Asteroid 99942 Apophis, measuring over 450 metres at its longest, will make its closest-ever recorded approach to Earth on April 13, 2029, passing inside the ring of geostationary satellites that power our GPS and television signals. (Photo: Esa)

An asteroid bigger than Eiffel Tower is set to buzz past Earth. Will it hit us?

An asteroid, bigger than the Eiffel Tower, and named after the Egyptian god of chaos, will pass closer to Earth than our geostationary satellites in April 2029, making it visible to the naked eye.

by · India Today

In Short

  • Apophis will fly inside Earth's ring of geostationary satellites in 2029.
  • The asteroid is over 450 metres long with a peanut-like shape.
  • Two spacecraft, OSIRIS-APEX and Ramses, are heading to study Apophis.

In just three years, a mountain-sized asteroid will streak past Earth so close that it will be visible to the naked eye from parts of India, and it will actually pass inside the ring of satellites orbiting our planet.

Asteroid 99942 Apophis, named after the ancient Egyptian god of chaos, will make its historic close approach on April 13, 2029.

And before you panic: scientists have confirmed with near-certainty that it will not hit us.

But what it will do is give humanity the most dramatic asteroid flyby ever recorded.

HOW CLOSE IS TOO CLOSE?

Apophis will come within about 32,000 kilometres of Earth's surface.

That sounds like a lot until you realise that the ring of geostationary satellites orbits at roughly 35,786 kilometres above Earth.

In 2029, an asteroid larger than the Eiffel Tower, and named after Egypt's god of chaos, will pass closer to Earth than our own satellites, and you might be able to see it without a telescope. (Photo: Esa)

Geostationary satellites are the ones that stay fixed above one spot on Earth because they orbit at exactly the speed Earth rotates. They power your television, GPS navigation, and weather forecasts.

Apophis will fly inside that ring. It will pass closer to us than our own satellites do.

For context, the Moon is about 3,84,400 kilometres away. Apophis will be roughly 12 times closer than that.

WHAT KIND OF ROCK IS IT?

Apophis is not a small pebble. It measures between 340 and 370 metres across on average, with its longest dimension stretching beyond 450 metres.

To put that in perspective, the Eiffel Tower in Paris stands 330 metres tall. Apophis, at its widest, is larger than that. Now imagine that hurtling through space at 7.4 kilometres per second.

Radar observations of Apophis obtained in March 2021 were used to rule out any chance of impact for at least the next 100 years. (GIF: ESA)

Radar images show it has a peanut-like, two-lobed shape. Scientists call this a bi-lobate structure, which simply means it looks like two blobs joined together.

It may once have been two separate objects that slowly drifted together and fused over billions of years.

It is a stony asteroid, made mostly of silicate rock, which is the same family of minerals that makes up most of Earth's crust, combined with metallic nickel-iron.

Scientists classify it as an S-type asteroid, which just means it is rocky and reflective rather than dark and carbon-rich.

Apophis currently follows an Aten-class orbit, spending most of its time inside Earth’s path around the Sun. Earth’s gravity during the 2029 flyby will permanently push it into a wider Apollo-class orbit, which is a larger orbit than that of Earth around the Sun. (GIF: ESA)

It closely resembles a type of space rock that sometimes falls to Earth as meteorites called LL chondrites, which are among the most primitive and ancient rocks known to science.

Apophis is a leftover fragment from when the solar system was forming, about 4.6 billion years ago.

The asteroid also tumbles as it travels through space. It rotates once every 30 hours, but it also wobbles on a secondary axis at the same time.

Scientists call this non-principal axis rotation. Think of a spinning top that is not perfectly balanced and rocks from side to side as it spins. That is what Apophis does.

WILL IT HIT EARTH?

No. When Apophis was first discovered in 2004, early calculations briefly suggested a 2.7 per cent chance of impact in 2029.

That was the highest probability ever assigned to a known asteroid, and it caused genuine alarm.

During its closest approach, Apophis will move at up to 42 degrees per hour across the night sky, roughly four fist-widths every hour, bright enough to see without a telescope from dark rural skies. (GIF: ESA)

But radar tracking in 2005, and again in 2021, eliminated all known impact scenarios for at least the next 100 years.

Radar astrometry, which is the technique of bouncing radio waves off an asteroid to measure its exact position and speed, gave scientists enough precision to rule out every dangerous pathway through space that Apophis could have taken.

WHAT WILL EARTH'S GRAVITY DO TO IT?

Even without hitting us, Earth will leave its mark on Apophis.

Our planet’s gravitational pull will physically stretch and squeeze the asteroid as it passes, a process called tidal stress.

The same force that causes ocean tides on Earth, created by the Moon’s gravity pulling on our planet’s water, will act on Apophis as it flies past us.

This could trigger small landslides on its surface and alter its spin.

Radar imaging reveals Apophis has a distinctive bi-lobate, peanut-like shape, suggesting it may be two ancient space rocks that merged billions of years ago during the early formation of the solar system. (File Photo, representational)

The flyby will also permanently change Apophis's orbital path around the Sun. Before 2029, it follows what is called an Aten-class orbit, which means it spends most of its time inside Earth’s path around the Sun and has an orbital period, the time it takes to complete one loop around the Sun, of less than one year.

After 2029, Earth’s gravity will nudge it into an Apollo-class orbit.

Apollo-class asteroids are those whose path around the Sun is larger than Earth’s, which means they cross Earth’s orbital lane as they travel, much like a car switching between lanes on a highway.

Apophis will take about 1.16 years to complete one full loop around the Sun in this new orbit. Neither of these orbits poses an impact risk for the foreseeable future.

CAN YOU SEE IT FROM INDIA?

Visibility from India will be limited during peak approach, but Apophis will reach an apparent magnitude of 3.1.

Magnitude is the scale astronomers use to measure how bright an object appears in the sky.

The lower the number, the brighter the object.

Anything below magnitude 6 is generally visible to the naked eye under dark skies.

Asteroid Ryugu. (File Photo)

At 3.1, Apophis will be comfortably visible without a telescope from rural areas away from city lights.

It will move visibly across the sky at up to 42 degrees per hour.

For reference, your clenched fist held at arm’s length covers about 10 degrees of sky.

So Apophis will move more than four fist-widths across the sky every hour. That is fast enough to watch it move in real time.

Europe, Africa, and Western Asia will have the best views on the night of April 13 to 14, 2029.

WHAT ARE SCIENTISTS PLANNING?

Two spacecraft are already being prepared for Apophis.

Nasa’s OSIRIS-APEX, previously known as OSIRIS-REx, the mission that successfully brought back soil samples from asteroid Bennu, will rendezvous with Apophis after the flyby and study it for 18 months.

It will fire its thrusters near the surface to kick up material, allowing scientists to study what lies underneath.

OSIRIS-APEX spacecraft: NASA's OSIRIS-APEX spacecraft, previously known as OSIRIS-REx after its successful mission to asteroid Bennu, will rendezvous with Apophis after the 2029 flyby and study its surface and interior for 18 months. (Photo: NASA)

The European Space Agency’s Ramses mission aims to arrive before the flyby, in February 2029, to observe the tidal effects on the asteroid in real time as it passes Earth.

This is not just science for the sake of curiosity.

Understanding how asteroids behave under gravitational stress, and how precisely we can track them decades in advance, is central to planetary defence, which is the broader scientific and governmental effort to detect, track, and if necessary, deflect any space rock that could one day threaten Earth.

Apophis is not coming for us. But it is absolutely coming.

- Ends