The Great … Black Spots?

By Phil Plait | August 1, 2006 12:06 am

The other day, I wrote about Jupiter’s drive-by spots. A new image of the close encounter between the über-hurricanes was just released, taken by the ginormous Keck 10-meter telescope (picture a mirror about as big as one side of a tennis court).

The image above shows the wide field view of Jupiter on the left. The colors look almost normal, but they’re not: they are in the near infrared, at about twice the reddest wavelength the human eye can detect. You can clearly see the Great Red Spot, and Red Jr (which I prefer to call Oval BA, its official name) right next to each other, though they look white in the infrared.

The (frankly creepy) close-up is way out in the IR, at 5 microns, where warmish things glow. By warm, I mean about 300 Centigrade, so a fair bit hotter than boiling water, if I did my math correctly. Note that the spots are black! That means they are cold compared to 300 C. According to the Keck folks, the clouds in the spots block the infrared light from the hotter stuff deeper down in the atmosphere, so they appear black. Still, heat leaks out around the edges, so you can see them faintly outlined by hot gas.

The weird polychromatic inkblot thing at the top is the moon Io (roughly the same size as our Moon). It looks funny because it moved a little bit between exposures, so it appears as a line of colored dots. What’s very interesting to me is that the blue image (at 1.65 microns) is significantly bigger than the other two. I emailed the folks at Keck about it, and got a reply right away. It turns out that this filter lets through light from methane. Jupiter is faint when viewed through that filter, so to make the color picture look right they had to increase the brightness of the blue image. That made Io look bigger. It goes to show you– seeing is not necessarily believing, and just looking at an image and trying to understand what you’re seeing is a lot harder than you think.

Not really a tip o’ the dew shield, since it’s her job to send out media stuff, but more of a shout-out to my friend Laura K. Kinoshita at Keck, listed on their page as a media contact. Since I knew her until recently as Laura Kraft, I assume her marriage went off… with a hitch. Hahahaha! Get it? She got hitched. Oh, I kill me. Anyway, she eventually answered my email even though she’s on maternity leave. So Hi Laura, and congrats!

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (12)

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  1. Moonage Spacedream | August 1, 2006
  1. Navneeth

    Amazing stuff!

  2. 300 Centigrade? How can Jupiter be so warm?

  3. Berlie

    Those are really cool pictures. I like the black and red one, it adds to the mystique of the gas giant.

    Merovingian, I might be wrong, and if I am someone please correct me, but Jupiter’s so dense that the pressure probably heats up the gases it’s made from. And since heat has to go somewhere, it escapes the surface and that’s what gives such great pictures in IR. That’s just a hypothesis, on my part. Not a theory, though. Can anyone verify (or villify) this?

  4. In the infra-red image, it looks like there is a third spot below the other two that I don’t see in the color picture. Any clue as to what that is?

  5. Irishman

    No One, I’m not sure what “third spot” you mean. There’s a fair amount of dark swirled in the bright. I don’t see any more spots per se, but looking at the bigger image on the Keck page, the brighter areas on the IR are the bluer elements on the color image.

    I think you’re just seeing darkness where the hotter skies below are obscured by clouds.

  6. I see someone has already made the obvious 2010: The Year We Make Contact wisecrack, so I’ll just shut up now. (-;

  7. hi, i was one of the observers who took these images at keck, and i put together the final graphics. so i’m pretty stoked that this is being blogged about. i have a few comments:
    it’s 300 K not 300 C. although we haven’t finished the calibration of the data, the brightest pixels in the thermal IR image are probably closer to 300 K, which is like room temperature.
    why jupiter is hot: heat is still coming out of the planet from when it formed. so over time jupiter is cooling off, partly by radiating its heat through holes in the clouds like in the picture. but the deeper you go into jupiter’s atmosphere, the hotter it gets. it’s just like how temperatures are nice at sea level here, but at the tops of mountains, the air is much colder. i think this is the effect that berlie was talking about.
    no one of consequence’s third spot: if you look closely at the big (reflected sunlight) picture, you can see that the bottom corner of the outline is falling on brighter clouds. these clouds block the thermal radiation from below and appear dark in the 5-micron image. i think it just LOOKS like a spot in the thermal image because there’s a little clearing in this band of clouds, and the border of the image cuts off the rest of the band. so there’s no 3rd spot, at least, none as big as the GRS and oval BA.

  8. Mike:

    I used Wien’s law to get 300 C.

    T(Kelvin) = .29 / wavelength (cm)

    5 microns = 5×10-4 cm so

    T = .29 / 5×10-4 = 580 K

    and subtract 273 to convert to C to get 580 – 273 = 307 C.

    This is assuming Jupiter acts like a blackbody, which it probably doesn’t even at those wavelengths. I don’t have a thermal IR spectrum of Jupiter handy. If you have one, link to it here! I’d be curious to see it, actually.

  9. alright… i hope this response isn’t TMI…

    this one shows the spectrum around 5 microns (for bright regions):

    and this one shows jupiter’s whole thermal and reflected spectrum:

    you were right when you said jupiter doesn’t act like a blackbody. since it has so many gases (mainly CH4, NH3, H2) that absorb/emit in the infrared, you end up looking at a different level of the atmosphere at every wavelength… and since temperature increases with depth, the spectrum is more complicated than a smooth blackbody spectrum.

    i see how you got 300 C tho. this looks like a misapplication of wein’s law. the wavelength in wein’s law is the wavelength at which a blackbody emits the most radiation. a blackbody at 300 C would have the peak of its spectrum at 5 microns, like you calculated. but a blackbody at 300 K would also radiate at 5 microns, even though it would radiate even more at 0.29 / 300 or about 10 microns.

    i guess it might have seemed like we picked 5 microns because that’s where the peak of the thermal spectrum was, but the real reasons are 1) earth’s atmosphere is relatively transparent at 5 microns and 2) jupiter’s atmosphere is relatively transparent at 5 microns.

  10. The red spot is bigger than earth, but it looks very small in this photo, when compared with jupiter!

  11. Class science project grade 6 B>>>>>>>>>>>>>>>>>>>>>>>>>>K>>>>>>>>>>>>>>>>>>>>>>>>>hizzee

    Wow I thought that there was only a red spot amazing!! (ㅇㅗㅇ)


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