Asteroid ‘1998 OR2’—most massive asteroid to fly so close to Earth this year—has a diameter of 1.8-4.1 km,  flew past Earth on Wednesday, April 29. The asteroid passed relatively close to Earth this morning at a safe distance, at some 4 million miles (6 million km), or about 16 times the Earth-moon distance.

Asteroid ‘1998 OR2’

  • This asteroid was found in 1998 and the diameter is around 2.1 km. The asteroid orbits around the Sun with a period of 3 years and 8 months, which means it will keep visiting Earth once in 4 years. It crosses the orbit of Mars and has a better chance to graze Mars than Earth.
  • In fact, the closest OR2 will approach Earth is in 2079 when it will be just 6 times Earth-Moon distance at 2.3 million km from Earth.
  • The asteroid is travelling at a fast speed of around 32,000 kms per hr for the proposed fly-by encounter on this Wednesday. Interestingly OR21998 has a strange look. It looks like it is wearing a mask!


  • Asteroids are small, rocky objects that orbit the Sun. Although asteroids orbit the Sun like planets, they are much smaller than planets. They are also known as planetoids or minor planets. There are millions of asteroids, ranging in size from hundreds of miles to several feet across.
  • In 1801, while making a star map, Italian priest and astronomer Giuseppe Piazzi accidentally discovered the first and largest asteroid, Ceres, orbiting between Mars and Jupiter. Ceres is now called a dwarf planet.
  • There are lots of asteroids in our solar system. Most of them are found in the main asteroid belt—a region between the orbits of Mars and Jupiter.
  • Largest in this belt is of course Ceres and millions of small rocks are going around the Sun at that distance. Currently over 1 million asteroids are catalogued
  • Nearly all asteroids are irregularly shaped, although a few of the largest are nearly spherical, such as Ceres. The surfaces of most asteroids are thought to be covered in dust.
  • The average temperature of the surface of a typical asteroid is minus 100 degrees Fahrenheit (minus 73 degrees Celsius).
  • Binary or double asteroids also exist, in which two asteroids of roughly equal size orbit each other, and triple asteroid systems are known as well.
  • Many asteroids seemingly have been captured by a planet’s gravity and become moons — likely candidates include Mars’ moons, Phobos and Deimos
Trojan asteroids orbit a larger planet in two special places, known as Lagrange points, where the gravitational pull of the sun and the planet are balanced.
Jupiter Trojans are the most numerous, boasting nearly as high a population as the main asteroid belt.

Asteroid belt

  • Asteroids are leftovers from the formation of our solar system about 4.6 billion years ago.
  • The asteroid belt came into existence during the origin of the Solar System.
  • Early on, the birth of Jupiter prevented any planetary bodies from forming in the gap between Mars and Jupiter, causing the small objects that were there to collide with each other and fragment into the asteroids seen today.
  • Asteroids lie within three regions of the solar system. Most asteroids lie in a vast ring between the orbits of Mars and Jupiter. This main asteroid belt holds more than 200 asteroids larger than 60 miles (100 km) in diameter. Scientists estimate the asteroid belt also contains between 1.1 million and 1.9 million asteroids larger than 1 km (3,281 feet) in diameter and millions of smaller ones.
Kuiper beltThe Kuiper belt, occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune to approximately 50 AU from the Sun.

The main difference between the Kuiper Belt and the Asteriod belt is that

  • Kuiper belt is much larger in size and more massive (that is, it has more objects) and
  • Objects in the Kuiper Belt are composed largely of various ices compared to the silicates (rocks) and metals of the Asteroid Belt.

Why are Asteroids important in space science?

  • Since asteroids formed at the same time as other objects in our solar system, these space rocks can give scientists lots of information about the history of planets and the sun. Scientists can learn about asteroids by studying meteorites: tiny bits of asteroids that have flown through our atmosphere and landed on Earth’s surface.
  • Asteroid and comet collisions may have delivered the water-ice and other carbon-based molecules to the planet that allowed life to evolve.
  • Further, some of the asteroids can impact Earth and hence are a potential threat to the planet Earth. They can devastate life on Earth.
  • 50,000 yrs ago, a large impact in Maharashtra near Aurangabad caused the formation of the famous Lonar Crater which is nearly 2 km in diameter and over 150 meter deep.
  • It is well known that a giant meteorite impact near Mexico resulted in a mass extinction that wiped out even the mighty dinosaurs around 65 million years ago and its remnant is the Chicxulub Crater under the Sea near Mexico. Hence, monitoring asteroids is crucial.
  • A program called the Near Earth Asteroid (NEA) program keeps an eye on the sky and finds out which asteroid has probability to collide with Earth.
  • There are over 20,000 such potentially dangerous asteroids. Some of these do come very close to Earth and have to be monitored regularly.

