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Headshot of Emily Lakdawalla

Cool animations of Phobos transits from Curiosity

Posted by Emily Lakdawalla

25-08-2014 16:41 CDT

Topics: pretty pictures, the Sun, Curiosity (Mars Science Laboratory), Phobos

Shooting video of a lumpy moon crossing the Sun and turning it into a giant googly eye is not a new activity for Curiosity, but I get a fresh thrill each time I see one of these sequences downlinked from the rover. A big pile of data from the most recent Phobos transit just landed on Earth, and I had to assemble them into an animation and share it with you. The animation runs faster than natural speed, but not a lot faster; Phobos transits take less than a minute. The data were taken on Curiosity's sol 713 (August 8), and downlinked just a couple of hours ago in the wee hours of Curiosity's sol 730. I believe I can see a pair of sunspots here, too, although they're a little hard to make out in the fuzz of the JPEG artifacts.

Note: an earlier version of this post had animations that were running backwards. Oops! I've uploaded fixed versions.

Curiosity sees a Phobos transit, sol 713

NASA / JPL / MSSS / TAMU / Emily Lakdawalla

Curiosity sees a Phobos transit, sol 713
Curiosity watched on sol 713 as lumpy Phobos passed across the face of the Sun. There are 84 images in this animation, which runs faster than natural speed. A couple of sunspots are faintly visible. The animation is composed of raw JPEG images, so contains artifacts, particularly at the high-contrast areas at the edges of the Sun and Phobos.

What do I mean by JPEG artifacts? When the Curiosity team shares its images with the public, they first adjust their contrast and convert them from a proprietary format to JPEG format. (Opportunity and Cassini do this too, and so will New Horizons.) JPEG is great for making images have small file sizes, but it is a "lossy" compression scheme that introduces artifacts, particularly in places where there are sharp edges between bright and dark things -- like the edge of the Sun against the much darker sky.

How much do JPEG artifacts affect the view? To answer that, I dug into the public Curiosity data for a transit that the rover observed just about a year ago, on sol 369. It's quite a bit crisper. You may also notice that Phobos looks a lot bigger. Phobos orbits so close to Mars that its apparent size changes dramatically, depending on whether you're looking at it closer to the horizon or overhead. (For more discussion of this and an explanation of what Phobos transit observations are useful for from Mars astronomer Mark Lemmon, read this blog post.)

Curiosity sees a Phobos transit, sol 369

NASA / JPL / MSSS / TAMU / Emily Lakdawalla

Curiosity sees a Phobos transit, sol 369
Curiosity watched Phobos pass across the Sun on sol 369, shooting one photo per second. This animation runs about 10 times natural speed.

I'll have to return to the sol 713 animation when its data are released publicly. Alas, we have just crossed a data-release boundary (data from sols 584 to 707 will be released on December 5), so I won't be able to get my grubby fingers on these data until March 16.

See other posts from August 2014


Or read more blog entries about: pretty pictures, the Sun, Curiosity (Mars Science Laboratory), Phobos


Xiaosi Zhou: 08/25/2014 08:40 CDT

Amazing!Thanks, Emily~

Michael Richmond: 08/26/2014 10:04 CDT

Are those really sunspots in the animation? I'm pretty sure that they are. You can find a picture of the Sun on Aug 8 at NASA's SOHO web site; here's a link: You can see two large sunspots to the left, with the label "2135" over them. Now, the view of the Sun from Mars is a bit different, since it's about 60 degrees from the Earth in its orbit right now, but my guess is that the double-blob-feature near the center of the Sun's disk in the animation may be these two spots.

Emily Lakdawalla: 08/26/2014 10:30 CDT

Michael, thanks so much for tracking down those sunspots -- I didn't have time to check for them myself.

widget3d: 08/31/2014 12:06 CDT

It would be nice to see a "map" with distances and scale . for this Rock to take up that much field of vision, i wonder how those stats would look. (too Cool)

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