The WISE family comets

By Phil Plait | June 3, 2011 7:00 am

In the little over one year that the Wide-field Infrared Survey Explorer (WISE) spacecraft surveyed the sky, it captured images of hundreds of millions of objects. Many of these were previously known stars, galaxies, and the like, but it also added a few newcomers to our catalogs, including a score of comets:

[Click to encomanate.]

Why did WISE find them, and not ground-based observers? Lots of reasons come to mind. Comets are not really the spectacular and brilliant objects commonly thought; at least, not all of them are. The solid part of a comet is usually a mix of rock and ice, the ice being made of water, ammonia, carbon dioxide, and other materials we tend to think of as gases here on Earth. But in the depths of space, where it’s cold, they can remain frozen solid… until the comet nears the Sun. Then, the materials go from a solid directly to a gas, surround the solid nucleus, and reflect a whole lot more sunlight. The comet gets bright and can be spotted more easily.

Even then, it may not be easy. The comet may be small and faint in optical light. It may be too near the Sun to spot. It may be too far away to be seen easily. Or it may simply not be in a place anyone on Earth is looking.

WISE scanned the entire sky, and was prone to seeing such things. And the lack of optical light isn’t so much an issue if the comet is warm enough to glow in the infrared, and that can be at temperatures a hundred degrees below 0 or more. And even then, WISE only found 20 such comets before anyone here on Earth did. I’ll note it also did see quite a few comets discovered on Earth first, like the comet C/2007 Q3, also known as Siding Spring.

It also racked up a huge number of previously unknown asteroids, some of which are potentially dangerous to the Earth some time in the (far, hopefully) future. The point is — and I’ve said this many times before — the more eyes we have on and in the sky, the better. And by looking at different wavelengths we’ll see even more.

Image Credit: NASA/JPL-Caltech/UCLA

Related posts:

The first spectacular views of the sky from WISE
WISE uncovers its first near-Earth asteroid
A taste of WISE galaxies
Orion’s WISE head

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: comets, infrared, WISE

Comments (13)

Links to this Post

  1. Comet Coma | The Cosmic Space | June 28, 2011
  1. ozprof

    minor nitpick BA

    It is not so much “reflected” light that renders a comet visible, but rather emission from the gasses in the coma. Only in a very few of the most dusty comets does reflected light play more than a minor role

  2. Electro

    I think BA was referring to the light reflecting off the sublimating gas.

    Unless you are saying the gas is luminescent? I was unaware that happened.

  3. panic

    Space is NOT cold. There happen to be some very cold things in space, but vast empty space is most approximately a thermos. The only way an object loses heat in space is through radiation, which is slow. A dead body in space (in the shade) would take days to freeze. In a central park winter, that same body would freeze in hours.

  4. Messier Tidy Upper

    @^ Panic : Doesn’t that depend on *where* in space that dead body is?

    If it’s near a star such as our Sun (eg. closer than Mercury’s orbit) there’s going to be a lot of radiation to cremate and vaporise the cadaver in question.

    But that is an atypical and unlikely spot to be because space is called that because “there’s a lot of it” (movie quote 😉 ) and most of space is a *very* long way from any star or highly radiative (?) object.

    So if the corpse is located out beyond Pluto’s orbit, say – wouldn’t it freeze pretty much straight away?

    As I understand it the cosmic microwave background which you could perhaps call the “temperature” of space far from stars – the vast majority of it – think all the planet’s beyond Jupiter and the vastness of the middle and outer solar system realms – is 3 degrees Kelvin or minus 270-ish degrees Celcius. (Minus 454 Fahrenheit.)

    But yeah, space is a vacuum and as such is a medium rather than a place with temperature not really applying exactly if I understand right. Might as well ask what the temp of “water” or “air” is. It depends where and what you’re referring to.

  5. Messier Tidy Upper

    Well done to those WISE guys for their cometary discoveries and so much more! 😉 :-)

    BTW. Aren’t they still going through the WISE data and isn’t it possible they might yet notice more comets still? (Or nearby brown dwarfs and other things hitherto unknown?) Or have they finished that process now?

