Science / Fri, 12 Jul 2024 The Indian Express

Explained: ISRO’s plans to venture into planetary defence

Somanath’s remarks reveal ISRO’s intent to develop capabilities in planetary defence — an area it has so far not entered. Initial observations showed that if not in 2029, Apophis could hit Earth in 2036 or 2068. Given the asteroid’s size — it measures about 450 m at its widest — a collision with Earth could cause large-scale damage. The asteroid will come the closest to Earth in 2029, when it flies by at a distance of 32,000 km. NASA has already redirected one of its spacecraft, one that previously studied the asteroid Bennu, to track Apophis.

Indian Space Research Organisation (ISRO) Chairman S Somanath said last week that “we should be able to go and meet” the asteroid Apophis when it passes by Earth at a distance of 32,000 km in 2029. However, “it is yet to be decided in what way [ISRO] should participate”.

The Indian space agency might send its own spacecraft, or collaborate with other space agencies. A NASA mission has already been confirmed.

Somanath’s remarks reveal ISRO’s intent to develop capabilities in planetary defence — an area it has so far not entered. A mission to study an asteroid would be the first step towards building a programme aimed at preventing celestial bodies from colliding with Earth with potentially catastrophic consequences.

Apophis, an alarming asteroid

When Apophis was discovered in 2004, scientists thought there was a 2.7% chance of a collision with Earth — the highest probability of any large asteroid hitting Earth in the recent past. Initial observations showed that if not in 2029, Apophis could hit Earth in 2036 or 2068.

Given the asteroid’s size — it measures about 450 m at its widest — a collision with Earth could cause large-scale damage. Some scientists compared the potential impact to the event that wiped out dinosaurs and most other extant life some 66 million years ago.

Subsequent observations showed these initial fears to have been unfounded — the Earth did not face any risk from Apophis in 2029, 2036, or 2068. The asteroid will come the closest to Earth in 2029, when it flies by at a distance of 32,000 km. This is close enough to be visible to the naked eye, and at a distance at which some communication satellites operate.

Objects in space. Objects in space.

What are the possible incoming threats from space?

Apophis may not pose a threat, but asteroids are headed towards Earth all the time.

In fact, thousands enter the Earth’s atmosphere every day. Most are very small and burn up in the atmosphere due to friction — some of the larger ones burn spectacularly, and show up as fireballs in the sky. In some cases, unburnt fragments make it to surface, although they are not large enough to cause much damage.

Once in a while, however, asteroids do cause damage. In 2013, a 20-metre wide asteroid entered the atmosphere and exploded about 30 km above a Russian town, releasing energy equivalent to the blast yield of 400-500 kilotons of TNT — 26 to 33 times the energy released by the atom bomb that detonated over Hiroshima. While most of this energy was absorbed by the atmosphere, shock waves travelled to the ground, flattened trees, damaged buildings, and injured 1,491 people, according to the Russian Ministry of Health.

Worryingly, the asteroid was detected only after it entered the atmosphere. This was in part because it came from the direction of the Sun, and was hidden by its glare.

Scientists know of at least 1.3 million asteroids, but there could be more surprises in store. A planetary defence programme seeks to track and neutralise these threats.

From sci-fi to reality

In 2022, NASA demonstrated technology that has long been a science fiction staple.

A spacecraft launched in the previous year crashed into an asteroid named Dimorphos, and changed both its shape and its trajectory. Dimorphos did not pose a threat to Earth, and was circling the Sun some 11 million km away from our planet. But this showed the beginning of a planetary defence programme. Asteroids are yet to be studied in detail, and very few missions have been dedicated to them.

This is why the approach of Apophis has generated huge interest among space agencies around the world. While formal announcements are yet to be made, several missions, including those from private agencies, are expected to be launched in order to study the asteroid from close quarters.

NASA has already redirected one of its spacecraft, one that previously studied the asteroid Bennu, to track Apophis. This spacecraft will go within a distance of 4,000 km of Apophis in April 2029, and then trail the asteroid for 18 months, collecting data and analysing its surface.

ISRO’s intention to join such an endeavour displays its growing confidence in taking on newer challenges, and contributing proactively to global space objectives. It is also a reaffirmation of its continuing evolution into a well-rounded space agency, with capabilities that match the best in the world.