08-03-2026, 05:50 PM
The 30% is just an estimate. I don't know how astronomers will use the TMT if it's built in La Palma. The site is not high enough to observe efficiently beyond a wavelength of around 2.3 microns (that's the upper limit for what's called the "near infrared". Water vapor then starts absorbing infrared radiation beyond that wavelength, then methane kicks in around 3.3 microns, and CO and CO2 also kick in, meaning there are discrete wavelength regimes you can observe the sky but they involve complicated observing techniques to carry them out. The longer the wavelength, the more the sky background caused by our atmosphere increases to the point where the sky is much brighter than any object you want to observe, sometimes hundreds or thousands of times brighter.
You can overcome this by certain observing techniques which are only possible at the driest observing sites: Mauna Kea, some places in Chile and the Antarctic. The idea is to continually "chop" your secondary mirror, i.e., move it between two positions at ~10 Hz while also "nodding" the telescope every 10 or so seconds. The time varies depending on the type of observation, but those are typical times.
At La Palma, you won't be able to do that because you're looking through too much atmosphere and the mid-IR light from the target will be absorbed by the atmosphere no matter what you do. It's why the JWST is so special; it's carrying out mid-IR observations and has no atmosphere to worry about. Another issue is that because the sky is so bright, your infrared detector will become saturated by the sky in milliseconds, so you have to use very short exposures, take many of them, and then make sure you can time those with the frequency of the secondary mirror chopping at ~10 Hz. Technically, it's very complicated and challenging but very rewarding when you get it to work!
The next question is: why do you need to observe in the mid-infrared? Well, if you want to observe stars being born, those are the wavelengths that penetrate through molecular clouds in space where stars are formed. Measuring the brightness of objects at those wavelengths tells you their spectral energy distribution; therefore, their temperature and the environment they are in. Given the expansion of the universe, the emission of hydrogen lines is sometimes shifted into the infrared due to the Doppler effect. Mid-IR observations also allow observations of colder objects such as brown dwarfs and exoplanets. Finally, most of the complex organic molecules that indicate life have spectral features that are in the mid-infrared, so you need to be able to look beyond 2.3 microns for those molecules.
Swift rescue mission update:
Spin rate of rescue satellite has been cut in half.
https://arstechnica.com/space/2026/08/he...t-mission/
You can overcome this by certain observing techniques which are only possible at the driest observing sites: Mauna Kea, some places in Chile and the Antarctic. The idea is to continually "chop" your secondary mirror, i.e., move it between two positions at ~10 Hz while also "nodding" the telescope every 10 or so seconds. The time varies depending on the type of observation, but those are typical times.
At La Palma, you won't be able to do that because you're looking through too much atmosphere and the mid-IR light from the target will be absorbed by the atmosphere no matter what you do. It's why the JWST is so special; it's carrying out mid-IR observations and has no atmosphere to worry about. Another issue is that because the sky is so bright, your infrared detector will become saturated by the sky in milliseconds, so you have to use very short exposures, take many of them, and then make sure you can time those with the frequency of the secondary mirror chopping at ~10 Hz. Technically, it's very complicated and challenging but very rewarding when you get it to work!
The next question is: why do you need to observe in the mid-infrared? Well, if you want to observe stars being born, those are the wavelengths that penetrate through molecular clouds in space where stars are formed. Measuring the brightness of objects at those wavelengths tells you their spectral energy distribution; therefore, their temperature and the environment they are in. Given the expansion of the universe, the emission of hydrogen lines is sometimes shifted into the infrared due to the Doppler effect. Mid-IR observations also allow observations of colder objects such as brown dwarfs and exoplanets. Finally, most of the complex organic molecules that indicate life have spectral features that are in the mid-infrared, so you need to be able to look beyond 2.3 microns for those molecules.
Swift rescue mission update:
Spin rate of rescue satellite has been cut in half.
https://arstechnica.com/space/2026/08/he...t-mission/