Lonar Lake, Maharashtra


Types of asteroids

Scientists use telescopes to keep tracking all these small objects. The asteroids are divided into various groups and depending on which group they belong—their threat potential is seen differently.

Near-Earth asteroids (NEAs) circle closer to Earth than the sun.

  1. AMOR: These asteroids have an orbit size larger than Earth and will never cross Earth. But they cross Mars orbit for sure. Some Amor asteroid may divert towards Earth and be dangerous. Otherwise these are seen as safe Asteroids.
  2. APOLLO: These asteroids are Earth Crossing Orbits with the overall size of the axis larger than that of Earth. Classified as Potentially Hazardous Asteroids (PHA), Apollo’s are the most observed and potential candidates for disaster on Earth.
  3. ATENS: Also Earth Crossing orbits but axis size smaller than that of the planet. These are also PHA’s and we should be keeping an eye on them.
  4. ATIRA: These are groups of asteroids with an entire orbit smaller than that of Earth. They come very close but never cross the orbit. So unless disturbed they will not be coming to hit us.

In addition to classifications of asteroids based on their orbits, most asteroids fall into three classes based on composition:

  • The C-type or carbonaceous asteroids are grayish in color and are the most common, including more than 75 percent of known asteroids. They probably consist of clay and stony silicate rocks, and inhabit the main belt’s outer regions.
  • The S-type or silicaceous asteroids are greenish to reddish in color, account for about 17 percent of known asteroids, and dominate the inner asteroid belt. They appear to be made of silicate materials and nickel-iron.
  • The M-type or metallic asteroids are reddish in color, make up most of the rest of the asteroids, and dwell in the middle region of the main belt. They seem to be made up of nickel-iron.

Large Asteroids hitting the Earth in the near future

Every year Earth is bombarded with countless rocks, debris from space.

  • These small bits of the solar system enter the Earth’s atmosphere and burn in the atmosphere.
  • On certain nights, like November 17 Leonids, there are Meteor Shower in the sky.
  • Based on the survey of craters around Earth and detailed simulations from impactors from space, small impacts like those responsible for Lonar lake type may happen once every million years whereas the large one like that of Dinosaur extinction may occur once every 100 to 300 million years.
  • These events have explosive power of over 100 million times that of the Hiroshima bomb. They can destroy the entire planet during the explosion.

Asteroid defense system

In the unlikely event that the asteroid is deemed a threat, NASA has a Planetary Defense Coordination Office that has scenarios for defusing the situation.

PDCO planetary defense has two technologies at the least that could be used:

  • A kinetic impactor (meaning, a spacecraft that slams into the asteroid to move its orbit) or
  • A gravity tractor (meaning, a spacecraft that remains near an asteroid for a long period of time, using its own gravity to gradually alter the asteroid’s path.)

Asteroid Exploration Missions

  • The first spacecraft to take close-up images of asteroids was NASA’s Galileo in 1991, which also discovered the first moon to orbit an asteroid in 1994.
  • In 2001, after NASA’s NEAR spacecraft intensely studied the near-earth asteroid Eros for more than a year from orbit, mission controllers decided to try and land the spacecraft. Although it wasn’t designed for landing, NEAR successfully touched down, setting the record as the first to successfully land on an asteroid.
  • In 2006, Japan’s Hayabusa became the first spacecraft to land on and take off from an asteroid. It returned to Earth in June 2010, and the samples it recovered are currently under study.
  • NASA’s Dawn mission, launched in 2007, began exploring Vesta in 2011. After a year, it left the asteroid for a trip to Ceres, arriving in 2015. Dawn was the first spacecraft to visit Vesta and Ceres. As of 2017, the spacecraft still orbits the extraordinary asteroid.
  • In September 2016, NASA launched the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx), which will explore the asteroid Bennu before grabbing a sample to return to Earth.
  • In January 2017, NASA selected two projects, Lucy and Psyche, via its Discovery Program. Planned to launch in October 2021, Lucy will visit an object in the asteroid belt before going on to study six Trojan asteroids. Psyche will travel to 16 Psyche, an enormous metallic asteroid that may be the core of an ancient Mars-size planet, stripped of its crust through violent collisions.
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