  6. At someone used the Stefan-Boltzmann Law to determine how long it would take a living body to freeze in space and came up with about an hour. I haven’t checked the math, but that sounds reasonable to me. You’d be in an environment where you’re radiating out and getting absolutely nothing (well 3 degrees Kelvin, which isn’t much different) back.

  7. Electro


    I have to wonder how many of the liquids in a human body would remain liquid at near vacuum?
    Because once they’re gone, by definition it’s frozen, regardless of temperature.

  8. Nigel Depledge

    MTU (4) said:

    So if the corpse is located out beyond Pluto’s orbit, say – wouldn’t it freeze pretty much straight away?

    Er, pretty much no.

    As the commenter to whom you were responding pointed out, the only way an object in space loses heat is through radiation. Add to that the residual internal heat of the object having first to reach the object’s durface by conduction before it can be radiated, and you have a process that takes time. How much time depends on the surface area / volume ratio.

  9. Nigel Depledge

    Electro (7) said:

    I have to wonder how many of the liquids in a human body would remain liquid at near vacuum?
    Because once they’re gone, by definition it’s frozen, regardless of temperature.

    Define what you mean by “liquid”.

    Most of the water in a human body (for example) is not in what you might call liquids (blood, lymph, cerebro-spinal fluid, interstitial fluid and so on). Most of it is in the cytoplasm of cells, where it exists as a kind of gel because of everything else that is present in the cytoplasm of cells.

    For the most part, even the liquid components of a human body would not be exposed to vacuum – even in the most vulnerable places (such as deep in the lungs) there would at least be the walls of capillaries between the body’s blood and the external environment.

    Our bodies are pretty tough, and we have evolved to deal with having a high-pressure circulatory system. Expose a person to vacuum (where the difference between internal and external pressure is perhaps 7 times what it might normally be) and they will certainly suffer, but you won’t have blood vessels bursting left, right and centre.

    So, the saliva will boil from the mouth, and the mucus coating of the airways will rapidly dry out (the stomach may even be emptied too) but most of the body’s fluids will stay inside it and won’t be exposed to the vacuum.

    And your definition of freezing is indistinguishable from desiccation, so it does not sit well with me. A body left in a cold part of space probably will freeze, and this freezing will involve water forming ice crystals throughout the body. Due to the damage those ice crystals will cause, some of that ice might then become exposed to vacuum and sublime off, but I think you should not expect a body exposed to the vacuum of space to be desiccated unless it has suffered massive and extensive trauma. Or been there for many years.

  10. Electro


    My tongue was pretty firmly in my cheek there.

    I haven’t done the math for the boiling point of various compounds at reely low pressures or worked out fast the pressure differential would equalize but combined with the latent heat of the body, I think it would dessicate pretty quickly.

    Admittedly there would be pockets of gas trapped within that would take a while to reach thermal equilibrium, but in simplest terms once the only states of matter remaining are solid, its frozen.

  11. Nigel Depledge

    @ Electro (10) –


    Just one more question – how? By which I mean how could a body left in the vacuum of space (without direct sunlight) desiccate rapidly?

    Bear in mind I’m not saying that bodily fluids will stay fluid, I simply think they’ll stay put. Mostly.

  12. Electro



    I was going to delete this entire reply because really, I am far from an expert at any of the relevant disciplines at play here.
    I simply approached it as a fun hypothetical and did not mean to speak from any position of authority on the subject.

    Having said that, I will leave my original reply as is.


    Touche…. I will concede your point that (mostly) they will stay put.
    ( Insofar as the immediate area, anyway ).
    However, almost all of these compounds will expand.

    Even through cellular membranes, I cant think of any bodily fluids that would not flash to vapor at that pressure and temperature.
    Direct sunlight or not, the body itself is an enormous source of thermal energy.

    I don’t think our intrepid team from CSI: Pluto would have any trouble describing a solid body amid a cloud of gas and vapor as dessicated. 😉


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