Comet Neowise is a dazzling sight, but it's also a reminder of how woefully unprepared we are for dangerous asteroids

• Comet Neowise has dazzled stargazers this week, but its surprise appearance highlights one of Earth's greatest vulnerabilities.
• NASA discovered the comet hurtling towards Earth three months ago, but only because one of its space telescopes got lucky.
• Our planet is woefully unprepared for the enormous, deadly rocks that hurtle towards us from deep space. But a telescope NASA is developing could track more dangerous asteroids.

A welcome distraction has turned the world's eyes to the sky this week. Comet Neowise, a 3-mile-wide chunk of space ice, is rocketing past our planet, creating a spectacle in the night: a brilliant ball of white light with long, colorful tails.

The comet is a benign and beautiful sight, but it highlights a global vulnerability. Tens of thousands of potentially dangerous objects regularly careen past Earth undetected, and some of them inevitably crash into it.

Comets — balls of space ice and dust — almost never pose a threat to Earth, but asteroids and meteors (smaller chunks of rock) come close more often. Although impacts are extremely rare, a space rock big enough to destroy a city (or worse) could hurtle towards Earth at any time, and scientists might not see it until it's far too late.

Nobody even knew Comet Neowise existed until a NASA space telescope discovered it approaching just three months ago. The spacecraft was scanning for asteroids and comets (balls of space ice and dust) that fly too close to Earth. The mission is called the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) — that's where the new comet gets its name.

"This is an example of an object coming out of deep space that our survey capabilities need to be able to spot," Lindley Johnson, a planetary defense officer at NASA, said in a press briefing about Comet Neowise on Wednesday. "In this case, we were lucky that it did cross the field of view of the NEOWISE spacecraft back in March."

Many "near-Earth objects" (NEOs) do not cross any telescope's line of sight, and several potentially dangerous asteroids have snuck up on Earth in recent years.

"Luck is not a plan," Richard Binzel, an asteroid researcher and professor of planetary sciences at MIT, told Business Insider in September.

Dangerous asteroids can fly under the radar

A 6-mile-wide asteroid surprised the dinosaurs 65 million years ago when it crashed into Earth. The impact caused a mile-high tsunami, sparked wildfires, and released billions of tons of sulfur into the atmosphere, blotting out the sun for years. That was the end of the age of big lizards.

In case scientists discover such an asteroid approaching Earth again, NASA has considered some ways to push it off its collision course: slamming a spacecraft into it, detonating an explosion near it, or firing lasers that heat and vaporize the rock enough to change its orbit.

But that takes time and the technology is unproven. What if nobody spots the asteroid until it's too late?

In recent years, scientists have missed plenty of large, dangerous objects approaching Earth.

"We feel we've only found about a third of the population of asteroids that are out there that could represent an impact hazard to the Earth," Johnson said.

In 2013, a meteor measuring about 65 feet in diameter and traveling at 40,000 mph entered the atmosphere and exploded over Chelyabinsk in central Russia. The blast sent out a shock wave that broke windows and damaged buildings across the region, injuring more than 1,400 people.

According to NASA modeling, an event like the Chelyabinsk meteor occurs about every 60 years. That same day, a larger asteroid came within 17,000 miles of Earth.

Then a year ago a 427-foot-wide, "city-killer" asteroid flew within 45,000 miles of Earth. NASA had almost no warning about it.

That's because right now, the only way scientists can track an NEO is by pointing a telescope toward the right place at the right time. Telescopes detect the sunlight that asteroids reflect, but the smaller the asteroid, the fainter the reflection. Plus, some asteroids just aren't very reflective.

NEOWISE (the NASA mission, not the comet) is not enough to protect us on its own, and it is living on borrowed time. Hunting asteroids is its second career, which came after it outlived its first mission: scanning the entire sky twice in infrared light. That initial project yielded copious data on distant stars and galaxies.

"This is a telescope that is well past its expiration date and, like a very old car, every day is a gift," Amy Mainzer, the telescope's principal investigator, said. "We're not really sure how much longer it's going to go. In theory, maybe another year at most."

When NEOWISE goes dark, it will leave Earth even more oblivious to threats from space.

NASA is planning its first planetary defense spacecraft

A plan for better NEO surveillance finally gained some traction in September, when NASA announced plans for a new asteroid-hunting space telescope. The project is still in its early stages, though.

Called the Near-Earth Object Surveillance Mission (NEOSM), the spacecraft would feature heat-sensing infrared sensors capable of detecting even dark asteroids, which are the most difficult to find. (Because the sun warms up space rocks, they emit infrared light even if they don't reflect much visible light.)

Unlike NEOWISE, NEOSM would be dedicated to tracking objects near Earth. It would also fix a major blind spot: It could pick up on objects coming from the direction of the sun, where most telescopes can't look.

"This is the first time NASA has ever voiced a commitment to flying a space-based asteroid survey," Binzel said of the mission. "They've always said 'we'll study it, we'll study it,' and now they say 'we are going to do it.'"

The agency's 2020 budget allotted nearly $36 million for the telescope's development. If funding continues, it could launch as early as 2025.

"Having knowledge of what's out there is something that the planetary science community has been advocating for for nearly 30 years," Binzel said. "This is a breakthrough decades in the making."