Scientists estimate that around 15,000 medium-sized asteroids — large enough to devastate a city — remain undetected within striking distance of Earth, News.Az reports, citing The Sun.
According to Dr. Kelly Fast, Planetary Defense Officer at NASA headquarters, these mid-sized space rocks pose the greatest concern.
Speaking at the American Association for the Advancement of Science (AAAS) conference in Arizona, Fast said, “What keeps me up at night is the asteroids we don’t know about.”
In 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully demonstrated that a spacecraft could deliberately crash into an asteroid to alter its trajectory in an emergency. However, mission leaders caution that such capabilities are not currently ready for rapid deployment if a real threat emerges.
Dr. Nancy Chabot, DART mission coordination lead at Johns Hopkins University in Maryland, said the risks remain significant.
“We worry about these city killer asteroids,” she said. “DART was a great demonstration, but we don’t have that sitting around ready to go if there was a threat we needed to use it for.”
Chabot noted that scientists still do not know the locations of roughly 50% of asteroids measuring around 140 meters in diameter — a size capable of causing severe regional destruction.
“We would not have any way to go and actively deflect one right now,” she said. “We could be prepared, but I don’t see that investment being made.”
She added that space agencies currently lack sufficient funding to maintain planetary defense systems at a constant state of readiness.
“Small stuff is hitting us all the time so we’re not so much worried about that.
“And we’re not so worried about the large ones from the movies because we know where they are.
“It’s the ones in between, about 140 metres and larger, that could really do regional rather than global damage and we don’t know where they are.
“It’s estimated there are about 25,000 of those and we’re only about 40 per cent of the way through.
“It takes time to find them, even with the best telescopes.”
Nasa is launching a mission called Surveyor in 2027 in a bid to find at least 90 per cent of asteroids measuring wider than 140m within a decade.
