Comets around an alien star reveal their sizes express
The TESS telescope, usually hunting for planets around other stars, spotted 24 dimmings around RZ Psc. These were comets — chunks ranging from 1 to 7 km in size, transiting the star's disk. Like a distant searchlight momentarily blocked by a tiny pebble: the deeper the shadow, the larger the object. This is how, without a direct image, they measure their diameter (transit method).
Among the comet flock in RZ Psc, small bodies far outnumbered large ones — exactly like in the dusty Kuiper Belt on the outskirts of our Solar System. This break in the size distribution hints that the birth of icy boulders follows a single scenario around many stars.
The data inspire the launch of the EVE telescope. By measuring the brightness of thousands of young stars in different colors (photometry from ultraviolet to infrared), it will not just count comets by the hundreds, but also determine what they are made of. This 'spectroscopy without a spectrograph' will reveal the chemistry of distant worlds — for instance, whether they contain graphite dust grains, cousins of our pencil lead.
Original abstract
as written by the authors arXiv:2510.09920
We present the TESS discovery of only the second system of transiting exocomets with a sufficient number of events to measure the size distribution in the RZ Psc system, enabling comparisons with the $$\beta$$ Pictoris and Solar System size distributions. Twenty-four transits with absorption depths (AD) of 1--20\% were observed across three TESS sectors of the 20-50 Myr K0V star, detected as part of our TESS survey of extreme debris disks identified by their IR excess. We discover that the ADs (and hence exocomet radii) follow a broken power-law cumulative frequency distribution not previously seen in extrasolar contexts but similar to that observed in Solar System Kuiper Belt Object sizes, with power-law slopes above and below the break of $$\gamma_\mathrm{AD>break}$$=2.32$$\pm$$0.12 and $$\gamma_\mathrm{AD
Some of these comets may be composed of graphite, the same material as pencil lead, and others of olivine, like that found in gemstones.