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Warm fractures on Enceladus
Warm Fractures on Enceladus

With its capacity to see light that's redder than the red we see, the Composite Infrared Spectrometer (CIRS) searches for heat and is capable of discerning an object's composition.

"Our instrument looks at the world the way a snake's tongue does -- always searching for heat, not light," explains Dr. Glenn Orton, a senior research scientist and CIRS co-investigator. "Another way to look at it is that we're looking at what our skin feels as heat, rather than what our eyes see as light."

But CIRS can do a lot more than just seeing beyond what our eyes can see.

"What's cool is that CIRS can tell us how hot something is and what's in it -- like finding out that there's a hot bowl of soup over there and that it's chicken noodle, not tomato."

Our noses, of course, are capable of doing the same thing, but only when up close. And, as Orton points out, "We can't get that close to Saturn or Titan."

Orton researches temperatures and compositions of planetary atmospheres using a variety of facilities, some based on Earth -- such as Keck Observatory and the Infrared Telescope Facility -- and some up in space, such as Hubble and Spitzer.

"We can measure pretty precisely how hot things are in planets and on their surfaces," Orton says. "That's a big deal for weather prediction."

Conor Nixon
Conor Nixon

From this information scientists can tell a lot about a planet, starting with how hot it is and also what it is made of. A planet's atmosphere, such as Saturn or the moon Titan, is composed of different gases distributed in layers upon layers of varying temperatures that increase and decrease from the surface up through the edge of space. Data from the instrument helps scientists figure out what an atmosphere is composed of.

"Each gas emits or absorbs heat rays in a characteristic way, some wavelengths more than others," explains Conor Nixon, assistant research scientist on the Cassini CIRS team. "By measuring the infrared spectrum we can tell what gases are in the atmosphere, and how much of each one."

CIRS has produced some exciting results so far.

"The most exciting results must be the discovery of 'hot cracks' on the south pole of the moon Enceladus. The cracks were seen by the Cassini cameras (ISS), but CIRS was able to tell that they are much hotter than the surroundings," Nixon says.

For more information, see the engineering technical write-up or visit the science team's Web site:

At a Glance

Composite Infrared Spectrometer (CIRS) on the Cassini Spacecraft
CIRS on the Cassini Spacecraft

CIRS is a spectrometer, which means that it splits light into different colors, like a glass prism, or a raindrop creating a rainbow. CIRS is special because it is sensitive to invisible heat rays, or infrared light, rather than ordinary visible light. CIRS measures the strength of the different colors, or 'wavelengths' of heat rays, given off by a planet.

CIRS Sensing Instruments:

  • Far-Infrared Focal Plane [FP1] (16.67 to 1000 µm; 4.3 mrad circular field of view)
  • Mid-Infrared Focal Plane [FP3] (9.09 to 16.67 µm; 1x10 array of 0.273 mrad squares)
  • Mid-Infrared Focal Plane [FP4] (7.16 to 9.09 µm; 1x10 array of 0.273 mrad squares)

CIRS Instrument Characteristics:

  • Mass (current best estimate) = 39.24 kg
  • Peak Operating Power (current best estimate) = 32.89 W
  • Average Operating Power (current best estimate) = 26.37 W
  • Peak Data Rate (current best estimate) = 6.000 kilobits/sec
  • Dimensions (approximate) = 50-cm diameter telescope; 89 cm x 76 cm x 52 cm