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What wavelengths of light are used/most suited to search for distant solar system objects like KBOs and Oort cloud members? I suppose they are brightest in reflected sunlight, so they are best searched for in visible and near infrared. Is that correct?

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  • $\begingroup$ The Spitzer Space Telescope has been used to observe KBOs. Its instruments cover a range from 3 to 180 microns (mid to far infrared). $\endgroup$ – aventurin Sep 2 '17 at 22:45
  • $\begingroup$ @aventurin Do you know if it was also used to search for new KBOs, or just making observations on known ones? $\endgroup$ – JanKanis Sep 3 '17 at 11:57
  • $\begingroup$ I don't know, but it seems that SST has not found any new KBOs to date. $\endgroup$ – aventurin Sep 3 '17 at 20:30
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Virtually all KBO searches use mosaic CCD cameras operating in the visible part of the spectrum, usually with a red filter like SDSS-r' (centered at approx. 622nm SDSS filters) on big (~4m telescopes). This is what we did with the OSSOS survey I was (lightly) involved with (http://www.ossos-survey.org/about.html). Although cold KBOs are brightest in the infrared, the background from the atmosphere is much higher which means you are less sensitive, unless you go to space (very expensive).

Also IR detectors are smaller and less sensitive than optical CCDs and much harder to make into mosaic cameras and keep cold (to increase sensitivity). This means you can't cover as much sky area per night which makes finding rare and faint KBOs much slower. A CCD and red filter is a good balance between brightness of the objects you are looking for, the sensitivity of your detector (CCDs get less sensitive as you move more to the red or blue of the green-red central part of the optical spectrum) and a low background from the atmosphere.

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  • $\begingroup$ Great answer. Do you know why KBOs are brightest in infrared? Is that thermal radiation or reflected infrared sunlight? $\endgroup$ – JanKanis Jul 21 '18 at 8:12
  • $\begingroup$ Because they are so cold (approx. 50 Kelvin), the peak of the blackbody radiation is well out in thermal infrared around 60 microns $\endgroup$ – astrosnapper Jul 21 '18 at 16:51

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