Earth-like planets are lost in the glare of their host stars, and it is impossible to observe them directly with existing instruments. Scientists have proposed a workaround based on the properties of individual particles of light. Calculations suggest that this method could separate two sources that merge into a single spot for an ordinary camera. So far, the idea has been tested only in a computer model.
The Rayleigh Limit
When two light sources are located too close to one another, their rays merge into a single blurred spot. The smallest angular distance at which they can still be distinguished is known as the Rayleigh limit. For an exoplanet, this means that its signal is completely overwhelmed by the radiation of its host star, while a conventional detector records only the arrival of radiation and cannot determine its origin.
In quantum optics, a photon is described in much greater detail. In addition to energy, the shape of its own wave is encoded within it, and this property can be measured separately. If particles are sorted according to the shape of their waves before they reach the detector, information unavailable to an ordinary camera becomes accessible.
Adaptive Sorting
The first author of the paper was Hyeonsu Choi of Hanyang University in Seoul, while the co-authors included researchers from South Korea and the United States. They posted their work on arXiv, so the findings have not yet undergone formal peer review. The calculations were described by Universe Today.
The essence of the approach is that the set of wave shapes is not fixed. The separator is adjusted during the observation itself in order to extract the maximum amount of quantum information from each captured particle of light.
The difference in brightness between a star and a planet is so great that a conventional scale is unsuitable, so the calculations are performed in logarithmic coordinates. The algorithm determines the number of objects in the system on its own, based on counting statistics and the Bayesian information criterion. Previously, this stage depended on a human assumption about how many planets should be sought.
Testing the Model
For testing, the researchers created a virtual system consisting of one star and two planets. One was ten thousand times fainter than the host star, while the other was one hundred million times fainter, and both were located too close to the star to be separated by conventional means.
Repeated runs with slightly different initial conditions, using the Monte Carlo method, showed that the correct number of objects was identified in 72.5% of cases. In successful trials, the planets’ positions were determined with an accuracy of one pixel, while the brightness of the faintest planet was estimated within a factor of two of the true value in 99.7% of those runs.
The researchers also examined what would happen if there were calibration errors. The alignment of the simulated telescope was deliberately disturbed, and the success rate fell only to 71.3%. Real instruments produce many more sources of noise, so the method’s effectiveness under actual conditions remains unknown.
The Contrast Gap
The key parameter here is contrast—that is, how many times fainter the planet is than its star. Previous quantum schemes worked with brightness differences of approximately one thousand times, whereas the new method, according to the calculations, remains effective even when the difference reaches one hundred million times.
An Earth-like planet orbiting a Sun-like star is approximately ten billion times fainter, so even this advance still leaves a gap of two orders of magnitude. This is the level targeted by the future Habitable Worlds Observatory, which NASA hopes to launch in the 2040s.
The physical implementation of such schemes usually lags behind theory by years. No ready-made instrument capable of sorting particles of light by modes with this level of precision currently exists.
