Context: National Aeronautics and Space Administration (NASA) has announced that there is a 3.8% chance that Asteroid YR4 could collide with the moon in December 2032.
Earlier, it was thought the asteroid might hit Earth, but the latest trajectory analysis concludes a very little chance of that happening. The asteroid is below the threshold size (140 metres), so it would not be a threat to Earth.
Relevance of the Topic:Prelims: Key facts about Asteroid 2024 YR4; Double Asteroid Redirection Test spacecraft (DART).
About Asteroid 2024 YR4
- The 2024 YR4 was first discovered in December 2024 by a telescope in Chile.
- It is a near-Earth asteroid measuring 40 to 100 metres across.
- It came closest to Earth in December 2024— passing within roughly 800,000 kilometres of Earth, about twice the distance of the moon.
- Scientists are using some of the most powerful telescopes to determine 2024 YR4’s path and size before it gets out of sight (becomes too faint to observe).
- One AU (Astronomical Unit) is approximately equal to 93 million miles - the distance between the Sun and the Earth.
- The closest asteroids which travel within 1.3 AU of the sun are called near-Earth objects (NEO).
If an NEO's orbit also intersects Earth's orbit, and the object is larger than about 140 metres in diameter, then it is classified as a potentially hazardous object (PHO).
The Challenge
- Determination of the size of Asteroid:
- To determine the size of an asteroid, astronomers examine the brightness of the object — brighter objects are bigger.
- However, the brightness depends on how reflective the asteroid’s surface is (asteroids do not emit a light of their own, they only reflect sunlight).
- As a result, it is a challenge to distinguish between a large, dark-colored asteroid and a small, highly reflective one.
- 1% chance of crashing into Earth:
- The 2024 YR4 is expected to release 8 to 10 megatons of energy in case of a crash. Its impact could be 100 times more powerful than an atomic bomb.
What are Asteroids?
- Asteroids are rocky remnants from the early formation of our solar system (about 4.6 billion years ago).
- They are rocky, metallic, or icy bodies with no atmosphere.
- Roughly one million asteroids are known. Majority of them are located between the orbits of Mars and Jupiter, in a region known as the main asteroid belt.
- The asteroid belt is a nearly flat ring that contains millions of asteroids, about 1000 kms or less in diameter.
- The largest asteroid in our solar system is Ceres (diameter ~940 kms), which is about one-quarter the size of Earth’s moon.
- They are generally classified to be of three types: C-type, M-type, and S-type, i.e., carbonaceous, metallic, and siliceous compositions, respectively.
- The first close-up observation of an asteroid was made by the NASA’s Galileo spacecraft (1991).
Asteroids as threats from Space
- Thousands of Asteroids enter the Earth’s atmosphere every day. Most are very small and burn up in the atmosphere due to friction.
- In some cases, unburnt fragments reach the Earth’s surface, although they are not large enough to cause much damage.
- In 2013, a 20-metre-wide asteroid entered the atmosphere and exploded about 30 km above a Russian town.
- Most of the energy released was absorbed by the atmosphere, however, shock waves travelled to the ground, damaged buildings, trees and injured people.
- Space agencies are working on planetary defence mechanisms that can prevent celestial bodies from colliding with Earth with potentially catastrophic consequences.
Planetary Defence Mechanisms:
1. Double Asteroid Redirection Test spacecraft (DART):
- DART was the first planetary defence mission of NASA, launched in 2021, to test a method for defending Earth from potentially hazardous asteroids.
- Target:
- It targeted the binary asteroid system which consists of a larger asteroid called Didymos and a smaller asteroid called Dimorphos.
- Dimorphos did not pose a threat to Earth, and was circling the Sun some 11 million kilometres away from the planet.
- Objective: To intentionally crash the DART spacecraft into Dimorphos to slightly alter its orbit around Didymos.
- Impact: In 2022, DART spacecraft crashed into Dimorphos, and successfully changed both its shape and its trajectory.
- Significance: The data gathered from DART will help scientists develop more effective strategies for deflecting asteroids that pose a threat to Earth in the future.
2. OSIRIS-APophis EXplorer (OSIRIS-APEX):
- NASA has redirected its Space-craft OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security – Regolith Explorer) that previously studied the asteroid Bennu, to track Asteroid Apophis.
- OSIRIS-APEX is a mission to study the physical changes to asteroid Apophis that will result from its rare close encounter with Earth in April 2029.
- Our planet’s gravitational pull is expected to alter the asteroid’s orbit, change how fast it spins on its axis, and possibly cause quakes or landslides that will alter its surface. OSIRIS-APEX will allow scientists on Earth to observe these changes.
- Additionally, the OSIRIS-APEX spacecraft will dip toward the surface of Apophis and fire its engines to kick up loose rocks and dust. This manoeuvre will give scientists a peek at the composition of material just below the asteroid’s surface.