NASA Reclassifies Hidden Comet Mistaken as Asteroid for Decades
- Object 2000 SG344 was thought to be an asteroid but is now confirmed as a dark comet.
- The comet has no visible tail, making it hard to detect with standard surveys.
- NASA says studying dark comets can improve planetary defense against potential threats.
A Decades-Long Mistake Uncovered
For nearly three decades, astronomers classified a small near-Earth object as an asteroid. NASA now says it is actually a comet — a 'dark comet' that has been hiding in plain sight.
The object, known as 2000 SG344, was first spotted in 2000. It measures roughly 40 to 100 metres across. Its orbit brought it close to Earth, and scientists initially labelled it a potentially hazardous asteroid.
New observations using the James Webb Space Telescope and ground-based instruments revealed something unexpected. The object showed signs of outgassing — the release of gas and dust typical of comets, not inert asteroids.
What Makes a Dark Comet Different
A dark comet is an object that behaves like a comet but lacks the bright tail that makes comets easy to spot. It is covered in dark, carbon-rich material that absorbs sunlight. This makes it nearly invisible to optical telescopes.
2000 SG344's tail, if it has one, is too faint to see. The outgassing was detected only through infrared and spectral analysis. This explains why the object was misidentified for so long.
NASA's Jet Propulsion Laboratory led the study. Researchers found that the comet's orbit had shifted slightly, but not due to gravitational forces. The change matched the pattern caused by cometary outgassing.
Implications for Planetary Defence
The discovery has direct consequences for planetary defence. Dark comets are harder to detect than asteroids or bright comets. If such an object were on a collision course with Earth, current warning systems might miss it.
NASA's Planetary Defense Coordination Office tracks near-Earth objects. It relies on optical telescopes that search for reflected sunlight. Dark comets reflect very little light, so they can slip through the net.
Scientists now say that the number of dark comets may be higher than previously thought. Some estimates suggest they could make up 10 to 20 percent of all near-Earth objects. If accurate, this means the current catalogue of potentially hazardous objects is incomplete.
New Detection Strategies Needed
NASA is already working on new methods to find dark comets. Infrared telescopes, both space-based and ground-based, can pick up the heat signature of these objects. The NEO Surveyor mission, set to launch in the late 2020s, is designed to spot such dark objects.
The study also highlights the value of revisiting old data. Many objects originally classified as asteroids may need to be re-examined with modern instruments. This could reveal more dark comets hiding in the existing catalogue.
Dr. Joseph Masiero, a scientist involved in the study, said that the findings force a rethink of how we classify and monitor small bodies in the solar system. He added that nature does not always fit neatly into categories created by humans.
What Comes Next
NASA plans to conduct a broader survey of known near-Earth objects using infrared telescopes. The goal is to identify other dark comets that may have been misclassified. The agency is also developing algorithms to detect outgassing patterns from existing data.
For now, 2000 SG344 poses no threat to Earth. Its orbit is well understood, and it will not come dangerously close for decades. But the lessons from its reclassification will shape how we prepare for the next object that may not be what it seems.