In October 2022, during the Orionids meteor shower, a fireball was captured on camera
in North America.
Other meteors left long streaks of glowing debris in the sky.
A little earlier, in March 2022, an asteroid crashed into Earth's atmosphere, and was captured
by one of the meteorological satellites.
Fortunately, the asteroid, named 2022 EB5, was only 2 meters [6.5 feet] wide, so it didn’t
result in a catastrophe.
But not all cosmic collisions are so safe.
Some of them are powerful enough to damage planets or even lead to their destruction.
What explosion captured on camera is hundreds of times the power of our entire nuclear arsenal?
Which cosmic explosion left a void the size of many galaxies around it?
And what single meteorite triggered the creation of an Earth defense program?
[LOGO]
Scientists often observe cosmic calamities.
And in 1993, they were preparing to watch the comet Shoemaker-Levy 9 [SL9] crash into
Jupiter by 1994.
But at the very last moment, it turned out that the collision would occur on the night
side of Jupiter, and the initial impact wouldn’t be visible from Earth.
Only NASA's Galileo spacecraft, which was on its way to the gas planet, had a front-row
seat for the spectacle.
The space probe captured the comet entering Jupiter's atmosphere at about 60 kilometers
per second [37 miles per second].
With one-second intervals, Galileo took a series of images showing the appearance of
a fireball and recorded its peak temperature of 23,700°C [42,700°F].
Soon Jupiter, which makes a complete rotation on its axis in just 10 hours, allowed this
fireball to be seen from Earth.
Then NASA's infrared telescope captured a fragment of SL9 that was still rising above
the edge of the planet after the initial impact on the night side of Jupiter.
But the best images were made by the Hubble Telescope using a high-resolution camera.
The telescope was broadcasting at least once a day for a week.
Slowly, as the planet rotated, it showed dark spots on Jupiter left from the impact of the
comet fragments.
The Hubble Space Telescope has recorded the collision of 21 SL9 fragments with the gas
giant.
The image showed fragments of the comet stretching nearly a million and a hundred forty kilometers
[710,000 miles], which is about three times the distance from Earth to the Moon.
Other observatories and telescopes also kept a constant watch.
The largest impact was caused by a huge fragment of a comet, named Fragment G.
The result was a giant dark spot on the surface of the planet, more than 12,000 kilometers
[7,500 miles] across.
This is almost the diameter of the entire Earth.
According to some estimates, the explosion released energy equivalent to six million
megatons of TNT.
At the time, this was 600 times the explosive power of the entire nuclear arsenal of the
world!
Meanwhile, the impacts continued.
At an interval of 12 hours, two more explosions followed, leaving trails almost as large as
the G Fragment left.
The collision sent gigantic plumes of debris flying into space, rising 3,000 kilometers
[1,900 miles] above the cloud tops.
A few minutes later they plummeted back to the planet's surface, turning it again into
a blazing furnace of flames.
In addition, the collisions generated huge waves of energy that swept across Jupiter
at 450 meters per second [1,476 feet per second].
The spots from this impact were visible on the surface of the gas giant for many months,
and some were even more noticeable than the famous Great Red Spot.
But regardless of how big the catastrophe was, it provided astronomers with many valuable
insights.
When debris from the comet crashed into Jupiter, scientists had a momentary window to look
into the gas giant's atmosphere.
Material from the lower layers was ejected into the dense upper clouds and astronomers
learned more about the planet's chemical composition.
Researchers found two-atom sulfur and sulfur-carbon, as well as the emission of heavy atoms of
iron, magnesium, and silicon.
Instruments have also detected a layer of water in the atmosphere, though less significant
than expected.
Researchers believe that a more water-bearing layer may be hiding deeper in the atmosphere,
where the SL9 fragments didn’t penetrate.
In addition, the shock waves that rushed across the planet after the impact helped track wind
movements.
And changes in the polar lights on the gas giant showed how the magnetosphere is affected
by comet and asteroid particles.
The event also made scientists think more about protecting the Earth from such celestial
bodies.
Most of them, like SL9, are caught by Jupiter's extreme gravity.
The frequency of comets and asteroids colliding with Jupiter is believed to be 2,000-8,000
times higher than on Earth.
Astronomers believe that without this cosmic vacuum cleaner, complex life might not have
developed on our planet.
But the gas giant cannot keep us safe all the time.
Craters from celestial rock impacts exist on the Moon, Mars, Venus, and, of course,
Earth.
One asteroid impact in the past has already created a huge crater on our planet, causing
natural disasters and making the dinosaurs go extinct.
And today, dangerous celestial visitors often come by Earth.
A huge asteroid flew close to Earth on Halloween 2022.
If this potentially hazardous object was placed next to one of the world's tallest skyscrapers,
the Burj Khalifa in Dubai, they would be almost equal in size.
