Could a Telescope Resolve a Person’s Face on Pluto? An Exploration of Limitations and Possibilities
For those fascinated by the possibility of discovering life on another planet, the question often arises: could a powerful enough telescope capture a human face on a distant planet like Pluto? The answer is intriguing and involves the interplay between optical interferometry, light gathering power, and the resolving power of telescopes.
Introduction to Optical Interferometry
Optical interferometry is a technique that pools data from multiple small mirrors to create a single, extremely powerful observational instrument. Seth Shostak, chief astronomer at SETI, has envisioned a tremendous optical interferometry space telescope array capable of imaging exoplanets nearly 100 light-years away with 2-meter resolution. Theoretically, with a resolution this fine, the size of a Honda Accord on Pluto would be visible from Earth. However, the practical limitations of current technology and the physics of light itself present significant challenges.
Limitations of Optical Telescopes
Even the largest optical telescopes are constrained by the intrinsic limitations of light and the design of the telescope. The amount of light collected by a telescope, known as its light gathering power, is essential for resolving details on distant objects. The resolving power, on the other hand, is a measure of how small an angle the telescope can detect accurately.
Light Gathering and Resolving Power
The resolution of any telescope can be modeled using the formula:
θ 1.22 λ / D
where θ is the angle of resolution, λ is the wavelength of light, and D is the diameter of the telescope. For visible light (λ ≈ 500 nm), a telescope with a diameter of 10 meters would yield a resolution of about 0.00000001 radians, or 0.000005 seconds of arc. However, the limitations of the telescope size and the waveriness of light result in a practical lower limit.
Interferometric Arraying
By combining data from multiple small telescopes, interferometry can effectively create a large telescope with a much larger effective diameter. The Very Large Array (VLA), for example, achieves an effective diameter of about 36 kilometers by combining signals from multiple radio telescopes. This technique can theoretically achieve resolutions much finer than those achievable with a single telescope.
Practical Challenges and Future Prospects
While interferometric arrays can push the limits of resolution, the light-gathering power of these arrays is still a limiting factor. The signal-to-noise ratio (SNR) is critical in astronomical observations. On a sunny day, the Earth receives about (10^{21}) photons per second. To capture a meaningful image, especially of a small and dim object like a person, the array would need to be extremely large.
To capture a person-sized object on Pluto at a distance of approximately 39.5 astronomical units (AU), the effective area of the telescope array would need to be several thousand times the Earth's surface area. This requires an array spread over a region the size of Earth's orbit, which is challenging but not necessarily impossible with advanced technology.
Another approach would be to use extremely long exposures, as the Hubble Deep Field image demonstrates. By capturing data over a long period, even a person-sized object could be discerned, but the practical implementation would require overcoming significant technical and logistical challenges.
Conclusion
While the idea of seeing a person’s face on Pluto with a powerful telescope is compelling, it faces formidable technical and physical limitations. Current and future advances in optical interferometry and telescope technology may bring us closer to such a goal, but capturing a clear, detailed image remains a challenge. Nonetheless, the exploration of these challenges drives scientific innovation and pushes the boundaries of our understanding of the universe.