Space often appears calm and empty to the naked eye. In reality, our planet moves through a crowded cosmic environment filled with rocks and debris traveling at tens of thousands of kilometers per hour. Scientists now acknowledge an uncomfortable truth: the greatest danger is not from the giant asteroids we already track, but from the ones we have not discovered yet.
According to planetary defense specialists, many of these objects are large enough to destroy an entire metropolitan area. Humanity has tested technology capable of deflecting them — but does not yet have a ready-to-use defense system.
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The real threat: the unknown objects
NASA planetary defense expert Kelly Fast explained during a meeting of the American Association for the Advancement of Science that extinction-level asteroids are not the most immediate concern. Nor are the tiny meteors that burn in the atmosphere every day.
Instead, scientists fear mid-size bodies roughly 150 meters wide — about the size of a skyscraper. These are often called “city killers.” An impact would not wipe out humanity but could devastate a region the size of a major city and cause massive economic and humanitarian consequences.
Astronomers estimate there are about 25,000 such near-Earth objects. Only around 40 percent have been identified and tracked. The rest remain effectively invisible, often approaching from the direction of the Sun or reflecting very little light.
A new telescope to find the invisible
Traditional observatories rely mainly on visible light, making dark asteroids difficult to detect. NASA plans to address this blind spot with the upcoming Near-Earth Object Surveyor space telescope.
Instead of reflected sunlight, it will detect heat signatures. That means even black or dim asteroids — currently hidden — should become visible.
Researchers believe this mission could dramatically improve planetary defense by identifying most hazardous objects years or decades earlier than before.
Technology proven, readiness missing
In 2022 NASA carried out the historic DART mission. A spacecraft deliberately struck the asteroid moonlet Dimorphos at about 22,500 km/h and successfully changed its orbit.
The experiment confirmed deflection works.
However, mission leaders warn that no standby interception spacecraft currently exists. Planetary defense remains a research capability rather than an operational emergency system.
The problem is political, not scientific
Experts emphasize the main barrier is funding and coordination, not engineering. A real defense network would require prepared spacecraft, rapid launch capability, and international decision protocols — essentially a global disaster-response infrastructure for space threats.
Without early detection and immediate action capability, even a preventable impact could become unavoidable.
A ticking cosmic clock
The issue is not theoretical. Astronomers are tracking asteroid YR4, which has a roughly four-percent chance of striking the Moon in 2032. While Earth is safe in this case, it demonstrates how real near-term celestial risks can be.
As a last-resort scenario, scientists have discussed nuclear disruption — similar to science-fiction movies — but no operational plan exists.
Early warning determines survival
Humanity now possesses the knowledge to alter an asteroid’s path. What it lacks is preparedness and reaction time.
The greatest danger is therefore not an asteroid impact itself, but discovering it too late.