The Burj Khalifa is 828 meters [2,716 feet] tall, while the maximum estimate for the size
of the asteroid, named 2022 RM4 is 740 meters [2,428 feet] in diameter.
This rock mountain was hurtling through space at about 84,500 kilometers per hour [52,500
mph].
And that is about 68 times the speed of sound!
The asteroid was captured on camera as part of the Virtual Telescope Project in Italy
on October 31.
The next day, it flew by 2.3 million kilometers [1.43 million miles] from Earth.
That is about six times farther than the average distance from Earth to the Moon, but still
very close by cosmic standards.
So our solar system is a much more peaceful place than it was 4.5 million years ago, there’s
still a lot happening here.
Some random celestial rock can one day easily damage Earth, just SL9 damaged Jupiter.
To prevent this possible catastrophe, it was decided to build a reliable line of defense
against comets and asteroids.
And the first step was the identification of potentially hazardous objects in space.
Until the mid-1990s, only a few teams of astronomers were searching for asteroids in the inner
solar system.
But after the Shoemaker-Levy comet hit Jupiter, we came up with the term "planetary defense",
and new teams joined the research.
Scientists now work together to track near-Earth objects, especially asteroids that come within
48 million kilometers [30 million miles] of Earth's orbit.
NASA has already detected 90% of potentially dangerous asteroids that are one kilometer
or larger.
The agency is now working to identify at least 90% of asteroids between 140-1,000 meters
[450-3,300 feet] wide.
At the same time, space organizations around the world are looking for ways to deflect
orbits of celestial bodies that threaten our planet.
In September 2022, the DART spacecraft diverted the asteroid Dimorphos by changing its orbit
in the very first test of Earth's defense system.
China has also planned a mission to alter the flight of the asteroid 2020 PN1 in 2026.
Scientists have also thought about space dangers to the planet on a global scale.
Researchers have many times captured extremely powerful explosions in other star systems
and galaxies.
The outburst in the Ophiuchus galaxy cluster is considered the strongest one captured on
camera.
The giant flash was captured by several telescopes.
The explosion was so powerful that it punched a cavity the size of 15 Milky Way galaxies
placed in a row in the plasma cluster surrounding a black hole!
It all happened very far away, about 390 million light-years from Earth.
This eruption of unprecedented power gave us stunning images, and scientists received
an opportunity to study this grand event using data from NASA's Chandra X-ray Observatory,
ESA's XMM-Newton, the Murchison Widefield Array, and the Giant Metrewave Radio Telescope.
But in October 2022, NASA recorded an explosion in the universe that reached our planet.
Astronomers believe it was caused by the birth of a black hole at the center of a supernova
1.9 billion years ago in the constellation Sagitta.
The explosion released the gamma-ray burst [GRB 221009A], and a wave of X-rays and gamma
rays reached the solar system, sweeping through it.
The detectors on the Fermi and Swift space telescopes were triggered by this event.
Fermi recorded gamma ray energy data, detecting photons with energies of more than 100 million
electron-volts.
By comparison, photons of visible light have energies of about 2 electron-volts.
The Swift X-ray telescope captured the afterglow of the gamma-ray burst about an hour after
it was first detected.
The bright rings on it are visible as a result of X-rays scattering among layers of dust
in our galaxy.
But the gamma-ray burst didn't do any harm to our planet this time either.
Its epicenter was too far away, and only a tiny fraction of the radiation reached Earth.
Had it happened closer to us, the Earth might have been in trouble.
A supernova explosion is one of nature's most powerful forces.
It can generate as much energy as the Sun will create in its lifetime.
Such a flood of gamma rays has incredible destructive power.
On Earth, it would vaporize the atmosphere and turn all living beings into ash.
And researchers believe our planet has experienced something like this at least once in the past.
According to NASA, about 445 million years ago, a flood of gamma rays hit Earth after
a supernova explosion.
It may have caused the Ordovician-Silurian extinction, one of the most massive on the
planet.
The culprit of the catastrophe is assumed to have been in the near-Earth arm of the
Milky Way.
Its radiation destroyed half of the ozone layer and made about 85% of all living creatures
go extinct.
A supernova explosion is only dangerous for us if it happens no further than 50 light-years
from Earth.
Fortunately, no supernova candidates have yet been found among our neighboring stars.
But, there is still a chance a wandering star could pop out of some cosmic corner, ready
to explode.
Or maybe, somewhere in a secluded corner of the Milky Way, there’s a dangerous star
hiding from astronomers.
So it would be a good idea to incorporate supernova detection into our planetary defense
program as well.
Which scenario do you think is more probable and dangerous for us, a wandering star ready
to go supernova, or a relatively small asteroid lurking somewhere in our solar system?
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