The Telescopes That Find and Study Small Bodies

Survey telescopes: the finders

A survey telescope is built for coverage, not for pretty pictures. It takes many short exposures of wide areas and compares them for movement. The Catalina Sky Survey, run by the University of Arizona's Steward Observatory, uses three telescopes in the mountains near Tucson, Arizona.

• A 1.5-meter (59-inch) survey telescope on Mt. Lemmon covers about 1,000 square degrees of sky per night, down to a brightness of magnitude 21.5.
• A 0.7-meter (28-inch) Schmidt telescope on nearby Mt. Bigelow covers about 4,000 square degrees per night, down to magnitude 19.5.
• A 1.0-meter (40-inch) follow-up telescope on Mt. Lemmon, run remotely, revisits 40 to 80 near-Earth objects a night to confirm and refine them.

The smaller telescope covers four times more sky because of its wider field of view. Bigger does not always mean better for finding things, and the two telescopes together balance depth and coverage. Catalina's record includes the asteroid 2008 TC3, a second asteroid called 2014 AA that was found on the last day of 2013 and struck the Atlantic Ocean about 21 hours later, and more than 570 comets.

Pan-STARRS, in Hawaii, pairs two 1.8-meter (71-inch) telescopes on the summit of Haleakalā on Maui. Most of its observing time goes to the search for potentially hazardous asteroids, with support from NASA's Near-Earth Object Observations program. The guide to near-Earth asteroids explains what that label means and how large the known population is.

Rubin: the newest finder

The NSF-DOE Vera C. Rubin Observatory is in Chile and is operated jointly by NSF NOIRLab and the Department of Energy's SLAC National Accelerator Laboratory. Its telescope carries a 3,200-megapixel camera, which NSF describes as the largest digital camera in the world. It takes a new image roughly every 40 seconds, about 1,000 images per night, and produces about 10 terabytes of data every night.

NSF announced on June 30, 2026 that the ten-year Legacy Survey of Space and Time had officially started. The plan is to image the entire southern sky every few nights and return to each point about 800 times. Early test runs lasting about a month and a half already found over 11,000 previously unseen asteroids, including 33 near-Earth objects and about 380 trans-Neptunian objects, which are small bodies beyond Neptune. All of that came before the survey officially began.

Rubin looks at the southern sky, while Catalina in Arizona and Pan-STARRS in Hawaii observe from the north, so their coverage overlaps only in part. What happens after a detection, from the first report to a confirmed orbit, is covered in the guide to how minor planets are discovered.

Infrared from space: NEOWISE

Visible-light telescopes have trouble with very dark asteroids, which reflect little light. An infrared telescope senses the heat a body radiates, which helps astronomers estimate its size and how dark its surface is. NASA's NEOWISE spacecraft did this work from orbit. Its reactivation mission ended operations on August 8, 2024, and its final data set covers December 13, 2023 to August 1, 2024.

Over its 10.6 years of survey operations, NEOWISE scanned the sky 21 times, with about six months between passes. The public archive holds about 26.9 million sets of images at two infrared wavelengths and about 199 billion source detections, all available through NASA/IPAC's Infrared Science Archive. Anyone can still use that archive for research.

Webb: a close reader

The James Webb Space Telescope is not a survey instrument. According to NASA, its large mirror and sensitivity to infrared light make it easier to see small, faint bodies such as Kuiper Belt objects, comets, asteroids and centaurs. Webb collects reflectance spectra, which show which wavelengths of light a surface absorbs. Those spectra reveal what a surface is made of. They can also show whether ice is amorphous, crystalline or irradiated, a hint at the object's temperature history.

NASA lists several results. Webb's NIRSpec instrument confirmed water vapor around Comet 238P/Read, a comet that orbits in the main asteroid belt. It captured the DART impact on Dimorphos. It also caught the shadows of starlight cast by the thin rings of the centaur Chariklo, and found a crystalline-ice signature there for the first time. The method behind those ring shadows is explained in the guide to stellar occultations. Webb has one limit: it cannot observe objects that lie between it and the Sun. How spectra turn into composition is covered in the guide to how we know what asteroids are made of.

Radar: shape, spin and orbits

Radar sends a radio beam at an asteroid and listens for the echo. According to JPL, depending on an object's size and distance, radar can image its surface in fine detail and measure its size, shape, spin rate and whether it has moons. Radar ranging also improves orbit knowledge, so that predictions of future motion can reach decades or centuries ahead.

The workhorse in the United States has been the Goldstone Solar System Radar in California, part of NASA's Deep Space Network. JPL reported in September 2021 that its 70-meter (230-foot) dish, Deep Space Station 14, and a 34-meter (112-foot) dish had observed 374 near-Earth asteroids. The 1,000th near-Earth asteroid observed by planetary radar since 1968 was 2021 PJ1, on August 14, 2021. The 305-meter (1,000-foot) Arecibo telescope in Puerto Rico had observed well over half of all radar-detected asteroids before it was damaged and decommissioned in 2020 and collapsed soon after.

Common mistakes and myths

"A bigger mirror always finds more asteroids." Field of view matters as much. Catalina's smaller 0.7-meter telescope covers four times as much sky per night as its 1.5-meter telescope, although it does not go as deep.

"Webb finds the asteroids that could threaten Earth." Webb is not a survey machine, and it cannot observe objects between it and the Sun. The sky watching is done by wide-field survey telescopes. Webb studies objects that are already known.

"Radar finds new asteroids." Radar needs a position that a survey has already provided. It then measures the object in detail. JPL's 2021 report describes it as a tool for characterizing near-Earth asteroids after discovery.

"Amateurs cannot compete with professionals." The survey projects work at a scale amateurs cannot match, but volunteers can inspect images and report measurements, as described in the guide to citizen science for asteroids and comets. Anyone using a home telescope should never point it, or binoculars, at the Sun without a solar filter made for that purpose.

"A telescope that ended is a failed telescope." NEOWISE ended in 2024 after more than ten years, and its archive is still in use.

Frequently asked questions

Which telescope has found the most near-Earth asteroids?

Catalina and Pan-STARRS are both dedicated near-Earth surveys, and both have long track records. Exact counts by survey change every month, so NASA's discovery statistics page for near-Earth objects is the place to check the current numbers.

Does Rubin see the whole sky?

No. It observes the Southern Hemisphere sky from Chile, covering the entire southern sky every few nights. Northern surveys cover what Rubin cannot.

What happened to NEOWISE?

NASA ended its operations on August 8, 2024. The data it collected remain available in the NASA/IPAC Infrared Science Archive.

Can a home telescope help with small bodies?

It can, within limits. The Minor Planet Center accepts position measurements from observers, and several projects invite volunteers to review survey images without any equipment.