The Tiniest Objects Visible from Satellite Photos and Space Telescopes
When it comes to identifying the smallest objects visible in both satellite photos and space telescopes, the answer is not straightforward. It depends on the type of satellite or telescope, the resolution, and the wavelength of light being observed. Let's delve into the intricacies of what we can see from the vantage points of commercial satellites, military satellites, and space telescopes.
Smallest Objects Visible from Satellite Photos
The smallest objects typically visible from satellite photos vary depending on the resolution of the satellite imagery. As of my last knowledge update in August 2023:
Commercial Satellites
High-resolution commercial satellite imagery, such as that from companies like Maxar or Planet Labs, can resolve objects down to about 30 centimeters (approximately 1 foot) in size. This means that objects like cars, small buildings, and large trees can be seen clearly. These satellites provide high-resolution imagery that is widely used for various applications, including urban planning and environmental monitoring.
Military Satellites
Some military satellites may have even higher resolutions, potentially detecting objects smaller than 10 centimeters (about 4 inches). However, such details are not usually publicly available, as military applications require stringent confidentiality.
Google Earth and Other Platforms
The imagery available through platforms like Google Earth is often lower resolution, with some images resolving down to about 1 meter (3.3 feet). This resolution is less detailed than what commercial satellites can provide, but it is still useful for a wide range of applications, including amateur observations and simple monitoring.
Smallest Objects Visible from Space Telescopes
While not exactly a telescope, the Space Surveillance Radar known as "Space Fence" can detect and track objects in Low Earth Orbit (LEO) as small as a marble. This demonstrates the remarkable precision of radar technology in detecting small objects in orbit.
For natural objects, the smallest quasi-moons, or natural moons temporarily caught in Earth's gravity, have been observed to be just a couple of meters in size. These objects are often transient and disappear quickly as they are influenced by Earth's gravity.
Artificial objects, such as CubeSats, can be observed to be as small as the standard CubeSat dimensions of 11x110 cm (approximately 4.33x3.94x3.94 inches).
Theoretical and Practical Limits
The question of what the best resolution for an orbital telescope can be answered by considering the theoretical and practical limits of optical systems. The theoretical resolving limit of any optical system is a function of the aperture and wavelength observed and is either the Rayleigh limit or Davies-Berry limit, depending on how you're defining the discernible separation of two point sources.
Using these theoretical limits, we can discuss the performance of some of the best telescopes in orbit:
JWST vs. Hubble
The James Webb Space Telescope (JWST), with a 6.25m diameter mirror, has a theoretical resolution of 1/10th (0.1 arcsecond) in the near-infrared. This is slightly worse than the Hubble Space Telescope's 2.4m mirror, which resolves down to 1/20th (0.05 arcsecond) in the visible spectrum. However, both telescopes are comparable in terms of spatial resolution.
To put this into perspective, Pluto appears as a dot with an angular diameter ranging from 0.06 to 0.1 arcseconds as seen from Earth. A 0.5 arcsecond resolution, which is about the limit for these telescopes, means that a human could theoretically read the letters of a stop sign at a distance of 12 miles or read a 1-centimeter newspaper headline at half a mile away.
It's important to note that the actual resolution depends on the brightness of the target object and whether the target is visible within the range of the telescope. Pluto, for example, is not visible in x-rays at all, while gas clouds that are opaque to visible light are transparent in the near-infrared, allowing the JWST to see into nebulae with similar resolution.
Conclusion
The answer to the smallest object visible in satellite photos and space telescopes is not a simple one. It depends on the specific technology, the resolution, the wavelength of light, and the target object itself. High-resolution commercial satellites can detect objects as small as 30 centimeters, while military satellites might be able to detect objects as small as 10 centimeters. Space telescopes, like the JWST, have a theoretical resolution limit of about 0.1 arcseconds and can provide incredible detail, but their performance also depends on the visibility and brightness of the target object.
The next time you look at a satellite photo or a space telescopic image, appreciate the remarkable technology that allows us to see the world in such incredible detail. At the same time, remember that the limitations of these tools are a testament to the complexity of the universe around us.