Every day, Portal Astra's NEOs tab lists asteroids making their closest approach to Earth, complete with distances, speeds, and the occasional alarming red "hazardous" label. It is natural to look at that and feel a flicker of worry. So let us answer the question directly and then back it up: no, you do not need to lie awake over it — but the topic is genuinely fascinating, and the work being done to track these objects is one of the quiet success stories of modern science.
A near-Earth object, or NEO, is any asteroid or comet whose orbit brings it within about 1.3 astronomical units of the Sun, which means it can pass relatively close to Earth's own orbit. The overwhelming majority are asteroids — rocky leftovers from the formation of the solar system 4.6 billion years ago that never coalesced into a planet. NASA's Center for Near-Earth Object Studies (cneos.jpl.nasa.gov) catalogues them all, and the numbers run to tens of thousands.
What "potentially hazardous" actually means
That red label looks scary, but it has a precise and surprisingly un-dramatic definition. A potentially hazardous asteroid, or PHA, is one that meets two specific criteria: it is larger than about 140 metres across, and its orbit brings it within 7.5 million kilometres of Earth's orbit. That distance — about nineteen times the distance to the Moon — is the official threshold, not a prediction of impact.
In other words, "potentially hazardous" is a category for long-term tracking, not an alarm. It means an object is big enough and its orbit close enough that astronomers want to keep a careful eye on it over decades and centuries, because small orbital nudges over very long timescales could eventually matter. It does not mean the object is on a collision course. The vast majority of PHAs will simply sail past, again and again, for the foreseeable future. When Portal Astra flags an asteroid as hazardous, it is reflecting this technical classification, not a warning of imminent danger.
Distance and size in perspective
The "close approaches" in any daily list sound close because space is being described in human terms, but the distances are usually enormous. A typical headline pass might be several million kilometres away. Even a genuinely close pass is often farther than the Moon. The Moon itself sits about 384,000 kilometres away, and most asteroid approaches are many times that. When you read a distance on the NEOs tab, comparing it to the Earth-Moon distance is the quickest way to feel how much room there really is.
Size matters as much as distance. Most objects that come near are small — tens of metres or less — and the truly large ones are rare and exceptionally well tracked. The dinosaur-extinction impactor 66 million years ago was an estimated 10 to 15 kilometres across, in a class of object for which astronomers believe they have already found essentially all the near-Earth examples. None of them is on a threatening path.
How we find and track them
The detective work is genuinely impressive. Networks of survey telescopes, such as the Catalina Sky Survey and Pan-STARRS, scan the sky night after night looking for points of light that move against the fixed stars. When a new object is spotted, its position is reported, more observations refine its orbit, and that orbit is projected forward for decades or longer. The more times an object is observed, the more precisely its future path is known — which is why "newly discovered" objects sometimes carry more uncertainty than ones tracked for years.
This is the same kind of careful, repeated observation that underlies all of practical astronomy, from following an asteroid to following the Moon across a month as we describe in Moon Phases Explained. Continuous monitoring is the whole game. NASA, the European Space Agency, and partners worldwide share data through the Minor Planet Center, and the system has matured to the point where genuinely threatening surprises are increasingly unlikely for large objects.
Planetary defence is now a real, tested capability
Here is the most reassuring part, and it is recent. In 2022, NASA's DART mission — the Double Asteroid Redirection Test — deliberately crashed a spacecraft into a small asteroid called Dimorphos to see whether a impact could change its orbit. It worked: the collision measurably shortened the asteroid's orbital period, proving that a kinetic impactor can nudge an asteroid's path. Dimorphos was never a threat; it was a test target. But the experiment demonstrated, for the first time, that humanity has a working technique to deflect a dangerous object if we ever found one with enough warning.
That combination — comprehensive tracking plus a demonstrated deflection method — is why the scientific consensus is calm. The strategy is to find threats early, because even a tiny orbital change applied years in advance is enough to turn a hit into a miss. Agencies like NASA publish their risk assessments openly, and you can read them; there is no hidden list of imminent dangers.
So, should we worry?
For the timescale of your life, the honest answer is no. The risk from any individual catalogued asteroid is vanishingly small, the large dangerous objects are nearly all found and none threaten us, and we now have both the surveillance and the technology to respond to the rare object that might. What is worth doing instead is appreciating the science. The asteroids drifting past on the NEOs tab are ancient fragments older than any planet's surface, and watching them is a front-row seat to the architecture of the solar system. For the storms that pose a more routine, if still harmless, kind of cosmic weather, The Kp Index and Space Weather, Explained covers the Sun's contribution to our daily sky.
Frequently asked questions:
Q: Does "potentially hazardous" mean an asteroid might hit Earth soon? A: No. It is a tracking classification meaning the object is larger than about 140 metres and its orbit passes within 7.5 million kilometres of Earth's orbit. It flags objects worth monitoring over long timescales, not objects on a collision course. Almost all of them will simply pass by harmlessly.
Q: How close is a "close approach," really? A: Usually millions of kilometres. For comparison, the Moon is about 384,000 kilometres away, and many asteroid passes are several times that distance or much more. A pass that makes headlines for being close is still typically a very wide miss in everyday terms.
Q: Could we actually stop an asteroid that was heading for us? A: With enough warning, yes — and this is no longer just theory. NASA's 2022 DART mission successfully changed a test asteroid's orbit by crashing a spacecraft into it. The key is early detection, since a small nudge applied years ahead is enough to deflect an object, which is exactly why continuous tracking is the priority.