New research led by scientists at NASA’s Jet Propulsion Laboratory in Southern California has revealed the identity of a puzzling near-Earth object by precisely tracking its movement through space and using powerful observatories that image faint celestial objects.

This object has a split personality: Previous images had revealed no obvious comet-like activity, suggesting it could be an asteroid, but its motion was recently shown to be irregular comet-like. The scientists detailed their findings in a study published in the journal Nature Astronomy.

The enigma began on August 28, 2025, when the object, provisionally known as asteroid 1998 SH2, safely passed within 3 million kilometers (2 million miles) of our planet during its four-and-a-half-year orbit around the Sun. Researchers seeking to observe 1998 SH2 with NASA’s Deep Space Network (DSN) planetary radar system had calculated its position using data from previous orbits and taking into account the effects that the Sun’s gravity and the planets would have in their path. But when 1998 SH2 didn’t appear where they expected, they realized that something unexpected had been influencing the object’s movement.

Using optical astrometry to precisely measure the object’s position in the sky, researchers were able to identify the cause.

“After measuring the non-gravitational perturbations affecting the motion of 1998 SH2 and recognizing that they were not consistent with the object being an asteroid, we suspected that the object could be an active comet,” said Davide Farnocchia, a navigation engineer at NASA’s Center for Near-Earth Object Studies at JPL and leader of the study.

Although 1998 SH2’s orbit around the Sun had been well tracked from 1998 to 2016, the object had completed two solar orbits without additional observations by telescopes until the 2025 DSN attempts. By analyzing all observations collected since the object’s discovery in 1998, the researchers determined perturbations in the motion of 1998 SH2 and hypothesized that the object may be generating a small thrust by releasing gas into space, thereby which causes it to deviate from its intended trajectory.

This ventilation is due to the Sun heating the ice mixed with rock material, converting the ice into gas. In normal comets, this activity forms a characteristic bright tail and coma: the gas and dust surrounding a comet’s nucleus. But when an object produces gas and dust in much smaller quantities, its tail and coma may not be detectable by most observatories.

The close approach to Earth of 1998 SH2 in August 2025 provided the perfect opportunity for the paper’s authors to gather observational evidence of visible comet activity. They approached astronomers at the Canada-France-Hawaii Telescope, a 3.6-meter (12-foot) optical/infrared telescope near the summit of Mauna Kea, Hawaii, and the European Southern Observatory’s 1.5-meter (5-foot) Danish Telescope in La Silla, Chile, to observe. Astronomers at the powerful 8.2-meter (27-foot) Very Large Telescope at the powerful European Southern Observatory on Chile’s Cerro Paranal mountain also tracked the object.

“The images we collected from these observatories showed a faint but clear tail, confirming that 1998 SH2 is, in fact, a comet,” said Olivier Hainaut, an astronomer at the European Southern Observatory and co-author of the study. “This is how science works: you formulate a hypothesis and set out to test it. These data are exactly what was needed to confirm our hypothesis that 1998 SH2 was a comet.”

As a result of the investigation, 1998 SH2 will receive an additional provisional comet designation, P/1998 SH2.

The research also sheds light on another, even more unusual class of objects, called dark comets. Like 1998 SH2, dark comets exhibit significant irregularities or perturbations in their trajectory, but lack other visible evidence of comet activity: there is no visible coma, tail, or outgassing. These enigmatic objects are divided into two distinct populations: larger ones with orbits similar to those of Jupiter family comets (short period comets with highly elliptical or eccentric orbits) and smaller ones that orbit closer to the Sun. Since the discovery of the first dark comet in 2016, about a dozen more have been identified.

The authors of the paper suggest that many of the largest dark comets, which have orbits like 1998 SH2, could turn out to be normal comets if astronomers had the right opportunity to observe them with powerful telescopes capable of imaging incredibly faint objects. And by analyzing the motion of all near-Earth objects using precision astrometry data, researchers can reveal more comets that were previously designated as asteroids if they exhibit comet-like non-gravitational perturbations.

“This work shows the importance of continuously tracking near-Earth objects,” Farnocchia said. “Due to outgassing, the motion of comets is perturbed more significantly than that of asteroids. Detecting these perturbations can be an important diagnostic tool for planetary defense that will help understand which objects may be comets rather than asteroids, how their orbits evolve, and how that influences their impact risks on Earth.”

NASA’s upcoming Near-Earth Object (NEO) Surveyor will collect data that can be used to support this effort. This next-generation mission, the first space reconnaissance telescope built for planetary defense, will search for some of the hardest-to-find near-Earth objects, such as dark asteroids and comets that don’t reflect much visible light.

NASA’s Near-Earth Object Studies Center, Goldstone Solar System Radar Group and NEO Surveyor are managed by JPL and supported by the agency’s Planetary Defense Coordination Office in Washington. Caltech in Pasadena manages JPL for NASA. The DSN receives programmatic oversight from the SCaN (Space Communications and Navigation) program office, also at NASA Headquarters.

More information about planetary radar, NASA’s Near-Earth Object Studies Center, and near-Earth objects can be found at:

https://www.jpl.nasa.gov/asteroid-watch

News Media Contacts

Ian J. O’Neill
Jet Propulsion Laboratory, Pasadena, California.
818-354-2649
ian.j.oneill@jpl.nasa.gov

Karen Fox/Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov

2026-046