Coin-sized camera spots distant planets express
The camera lens is no bigger than a quarter. You'd find it in a smartphone, but here it was mounted on the Hayabusa2 probe for asteroid landings. Yet scientists asked it to gaze afar (and the little thing pulled off the transit method (watching a planet cross its star's disk and slightly dim its light) for the first time, spotting exoplanets) worlds around other suns.
The camera caught the shadows of two scorching gas giants. Their passages caused brightness dips of mere fractions of a percent, like a chandelier's glow momentarily flickering as a mosquito flits by. By repeatedly capturing eclipses, astronomers stacked the signals and performed precise photometry (light measurement). One planet's orbital period had to be corrected — the discrepancy with earlier data was too large to ignore.
This success proves you don't need giants to hunt for worlds. Sometimes a baby camera is enough. The real twist? The instrument was built for navigation during landing on asteroid Ryugu, not astronomy. Now miniature tools can blaze a trail to finding long-period planets that big surveys miss.
Original abstract
as written by the authors arXiv:2510.14229
Observations of exoplanet transits by small satellites have gained increasing attention for reducing detection biases. However, no unambiguous detection of an exoplanet has yet been demonstrated using optics with apertures smaller than 60 mm. Here, we investigated the detectability of exoplanet transits using the telescopic Optical Navigation Camera (ONC-T) onboard the Hayabusa2 spacecraft, which has an effective aperture of only 15 mm. We conducted transit observations of the hot Jupiters WASP-189 b and MASCARA-1 b, collecting data for ten and four events, respectively. The transit signal was detected with a signal-to-noise ratio (SNR) of 13 for WASP-189 b and 8 for MASCARA-1 b for each event. Stacking all events improved the SNR to 40 and 16, respectively. The transit mid-times of each event were measured with a precision of 6 minutes and were consistent with Transiting Exoplanet Survey Satellite (TESS) data to within 2 minutes. The planet-to-star radius ratio was determined with an absolute precision of 0.004 (6% relative) and agreed with TESS results to within 0.002 (3% relative). The recent ONC-T and TESS data enabled an update to the planetary ephemerides. We report a 4 sigma discrepancy between the updated orbital period of MASCARA-1 b and previously reported values. ONC-T sets a new record for the smallest-aperture instrument to detect an exoplanet transit from space, advancing the frontier of exoplanet science with miniature instrumentation. Our results suggest that optics as small as ONC-T may be capable of detecting transiting long-period Jupiters: a population that remains underrepresented in current surveys.
The ONC-T camera was originally built for navigation during landing on asteroid Ryugu — now it's snagged an astronomical record.