Among the space telescopes that have been launched, the Hubble Space Telescope has attracted much attention for its excellent observation capabilities and rich scientific achievements, but this has quietly changed after the launch of the James Webb Space Telescope.
To understand this more intuitively, the Webb telescope has more advanced technology and more powerful observation capabilities than the Hubble telescope, and it provides more accurate and detailed cosmic observations than the Hubble telescope with a larger aperture and wider band coverage.
This is a classic image taken by the Hubble Telescope – the "Pillar of Creation" located in the Eagle Nebula about 6,500 light-years away:
This is the "Pillar of Creation" photographed by the Webb Telescope in 2022:
We can clearly see that the Webb telescope is significantly more powerful than the Hubble telescope, and the photos taken by it show more detail and are much clearer. Because of this, after the launch of the Webb Space Telescope, it quickly occupied an important place in the field of exploring the universe, and its name gradually became familiar to us.
Maybe we can think that since the Webb Space Telescope is so powerful, it should also be much clearer than the Hubble Telescope? But is that really the case? Let's take a look at the picture.
Here's what Hubble captured from Mars in 2016:
It can be seen that the clarity of this image of Mars taken by the Hubble telescope is not very high, and it can only show some rough outlines of the Martian surface, and does not fully show the details of the Martian surface.
However, the Webb telescope captured Mars like this:
This is an image of Mars taken by the Webb telescope on September 5, 2022, and it can be seen that the Mars captured by the Webb telescope can be said to be blurry, while the Mars captured by the Hubble telescope is much clearer in comparison. So the question is, why can't the famous James Webb Space Telescope even shoot Mars?
Could it be that its equipment is malfunctioning? The answer is no, in fact, the reason for this is actually because the Webb telescope is not designed for visible light-based imaging of Mars.
To put it simply, the Webb telescope has a number of major missions, including "detecting the first stars and galaxies in the universe", "studying the formation and evolution of galaxies, stars and their planetary systems", "studying the atmospheric composition of exoplanets", "exploring possible signs of life on exoplanets", and so on.
To accomplish these tasks, the Webb telescope was designed to emphasize its outstanding deep space exploration capabilities. For the Webb telescope, it observes electromagnetic waves with a wavelength of 600-28300 nanometers, in this range, in fact, only a few wavelengths of visible light (such as orange light, red light), and the rest are infrared.
There are three main reasons for this: first, the wavelength of infrared rays is longer than that of visible light, and it can more easily pass through the gas and dust dispersed in the universe; second, those objects with lower temperatures in the universe (such as exoplanets) mainly release radiation in the infrared band; third, the light emitted by those distant celestial bodies in the universe will be redshifted due to the expansion of the universe during propagation, and then converted into infrared rays.
In order to detect as much information as possible in the depths of the universe, the Webb telescope is designed to be extremely sensitive to electromagnetic waves, but this design also has the disadvantage of being prone to "detector saturation" if the light source is slightly stronger.
The so-called "detector saturation" refers to the state when the detector is irradiated by an excessively strong light source, its response reaches its maximum processing capacity, in this state, the output signal of the detector no longer increases linearly with the increase of the input signal, but tends to be fixed, which will lead to serious distortion of the observation data, a large decrease in the signal-to-noise ratio, etc., and if it is in this state for a long time, it may lead to permanent damage to the detector.
For the Webb telescope, Mars is actually a very strong light source, so when photographing Mars, in order to avoid the Webb telescope "detector saturation", people can only greatly reduce the exposure time, and only measure a small part of the light it receives.
Relatively speaking, the Hubble telescope observes electromagnetic waves with a wavelength of 100-1000 nanometers, which actually includes all the bands of visible light, in addition, the Hubble telescope has a smaller aperture, and its sensitivity to electromagnetic waves is not as high as that of the Webb telescope, so the Hubble telescope is relatively more suitable for visible light-based imaging of Mars, and the Mars it captures is of course much clearer.