read this post (, a body with greater mass needs a LOWER velocity to maintain the same orbit. This doesn’t make sense to me, but as it turns out isn’t the main issue…

            If you read the other responses in that thread (, you find that even a doubling of an object’s mass has a NEGLIGIBLE effect on the orbital period (and thus velocity). This says to me that your original thinking was more accurate – that the small object travelling at Mercury’s approximate velocity would be tightly-coupled with the Sun’s gravity, and would need to slingshot around the Sun or otherwise be going stupidly fast for its orbit to reach out to Earth’s orbit.

            I’m quite upset that I misled you, and I apologize. I thought I had a firm grasp on this stuff (though just a conceptual, not a mathematical one). Now I’ve got to shake my Etch-a-Sketch upside down and start all over.

          • CitizenX

            It would seem to me to have to be going “stupidly fast”, as you say to escape the gravitational pull of Mercury AND the Sun. Mercury I could see not being a problem but the Sun is another matter.

            It would have to have enough inertia to go the 110 thousand kilometers average distance between the Earth and Mercury. So maybe millions of years ago a lucky chunk of Mercury hit the earth. What are the odds. Or a chunk slingshotted around the sun and over the aeons finally hit the earth.

            I truly hope it is from Mercury. It just seems to be a miracle that it is.

          • Mike Diamond

            So I broke out an old game called “Universe Sandbox” to play around with this scenario. It’s only a game and it’s hard to say whether my results are realistic. The actual orbital velocity (OV) of Mercury is about 47 km/s (, which seems consistent with the game’s values. All other values in the game such as mass and distances also seem accurate. That said, none of what follows proves anything – the game is not a proper scientific simulator, and I have not verified any of my findings mathematically…

            I changed Mercury’s mass to 1 kg (which as said above, wouldn’t change anything regarding its orbit – and it didn’t), and then played with increasing and decreasing its OV until it reached Earth’s orbit.

            Lowering the OV just had it turn in towards the Sun, and enter a comet-like orbit. But the max distance was never any farther than Mercury’s current orbit.

            Raising the OV also had it enter a comet-like orbit, by first accelerating away from the Sun and eventually turning back in. I found I only had to increase the OV by about 15-20 km/s to have it reach Earth’s orbit.

            I have no idea if 15-20 km/s is a realistic ejection velocity for debris from a meteorite impact *on Mercury*. But it would be interesting to verify!

          • CitizenX

            So somewhere around 62 to 67 km/s would be enough for an object to escape the influence of the Suns gravity starting from the orbit of Venus?

          • Mike Diamond

            According to my toying around in Universe Sandbox, yes. I sped Mercury up to about 70 km/s and it easily sailed right out to Earth’s orbit and a bit beyond before turning back in toward the Sun, orbiting like a comet.

            I just fired it up again to verify. Mercury’s orbit is not centered perfectly on the Sun. At Perihelion (closest) it’s travelling fastest, at ~ 59 km/s. At Aphelion it’s travelling slowest, at ~ 39 km/s.

            The velocity needed to escape it’s current orbit and reach Earth’s orbit differs depending on where Mercury is on its current orbit. At Perihelion, we need to change its velocity from 59 to 67 km/s (your estimate is right on the money). At Aphelion, we need to change it from 39 to 51 km/s.

            Good find on the article btw. :)

          • CitizenX

            Interesting discussion. Thanks.

          • CitizenX


            An additional article about the object.


            Their conclusion was that it was unlikely to be from Mercury.

  • Pingback: Como é a Terra vista por uma sonda próxima ao Sol()

  • Carley H. Young

    until I looked at the receipt for $6957, I be certain
    …that…my sister woz like they say realey taking home money part time on
    their apple laptop.. there best friend has done this for less than 17 months
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  • medsackers

    i have some that meteoret i have 71 grams i swear
    i’m from western sahara and i live in the same place when thats stone founded
    i can send some photo about it this my mail



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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