In 2004, astronomers discovered a dangerous asteroid lurking in space, whose collision
could cause as much damage to Earth as done by the Chicxulub impactor wiping out the entire
population of non-avian dinosaurs some 66 million years ago.
Initially designated 2004
MN4, this 340-meter-wide rock at 170 million kilometers from Earth didn't seem very interesting.
But soon, the analysis suggested that it had a 1-in-37 probability of hitting the Earth
in 2029.
That's the highest probability ever calculated for a substantial asteroid strike
recorded in history.
The rock was regarded as the most dangerous asteroid discovered
so far.
It scared people, and the asteroid was soon named Apophis, after the Egyptian
demon of chaos and destruction.
In March 2021, Apophis made a distant flyby of the Earth, and astronomers used powerful
radar observations to refine the estimates of its orbit around the Sun with extreme precision.
In 2029, it will pass just 32,000 kilometers from our planet.
In doing so, the asteroid
will swoop below the orbits of geostationary satellites.
As a result, it will appear as
bright as a satellite, becoming visible to billions of naked-eye observers across the
globe.
Such encounters are believed to occur only once every few thousand years, and astronomers
do not want to miss this opportunity.
So they have proposed possible missions to explore
Apophis on or around its passage in 2029.
The first confirmed mission to this rock will be NASA's OSIRIS-REx mission.
It's the same
spacecraft initially launched in 2016 on a mission to collect samples from another asteroid,
Bennu.
On 20 October 2020, OSIRIS-REx touched down on Bennu's surface and successfully collected
a sample, and currently, the probe is on its way back home.
The spacecraft is scheduled
to drop off its invaluable samples collected from Bennu in September 2023.
However, it
won't be the end of OSIRIS-REx's space excavation.
The spacecraft will continue to fly through
space after getting a $200-million extension to its planned mission, thereby setting itself
on its journey to visit Apophis and becoming OSIRIS-APEX, which stands for OSIRIS–Apophis
Explorer.
The spacecraft will make its first maneuver toward Apophis just 30 days after delivering
the sample collected from Bennu to Earth.
It will enter the orbit around Apophis soon
after the asteroid's Earth flyby of 2029.
OSIRIS-APEX will study the asteroid for 18
months and collect data along the way.
However, unlike in the case of Bennu, there are no
plans yet for the probe to collect a sample from Apophis' surface.
But, it will approach
the asteroid's surface and fire its thrusters to carry out a maneuver that is specifically
designed to expose Apophis' subsurface to learn more about the asteroid's physical and
chemical composition.
OSIRIS-APEX will aggressively map the asteroid's surface for a year and a half to enable the
mission scientists to look for any interesting changes incorporated by Apophis's brief plunge
through our planet's gravitational grip.
Even if the tidal forces are small, they can still
cause small landslides and expose some fresh material to study from the asteroid.
In addition,
the spacecraft will pin down the rock's orbital motion to meter-scale precision.
This will
further allow researchers to figure out Apophis's future trajectory more precisely.
At present,
predictions only till 2116 can be made.
But OSIRIS-APEX's measurements are expected to
extend such forecasts significantly.
The mission will also study Apophis to understand the Yarkovsky effect in a detailed manner.
The Yarkovsky effect is a phenomenon in which uneven heating from sunlight can affect an
asteroid's trajectory through space.
So the spacecraft will measure the potential changes
in the asteroid's orbital velocity and rotation arising from its 2029 Earth flyby to allow
researchers to understand the implications of this effect on more such objects in greater
detail.
That being said, OSIRIS-APEX isn't the only spacecraft that will visit Apophis.
Several
missions are aiming for the same.
One among the list has been proposed by the South Korean
team, which plans to launch a spacecraft in 2027 that will reach Apophis in January 2029,
just before its Earth flyby.
The mission aims to better view the asteroid's structural changes
due to its close encounter with Earth.
Then, missions with smaller spacecraft, such as
Apophis Pathfinder, have also been put forward.
This spacecraft will launch in 2025-2026 and
will perform the first-ever close flyby of Apophis by reaching the asteroid within approximately
one year of its launch.
Perhaps even some private astronauts might consider flying up
to the asteroid to lay human eyes on it.
Well, it's a long shot, but still possible.
A detailed study of Apophis will pave the way to a better understanding of several dangerous
asteroids lurking around us.
Furthermore, these missions will act as a phenomenal step
forward in advancing our knowledge of the behavior of Apophis, thereby guiding us to
develop effective defense mechanisms against such strikes.
Recently, geologists discovered that the asteroid that wiped out the dinosaurs didn't come alone.
Instead, it had a companion whose impact created the newly discovered Nadir Crater.
It lies
some 350 kilometers out of the coast of the African countries Guinea and Guinea Bissau
and spans around 9 kilometers in diameter.
We have explained this discovery in detail
in the 25th episode of the Sunday Discovery Series.
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